Schmidt Cassegrain Telescope (SCT) Modification
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- Опубліковано 1 гру 2024
- Here we show step by step how to make 5 upgrades to a Celestron C11 SCT optical tube which include:
1. Adding nylon screws to the baffle tubes to try and reduce mirror shift
2. Adding internal fans with deflection plates to create a laminar flow acros the face of the primary mirror
3. Adding a temperature sensor to the backside of the mirror
4. Replacing the stock grease with a much better high temp low vapor pressure grease
5. Flocking the inside of the optical tube
At the end of the video we discuss the performance of each improvement after a year of testing and share Dave's latest astro-image of the Orion Nebula taken with the improved telescope
This is the companion video to two videos posted previously:
1. Celestron 11" SCT Tear Down video • Celestron C11 SCT Disa...
2. Celestron Motorized Focuser • Celestron Motorized Fo...
For more astronomy content like this and astro equipment reviews you might want to visit my web site www.california...
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Here are links to some of the items shown in the video. Some are affiliate links which can earn a commission at no cost to you and help to support this channel.
1. Noctua Cooling Fans: amzn.to/3HP5cDv
2. Krytox LVP Lubricant: www.zoro.com/k...
3. Panel Connector: amzn.to/3VgrP6I
4. Right Angle 5.5 x 2.1mm Power Cord: amzn.to/3YJZ0Ts
5. Yocto Environmental Sensor: www.yoctopuce....
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7. ASTROMI.CH Weather Station: www.astromi.ch...
8. Protostar Flocking Material: www.fpi-protos...
Great watching your series and seeing the ingenious mods. Liked the disassembly video-I part-disassembled my first Celestron, a 1970s C5, for cleaning back in the 1980s, but it was excellent getting a close look inside the C11 Edge. Choice of a premium low vibration, long-life fan must have been important-but I guess it’s off during imaging? Your Great Nebula image is brilliant, very 3D :-)
The fans are kept on even while imaging. The objective of the fans is to try and get a laminar flow across the face of the mirror, not so much for cooling. Anyway, it is not clear if the fans actually help in that regard.
Amazing. I performed the Nylon screws install on my C11 XLT and in hindsight, i would not have done it if i knew what i now know; the difference in improvement was minimum. I mostly capture planetary so I'm always capturing at high magnifications were mirror shift/flop is a real problem and installing the Nylon screws did very little to improved this. The scope really could do with a redesign, perhaps installing bearings on the outer baffle tube, were they would glide up and down on the inner baffle tube to stabilise the mirror instead of relaying on vacuum grease!. I did install cooling fans too. On the XLT there is no option to install fans without taking the scope apart, there are no ready made recesses for fans to be installed. This has made a big difference for me, so was worth taking the scope apart for this. Thanks for the video.
You are welcome. Sounds like your experience with the Nylon screws and internal fans matches Daves. Not so much improvement for the screws but noticeable improvement with the fans.
@@astronomytipsreviewswithcu740
Hello! I have some issues with my 9.25 HD while doing deep Sky imaging using the 0.7x reducer. During 1-2 hours the captured single frames of 90 seconds will slowly move down in RA axes. So when I'm over laying the first and last image of the whole session, Orion moved roughly through 1/5 of the aps-c Sensor. I'm guiding via a separate guide scope and checked the graphs. I could reproduce the very same results on the next clear evening. I'm wondering if this could be caused by mirror flop too or if this happens suddenly but not steady over the entire imaging Session..what do you think? Thank a for the great Video!!
I quickly made 2 vids from some of the frames of 2 nights of roughly 2 hours of exposures each. so the image drift represents roughly 2 hours and guiding was super stable all the time: ua-cam.com/video/M9dvJ_iYpz0/v-deo.html
ua-cam.com/video/xd1t2lO3Om4/v-deo.html
@@andreas_r136 Mirror flop. I suggest an on axis guider as I have the same problem using a separate guide scope.
@@astronomytipsreviewswithcu740 hi! thanks for your reply. I will get mine tomorrow (decided to go with the bigger celestron one to have enough margin to the aps-c sensor. but is there nothing to fix that? I thought I might remove the whole main mirror cell for once and check if the retainer ring of the main mirror is properly tightened up .. maybe .. Its hard to believe that this is a general design flaw of the edgeHD's as so many ppl are doing deep sky imaging with them . .
That is an amazing shot. Would have liked to have seen a before/after.
Very precious information about these mods I've already heard before, thank you so much Curtis !
But to scary for me to try on my C8 edgeHD, I've just replaced the original red grease by a much higher grade one made by Baader and it reduced shifting significantly.
To equalize telescope temperature, I'm just using one Cool Edge fan from Arizona, but secondary mirror needs to be removed (not really a problem for me as I often shoot with an HyperStar).
Awesome work gents!
Happy to hear that!
Thank you for posting this. This video is great. I've been looking for this info for a while.
One quick question - can you please provide the prat number for the Krytox grease? There appear to be a few different version, and I'd hate to get the wrong one.
Thank you
There is a link below the video to all of the components used in this modification. Here is the link to the high vacuum Krytox grease Krytox LVP Lubricant: www.zoro.com/krytox-vacuum-gr...
