Hope this was useful! I still love the Hyperstar and having a lot of fun with it! And in a way, having only high incidence light ray angles makes it easier to design pre-shifted filters :) There are workarounds for OSC cameras like the IDAS NBZ (which I use and really enjoy - see my Instagram) or the L-eXtreme (only if you are lucky - subscribe for the next video which will touch on that!) as well as the Baader highspeed narrowband filters for monochrome cameras (but note that I'm having issues with my Baader highspeed ultra-narrowband filters: one arrived chipped, another had ink on one surface, and a last one doesn't seem to be passing its rated wavelength - no completely sure, so currently getting this checked via spectrometer, and will update, likely in a video).
IDAS NBZ UHS exists and I own one. I wonder how your experience would be impacted by it compared to the non-UHS. No getting around the CO of course. RASA 11 here.
I came across your channel yesterday. I've watched hundreds if not thousands of hours of other astro channels and I have to say, you do a FAR better job of explaining the details of any particular subject than any of those other channels. Great stuff.
Excellent explanations as always Cuiv. Interesting as I was thinking about the C6 obstruction being worse than the C8 or larger when you mentioned it. - Cheers Kurt
Very interesting review! From what I learned from your review, maybe a StarArizona Apex L is the best option, since I'm passionate about refractors. Thanks again for your videos, which help the Astrofography guys a lot. Thanks Cuiv.
I’ve been contemplating this same issue. YOUR EXPLANATION IS GREAT! With conventional narrow band filters we have things going off band at the step angles around the outside of the objective, but on-band in the center where the F number is higher. But since most of the light is gathered around the outside, the “pre-band-shifted” filters might seem to be a solution. Now the outside is on-band, but now the center is off-band. However since the hyperstar already makes a large central obstruction, you aren’t loosing anything. I’ve some very fast large camera lenses Nikon F2.8 300 mm, these don’t have a central obstruction. So in this case, I looked at the IDAS NBZ 12 nm OIII HA it has the flat top band pass curves. It seems to work well for the color cameras. I’ve also used the 12nm Astronomik 12 nm HA and SII. Still waiting for the OIII to come in. I ordered in October, looks to come along in mid to late December. Once again, you cover all the points so well and helped me make an intelligent choice for fast systems! Thank you so much!
Flat top filters this narrow are extremely difficult to manufacture. And the centering becomes critical. The argument regarding "manufacturing luck" is totally true. Pre-red-shifting dedicated filters tailored for Raza and Hperstar is probably the only economical solution. A nice flat topped filter at < 7nm is a bit of a pipe dream unless the company is ok with low manufacturing yields, and money is no object.
This is a really interesting topic that I am exploring as well. I'm looking forward to seeing more about this as you do more testing! I have an Celestron Edge 11- I'm thinking about ditching the RASA8 and getting a hyperstar for it. It sounds like that would be the right move to get the most from my iDAS NBZ.
I'm jealous of you! I have those filters, the Ha and SII seem fine, but the OIII doesn't pass OIII. I'm getting them analyzed via spectrometer... Also, one filter came chipped, and the other with dark pain on one surface. Great QC from Baader.
Excellent video as usual. I use an inexpensive Astromania 12nm Ha filter with my ASI294 mc pro OSC camera and RASA 8 for the Ha part of HaRGB images and get very good results. I think the wider band-pass helps a lot but I don't have Tokyo level light pollution here.
I have a Hyperstar system and my L-extreme did not work at all I lost a lot of Hydrogen. I am using 12nm Astronomik narrowband filters on a C11 and no halos so far in Oxygen. The Hyperstar group I belong to love the NBZ. Theses are great episodes thank you!
Different purposes, different styles :) I'd argue that sitting at the eyepiece in the cold at 1AM, adjusting focus with trembling fingers, and using corner vision to better see those faint fuzzies is far from lazy! But it is a form of meditation :)
This is a superb explanation of the issues here, and it also helps my understanding of light path issues with other systems - thanks for making this. Looks like the RASA 8 is still on my wish list! I'm looking forward to your upcoming videos on this narrowband filter series.
Thanks Cuiv for the Altair article.I believe it confirms my theory that using dichroic filters like L-extreme on fast optical systems with an unmodified camera will have two benefits. First that we all know, fast optics = more photons, but since the filter in front of the sensor blueshifts the wavelengths, more of the intended blocked IR wavelengths can pass the sensors IR-filter making it easier to record Ha-data. This is perhaps the reason, I get so good images with Ha in my images using Sigma 85/1.4 Art on a stock camera Sony A7R4 with CLS filter. Perhaps a video for you to make in the future? :)
Very interesting point - yes at F1.4 there would be a lot of shift towards the blue, enough to maybe increase sensitivity to Ha considerably (maybe from 20% transmittance to around 35% transmittance, depending on the slope of the filter).
It's the fast F ratios that cause the problem, not the central obstruction as far as narrow band filters go. These filters are formed by many thin layers that are tuned to a particular wavelength of light. The high angle of incidence changes the path length through a layer resulting in a shift in band path. The filters simply need to be manufactured with this in mind. My F10 C8 SCT is fine with normal filters but if I operate it in f1.9 mode it needs special high speed filters or broader band pass filters. The central obstruction does not reduce light that much nor effect resolution. A 50% obstruction (by diameter) only reduces light by 25%. It does reduce contrast because of increased diffraction.
