@marvinwhisman3333 - thanks for the comment. I got first light in last night, finishing the deployment video today, will flash a couple of subs from the sequence for all to see. I plan on shooting with the AT115EDT for the next 3 months. Focusing on targets in Gemini during January. Cheers!
You need more back focus with a filter, not less. Adding "1.5" in your calculation due to filter is exactly the opposite of what should have been done. The correct calculation, in the style shown in the video, should have been 12.5+20-1.5+2+22=55 . The traditional calculation goes something like this: 1) manufacturer required back focus = 55 mm, 2) adding a filter requires {filter thickness}/3 extra back focus, 3) total back focus required = 55 + {filter thickness}/3 , 4) the required length of extension tube would then be 55 + {filter thickness}/3 - 12.5 - 20 - 2 = 20.5 + {filter thickness}/3 .
@Nabby14 - You are absolutely correct. I think the best way to represent this would be that the back focus requirement should be increased by 1/3 the filter distance. So - if the original back focus requirement is 55, it becomes 56.5 in this case. That makes it clear that inserting an optical element with a higher refractive index results in a pushing out of the focal plane. Makes sense. The good news is that these calculations are really meant as the starting point - and actual field flatness and correction should be evaluated first hand. Thank you for pointing out my miscalculation - again you are spot on!
If you are benching the Celestron, try extending the the back focuser by 8" and pushing the mirror forward to obtain focus. If you like the out come you need to reduce the length of the centre tube in the mirror. My expreiment with a Mak produced a 'defraction limited' image.
@rodm1949 - interesting! I am going to focus on switching to an off-axis-guider as my primary C8 project this winter. Most of my frustration has been due to differential flexure. But I will research what you are suggesting as well. Interested in the Physics and Optics side of that modification!
@@AstroDNAObservatory I saw it as the angle of inception to the eye. By shortening the primary focus you need to increase the secondary length and reduce the north axis tube, using the mirror focuser there is too much mirror shift and a SCT focuser is essential.
The back focus is critic on all scopes so be aware, I bought an 8” Orion from a place called “All-Star” out of Canada and they told me back focus was 75mm..wrong, then they said 82.3…wrong again. Ended up being 55mm, very frustrating.
I've been there... Can be a challenge to get it right, but patience is everything I find... It may take a night of adjustments to get it nailed. Fortunately, my back-focus calculations worked well for the AT115EDT. I'm happy with the images with no visible aberrations in the outer fields. Thanks for commenting!
Thanks, Ken. I purchased mine from Astronomics. Here is a link to their website: www.astronomics.com/astro-tech-at115edt-f-7-ed-triplet-refractor-ota.html
Hello, nicely produced video, I stumbled upon your channel as I'm now looking into getting some longer range optics to dive more into deepsky. And after seeing some videos I've been left wondering, how would these telescopes compare to regular ultra-telephoto lenses? I'm asking mainly because these telescopes are just way too huge and heavy not just for transportation but also for my current sky watcher star tracker (that has 5kg max payload). For example new Canon RF 200-800mm seems pretty attractive in that regard. I just can't seem to find telescope that would quite fit my expectations, but if there was reasonable lightweight one which is at least +500mm, I'm pretty sure it would yield better results. What are your thoughts?
@Kori - thanks for the question. I have to say, longer focal lengths alone will not get you what you need for imaging deep sky objects. In fact the most important factor is Aperture - which is the diameter of the main objective or mirror used in the optics system. The larger the aperture, the more photons you can capture and condense onto your camera sensor. Regrettably, the larger the aperture - the more expensive - and often heavier - the system. I'm not experienced with the Canon lens you mentioned, but I have to believe it is heavy as well... I will be shooting some full frame images using my StarTracker, a Nikon mirror-less camera and lens setup each month in 2024 - but I'll be focusing on wide angle night-scapes, the constellations... Honestly, I don't think you'll get the results you are after with a long focal length camera lens - but I could be wrong and I yield to others in the hobby that have tried!
