Rebuilding a 12-inch Reflector: Budget Astrograph Setup
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- เผยแพร่เมื่อ 4 ก.พ. 2025
- In Part 3 of the Newtonian Rebuild series, I fine-tune the telescope's optics using a laser collimation eyepiece and implement a budget imaging setup. The image train includes a ZWO Electronic Automatic Focuser (EAF), ZWO 7x1.25” Electronic Filter Wheel (EFW), and the ASI1600MM Pro camera. This setup transforms the scope into a deep-sky astrograph!
Part 1: • Restoring a 12-Inch Ne...
Part2: • Rebuilding a 12-Inch R...
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Looking good, pretty exciting.
Hoping to get it deployed Monday - weather permitting. All the best Larry!
Maybe the answer is obvious, but curious why such a big telescope is on a tripod mount instead of an EQ platform style?
Is it to do with your observatory, or some other reason I'm not thinking about?
I'm in the process of building a DIY EQ platform for my 10", and I'm realizing I've never even considered a giant tripod/EQ mount style for it.
Are there advantages?
Thanks for the question! So, the tripod EQ mount that you saw in this particular video is not the deployment mount. It is a mount that I have in my workshop for testing and it is a mount that I use with grab and go setups. All of my telescope deployments are to my CEM120 mount which is affixed to a permanent pier inside my observatory. In my next video I will share the actual deployment and you will see what I am referring to in this comment. Many of my other videos, including a playlist on the CEM120, feature this more explicitly. Sorry for the confusion, I was simply using the GEM45 as a way to judge where the clam shell rings would be positioned inorder to achieve balance in the DEC axis. Most of the wight is in the primary mirror and its cell, so the center of gravity is shifted towards the read of the tube. That means the front of the tube will be extended forward. My concern is the rise (32") from center of gravity to the highest point of the OTA when mounted in my latitude (41deg). Given my dome is an 8' diameter I have about 48" or radius from saddle to dome ceiling - however, the dome shutter is cable driven and that cable does run down the center of the dome and limits headroom to something much lower. I have to see if the cable sits above the high point of the OTA in the home position (pointing celstial north). As for your plan - it sounds like you are going to build a permanent pier? If so, I applaud that approach. Life becomes much easier with a permanent pier. You will need a mount that can handle the wight of your scope and image train. On a permanent pier I would use 60-70% of the mounts rating. So if it is rated for 60lbs, plan on your rig weighing in around 40lbs max. Cheers!
Huh. I've been (naively?) relying on a laser collimator - doing collimation each night. I'll have to try the star approach. It would avoid having to take the camera train out, redo the rotation, etc. (Also, I treat my 10" Newtonian as a grab-n-go OTA. Not sure I could handle something larger that way, but mine is manageable for set up and tear down each night.)
I think the laser and or Cheshire eyepiece method produces acceptable results - however, best practice is to do a star test (inside and outside of focus) for best results. We'll see soon enough with this beast. What's the weight on your 10" OTA? I think my comfort for grab and go tops out in the 25-30lb zone. Cheers and thanks for the comment!
@AstroDNAObservatory I have the Apertura 10" f/4 Imaging Newtonian, which is just under 30 lbs. I set my tripod+mount, then bring the OTA out, with the image train, mini-PC, etc. all in place. So I only have to make 3 trips. I imagine the OTA with equipment on it is ~35 lbs.
If you're going to use a laser the FIRST Thing you have to do is make sure that the LASER is collimated. There are videos on how to check it so I won't get into that. Now how to do a 'proper' collimation without the laser. The VERY FIRST thing you do is to ALIGN the main MIRROR in the TUBE! The mirror should be exactly centered in the tube by adjusting it in the mirror mount. Then you make it's optical axis perfectly aligned with the tube axis. To do this you can use the secondary holder, which has a central hole to hold the secondary mirror holder, you remove the secondary and adjust the spider so that central hole is perfectly centered in the tube. Now you sight down and observe the reflection of the spider looking thru the central hole to observe the center dot, put one on the main mirror if it doesn't have one, and using the adjusters on the back of the main mirror you center the image of the secondary's hole with the dot. You will NEVER touch these adjusters again in the collimation process once the mirror axis is centered with the tube axis. Now you put the secondary mirror back in and do the adjustments needed to it and you're basically finished! I won't get into adjusting the eyepiece holder tilt as most don't have the means to do it unless you use shims. There are some newer ones I have seen that do have tilt screws.
Thanks for sharing your guidance and insight. Agreed, another common issue with laser collimation tools is collimation of the laser itself... I opted not to cover gross alignment of primary and secondary in the video, perhaps I should have covered it. I kept the secondary assembled during the rebuild process and the post reassembly alignment was actually quite good. I plan to re-silver the mirror later this year and I will tackle the collimation process again at that time. Cheers!
@@AstroDNAObservatory I learned this method YEARS ago in a book I read on telescope making... and I mean 58 yrs ago when I was 12 and grinding my first mirror. I tried to find it in my book collection a few yrs ago but couldn't so I looked on the net. The exact method I have used for all that time was there with so much more info than that original article I read had so I want to give you this info to spread into the astro community. Enjoy!
memphisastro.org/wp-content/uploads/2023/08/Newtonian-Alignment.pdf
"Dome Geometry" .... Dude, I had to enlist the help of a russian mathematician to run monte carlo optimizations to help me figure out my dome offsets. I know that sounds like a joke, I wish it was.
The good news is that my offsets don't change with each telescope deployment. The mount remains fixed on the permanent pier. So all I need to do is calculate the GEM axis change. Due to the length and diameter of this OTA, I will have a problem at the home position (pointing polar north) when the dome shutter is closed. The cable does not clear the 32" rise of the OTA. The solution is to park the scope before closing. I'll demo in the deployment/first light video. Thanks for your comment!
@@AstroDNAObservatory Ya I mean on the plus side I now have an open source applet that anybody with a 300lb alt/az scope that's offset inside their dome can use to determine their own offsets just by slewing the dome and scope and doing very little actual work other than recording some numbers. Without trying to rack their brain over 3 dimensional euclidean geometry and nonsense that made my brain hurt.
Sounds like a nice setup. Are you running one of the planewave mounts with a rotator? Which Dome structure are you using for your obsy?
@@AstroDNAObservatory Ya it's a 24" with the rotator, the dome is an ACE Dome.