Great video as always, Cuiv. This begs the question: will we see off-axis optical design telescopes in the future? A Herschelian Telescope (which has no central obstruction) combined with a RASA design could be extremely interesting for astrophotographers.
It's only through the pole (dead centre) of the lens that you get normal incidence on the filter. Any distance away from the pole and the light will come in at some angle to the normal on the filter. The half cone angle, that is the angle between a light beam going through the pole of the lens and the outer edge of the lens measured at the focus is 14 degrees for an f#2 system and only 2.86 degrees for an f#10 system. This angle of course decreases down to zero as you go from the outer edge of the lens to the pole, but decreases to a larger (non-zero figure for a mirror) as you don't get light passing through the central obstruction on a mirror system. Now for an f#10 system where the maximum deviation is only 2.86 degrees away from the normal, a filter, whose layer thicknesses are calculated for normal incidence of light, isn't going to do too badly. However, the f#2 system is clearly going to be a much bigger problem - and it's even worse than that. As you come in from the outer edge of the lens (or mirror) the cone angle will decrease, but it is still a sizeable value even by the time you get to the edge of the obstruction (in the case of the mirror). So not only do you have the wrong layer thicknesses in your filter (as your light is coming in way off normal) but if you take this into consideration by recalculating the layer thickness required for an f#2 cone angle, then that thickness will be incorrect for all the light paths coming inside the outer diameter of the mirror to the edge of the obstruction. A filter that can accommodate this would have to have layer thicknesses that change as a function of distance away from the centre of the filter - and you can't make a filter with those properties. The filter manufacturers will know you can't make a filter with layer thickness that is a function of distance away from the centre and so they know that any "solution" they come up with for fast optical systems is at best going to be some sort of very poor compromise. It's all just Physics (or optics) - and as ye know, ye cannot change the Laws of Physics :)
@@phadeezz If it was totally possible - you would have said how it could be done for very thin layers as in an intereference filter. As you make absolutely no mention of how it could be done I will simply assume you are full of s**t :)
Cuiv, hope you can review Astronomik MaxFR 6 or 12nm filters on the Hyperstar. The MaxFR emission line filter series were designed for fast systems like the RASA and surprisingly also longer fl, f2-f8. Narrowband Ha Sii and Oiii Mono. Those of us who would want to go longer fl would benefit on a single filter set. Astronomik site described the filters as high contrast and no halo. Thanks 😊
It is possible the reason your Optolong L-eXtreme works "better" with your Hyperstar is because it might actually be a *worse* sample. If your sample has a 9nm bandpass instead of 7nm, it could be just enough to allow more signal (although more noise too).
Possible! Based on spectrometer readings of other L-eXtremes though, it seems the bandpass width isn't usually the issue, but the bandpass placement is. I might have a bandpass placed so that Ha is on the left edge of the bandpass. I can't know for sure without measuring!
Hi Cuiv, that was great! These series of Hyperstar videos have been invaluable! I have the C8, Hyperstar V4 and L’eXtreme - but, the NBZ filter makes sense! Whether I’ve won the production line “lottery” with my L’eXtreme is yet to be determined, but I know what to get if I’m unlucky!! But a simple, anecdotal observation, wouldn’t the larger diameter SCTs (C8, C11, etc) have an advantage over your C6? Markedly I would have thought. Greater mirror areas with the same obstruction- proportionally less with the bigger dia SCTs.
@@CuivTheLazyGeek Why's that? The solid angle is the same, but the wasted solid angle gets smaller, Area/ditance^2. Can you explain why do you expect more issues then?
@@phadeezz There's simply less of a range of incidence angles to think about when pre-shifting a filter for a large obstruction (by diameter). In other words in theory, it would be easier to create a pre-shifted filter for that. From some spectrometer measurements of Baader F2 filters, they seem to preshift with RASA8 in mind (e.g. the filter doesn't perform as well on an F2 refractor - because then the part in the middle of the lens doesn't let in the desired signal since the bandpass isn't shifted enough... But it lets in light pollution).
Hey Cuiv, cool video as usual! I was wondering if you'd be keen on doing a video about how to chose the right camera? What to look for depending on what type of object you're planning on imaging. There's a lot of different type of cameras, and I'm not convinced that more expensive always means better depending on what you're after. I'm definitely a bit lost on the impacts that pixel size, Well capacity, read noise etc. can have. Also, how much do you actually gain from going mono+ filters against using an colour sensor.
That's a huge, huge roadmap there :-) just mono vs OSC can start discussions that span months and hundreds of posts :p As a short intro, Nico from Nebula photos has a great summary: ua-cam.com/video/LQCSAeKzqjM/v-deo.html
Cuiv, have you tried the new NBZ II? How about the NBZ UHC? Love to see the difference if any to the NBZ or L-Extreme. I'm also putting together a C6 hyperstar!
Should have watched this video before I bought the Optolong Extreme for my Hyperstar. Luckily I can still return it. Especially embarrassing for me since I have a background in optical engineering, and knew that thin film filter center wavelength shifts shorter with angle. But I was too dumb to consider my increase in focal ratio would increase the light cone angle at the filter (facepalm). Has anyone in the industry considered thermal control of these filters to compensate? I know from experience that thermal expansion of thin film filters can change the dielectric coating layer thickness, and shift the center wavelength in the opposite (longer) direction.