@@AstroDNAObservatory Thank you for the answer. Yes I was thinking that aperture must play a huge role. But if I'm doing my math right the lens in question that is F9 at 800mm should be aperture of ~89mm (also the lens is only 2kg/4.5lbs). When I was searching some lighter telescopes I found Tele Vue TV-85 which is 6.1lbs 600mm with 85mm aperture and also more expensive then the lens. So it's keeping me kinda confused, because by pure numbers one can't justify it over the other. So I'm assuming the extra cost comes from higher precision glass elements and maybe some specialized coating, inbuilt filters, weather sealing, etc.? I'll be looking forward for your 2024 shootings ^^
Your math is correct in that the focal length is the product of Aperture and Focal Ratio. So an F9 x 89mm of aperture gets you your 800mm. However, now you have a limiting factor of the F9 - which is very slow in the world of Astrophotography. Your exposure times for DSOs would be prohibitively long in my opinion. It is a bit tricky - but the nice part about this hobby (and any other) is that you can/should try out all scenarios. You have a thesis you can test. Thanks for watching!
I'm not in to astrophotography, just visual astronomy. My main is a 10 inch Dob, grab and go is a celestron 102 az refractor. Im just a year in, learning the basics, but when I upgrade telescopes, it will be the 102mm.
Hi, I enjoyed your video and the telescope looks great but as a beginner it's out of my budget of £600. I'm trying to cut through all the jargon and your video was straight to the point so I wondered if you could recommend anything? I'm using a Nikon D5000 DSLR if this makes a difference? TIA
@stevejones3812 - First, thank you for your comments and Happy New Year! Welcome to astrophotography. I would highly recommend looking at a telescope with a shorter focal length. Many say that an 80mm refractor is the best place to start, and I tend to agree. Since you wish to image, you should also look at Triplet designs - there are very good Doublets (two lens design) out there as well, but I think a triplet is your best bet. Finally, I would register with CloudyNights and begin scanning the Classifieds. I have made many purchases from forum members and have never been disappointed. The AT80EDT sells new for about $800, I am sure you can find a used sample in excellent condition well under your budget. If you should go with a doublet, look at William Optics Zenith Star lineup - I have enjoyed the 61mm model. Again, you'll find these at very good price points in the Classifieds. Keep in mind, you will need a field flattener with the scope, They are often sold in bundles. Final statement, if you stick with the main makers, you will be fine. Do not become obsessed with the specifications and the aperture. Just buy what you can afford and enjoy the journey. It is a long one!
What mount do you have or plan to use? Don't fall in the trap of buying a scope that's too big for the mount. Also you can get some good wide field images with lenses such as the Samyang 135 F2 which by the way doesn't need a field flattener. These sell for around £450 Any of the Cat51s give good results, again because of its petzval design you do not need a flattener. I've never used a Zenith Star 61 which does require a flattened (I bought a Cat 51, but it was close) but lots of people like them. Any scope in these sizes can normally be used with a star tracker size mount such as a Star Adventurer. They are also very portable if you plan to drive to a darker area to image the night sky. Most reputable suppliers sell decent short focal length scopes in the 50-72 mm dia range. If your budget is £600 and you are looking for a new scope, something around 60 mm is probably the way to go. There are many stunning images taken with scopes of this size, just don't expect to get close up images of galaxies and globular clusters. Some suppliers do sell decent used gear as well as do people on the various astronomy forums. Whatever you decide to do I hope you enjoy the journey, It can be expensive but you don't have to spend the money all at once, just upgrade your set up as and when funds become available.
@@KevinRudd-w8s thanks very much for your advise. From doing endless research it gets very difficult as a newcomer to distinguish between different models.of scope. From what I've learned in a brief few days it seems a very good quality mount is more important, my garden is bortle 3 so I've no real news to transport over big distance. I'm thinking about buying a decent mount, that tracks, now that will last up to slightly bigger scopes in the future and then focus on a scope in a few months. Does this sound about right?
