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I've always used a separate guide scope and like the simplicity that it offers, but I now have pretty clear evidence of differential flexure despite doing everything imaginable to make a solid connection between the 2 scopes. So I want to try an off-axis guider and am looking for recommendations. I think it should be very adjustable (both rotation and prism position) to be able to find a good guide star. My current setup uses 2" SCT threads to connect the reducer/flattener to the scope. This could be changed to T threads, but I don't want to use a "nosepiece" or anything that is held in place with a thumbscrew. It is also possible to put an OAG between the reducer/flattener and the camera (using T threads) if the OAG body is 20mm or less. That might be preferrable, as it would provide a better match between imager and guider image scales. On the other hand, there is a larger image circle before the reducer, so putting the OAG there might make it easier to get good illumination on the guide star without obstructing the main image.

I have heard that OAGs often distort the star image and I'm concerned that that could degrade guiding accuracy.

So, what do you guys use and recommend? Thanks!

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Comment by Marc Basti on September 13, 2012 at 10:29pm

Greg, your review/insights between the two blogs have been very helpful (and interesting-never thought about the filter focus issue). Good luck w/your new setup. Marc

Comment by Greg Marshall on September 12, 2012 at 12:18pm

I reported in another thread that the Orion OAG worked, but doesn't fit between my reducer/flattener and the camera, so I upgraded the camera (a QSI 583ws) to the "wsg" version. Last night was the first real imaging test of this setup and I can report that it worked beautifully. Seeing was not great, so I didn't get really tight stars, but they were all perfectly round. What I didn't try last night was my O3 filter, which does not match the others and may cause a problem with focus of the guide camera.

Comment by Greg Marshall on August 25, 2012 at 10:56pm

Thanks, Charles. Since I'm not entirely confident that this is the right way for me to go I have ordered the relatively inexpensive Orion OAG unit to test. I think the MOAG actually costs more than upgrading my QSI ws to wsg! But there are other options between these price points.

Comment by Charles Dunlop on August 25, 2012 at 7:17pm

My OAG distorts the shape of stars slightly but it doesn't affect guiding. I've got the QSI WSG. You're likely looking for a MOAG or something not a whole new CCD, but I'll tell you, I LOVE OAG. Wondering now why I ever even had a guidescope. Have not had a bad sub since switching to OAG.

Comment by Marc Basti on August 23, 2012 at 12:04pm

I got it 5/11 (been awhile) and tried it out on my 80mm fl560 and C8 (fr6.3). I was only able to catch a couple stars visually, but not w/the ssag. Didn't seem like the pickoff prism was big enough, but to counter that I know at a certain point it becomes an obstruction. Like you mention the star image was distorted, but I didn't get any farther than that. One thing to mention is that I felt it was good and secure (or I wouldn't have hung $3K worth of cam and whl off of it). The awkward part definitely depends where in your image train it goes (and the sz. of your fingers)-maybe, maybe not. The construction is Orion, enough to get by and no more. My thought at the time was to try it out and if worked great, if not I'd return it and pay a restock fee if I had to. Orion is known for pushing the limit of the truth when it comes to the performance/quality of their products. Like I said previous when I get a ccd guide cam to replace my ssag, I'll probably try it again. Marc PS Hey thanks for that thread info.

Comment by Greg Marshall on August 22, 2012 at 1:07pm

Yes, I could upgrade from ws to wsg on the QSI camera, but that is expensive and not as adjustable as I would like (it does not provide any rotation). Ignoring issues with the SSAG, what did you think of the Orion OAG? I looked at one, but haven't actually used it. It looked like it would be a bit awkward and that it might be difficult to get things adequately tightened.

I am using the William Optics "Flat 4" and, yes, when you remove the 2" nosepiece it leaves 2" SCT threads. I fabricated an adapter to thread this on to the back of my scope. One reason I like the 2" SCT threads is that they are 24 tpi (not metric). I know many people that have lathes, but none of them can do metric threads very well.

Comment by Marc Basti on August 22, 2012 at 12:04pm

Greg,thought you could get an integrated oag for QSI cams. I'll tell you something I'm sure you already know, I tried out an Orion oag w/my ssag and that was a waste of time. I don't think the ssag is sensitive enough. Although if (when) I get a new guide camera, for the price, I'd try it again. Question, the red/flat you are talking about is that the WO ff4, if so you mention making sct thread connection--does the 2" nose piece/barrel come off it exposing sct threads? I have mine set up on my scope and I'm in the middle of some projects (so I don't want to take it off yet). I've been wanting to make a threaded connection between my imaging train and the scope (for the same reasons-eliminate another poss of flex). Thanks, Marc

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