I noticed that Antlia says their 3 nm Pro filters can be used with nearly all systems as fast as f/3. So if I get a Hyperstar at F2, it is likely to be a problem with those filters?
Sort of offtopic but how are you liking the CEM60?? Wish they still sold that model. Been looking on the used market but not having any luck currently. As always, another great video.
This video is over a year old and I would love an update as there are a LOT of new NB filters for OSC cameras coming out that are supposedly suitable for Hyperstar and RASA scopes. i have both 11" SCT non HD as well as a 8" SCT HD....both with Hyperstar V4. I also use refractors from 80mm to 156mm. I have had excellent results with a TRIAD filter on the refractors but looking for a better solution for the Hyperstars. These filters are expensive so looking for the best bang for the dollar.
Thanks! You made a very quick reference remark to this on your last video and I was wondering just what the heck that meant. Now I know! So. Are you considering getting a C8 Edge or something even bigger (I have both, the C8 is really not all that much bigger than the C6 when it comes to ease of handling and I hear the Edge version is the one to get if you image - not sure that is a rabbit hole I want to go down..... :^) ).
I'll keep my Hyperstar C6 - there are workarounds such as pre-shifted filters that work great with it (in theory, in practice the filters I got from Baader have QC issues).
I just ordered IDAS NBZ filter. I wonder if the data in Altair shows same results as IDAS, where there is difference between f/2 and RASA. Well, I can actually test filters. I have nice spectrometers. Will show you results, if I get to them. Since you are covering RASAs now, it would be great if you can cover some backfocus details. I.e. now I'm thinking about getting a new ZWO camera with 17.5mm backfocus, while my present has 6.5 mm. However on the Starizona store there is only 4 options for ZWO: cooled and cooled 54mm flange, uncooled x 2. I'm not quite sure if I can get into focus with the new one. Ordered some extensions, so I think I can check that. Still, would be nice to hear more from you on the subject.
I wish I had spectrometers.... One of those filters from Baader I got is REALLY dodgy and doesn't seem to pass its advertised bandpass :/ On the backfocus, I won't cover that, simply because I only know for my telescope (ZWO cooled camera means 17.5mm back focus on the camera side, no idea about the rest). Your best bet would be to ask Starizona directly!
Thanks for sharing this info.. but wouldn't a larger primary (say the 14" RASA) increase the efficiency of this NB filter, considering having the same obstruction dimensions from the front mounted camera?
Maximum incidence angle would still be the same, but minimum incidence angle will be lower - so there will be a larger range of incidence angles to consider. We then have the choice of using 12nm bandpasses like IDAS NBZ to have Ha pass to some extent across those incidence angles , or preshift the bandpass (while keeping the ability to make it narrower) for the average incidence angle (perhaps tweaking towards higher incidence angles, which represent more light - but it means we'll likely be "closing off" the central aperture more to Ha (while keeping it open for light pollution).
SIr can you make a video showing us how to get proper flats. my conners are always whited out and i can not get background extraction to remove this. do we need to increase our adu or decrease adu target? this video will be very much appreciated
Mr Cuiv. Your hopes are ok, this video is very useful! Thanks for sharing. I just have some questions (as I have a C6 and an Hyperstar sounds interesting). An Optolong L enhance and a L pro filter would work with a setup like yours?? And the last question (as Hyperstar for C6 is not so cheap) as a final conclusion, do you recommend buying it? Thanks again for this invaluable information!
I still love my Hyperstar C6 - for me it works great. An L-eNhance would work great (and rather than an L-Pro, I'd just use a UV/IR cut filter), and an IDAS NBZ as well!
This is SPOT on with what I saw when using my Optolong Extreme filter with my Hyperstar f1.9 !! It gathered very little HA compared to OIII . I am going to start using monochrome on my hyperstar but I need to invest in FAST filters should I go with baader or should I look at some on else’s ??? It’s quite an investment they are expensive.
OK so I will give you my experience with the Baader fast filters: terrible. Out of 6 filters ordered (two filter sets), one had a chip in the middle, one had black paint on the surface, and at least one had the bandpass in the wrong place (causing very little OIII to pass through - verified via spectrometer). I'm in the process of getting all of those replaced - I sure as heck am not buying from Baader anymore.
@@CuivTheLazyGeek I think I recall watching that on a video of yours. I see they are now making special “CMOS” versions is that the ones you got? So what set do you recommend that will reach f1.9 on my Edge 8HD
Is it possible to create a positive angle of incidence to the primary mirror and incoming light so that the central obstruction is not in the center, rather off to the side instead?
I had a feeling this video would come out. Almost predicted it just not publicly. Looks like that cold wind has started over there. I hope some people do come out with some way to reduce the obstruction. Rasa images to me seam to always lack contrast.
So to be clear, I still think RASA and Hyperstar are amazing! They do have considerations in terms of narrowband, you need to use the right tools for them :-)
Thanks Cuiv! But I don’t get your “double whammy” point (at 8:38). Why would the light pollution frequencies not also be stopped by the central obstruction? Surely all the light rays will be parallel, whatever their frequency?
The part of the LP that overlaps the target signal will also get stopped yes as incidence is the same. But light pollution is present throughout the whole spectrum, so other LP wavelengths just step in through the shifted bandpass - in other words the shifted bandpass can end up passing only LP, and no signal.