@@stevejones3812 Yes, it is a very sound idea to start with the best mount you can afford that will have a large enough payload capacity to enable you to upgrade to a larger scope later on. Like all things astro photography, mounts are expensive especially if you buy the harmonic drive type. I started with a star tracker (star adventurer) which will take a scope up to around 61mm. There are a number of versions of these from companies such as I-optron and Sky Watcher, the more expensive ones have a motorised declination axis and go-to functions, the cheaper ones don't. They can all give good results. They sell for between £300 and £600 in the UK. Some come with tripods and some don't, it is very important that the tripod is sturdy enough to take the weight of the tracker and the imaging equipment if you plan on buying separately. You could of course start with a larger mount, such as an EQ5 or EQ6 size. These start up at around £1000 ( new) though you may find them cheaper second hand. Both of these have a far greater payload capacity than a tracker and are both very stable.
Good review. In your documentation, you mention a soft case for the ADT115EDT but the one I bought last year came with a hard case and the web site still indicates a hard case. Did something change? Have to watch your testing vid now to see what you think especially around the flattener and focuser.
I received a soft case with mine - interesting. When you say hard case - are you saying that the case was metal - like aluminum? The case mine came with is made of a material that feels like a cross between canvas and nylon. It has foam cutouts for the main OTA with eye piece adaptor attached. There are also slots for other accessories as well. I don't think there is room for the .8x reducer though.
@@AstroDNAObservatory Yes. Hard. Not I don't think it's aluminum all over but it's got metal handles, aluminum supports, locks, etc. In looking at the description now, it looks like a change after the last sale. The title still says "Hard" but the description is different, so I guess that's the current config. My bad. "Hard Carry Case: The scope comes standard in a heavy duty nyolon carry case. The case has a some nice pockets in the lid for paper storage as well as 7 different cutouts in the foam for accessory storage." If they changed it, I was hoping he would just enhance the case to allow for extra accessories like you mentioned. Would be nice to be able to store the scope for traveling and not remove the EAF.
One other tidbit as long as I'm typing. That visual back comes apart and you can remove the first piece which, I believe, is an M63 rotator with the locking thumbscrew. If you add that piece back in, you can then rotate the imaging train and leave the focuser locked in position. Make sure you lock it back though because it will cause sag if you don't.
@skye7690 - thanks for the comment! The 2" Filter wheel is actually secured to the camera using screws. You have to remove the tilt plate adjuster from the ASI2600 to reveal the holes. This is a little tricky, but there are a few videos out there on the procedure. Yes - you can use the 1/3 rule as a starting point. I have simply found 1.5mm works for my train calculation. I'll post some subs with this next video that shows my calcs seem to have worked out well. Nice flat field and round stars to the corners... Cheers!
@@AstroDNAObservatory Yes I've seen that method, interesting. Having a tough time calculating 55mm of spacers for my scope, but still working to achieve it.
Hey Nick - thanks for the comment. I think I speak directly to the glass quality at 04:45 in this video. It is the just after my brief commentary about APO triplet designs. I think the quality of the glass if FPL51 or higher. The triplet design does a good job in terms of color correction and chromatic aberration is well mitigated. Check out my latest video if you want to see how the glass performed on my first 15 images with the scope. The video presents them chronologically, so they generally improve as I became more in-tune with the rig and was able to dial it in to a state I was happy with. Thanks again - Cheers!
@anata5127 - I have not. Mostly because the cost of the Tak makes it inaccessible to many. I have never viewed or imaged with a Takahashi - but it is on my bucket list!
@Astro_Shed - good to know... sorry to hear. I actually have a Stellarvue SVX90T to cover that focal length. I plan on rotating it into the observatory second quarter of the year. Will do a review then... All the Best!
Great video! I love my AT60ED, have had it for a few years. Getting a larger AT refractor is on my list in the future.
Clear skies!
Thanks, will be publishing more images/experiences with the AT115EDT over these next couple of months. Loving so far!
Nice video. Appreciate all of the data you supplied on setting up the scope. Looking forward to seeing some photos that you might have taken.
@marvinwhisman3333 - thanks for the comment. I got first light in last night, finishing the deployment video today, will flash a couple of subs from the sequence for all to see. I plan on shooting with the AT115EDT for the next 3 months. Focusing on targets in Gemini during January. Cheers!
