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New Orion "thin" OAG

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#76 petemumbower

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Posted 03 November 2013 - 04:09 PM

Chris,

Yeah, there is just the one set screw on the TOAG body that holds the prism part in place. It comes in from the side, since the prism stalk is a bit smaller that the opening in the TOAG, there is play. I can wiggle it with my fingers. Not sure how much would actually move while imaging, especially once the one set screw is tightened. But it does move, so I am serious thinking of adding a set screw 90deg to the existing one just in case.

#77 josh smith

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Posted 03 November 2013 - 04:15 PM

Chris,

Yeah, there is just the one set screw on the TOAG body that holds the prism part in place. It comes in from the side, since the prism stalk is a bit smaller that the opening in the TOAG, there is play. I can wiggle it with my fingers. Not sure how much would actually move while imaging, especially once the one set screw is tightened. But it does move, so I am serious thinking of adding a set screw 90deg to the existing one just in case.


Two questions...

Is the stalk made out of aluminum and use a steel set screw? Does that create divots in the aluminum that make it hard to adjust focus without set screw falling into previous divots?

Do you guys just user spacers for the guide cam and thread it or does anyone use a t thread to insert tube or t thread to helical focuser? Seems like a threaded connection would make orientation adjustments difficult.

#78 petemumbower

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Posted 03 November 2013 - 04:30 PM

Josh,

Yes, the stalk appears to be made out of aluminum and the set screws are steel. At this point, I do not see any divots that would cause issues down the road. For focus, I got a 1.25" eyepiece adapter from Agena. See below pic. I use a QHY5L-II guider and basically slide it up and down until I got focus (after I focused the DSLR first). Then I used the suppied QHY focus collar. That focus should not change unless I change my setup.

Also, since I do not need to move the prism stalk up and down for focus, I really am not too worried about divots.

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#79 josh smith

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Posted 03 November 2013 - 04:44 PM

Thanks Pete.... I figured that would be the better solution, but didn't know if the stalk could handle it or not. Since I am using clip filters, it is likely that I will have to adjust focus on the guide cam (ST-i) regularly by ver small amounts. Not even sure if the filters will change backfocus enough to require guide cam adjustments, but nice to be prepared. I feel pretty convinced now that this is the way to go.

My 2 cents on the stalk issue would be to just permanently bolt it into place and use an attached 1.25" tube for focus. Seems like sensitive guide cams should be able to pick up bright enough stars anywhere if imaging at less 800-900mm focal length.

#80 josh smith

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Posted 03 November 2013 - 04:51 PM

One other thing... Would any of you know the distance from the center of the pickoff prism to the top of the stalk to determine spacing requirements? Thanks in advance for any answers.

#81 Wmacky

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Posted 06 November 2013 - 09:31 PM

It works with a field flattener just fine. I have a at2ff. It really just needs an additional set screw on the adjustable part.


Hmmm, tell me more about this. I just tried my AT2FF and the flattner hits the prism stalk well before it bottoms out? Same issue with the C8 Edge T- adapter. Looks like it still has a couple MM to go. Are you using some kinda spacer?

#82 Madratter

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Posted 06 November 2013 - 09:55 PM

I'm wondering if you could eliminate the play with the stalk by wrapping it in a layer or two of plumbers teflon tape.

#83 josh smith

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Posted 06 November 2013 - 10:08 PM

Mine should be arriving tomorrow. I will let you know how my experimenting goes. I got some plumbers tape, set screws, plastic shim stock, o-rings, and rare earth magnets (I know it's aluminum) to play with. As far as the field flattener goes, I was under the impression that it would be threaded into the adapter.... Is that not what everyone else does for this setup? Or are you saying the threads don't bottom out till they hit the prism?

#84 Raginar

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Posted 06 November 2013 - 10:32 PM

Wmacky, yes, I use a space between the AT2FF and the OAG. my filterwheel combo isn't quite there.

#85 Stargazer78

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Posted 06 November 2013 - 10:36 PM

Wmacky, yes, I use a space between the AT2FF and the OAG. my filterwheel combo isn't quite there.


What size spacer do you use? I am trying to figure out the spacing as well. I have my T3i to the TOAG then coma corrector. What would I need to get my orion auto guider to focus?

#86 Wmacky

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Posted 06 November 2013 - 11:37 PM

Wmacky, yes, I use a space between the AT2FF and the OAG. my filterwheel combo isn't quite there.


What size spacer do you use? I am trying to figure out the spacing as well. I have my T3i to the TOAG then coma corrector. What would I need to get my orion auto guider to focus?


What he said! I just ordered a set of brass t2 washers/spacers as i'm hoping to get better flattening than I'm getting now with a EON 80mm and the AT2FF with my regular T-ring. I was going to try to use them on the OAG too hoping to fix this collision issue!

#87 Wmacky

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Posted 06 November 2013 - 11:41 PM

Mine should be arriving tomorrow. I will let you know how my experimenting goes. I got some plumbers tape, set screws, plastic shim stock, o-rings, and rare earth magnets (I know it's aluminum) to play with. As far as the field flattener goes, I was under the impression that it would be threaded into the adapter.... Is that not what everyone else does for this setup? Or are you saying the threads don't bottom out till they hit the prism?