Thanks for the information. I'd been considering the hyperstar for my 9.25 and after watching your initial video on the C6, went ahead and purchased it as I hadn't previously known of it's existance. My wife has since intercepted it and couriered it off to Santa, who has promised that he will deliver it in another 33 476 minutes. Do you remain enthusiastic about the setup, and will you continue to use it much? I live in a bortle class 5 area, so not as bad as Tokyo, and have a couple of CLS, UHC and LPR filters to try out but am hoping to take advantage of the shorter exposure times.
I don't have the Celestron filter and don't plan on getting it - it's for RASA, not Hyperstar, not even sure it would fit! Overall it's very similar to any other general purpose filter like the Optolong L-Pro for instance (which I already have - but don't use much because I prefer to just go UV/IR cut in that case for easier color balance). Still, it's very different from narrowband, which is the topic of the video.
I don't completely get the reason for the blue shift. Seems that it should be shifted to longer wavelengths (i.e. red shift). I come to this conclusion by assuming the filter passes a particular wavelength at normal incidence. For broadband white light coming in at an angle, it would seem to require a longer wavelength of light to project onto the normal direction at the pass wavelength, not shorter. I must be missing something. I would love a more technical reference on this if you know of one.
@@CuivTheLazyGeek Thanks for the reference. That certainly has the equation showing the "blue shift," but didn't explain how it was derived. In the mean time, after doing a bit of google investigating, i think I understand it now. My original assumption as to how the filters work was wrong. BTW -- I'm a recent/new subscriber and love the channel.
Best would be to put the filter in front of the objective lense i.e. outside the telescope at the front but that would require a massive filter costing $$$$$
I finished a detailed review and some simulations of fast filters for hyperstar on my channel - inspired by this video I think you will find it interesting
The video is over a year old by now, there weren't many highspeed specific filters at the time! Glad the highspeed SHO filters are working for you - mine didn't, the band passes were very poorly placed (checked via spectrometer), leading to some signal coming through, but less than 30% or so transmission. So overall it looked like the filters were working, but far, far from spec! Since then, based on further measurements I did, Baader fixed their filters and separated them further depending on the use-case. Just saying, it's possible that the filters you have are great in part because of my videos' impact :p
Yep, I think it's cheaper because it's less versatile. For RASA8 it does add a few percentage points to overall H-Alpha transmission, but on slower FLs you lose quite a bit compared to the non-UHS version
@@CuivTheLazyGeek I'll tell you my secret... I have the bell notification set to 'on' so I can get that fresh AP info hot off the press! I also have the next week of clear skies and I'm stoked! Thinking of hitting Orion tonight... it's like cooking eggs to a chef, very basic, but also very technical to get it perfect and improve one's skills.
Excellent info as always, Cuiv!
Thank you Chuck!
Hope this was useful! I still love the Hyperstar and having a lot of fun with it! And in a way, having only high incidence light ray angles makes it easier to design pre-shifted filters :)
There are workarounds for OSC cameras like the IDAS NBZ (which I use and really enjoy - see my Instagram) or the L-eXtreme (only if you are lucky - subscribe for the next video which will touch on that!) as well as the Baader highspeed narrowband filters for monochrome cameras (but note that I'm having issues with my Baader highspeed ultra-narrowband filters: one arrived chipped, another had ink on one surface, and a last one doesn't seem to be passing its rated wavelength - no completely sure, so currently getting this checked via spectrometer, and will update, likely in a video).
IDAS NBZ UHS exists and I own one. I wonder how your experience would be impacted by it compared to the non-UHS. No getting around the CO of course. RASA 11 here.
@@AzCrawler00 Yet you have a much smaller ratio of CO to useful area.
Great deeper dive into this key topic for this type of scope vs. imaging limitations. Thanks Cuiv!
Yes, I always learn something from your videos Cuiv!
Loads of fun as always!
I came across your channel yesterday. I've watched hundreds if not thousands of hours of other astro channels and I have to say, you do a FAR better job of explaining the details of any particular subject than any of those other channels. Great stuff.
Wow, thank you! And welcome to the channel!
Once again, very informative. Thanks Cuiv!
Excellent video and explanations. You go into the best detail in your videos.
Thanks Jeff!
Incredible video! Thanks for making this easy to understand 🙂
I bought the IDAS NBZ UHS for my Hyperstar C925, this video totally confirms it was a great move, thanks Cuiv.
Excellent explanations as always Cuiv. Interesting as I was thinking about the C6 obstruction being worse than the C8 or larger when you mentioned it. - Cheers Kurt
Very interesting review! From what I learned from your review, maybe a StarArizona Apex L is the best option, since I'm passionate about refractors. Thanks again for your videos, which help the Astrofography guys a lot. Thanks Cuiv.
I’ve been contemplating this same issue. YOUR EXPLANATION IS GREAT!
With conventional narrow band filters we have things going off band at the step angles around the outside of the objective, but on-band in the center where the F number is higher. But since most of the light is gathered around the outside, the “pre-band-shifted” filters might seem to be a solution. Now the outside is on-band, but now the center is off-band. However since the hyperstar already makes a large central obstruction, you aren’t loosing anything. I’ve some very fast large camera lenses Nikon F2.8 300 mm, these don’t have a central obstruction. So in this case, I looked at the IDAS NBZ 12 nm OIII HA it has the flat top band pass curves. It seems to work well for the color cameras. I’ve also used the 12nm Astronomik 12 nm HA and SII. Still waiting for the OIII to come in. I ordered in October, looks to come along in mid to late December.