You need more back focus with a filter, not less. Adding "1.5" in your calculation due to filter is exactly the opposite of what should have been done. The correct calculation, in the style shown in the video, should have been 12.5+20-1.5+2+22=55 . The traditional calculation goes something like this: 1) manufacturer required back focus = 55 mm, 2) adding a filter requires {filter thickness}/3 extra back focus, 3) total back focus required = 55 + {filter thickness}/3 , 4) the required length of extension tube would then be 55 + {filter thickness}/3 - 12.5 - 20 - 2 = 20.5 + {filter thickness}/3 .
@Nabby14 - You are absolutely correct. I think the best way to represent this would be that the back focus requirement should be increased by 1/3 the filter distance. So - if the original back focus requirement is 55, it becomes 56.5 in this case. That makes it clear that inserting an optical element with a higher refractive index results in a pushing out of the focal plane. Makes sense. The good news is that these calculations are really meant as the starting point - and actual field flatness and correction should be evaluated first hand. Thank you for pointing out my miscalculation - again you are spot on!
Excellent video! I've been considering this scope for my next big purchase. I'm looking forward to seeing your results with it.
If you are benching the Celestron, try extending the the back focuser by 8" and pushing the mirror forward to obtain focus. If you like the out come you need to reduce the length of the centre tube in the mirror. My expreiment with a Mak produced a 'defraction limited' image.
@rodm1949 - interesting! I am going to focus on switching to an off-axis-guider as my primary C8 project this winter. Most of my frustration has been due to differential flexure. But I will research what you are suggesting as well. Interested in the Physics and Optics side of that modification!
@@AstroDNAObservatory I saw it as the angle of inception to the eye. By shortening the primary focus you need to increase the secondary length and reduce the north axis tube, using the mirror focuser there is too much mirror shift and a SCT focuser is essential.
I'm actually considering buying a scope of this size, so thankyou for this interesting video.
My pleasure - enjoy!
The back focus is critic on all scopes so be aware, I bought an 8” Orion from a place called “All-Star” out of Canada and they told me back focus was 75mm..wrong, then they said 82.3…wrong again. Ended up being 55mm, very frustrating.
I've been there... Can be a challenge to get it right, but patience is everything I find... It may take a night of adjustments to get it nailed. Fortunately, my back-focus calculations worked well for the AT115EDT. I'm happy with the images with no visible aberrations in the outer fields. Thanks for commenting!
Thanks for sharing your great video. Looks like a excellent telescope, but I can't find it in stock anywhere in the US.
Thanks, Ken. I purchased mine from Astronomics. Here is a link to their website: www.astronomics.com/astro-tech-at115edt-f-7-ed-triplet-refractor-ota.html
Hello, nicely produced video, I stumbled upon your channel as I'm now looking into getting some longer range optics to dive more into deepsky. And after seeing some videos I've been left wondering, how would these telescopes compare to regular ultra-telephoto lenses? I'm asking mainly because these telescopes are just way too huge and heavy not just for transportation but also for my current sky watcher star tracker (that has 5kg max payload). For example new Canon RF 200-800mm seems pretty attractive in that regard. I just can't seem to find telescope that would quite fit my expectations, but if there was reasonable lightweight one which is at least +500mm, I'm pretty sure it would yield better results. What are your thoughts?
@Kori - thanks for the question. I have to say, longer focal lengths alone will not get you what you need for imaging deep sky objects. In fact the most important factor is Aperture - which is the diameter of the main objective or mirror used in the optics system. The larger the aperture, the more photons you can capture and condense onto your camera sensor. Regrettably, the larger the aperture - the more expensive - and often heavier - the system. I'm not experienced with the Canon lens you mentioned, but I have to believe it is heavy as well... I will be shooting some full frame images using my StarTracker, a Nikon mirror-less camera and lens setup each month in 2024 - but I'll be focusing on wide angle night-scapes, the constellations... Honestly, I don't think you'll get the results you are after with a long focal length camera lens - but I could be wrong and I yield to others in the hobby that have tried!