Exactly, The At2ff threads are too long. Same with the Edge 8 T-adapter. When I was hoping for an extra thin OAG, I didn't think about this issue. :p

#88 josh smith

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Posted 09 November 2013 - 09:01 AM

My first night was a mixed experience. My train includes sv102ed, hotech 2" field flattener, m48/m42 adapter, orion toag, canon bayonet adapter loaded with Teflon tape to get a snug fit, and canon T3 modded. So the good news is that the images were very sharp and crisp all the way to the edge so the spacing for my setup seems to have worked very well.

The bad is, as others have shared, the stalk is shockingly wobbly. For the stalk I have a short t ring spacer, baader 1.25 micro helical focuser, and st-i color guide cam. I had everything tightened down very well before starting and it seemed good and stiff. Adding the lever arm of the camera almost immediately introduced pivoting and by the end of the session, the set screws became so loose the t mount almost slid right off the stalk. Wrapping the stalk in plumbers tape stiffened the assembly quite a bit, but wobble still happened pretty quickly. I was hoping to avoid the set screws, but I feel I am going to have to tap those and try then out. I'm assuming lock screws would be an even better option so I will try that and report back.

#89 josh smith

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Posted 09 November 2013 - 10:38 AM

WARNING... The stalk is soft and thin enough that set screws will bend it. I inserted two 6-32 set screw at right angles with some loctite. I also got a little over zealous tightening them and they deformed the stalk very slightly. Hopefully not enough to introduce any vignetting if that is an issue on a guide cam. Initial impressions say it is still not as stiff as I would like, but a marked improvement. I will report back when I get an opportunity to test... Here in Pittsburgh, that may be the spring.

#90 Raginar

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Posted 24 November 2013 - 09:43 PM

Well, I installed mine today. I replaced the little set screws just like John did and that seems to give you enough crank to settle it down. I bought a third one and was going to drill my 90 off one too but found it wasn't needed.

ATFF does not hit my stalk. I do need a 10mm spacer to make it CMR to focus unfortunately and I don't have one on hand so that's in the mail now. Otherwise, I could tell I was just barely out of focus at the top of the stack so I think it's going to work. In addition, as advertised, it will put my camera exactly the right distance away.

I dunno, I think if they just included a better Allen wrench and some better screws it would be a win.

#91 Wmacky

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Posted 24 November 2013 - 10:26 PM

What size spacer between the ATff and OAG?

#92 Raginar

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Posted 25 November 2013 - 09:08 AM

None. It's screwed directly to it. The only spacer I have/need is a 10mm on the backside of it going to the camera.

#93 Wmacky

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Posted 25 November 2013 - 10:55 AM

Strange? How close to your ATFF thread come to the stalk? Can you measure them with a caliper? Mine hitthe stalk just before bottoming out the threads.

#94 Raginar

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Posted 25 November 2013 - 09:02 PM

I don't have a caliper unfortunately. I'll see if I can pick one up. Why does it matter if it's snug against the stalk? I'm not noticing any problems... My 10mm spacer should be here on Wednesday. I'll let you know if my stars look off.

#95 Stargazer78

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Posted 25 November 2013 - 10:34 PM

I'm having all sorts of spacing issues with mine. I have a Canon t3i-oag-atcc. I have tried 5 mm, 10mm, with no luck getting the auto guider to focus. Any body using my setup above? Would really like to use my AT8IN more but not until I get the spacer thing figured out

#96 Raginar

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Posted 26 November 2013 - 09:18 AM

Are you making sure your spacing is from the prism to te auto guider ccd is the same as the spacing from the prism to the main ccd chip?

It should be that simple. When I played with mine I had stars but it didn't have enough stalk remaining to clamp it down.

#97 Stargazer78

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Posted 26 November 2013 - 05:13 PM

I'll have to play with it some more

#98 josh smith

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Posted 26 November 2013 - 08:12 PM

I found the spacing from the center of the pickoff mirror to the base of threads for the guide cam to be 31mm. I am using an (st-i) and the backfocus for that is 13.7 mm. From the pickoff mirror to the canon sensor (T3 or T3i) is ~46.6 mm. In my case I only needed about 1.9 mm of spacing. Because optics can change and distances change a little with temp and so forth, I got a micro helical focuser from Agena that has 10 mm of travel. It is a perfect fit. I'm assuming from your signature you are using the ssag, which has 15mm of backfocus from the threads. Based on that, you probably need ~3.2 mm of spacing. I would guess 3mm would do the job, but the micro helical focuser will take care of you for sure.

#99 Raginar

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Posted 26 November 2013 - 08:18 PM

Josh, that's a really neat idea. I can't wait for my spacer to get here and give this thing a whirl.

#100 josh smith

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Posted 26 November 2013 - 08:44 PM

The one I got is...

http://agenaastro.co...q=PAAR-BP-T2-8A

It's a little pricey, but well worth it and a very well built piece in my opinion.






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