Telescope questions (and a really long story)

[michael-lloyd]

I finally spent some time troubleshooting the Celestron CG5 mount for my 8" Newtonian telescope today. It's been out of service for more years than I can remember. About a year ago I replaced the motor control board and hand controller. I ordered both from Amazon and managed to order the parts for an Alt-Az mount. I figured out that I had the wrong controller because of a post on this forum, by accident, a few weeks ago. I found out that the mother board was the wrong board today.

Guess what... the Alt-Az stuff almost works. Ok, not really. The dec motor runs in both directions but the Az motor only ran in one direction. And a few other things were wonky.

While I was waiting for the wrong parts to come in, a few years ago, I ordered some parts so I could mount one of my Canon DSLR's to the telescope. Then I ordered an Orion thin off-axis guider (you have to go off axis... they said so in the movie Contact) and an Orion Starshoot Autoguider. I figured I may as well use the AG port since it was there.

I should point out that while I have a good understanding of terrestrial photography (still shoot a 4x5 and develop my own film, plus have too many DSLR's, yes that's possible, all vacations are for photography, etc), I am clueless when it comes to astrophotography. How hard can it be right... just plug some stuff in, click some buttons, poof... Hubble images. Uh... WRONG!!

Which leads me back to where I was around this time last year. Since the mother board and controller didn't work I decided to put my astrophotography stuff together. I still remember sitting on the couch looking at a pile of metal and electronics with no clue how it should go together. I have adapters and gizmos but I don't know if I have enough adapters and gizmos or even if they are the right adapters and gizmos. I need some help figuring all that out.

I ordered the right board today. BTW- if you have an older Celestron mount CG-5 AGT, Celestron doesn't make or sell parts anymore. I found the power supply (which I didn't need but thought I should stock one) and mother board on a site called Agena Astroproducts. They were the only site that carried the power supply and their mother board price was significantly cheaper than anyone else (I didn't say cheap). I seriously considered abandoning the mount in favor of something newer but it's barely been used and for my needs it should be fine.

I need some time to get familiarized with the telescope drive with eyepieces again before I consider putting a camera on it. I know it's not the greatest mount for astrophotography but it's what I have and it'll surely be useful for teaching me something. To the point (finally), I need someone to look at my little pile of electronics and aluminum and tell me what to do with it.

I collimated the telescope after the failed board replacement. About 15 times It's the only thing I could do. I have a 2" Glatter collimator. That thing is nice. It makes collimation pretty easy. I doubt I can remember how to do that but it didn't take much to figure it out the first time I used it.

I have a small selection of eyepieces-

Celestron 1.25" 2X Barlow. Ultima series
Celestron 1.25" 5mm Ultima series that for some reason has a blue filter on it. I'm the guy that put it on there but I don't remember why

Sirius 1.25" Plossl eyepieces
7.5mm
10mm
17mm
25mm

20mm 1.25" Plossl but no idea who makes it

2" Scopetronix Maxview 40. The eyepiece is 2" but it fits into a 1.25" focuser

I'll pop back in here once I get my parts in and have gotten familiar with the telescope again

[steve-fung]

Hi Michael, I read your post and would like to help, but I'm not sure what are the specific question(s). One sounds like how to get your CG5 electronics working. Have to see it in person to make any comments on that. Another sounds like how to get your optical chain together for astrophotography. Seems like you already got collimation down. As a quick test, are you able to take sharp terrestrial pictures through the scope? Next step is to get some quick shots of the moon and planets, which should not need guiding.


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[michael-lloyd]

Steve,

Thanks for the reply to my rambling message. I think I had a case of too much info.

I can handle repairing the electronics, even to the point of making another board.

I don't know what parts go where in the optical chain. I was able to mount the camera to the focuser. I did not try to make a terrestrial image. That's a great idea. I may try that today. I could not figure out what to do with the off axis guider, coma corrector, and camera. I'm not even sure if I need all of it.

Thanks again,

Mike

[steve-fung]

Mike,

My experience is mostly with SCTs and short tube refractors, and there are a lot more experienced HAS members using Newtonian for AP, so I’m hoping they can chime in. That said, these are my thoughts.

First, see if you can get the camera into focus without any optics or spacers between the scope and camera. One problem with some Newtonians built for visual use is there may not be enough back focus with your camera setup using prime focus technique. In that case, you may have to (1) get a shallower focuser, (2) move the mirror forward, or (3) use afocal or eyepiece projection technique.

Next, try to see if you can get the camera into focus with your coma corrector between the scope and camera. You did not specify the model of your coma corrector, but I have listed two common ones – TeleVue Paracorr and Baader MPCC. You have to remove the tunable top to the TeleVue Paracorr for AP work.

http://www.televue.com/pdf/literature/Pacacorr%20Type-2%20Instructions.pdf

http://www.baader-planetarium.com/pdf/mpcc_e.pdf

These have been designed to follow standard T-mount flange focal distance of 55 mm. For DSLR cameras, Cannon EF-mount has flange focal distance of 44 mm, and Nikon F-mount has flange focal distance of 46.5 mm, average 45 mm, so you need additional 10 mm spacing between the coma corrector and DLSR camera for best focus, which is the thickness of standard T-ring adapter.