@@AstroDNAObservatory Thank you for the answer. Yes I was thinking that aperture must play a huge role. But if I'm doing my math right the lens in question that is F9 at 800mm should be aperture of ~89mm (also the lens is only 2kg/4.5lbs). When I was searching some lighter telescopes I found Tele Vue TV-85 which is 6.1lbs 600mm with 85mm aperture and also more expensive then the lens. So it's keeping me kinda confused, because by pure numbers one can't justify it over the other. So I'm assuming the extra cost comes from higher precision glass elements and maybe some specialized coating, inbuilt filters, weather sealing, etc.? I'll be looking forward for your 2024 shootings ^^
Your math is correct in that the focal length is the product of Aperture and Focal Ratio. So an F9 x 89mm of aperture gets you your 800mm. However, now you have a limiting factor of the F9 - which is very slow in the world of Astrophotography. Your exposure times for DSOs would be prohibitively long in my opinion. It is a bit tricky - but the nice part about this hobby (and any other) is that you can/should try out all scenarios. You have a thesis you can test. Thanks for watching!
I'm not in to astrophotography, just visual astronomy. My main is a 10 inch Dob, grab and go is a celestron 102 az refractor. Im just a year in, learning the basics, but when I upgrade telescopes, it will be the 102mm.
Hi, I enjoyed your video and the telescope looks great but as a beginner it's out of my budget of £600. I'm trying to cut through all the jargon and your video was straight to the point so I wondered if you could recommend anything? I'm using a Nikon D5000 DSLR if this makes a difference? TIA
@stevejones3812 - First, thank you for your comments and Happy New Year! Welcome to astrophotography. I would highly recommend looking at a telescope with a shorter focal length. Many say that an 80mm refractor is the best place to start, and I tend to agree. Since you wish to image, you should also look at Triplet designs - there are very good Doublets (two lens design) out there as well, but I think a triplet is your best bet. Finally, I would register with CloudyNights and begin scanning the Classifieds. I have made many purchases from forum members and have never been disappointed. The AT80EDT sells new for about $800, I am sure you can find a used sample in excellent condition well under your budget. If you should go with a doublet, look at William Optics Zenith Star lineup - I have enjoyed the 61mm model. Again, you'll find these at very good price points in the Classifieds. Keep in mind, you will need a field flattener with the scope, They are often sold in bundles. Final statement, if you stick with the main makers, you will be fine. Do not become obsessed with the specifications and the aperture. Just buy what you can afford and enjoy the journey. It is a long one!
What mount do you have or plan to use? Don't fall in the trap of buying a scope that's too big for the mount. Also you can get some good wide field images with lenses such as the Samyang 135 F2 which by the way doesn't need a field flattener. These sell for around £450 Any of the Cat51s give good results, again because of its petzval design you do not need a flattener. I've never used a Zenith Star 61 which does require a flattened (I bought a Cat 51, but it was close) but lots of people like them. Any scope in these sizes can normally be used with a star tracker size mount such as a Star Adventurer. They are also very portable if you plan to drive to a darker area to image the night sky. Most reputable suppliers sell decent short focal length scopes in the 50-72 mm dia range. If your budget is £600 and you are looking for a new scope, something around 60 mm is probably the way to go. There are many stunning images taken with scopes of this size, just don't expect to get close up images of galaxies and globular clusters. Some suppliers do sell decent used gear as well as do people on the various astronomy forums. Whatever you decide to do I hope you enjoy the journey, It can be expensive but you don't have to spend the money all at once, just upgrade your set up as and when funds become available.
Sage advice...
@@KevinRudd-w8s thanks very much for your advise. From doing endless research it gets very difficult as a newcomer to distinguish between different models.of scope. From what I've learned in a brief few days it seems a very good quality mount is more important, my garden is bortle 3 so I've no real news to transport over big distance. I'm thinking about buying a decent mount, that tracks, now that will last up to slightly bigger scopes in the future and then focus on a scope in a few months. Does this sound about right?
