OAG & Autoguider/imager, what to do, what to do!

[ncwolfie]

I'm trying to make a final decision on an OAG and autoguider/planetary imager for my setup and it is about to make my head explode. So much info, I just want to make sure I make the best decision in the end. So once again, I am looking to the knowledge of the community to steer me in the right direction with their experiences.

Here is my current setup: My main instrument is a pier mounted Celestron Edge HD8 on an advanced VX mount. I have a Celestron, .7x focal reducer. For short exposure imaging, I use a Canon EOS T4i (650d).

I am now looking to move up to longer exposure so its time to pull the trigger on buying some equipment.

I use BYEOS, Nexremote and Stellarium for camera and telescope control. I will use PHD2 for autoguiding and Astrotortilla for plate solving. At least that is the current plan.

Based on discussions on this forum and others, I am leaning toward a thin OAG, probably the Orion OAG. I am still open to other ideas. I do have an extra 9x50 finder I could mount beside my right angle 9x50 finder, but from what I gather, OAG is the way to go with this scope and a thin one in this case due to the focal reducer.

The next part of the equation of course is the imager. I go back and forth on what to purchase. I am looking for something that will be a solid autoguider/planetary imager 1st and foremost. The Canon T4i suffers from limited fps in live view so an autoguider /planetary imager could really help me on the planetary imaging front. For now I will be satisfied with the Canon for deep sky work as long as I can get some reliable autoguiding going, but if the imager did allow some deep sky that would be icing.

My intention is to primarily use my small observatory for imaging and some small scale educational outreach. So if the camera also offered the ability to be used  as a live video feed to a monitor, I can see that being very useful as well. This is not as important as the autoguiding feature but it would aid in keeping visitors from causing alignment issues.

So I'm looking for any and all advice for getting the best imagery I can out of my Edge HD. I've been reading about QHY5L-II, Lodestar, ZWO etc. Hoping that someone with first hand knowledge and possibly with a similar setup, can help me make the best choice.

As always, thanks in advance for any advice.

Randy

[MarsG76]

Hi Randy,

I use a Celestron OAG on my NX8... The guiders I use are the NexGuide... Works great on stars upto mag. 8 and if a guide star in the vicinity of the object imaged if fainter I just use my IS DMK21au618 CCD as a guide CCD with PHD. Either way the hardest thing is to actually find a guide star, especially when imaging at F10.

When I plan on imaging an object, I'll look it up on StarryNight 6 and see if there is a bright enough star in the area. I did set up a few FOV markers for all of my CCDs, DSLR and circles for the OAG FOV around the camera view.

Most of the time there is a star in the right distance from the object, occasionally I'll have to put the object slightly off center. Now, depending on how bright the star is will depend if I AutoGuide using the NexGuide or the DMK...

After everything is setup and I'm guiding, I am taking narrowband subs of upto 45 minutes on my modded 40D, and that's not a limit, since i can be imaging and taking subs at 20, 30 or 40 minutes for 5-6 hours and when looking at all of the subs later on the LCD and switching between them, the stars do not move AT ALL from frame to frame... So the system definitely works beautifully.

Mariusz

[ncwolfie]

And so my headache has begun. Trying to use an Orion Thin OAG with my EdgeHD8 and the celestron .7 focal reducer. I have a ASI120MM-S for my guide camera, a Canon T4i as my imaging camera. I can not for the life of me figure out what spacers I need. Surely someone has had some success with this setup using a thin OAG to overcome the back focus issue. Trying to keep from ordering a bucket full of spacers just to see which one works.

Any advice on making this work?

[D4N]

DSLR's are normally 55mm flange to chip, the asi120mm is 14mm.

Measure the distance from the prism to the OAG camera threads call the imaging camera side X and the guide cam Y.

Required spacers = (55+X)-(14+Y)

The T2 threads can throw this out a bit if they are either too long or too short but this should get you roughly where you need to be.

The OAG should have some adjustment available as well but I would advise having some contingency spacers, you can never have too many spare spacers!

/Dan

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[ncwolfie]

The problem is I must maintain a 105 mm back focus for the edge hd and celestron focal reducer/Dslr combo. Which I am at now without adding the Thin OAG. If I add even a thin OAG, I exceed the 105mm. Seems I need a shorter T Adapter?

X being the distance from the focal reducer to the OAG prism is approx 57-59mm  so plugging that in I am already over 105mm on the main imaging camera with no way to shorten the T adpater.

See this thread. http://stargazerslounge.com/topic/256766-celestron-edgehd8-07-focal-reducer-oag-owners/

[D4N]

Yeh it looks like you need a shorter T adaptor to do that.

/Dan

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[opticalpath]

Have you looked on the CloudyNights forum? There are several threads there that discuss how much of the 105mm available is taken up by the various adapters and OAG.  E.g.

http://www.cloudynights.com/topic/490421-celestron-8%E2%80%9D-edge-07-focal-reducer-will-not-accept-oag-plus-dslr-what-can-i-do/

I believe that the camera flange to chip distance for your camera is actually 44 mm (not 55 mm).  https://en.wikipedia.org/wiki/Flange_focal_distance.

As well as using a thin OAG, there are a couple of ways you could save some more 'length' in the connection from reducer to camera:

Instead of the (rather long) Celestron adapter that goes from focal reducer (SCT thread) to a T-thread, you could use a very short SCT to T-thread adapter like this:

http://www.modernastronomy.com/shop/accessories/adapters/low-profile-sct-to-t-thread-adapter/   or

http://agenaastro.com/blue-fireball-sct-thread-t-thread-adapter.html

Also, you could use an ultra low profile Canon-EOS to T-thread adapter instead of using the standard longer Celestron item.  For example:

http://www.modernastronomy.com/shop/accessories/t-rings/low-profile-canon-eos-t-ring/

Either of those will save you quite some length.   I would have thought that some such combination, plus the slim OAG, plus the 44 mm camera back focus could easily come under 105mm.  But it may be hard to work out exactly until you have the items in your hands!

Adrian