The off-axis guider should go between the coma corrector and the camera, but from above, you have maximum 10 mm distance between the coma corrector and DSLR camera if you use one of the standard coma correctors listed above. One solution is to get a thin 10-mm off-axis guider, e.g.

http://www.telescope.com/Orion-Thin-Off-Axis-Guider-for-Astrophotography/p/102812.uts

Another option is to get a Rowe coma corrector (RCC-I)

http://www.alpineastro.com/optical_accessories/optical_accessories.htm#RCC

which has a longer 91.5 mm flange focal distance, allowing 46.5 mm spacing between the coma corrector and DSLR camera. Baader provides an off-axis guider that is optimized for use with the Rowe coma corrector

http://www.alpineastro.com/optical_accessories/optical_accessories.htm#Guider

which has a 36.5 mm body length and comes out to 46.5 mm with standard 10-mm thick T-ring adapter.

Good luck and let me know if everything works out.

Steve

[michael-lloyd]

Thanks for the detailed reply.

I have the Orion Thin Off Axis guider and Baader MPCCIII. I also have some "adapters" that I think I bought with the TOAG.

I'll study on what you have given me. The main thing that I think I need to try is to focus on something terrestrial and go from there.

[steve-fung]

That's great! Looks like you should have all the right equipment. Looking forward to seeing some great pictures with your setup!

[michael-lloyd]

I made some changes to my setup. I changed the finder scope to an Orion Shortube 80 and I'll use it for the guider rather than mess with the narrow field of view that the off axis guider would have given me. I'm nowhere near ready to worry about a guider though.

I also changed the focuser to a Moonlite CF 2" focuser. And that is where my next question is going to come from.

The focuser comes with a 1" spacer and a 0.5" spacer. Currently I have the 1" spacer installed and the racked in height from the tube is about 3.5" vs about 4" with the old Model A differential that Celestron used for a focuser . I didn't use a micrometer so I'm using about as a qualifier. I may end up answering my own question later this evening but I'm wondering if 1/2" closer to the secondary mirror is going to be enough to focus my camera. Eyeballing the camera body it seems like it might (there's lots of very non-precision binary calculus going on here tonight )

Hopefully I'll get enough range to focus the camera and an eyepiece if I choose to go that route.

[michael-lloyd]

If I answer my own post is that like talking to myself and answering back?

Well shoot. I can't tell how much shorter it needs to be and I didn't want to unbolt the focuser in the dark so I guess I'll have to take the 1" spacer out and install the 0.5" spacer and try again tomorrow night. It's great like it is for visual observing but it won't focus in the camera. I'm not sure another 0.5" closer is going to get there. I may end up with no spacers and still not have enough. But that was the risk I was taking when I decided to go forward with the existing tube.

I had fun with the short tube 80. Fun like irritated fun. None of my eyepieces would focus. Then I remembered that it either came with or I bought an extension tube. Once that was installed I put a 25mm eyepiece in and everything looked nice and sharp.

The moon looked nice. I was really hoping to photograph it but it just wouldn't come in to focus. ∏ Hercules focused nice in the finder and telescope. I wish I had known that's what I was looking at I would have spent some time on the Hercules Cluster and Messier ?? (forget the number). Next time...

I've got to inform myself better about the eyepieces that I have. 40mm is wider than 5mm... that's just odd sounding to me.

[michael-lloyd]

Onward thru the fog...

The online DOF calculator says that the hyperfocal distance of a 1000mm f5.6 lens and 60Da (which now won't power up with a new battery btw) is 30,000-ish feet. Schulenburg is about 6 miles from me. It wasn't too hard to set the telescope up and shoot through the lean-to on my barn to the water tower so I could test focus. I had to remove the spacers to get it to focus. Focus is a relative term. The mirage was already getting bad when I did my test (shooters know what this is. You know the wavy air that they show in a movie shot in the desert? That's mirage). The real test will be at night and I'm confident that there will be enough travel to focus the camera. There wasn't an abundance of travel left though so I may still be trying to fit a cow into a pig suite. I had to use an extension tube to focus with an eyepiece. A dedicated astrophotography tube is looking pretty good right now. And another mount. Some nice 2" eyepieces sounds pretty good too. A private observatory would be real nice... Oh lord...

I'm going to see what the setup that I have can do

BTW- this is an exposure that I made with the camera and 8" reflector. Not sharp but the seeing was terrible...

The Water Tower Nebula in the constellation Schulenburg

[steve-fung]

Michael, I just love reading your posts - like reading your thoughts. I think you're getting close. BTW, great shot of Water Tower Nebula!