@@stevejones3812 Yes, it is a very sound idea to start with the best mount you can afford that will have a large enough payload capacity to enable you to upgrade to a larger scope later on. Like all things astro photography, mounts are expensive especially if you buy the harmonic drive type. I started with a star tracker (star adventurer) which will take a scope up to around 61mm. There are a number of versions of these from companies such as I-optron and Sky Watcher, the more expensive ones have a motorised declination axis and go-to functions, the cheaper ones don't. They can all give good results. They sell for between £300 and £600 in the UK. Some come with tripods and some don't, it is very important that the tripod is sturdy enough to take the weight of the tracker and the imaging equipment if you plan on buying separately. You could of course start with a larger mount, such as an EQ5 or EQ6 size. These start up at around £1000 ( new) though you may find them cheaper second hand. Both of these have a far greater payload capacity than a tracker and are both very stable.
Good review. In your documentation, you mention a soft case for the ADT115EDT but the one I bought last year came with a hard case and the web site still indicates a hard case. Did something change? Have to watch your testing vid now to see what you think especially around the flattener and focuser.
I received a soft case with mine - interesting. When you say hard case - are you saying that the case was metal - like aluminum? The case mine came with is made of a material that feels like a cross between canvas and nylon. It has foam cutouts for the main OTA with eye piece adaptor attached. There are also slots for other accessories as well. I don't think there is room for the .8x reducer though.
@@AstroDNAObservatory Yes. Hard. Not I don't think it's aluminum all over but it's got metal handles, aluminum supports, locks, etc. In looking at the description now, it looks like a change after the last sale. The title still says "Hard" but the description is different, so I guess that's the current config. My bad.
"Hard Carry Case: The scope comes standard in a heavy duty nyolon carry case. The case has a some nice pockets in the lid for paper storage as well as 7 different cutouts in the foam for accessory storage."
If they changed it, I was hoping he would just enhance the case to allow for extra accessories like you mentioned. Would be nice to be able to store the scope for traveling and not remove the EAF.
One other tidbit as long as I'm typing. That visual back comes apart and you can remove the first piece which, I believe, is an M63 rotator with the locking thumbscrew. If you add that piece back in, you can then rotate the imaging train and leave the focuser locked in position. Make sure you lock it back though because it will cause sag if you don't.
Excellent, good to know. I'll have to measure the width and plug that into the backfocus spreadsheet!
Interesting video. How did you attach camera to wheel since both are female. Also isn't the formula 1/3 of the filter width?
@skye7690 - thanks for the comment! The 2" Filter wheel is actually secured to the camera using screws. You have to remove the tilt plate adjuster from the ASI2600 to reveal the holes. This is a little tricky, but there are a few videos out there on the procedure. Yes - you can use the 1/3 rule as a starting point. I have simply found 1.5mm works for my train calculation. I'll post some subs with this next video that shows my calcs seem to have worked out well. Nice flat field and round stars to the corners... Cheers!
@@AstroDNAObservatory Yes I've seen that method, interesting. Having a tough time calculating 55mm of spacers for my scope, but still working to achieve it.
You forgot the single most important variable in your review. The quality of glass. 😮😮😮😮
Hey Nick - thanks for the comment. I think I speak directly to the glass quality at 04:45 in this video. It is the just after my brief commentary about APO triplet designs. I think the quality of the glass if FPL51 or higher. The triplet design does a good job in terms of color correction and chromatic aberration is well mitigated. Check out my latest video if you want to see how the glass performed on my first 15 images with the scope. The video presents them chronologically, so they generally improve as I became more in-tune with the rig and was able to dial it in to a state I was happy with. Thanks again - Cheers!
Have you tried to compare this refractor with Tak 120 and 130?
@anata5127 - I have not. Mostly because the cost of the Tak makes it inaccessible to many. I have never viewed or imaged with a Takahashi - but it is on my bucket list!
@@AstroDNAObservatory well don’t bother with the TAKFSQ85, its not good at all with modern small pixel cameras…I sold mine..☹
@Astro_Shed - good to know... sorry to hear. I actually have a Stellarvue SVX90T to cover that focal length. I plan on rotating it into the observatory second quarter of the year. Will do a review then... All the Best!
@@Astro_ShedCorrect!
@@AstroDNAObservatoryWhat about Esprit 120?
A wireless mic pinned to your jacket will reduce the echo and produce a more pleasant listening experience for the audience.
Agreed, I have one somewhere in my gear bin. I will break it out - thanks for the feedback, you are 100% correct.