Once again, you cover all the points so well and helped me make an intelligent choice for fast systems!
Thank you so much!
Love this series..
Good video Cuiv explaining flaws of rasa.
Flat top filters this narrow are extremely difficult to manufacture. And the centering becomes critical. The argument regarding "manufacturing luck" is totally true. Pre-red-shifting dedicated filters tailored for Raza and Hperstar is probably the only economical solution. A nice flat topped filter at < 7nm is a bit of a pipe dream unless the company is ok with low manufacturing yields, and money is no object.
This is a really interesting topic that I am exploring as well. I'm looking forward to seeing more about this as you do more testing! I have an Celestron Edge 11- I'm thinking about ditching the RASA8 and getting a hyperstar for it. It sounds like that would be the right move to get the most from my iDAS NBZ.
The IDAS NBZ would definitely work excellently for that!
Great video as always! Good to see all of this discussed so clearly 😀I have been very happy with the 2" f/2 3.5/4nm Baader filters and the RASA 8
I'm jealous of you! I have those filters, the Ha and SII seem fine, but the OIII doesn't pass OIII. I'm getting them analyzed via spectrometer...
Also, one filter came chipped, and the other with dark pain on one surface. Great QC from Baader.
@@CuivTheLazyGeek ohhh not good!
Very interesting and informative Cuiv. Thanks for sharing.
great as always
Great explanation. Thanks, for sharing this.
This was incredibly helpful, I can't thank you enough, Cuiv!
Thanks Sarah!! Are you using Hyperstar on your massive SCT?
@@CuivTheLazyGeek I’m thinking about it!
Very interesting review! Thanks so much!!!
Many thanks, a very interesting explanation.
Always interesting!
Bon clip, comme toujours
Very informative!
Very good explanation
I never thought about the central obstruction issue, makes perfect sense though!
Very educational, thanks!!
Great video , thanks mate 👌🏻
Great video, very instructive. Many thanks. :-)
Hey Cuiv! Just to let you know, I have the Radian Triad Ultra F3 and it is amazing on my C6 HyperStar. Hyper fast narrow band using a OSC!
Excellent video as usual. I use an inexpensive Astromania 12nm Ha filter with my ASI294 mc pro OSC camera and RASA 8 for the Ha part of HaRGB images and get very good results. I think the wider band-pass helps a lot but I don't have Tokyo level light pollution here.
12nm is a good sweet spot for the RASA 8, very little affected by bandpass shift!
I have a Hyperstar system and my L-extreme did not work at all I lost a lot of Hydrogen. I am using 12nm Astronomik narrowband filters on a C11 and no halos so far in Oxygen. The Hyperstar group I belong to love the NBZ. Theses are great episodes thank you!
Yeeeah, the L-eXtreme can be very variable... They all work at slower focal ratios though! 12nm without any preshift seems to be a very safe bet :-)
Top quality content! Thanks a lot :-)
Thanks Mathias!
Setting up all those wires etc is NOT LAZY! Looking through the eyepiece IS, and is far more mind-blowing xx
Different purposes, different styles :) I'd argue that sitting at the eyepiece in the cold at 1AM, adjusting focus with trembling fingers, and using corner vision to better see those faint fuzzies is far from lazy! But it is a form of meditation :)
This is a superb explanation of the issues here, and it also helps my understanding of light path issues with other systems - thanks for making this. Looks like the RASA 8 is still on my wish list! I'm looking forward to your upcoming videos on this narrowband filter series.
Nice I look forward to seeing some sho test later 😆
Already on Instagram :-)
Thanks Cuiv for the Altair article.I believe it confirms my theory that using dichroic filters like L-extreme on fast optical systems with an unmodified camera will have two benefits. First that we all know, fast optics = more photons, but since the filter in front of the sensor blueshifts the wavelengths, more of the intended blocked IR wavelengths can pass the sensors IR-filter making it easier to record Ha-data.
This is perhaps the reason, I get so good images with Ha in my images using Sigma 85/1.4 Art on a stock camera Sony A7R4 with CLS filter.
Perhaps a video for you to make in the future? :)
Very interesting point - yes at F1.4 there would be a lot of shift towards the blue, enough to maybe increase sensitivity to Ha considerably (maybe from 20% transmittance to around 35% transmittance, depending on the slope of the filter).
It's the fast F ratios that cause the problem, not the central obstruction as far as narrow band filters go. These filters are formed by many thin layers that are tuned to a particular wavelength of light. The high angle of incidence changes the path length through a layer resulting in a shift in band path. The filters simply need to be manufactured with this in mind. My F10 C8 SCT is fine with normal filters but if I operate it in f1.9 mode it needs special high speed filters or broader band pass filters. The central obstruction does not reduce light that much nor effect resolution. A 50% obstruction (by diameter) only reduces light by 25%. It does reduce contrast because of increased diffraction.
Great video as always, Cuiv. This begs the question: will we see off-axis optical design telescopes in the future? A Herschelian Telescope (which has no central obstruction) combined with a RASA design could be extremely interesting for astrophotographers.
Yeah, off axis reflectors exist already, but I don't think it would be trivial to bring one back to F2!
