Here's a quick mod you can do to any standard GSO 8x50mm finder. You can then screw on a QHY5 and guide through the finder. The guider image scale is about 4 arcsec/pixel. I found it suitable to guide the C11/Hyperstar combo at an image scale of 2.5arcsec/pixel, so it would also guide a 5" newtonian at F/5 (600mm). It's light and no flex. Ideal if you piggy back a DSLR and want to do widefield and good enough for 500-1000mm FL work.
I've acceptably guided my C11 @ F/6.3 with a setup like that... For my setup now, that would be the next best option to my OAG I think... Being that I image at 480mm F/L, a 200mm guide scope is plenty....
Its quite a neat, elegant setup, and for most people, easy to do.. Nearly everyone has a finder lying around..
I made mine a little differently.. I ground down a spare 2" to T-thread adapter about 0.5mm in overall diameter, using a rubber mallet I banged the 2" adapter into the rear of the finder.. Obviously, this makes it a dedicated guider from then on, not possible to revert it back to a normal finder scope...
I did have to remove the locking ring from the objective focusing thread, and then screw the objective the whole way on until it was tight, this gave me very good focus, and guiding results were great.. I've done this a couple of times in this way.. I will say that a 9x50 finder will need a small amount of the tube removed to reach focus, 7mm from memory....
Hi Marc, not sure I follow - what exactly is the mod and how do you attach the QHY . Looks to be a great economic way to get into guided imaging which is what I'd like to do
Hi Marc, not sure I follow - what exactly is the mod and how do you attach the QHY . Looks to be a great economic way to get into guided imaging which is what I'd like to do
You just need to add a thread (M42x.75) to the original ring at the back of the finder. The diameter is almost right. The QHY5 will screw right on and will focus.
Last edited by multiweb; 09-12-2009 at 11:48 AM.
Reason: Picture added
You just need to add a thread (M42x.75) to the original ring at the back of the finder. The diameter is almost right. The QHY5 will screw right on and will focus.
So get someone to mill a thread on to the existing metal of the finder?
So get someone to mill a thread on to the existing metal of the finder?
Correct. I had a chat with a retailer and they might make it standard in the GSO finders now. It just makes sense with small guiders available everywhere nowadays.
Have a look at this article and the calculator at the bottom. According to that, with the QHY5 pixel size being 5.2 um, the calculated focal length of a guide scope can be as low as 35mm.
If I mount the QHY5 on 9x50 finder, do I still need to cut short the finder tube? If yes, how many mm?
Regards,
Tommy
Hi Tommy, best thing is to remove the back of the finder all together, stick the QHY5 flash with the tube and check if you can reach focus with the front rings. That should give you an idea of how far you are in or out.
I just recently made a brass fitting for the back of my finder in the machine shop slapped a thread onto it and it screws directly into the back as a replacement to the eye piece. happy days ive seen others using this same set up so i have no fear that it will work! (roger if you want something like this have a chat with me).
and thats with the Skywatcher 9x 50 finder scope too
Hi Tommy, best thing is to remove the back of the finder all together, stick the QHY5 flash with the tube and check if you can reach focus with the front rings. That should give you an idea of how far you are in or out.
I cut 35mm off the back of a cheap 9 x 50 and turned down a bit of aluminium to slide snugly inside the tube (with a couple of locking screws) and to give a 1 1/4 inch slot for a DSI that now sits happily in place, finds focus with the help of a lock screw and also adjusting the primary lens cell a bit. I'm going to test the theory that guiding systems operate at a level of about 1/15th of a pixel accuracy so according to theory (with seeing rarely being better than 1-1.5 arcsec/pixel anyway) that this system (with a focal length of about 150mm) should be able to guide anything up to 2000mm FL or so. I know this conflicts with conventional wisdoms, but what the hey!! It'll be interesting to see the results.
Peter
I tested my setup this weekend, the wind was boardering on extreme with wind gusts i predict somewhere in the 30/40kmh and it held the stars tightly at 10 min
I turned a adaptor out of brass that screws in as a replacement to the normal finder ep. i then removed the locking ring for the front lens assymbly and used that as a helectical focuser, quite interesting that it was a very similar FOV to my ED 80.
Settings that i used in phd where 15000 ms calibration steps (close to the SCP) min dec was 100ms, min movement was .15
The only pain was that the calibration took so long but that was far outweighed the fact out of 17 shots i only lost 3 and that was due to PHD having a error and dropping its guiding in DEC.
. Looks to be a great economic way to get into guided imaging which is what I'd like to do 
(I would have to buy a finderscope)