@@astronomytipsreviewswithcu740 thank you. This will teach me to read descriptions under the video... :)
He didn't need to explain the shirt...ICONIC Simon & Garfunkel. His wife has a brilliant sense of humor. Nice work!!! Carpe noctem.
Garfunkel, one half of the duo and co-writer of the famous song, summed up the meaning of this song by stating, “this is a song about the inability of people to communicate with each other”
Not to mention the cover by Disturbed that has been widely popular for the past 7 years.
Thank you for the very interesting video. Someone was using a method of drilling a hole in the outer wall near the mirror and pushing it from the outside to secure it. I would like to try this myself.
How much does the primary mirror travel in / out max ?
Please state which video you improved or fixed the motorized motor. I am struggling to get the motor to complete the focus calibration. Thank you
Here is the link ua-cam.com/video/zdADiHmGLpw/v-deo.html
Thank you for the link.
I’ve found an ingress of dust on my mirrors and corrector plate after installing my fans. I keep them turned off when imagining because of vibrations. Do you have any tips regarding the dust?
Filters on the fans.
@@astronomytipsreviewswithcu740RGB or narrowband?
@@christopherleveck6835 Not clear what you are asking.
Did you find flocking the inside to be benefical? My RASA corrector plate is quite dirty and when going to uninstall it for cleaning, i´m very tempted to remove the primary and flock the inside :)
Dave said he did not see a compelling improvement from it. But since it was very simple and inexpensive while he had everything apart you may want to do it. You don't have to remove the primary, just the sides of the tube.
Curtis and Dave thanks for the very instructional video. as you know i only watch your astronomy activities from the outside or better to say i like to watch your beautiful images at the end of the often tedious activities. the good news is your system was not worse after the modification but better as you hoped for. i say this because i think it is always easy to mess things up when they need very high precision handling. i would be curious if the design flaw should/could have been avoided by the company in the first place or is that only obvious after specific use?
Mirror flop is inherent to the way the focus mechanism works. Probably could make it better but at a higher cost.
@@astronomytipsreviewswithcu740 I had a takahshi 180-c before. it has the same slight mirror movements when focusing in /out as the celestron (also using a similar prim mirror focus system) . .. but when doing orion with the only reducer they provide at F9,8 - there was no moving of the image throughout the whole ~ 2 hours session. I just checked my raw images from last year.
I did not see the repair to the Focus Motor ?
Not in this video. Try the one on the Focus Motor Fix
I thought the last thing you want is air swirling around inside the optical tube and in front of the primary mirror?
Correct. You want a laminar flow of air across the mirror if you can get it. Same with the upper atmosphere.
Disappointed you didn’t cover how you realigned and collimated everything again after such a major strip down. Hopefully you will cover that in the next video
I considered that but the video was getting to be too long. We just used my Hotech SC Collimator to do the full re-alignment. With the SCT on the mount set at 90 deg it is relatively simple to set up.
@@astronomytipsreviewswithcu740 I take it then that there is no adjustments that need done to the primary mirror at all. It’s just a matter or re assembling each part in the original position and then collimating the secondary with the hotech
@@teslar1 Correct.
Trouble is you start Inttoducing fans, they also suck in dust. If you have filter to stop dust it also restricts airflow. Would not use a fan to cool mirror on an SCT
I've used fans on my 14" and now 11" SCT for years and they help cool down the primary without any problems that I have encountered. But, to each their own choice.
You are an experienced astronomer. You probably know that motorized focuser that shifts mirror all the time will eventually bring to disaster.
You have to use off line focuser and lock mirror on your telescope.
I could recommend Moonlite motorized focuser. Then, you will never touch mirror, and avoid trickery in fixing self inflicted problem.
SCTs focus by moving the mirror as you say. This cause mirror shift when focusing which moves the target off center. Other than an inconvenience, this is not a major problem. The other problem with using the mirror to focus is mirror flop which describes the shifting of the mirror under its own weight when the angle of the telescope shifts significantly while tracking across the sky. This can also cause frustration but with plate solving it is not a killer problem. Indeed, an external focuser can help eliminate focus shift but will not fix mirror flop. That is because the "locks" on the Celestron SCT are not really locks. They are merely long protrusions which push up against the back the mirror to provide friction but they do not completely prevent the mirror from shifting. It helps, but doesn't completely eliminate the flop.
@@astronomytipsreviewswithcu740 External focuser WILL solve mirror shift. Ok.
First, lock of mirror is critical as external focus is.
Second, any shift or flop of mirror and I will never build sky model for 10 micron. As a fact, locking mirror and external focus allows building sky model with 5-6” rms precision and at least 7 min unguided with f10 and image scale of 0.4”/pixel.
Third, I don’t refocus after meridian flip, and speed of slewing is whooping 8 degree per second.
One more thing, I had once upon time sheeit Edge 9.25 that flopped and couldn’t collimate. I returned it, and ask for replacement from Celestron (no repair, but replacement). They sent my current scope. Never needed collimation, and never misbehaved. 1.5-1.8” FWHM and 0.3-0.4 eccentricity obtained in 70% sessions.
Unfortunately you can't use an external focuser like a moonlight whilst using a hyperstar.
@@Dasman5624 Yes, but I don’t care about hyperstar.
@@anata5127 sorry it sounded like you were recommending the guy thats using a hyperstar to get a moonlight!