@@CuivTheLazyGeek I think they said the same thing before making the RASA :)
It's only through the pole (dead centre) of the lens that you get normal incidence on the filter. Any distance away from the pole and the light will come in at some angle to the normal on the filter. The half cone angle, that is the angle between a light beam going through the pole of the lens and the outer edge of the lens measured at the focus is 14 degrees for an f#2 system and only 2.86 degrees for an f#10 system. This angle of course decreases down to zero as you go from the outer edge of the lens to the pole, but decreases to a larger (non-zero figure for a mirror) as you don't get light passing through the central obstruction on a mirror system. Now for an f#10 system where the maximum deviation is only 2.86 degrees away from the normal, a filter, whose layer thicknesses are calculated for normal incidence of light, isn't going to do too badly. However, the f#2 system is clearly going to be a much bigger problem - and it's even worse than that. As you come in from the outer edge of the lens (or mirror) the cone angle will decrease, but it is still a sizeable value even by the time you get to the edge of the obstruction (in the case of the mirror). So not only do you have the wrong layer thicknesses in your filter (as your light is coming in way off normal) but if you take this into consideration by recalculating the layer thickness required for an f#2 cone angle, then that thickness will be incorrect for all the light paths coming inside the outer diameter of the mirror to the edge of the obstruction. A filter that can accommodate this would have to have layer thicknesses that change as a function of distance away from the centre of the filter - and you can't make a filter with those properties. The filter manufacturers will know you can't make a filter with layer thickness that is a function of distance away from the centre and so they know that any "solution" they come up with for fast optical systems is at best going to be some sort of very poor compromise. It's all just Physics (or optics) - and as ye know, ye cannot change the Laws of Physics :)
In a way the central obstruction can help for pre-shifted filters, since there's then a narrower range of incidence angles to consider!
Glad I read through the comments as you answered some questions I had for f10 systems, Clear skies at Stoney Cross
Actually it is totally possible to deposit a layer with varying thickness. It's much more technically challenging, but far from impossible.
@@phadeezz If it was totally possible - you would have said how it could be done for very thin layers as in an intereference filter. As you make absolutely no mention of how it could be done I will simply assume you are full of s**t :)
@@CuivTheLazyGeek That is probably the case! And still they don't do too well :)
Cuiv, hope you can review Astronomik MaxFR 6 or 12nm filters on the Hyperstar. The MaxFR emission line filter series were designed for fast systems like the RASA and surprisingly also longer fl, f2-f8. Narrowband Ha Sii and Oiii Mono. Those of us who would want to go longer fl would benefit on a single filter set. Astronomik site described the filters as high contrast and no halo. Thanks 😊
If I get them :) Right now I have too much invested in the Baader!
It is possible the reason your Optolong L-eXtreme works "better" with your Hyperstar is because it might actually be a *worse* sample. If your sample has a 9nm bandpass instead of 7nm, it could be just enough to allow more signal (although more noise too).
Possible! Based on spectrometer readings of other L-eXtremes though, it seems the bandpass width isn't usually the issue, but the bandpass placement is. I might have a bandpass placed so that Ha is on the left edge of the bandpass. I can't know for sure without measuring!
Hi Cuiv, that was great! These series of Hyperstar videos have been invaluable!
I have the C8, Hyperstar V4 and L’eXtreme - but, the NBZ filter makes sense!
Whether I’ve won the production line “lottery” with my L’eXtreme is yet to be determined, but I know what to get if I’m unlucky!!
But a simple, anecdotal observation, wouldn’t the larger diameter SCTs (C8, C11, etc) have an advantage over your C6? Markedly I would have thought. Greater mirror areas with the same obstruction- proportionally less with the bigger dia SCTs.
You're correct, larger SCTs will have less of an issue on that front! But in a way they might have more issues with pre-shifted filters :)
@@CuivTheLazyGeek Why's that? The solid angle is the same, but the wasted solid angle gets smaller, Area/ditance^2. Can you explain why do you expect more issues then?
@@phadeezz There's simply less of a range of incidence angles to think about when pre-shifting a filter for a large obstruction (by diameter). In other words in theory, it would be easier to create a pre-shifted filter for that. From some spectrometer measurements of Baader F2 filters, they seem to preshift with RASA8 in mind (e.g. the filter doesn't perform as well on an F2 refractor - because then the part in the middle of the lens doesn't let in the desired signal since the bandpass isn't shifted enough... But it lets in light pollution).
Hey Cuiv, cool video as usual!
I was wondering if you'd be keen on doing a video about how to chose the right camera? What to look for depending on what type of object you're planning on imaging. There's a lot of different type of cameras, and I'm not convinced that more expensive always means better depending on what you're after. I'm definitely a bit lost on the impacts that pixel size, Well capacity, read noise etc. can have. Also, how much do you actually gain from going mono+ filters against using an colour sensor.
That's a huge, huge roadmap there :-) just mono vs OSC can start discussions that span months and hundreds of posts :p
As a short intro, Nico from Nebula photos has a great summary: ua-cam.com/video/LQCSAeKzqjM/v-deo.html
Cuiv, have you tried the new NBZ II? How about the NBZ UHC? Love to see the difference if any to the NBZ or L-Extreme. I'm also putting together a C6 hyperstar!
Should have watched this video before I bought the Optolong Extreme for my Hyperstar. Luckily I can still return it. Especially embarrassing for me since I have a background in optical engineering, and knew that thin film filter center wavelength shifts shorter with angle. But I was too dumb to consider my increase in focal ratio would increase the light cone angle at the filter (facepalm).
Has anyone in the industry considered thermal control of these filters to compensate? I know from experience that thermal expansion of thin film filters can change the dielectric coating layer thickness, and shift the center wavelength in the opposite (longer) direction.
I noticed that Antlia says their 3 nm Pro filters can be used with nearly all systems as fast as f/3. So if I get a Hyperstar at F2, it is likely to be a problem with those filters?
Sort of offtopic but how are you liking the CEM60?? Wish they still sold that model. Been looking on the used market but not having any luck currently. As always, another great video.
For now it's excellent and very reliable!
This video is over a year old and I would love an update as there are a LOT of new NB filters for OSC cameras coming out that are supposedly suitable for Hyperstar and RASA scopes. i have both 11" SCT non HD as well as a 8" SCT HD....both with Hyperstar V4. I also use refractors from 80mm to 156mm. I have had excellent results with a TRIAD filter on the refractors but looking for a better solution for the Hyperstars. These filters are expensive so looking for the best bang for the dollar.
Thanks! You made a very quick reference remark to this on your last video and I was wondering just what the heck that meant. Now I know!
So. Are you considering getting a C8 Edge or something even bigger (I have both, the C8 is really not all that much bigger than the C6 when it comes to ease of handling and I hear the Edge version is the one to get if you image - not sure that is a rabbit hole I want to go down..... :^) ).
I'll keep my Hyperstar C6 - there are workarounds such as pre-shifted filters that work great with it (in theory, in practice the filters I got from Baader have QC issues).
I just ordered IDAS NBZ filter. I wonder if the data in Altair shows same results as IDAS, where there is difference between f/2 and RASA. Well, I can actually test filters. I have nice spectrometers. Will show you results, if I get to them.
Since you are covering RASAs now, it would be great if you can cover some backfocus details. I.e. now I'm thinking about getting a new ZWO camera with 17.5mm backfocus, while my present has 6.5 mm. However on the Starizona store there is only 4 options for ZWO: cooled and cooled 54mm flange, uncooled x 2. I'm not quite sure if I can get into focus with the new one. Ordered some extensions, so I think I can check that. Still, would be nice to hear more from you on the subject.
I wish I had spectrometers.... One of those filters from Baader I got is REALLY dodgy and doesn't seem to pass its advertised bandpass :/
On the backfocus, I won't cover that, simply because I only know for my telescope (ZWO cooled camera means 17.5mm back focus on the camera side, no idea about the rest). Your best bet would be to ask Starizona directly!
Thanks for sharing this info.. but wouldn't a larger primary (say the 14" RASA) increase the efficiency of this NB filter, considering having the same obstruction dimensions from the front mounted camera?
Maximum incidence angle would still be the same, but minimum incidence angle will be lower - so there will be a larger range of incidence angles to consider. We then have the choice of using 12nm bandpasses like IDAS NBZ to have Ha pass to some extent across those incidence angles , or preshift the bandpass (while keeping the ability to make it narrower) for the average incidence angle (perhaps tweaking towards higher incidence angles, which represent more light - but it means we'll likely be "closing off" the central aperture more to Ha (while keeping it open for light pollution).
It is a pity someone does not make an astro camera with a curved surface sensor for f2.2...just how good would that be?
I am always wondering if the cables from the camera which obstruct some light create some sort of weird diffraction spike.
It does in theory, although for now I haven't had issues!
SIr can you make a video showing us how to get proper flats. my conners are always whited out and i can not get background extraction to remove this. do we need to increase our adu or decrease adu target? this video will be very much appreciated
Sounds like overcorrection of flats, have you applied bias or dark flats to them?
Mr Cuiv. Your hopes are ok, this video is very useful! Thanks for sharing. I just have some questions (as I have a C6 and an Hyperstar sounds interesting). An Optolong L enhance and a L pro filter would work with a setup like yours??
And the last question (as Hyperstar for C6 is not so cheap) as a final conclusion, do you recommend buying it?
Thanks again for this invaluable information!
I still love my Hyperstar C6 - for me it works great. An L-eNhance would work great (and rather than an L-Pro, I'd just use a UV/IR cut filter), and an IDAS NBZ as well!
@@CuivTheLazyGeek thank you very much!!
This is SPOT on with what I saw when using my Optolong Extreme filter with my Hyperstar f1.9 !! It gathered very little HA compared to OIII . I am going to start using monochrome on my hyperstar but I need to invest in FAST filters should I go with baader or should I look at some on else’s ??? It’s quite an investment they are expensive.
OK so I will give you my experience with the Baader fast filters: terrible. Out of 6 filters ordered (two filter sets), one had a chip in the middle, one had black paint on the surface, and at least one had the bandpass in the wrong place (causing very little OIII to pass through - verified via spectrometer). I'm in the process of getting all of those replaced - I sure as heck am not buying from Baader anymore.
@@CuivTheLazyGeek I think I recall watching that on a video of yours. I see they are now making special “CMOS” versions is that the ones you got? So what set do you recommend that will reach f1.9 on my Edge 8HD
Is it possible to create a positive angle of incidence to the primary mirror and incoming light so that the central obstruction is not in the center, rather off to the side instead?
Yes, there are designs like that, but they come with a slew of problems to overcome
I had a feeling this video would come out. Almost predicted it just not publicly.
Looks like that cold wind has started over there.
I hope some people do come out with some way to reduce the obstruction. Rasa images to me seam to always lack contrast.
So to be clear, I still think RASA and Hyperstar are amazing! They do have considerations in terms of narrowband, you need to use the right tools for them :-)
@@CuivTheLazyGeek I do agree. If only using a mono camera with a RASA was easier.
Thanks Cuiv! But I don’t get your “double whammy” point (at 8:38). Why would the light pollution frequencies not also be stopped by the central obstruction? Surely all the light rays will be parallel, whatever their frequency?
The part of the LP that overlaps the target signal will also get stopped yes as incidence is the same. But light pollution is present throughout the whole spectrum, so other LP wavelengths just step in through the shifted bandpass - in other words the shifted bandpass can end up passing only LP, and no signal.
Thanks for the information. I'd been considering the hyperstar for my 9.25 and after watching your initial video on the C6, went ahead and purchased it as I hadn't previously known of it's existance. My wife has since intercepted it and couriered it off to Santa, who has promised that he will deliver it in another 33 476 minutes.
Do you remain enthusiastic about the setup, and will you continue to use it much?
I live in a bortle class 5 area, so not as bad as Tokyo, and have a couple of CLS, UHC and LPR filters to try out but am hoping to take advantage of the shorter exposure times.
I LOVE the Hyperstar, and I've been using it pretty much exclusively!
Please review the Celestron Filter. I do not understand why you don't use the manufacturer's recommended filter.
I don't have the Celestron filter and don't plan on getting it - it's for RASA, not Hyperstar, not even sure it would fit! Overall it's very similar to any other general purpose filter like the Optolong L-Pro for instance (which I already have - but don't use much because I prefer to just go UV/IR cut in that case for easier color balance). Still, it's very different from narrowband, which is the topic of the video.
@@CuivTheLazyGeek Thanks, I am still in the OSC clan. I am studying before going mono.
Are there actually any lens-based optical systems at f/2?
Sure, the Samyang 135mm F2 Lens for instance ;)
@@CuivTheLazyGeek Oh yeah. Forgot about that one.
I have a Celestron C6 too and I didn't know it was compatible with Hyperstar. I thought that only the Celestron C8 Edge HD and above had this feature.
It's awesome with Hyperstar! But yes the CO is large - still, it's the smallest and lightest hyperstar setup I can think of :)
@@CuivTheLazyGeek I don't think I'll try this setup. The Hyperstar is as expensive as the C6 OTA and also there's the camera.
Makes me glad I don't use narrow band filters with my Hyperstar.
I don't completely get the reason for the blue shift. Seems that it should be shifted to longer wavelengths (i.e. red shift). I come to this conclusion by assuming the filter passes a particular wavelength at normal incidence. For broadband white light coming in at an angle, it would seem to require a longer wavelength of light to project onto the normal direction at the pass wavelength, not shorter. I must be missing something. I would love a more technical reference on this if you know of one.
www.alluxa.com/optical-filter-specs/angle-of-incidence-aoi-and-polarization/
@@CuivTheLazyGeek Thanks for the reference. That certainly has the equation showing the "blue shift," but didn't explain how it was derived. In the mean time, after doing a bit of google investigating, i think I understand it now. My original assumption as to how the filters work was wrong. BTW -- I'm a recent/new subscriber and love the channel.
Best would be to put the filter in front of the objective lense i.e. outside the telescope at the front but that would require a massive filter costing $$$$$
Yeah, like a solar telescope for instance... Not exactly cheap indeed!
I finished a detailed review and some simulations of fast filters for hyperstar on my channel - inspired by this video I think you will find it interesting
Hang on... is that a CEM70? When did that happen? Did I miss a video? :)
CEM60 - got it second hand recently, haven't made a video on it at this point
I have a RASA 8 and use ultra highspeed SHO filters, so I have no idea what you are talking about. My pics look fine.
The video is over a year old by now, there weren't many highspeed specific filters at the time! Glad the highspeed SHO filters are working for you - mine didn't, the band passes were very poorly placed (checked via spectrometer), leading to some signal coming through, but less than 30% or so transmission.
So overall it looked like the filters were working, but far, far from spec!
Since then, based on further measurements I did, Baader fixed their filters and separated them further depending on the use-case.
Just saying, it's possible that the filters you have are great in part because of my videos' impact :p
So, my astronomik max fr filters are okay for my RASA 8, right? I sold one of my kidneys to get those filters
Should be OK! I haven't tested them though :-)
There is a IDAS NBZ Ultra High Speed version and it's cheaper.
Yep, I think it's cheaper because it's less versatile. For RASA8 it does add a few percentage points to overall H-Alpha transmission, but on slower FLs you lose quite a bit compared to the non-UHS version
Instead of hyperstar method isn’t worth just put piggy back fast triplets refractor for the same money?
Could make sense indeed :p But slower optics.... Sigh, always a difficult choice!
@@CuivTheLazyGeek
That’s true
I know this video is an older video, but your affiliate links are out of date. Just FYI.
First!
Why do I get the feeling you're often first Derek? :D
@@CuivTheLazyGeek I'll tell you my secret... I have the bell notification set to 'on' so I can get that fresh AP info hot off the press! I also have the next week of clear skies and I'm stoked! Thinking of hitting Orion tonight... it's like cooking eggs to a chef, very basic, but also very technical to get it perfect and improve one's skills.
Great info, very scientific, well done, thanks. 🪐