Cannot focus QHY 16200A CFW7

[stephen2615 (Stephen)]

Greetings,

I have two QHY cameras. A QHY 163C which behaves perfectly with my setup. My Sesto Senso autofocuser sits on about 50,000 out of a range of 1 to about 92,000 with the 163C.

I recently purchased the 16200A and waited months to get the filters and last night I tried to use it. It will not focus. Winding the autofocuser to 100 (is that all the way out?) still shows a large round blob that is Acrux. It looks like it has to go into negative territory and I would guess about -40,000 might get there.

Is the solution putting a spacer in between the telescope (which has the focusing device) and the flattener/reducer that I have. Given my back focus requirements, I can't do anything in between the camera and the reducer.

Why would the 16200A be so different to the 163C when it comes to focusing?

Any assistance would be extremely welcome.

Regards

Stephen

[The_bluester (Paul)]

Comparing the two cameras it looks like all things being equal (Not knowing how your image train is built) that the 16200 has about 34mm back focus distance (I don't know if that includes an allowance for filters) and the 163C about 9.5 to the front face of the camera (They give 17.5 to the front face of the tapered mount flange)

Not knowing the direction of travel I cant suggest a step direction, but I would start by racking the focuser all the way in and work your way out from there. You might need to have the focuser racked in about 25mm from the position the 163C is in focus at.

[stephen2615 (Stephen)]

Thanks for the response.

I have the correct back focus for both cameras. I have to have 55 mm.

The 16200A CFW7 with the OAG M = 55 mm (54.5 to 55.5 mm from QHY). I have to screw the OAG directly onto the flattener/reducer. A filter in the filterwheel should give me about one mm gain in the back focus. I measured the distance from the 16200A filter wheel cover plate and because of the thread distance on the reducer, my back focus distance is 56.7 mm. I think with the filter, it takes it down to about 56 so it is one mm too long. I am pretty sure that one mm out with back focus is not going to stop the camera from focusing.

The 163C has 55 mm back focus by way of spacers and the OAG. So both have (almost) the correct back focus.

As far as the focuser goes, 92,000 has a huge blob of Acrux, while 100 has a moon sized blob of Acrux. The focuser travel distance is about 90 mm.

I am somewhat gobsmacked at this problem.

[The_bluester (Paul)]

Originally Posted by stephen2615

Thank for the response.

I have the correct back focus for both cameras. I have to have 55 mm.

The 16200A CFW7 with the OAG M = 55 mm (54.5 to 55.5 mm from QHY). I have to screw the OAG directly onto the flattener/reducer. A filter in the filterwheel should give me about one mm gain in the back focus. I measured the distance from the 16200A filter wheel cover plate and because of the thread distance on the reducer, my back focus distance is 56.7 mm. I think with the filter, it takes it down to about 56 so it is one mm too long. I am pretty sure that one mm out with back focus is not going to stop the camera from focusing.

The 163C has 55 mm back focus by way of spacers and the OAG. So both have (almost) the correct back focus.

As far as the focuser goes, 92,000 has a huge blob of Acrux, while 100 has a moon sized blob of Acrux. The focuser travel distance is about 90 mm.

I am somewhat gobsmacked at this problem.

Sorry, I was thinking of that the wrong way, pure focus not corrector spacing. To get the right spacing to your corrector you should need approx 25mm less spacer between the camera and the corrector with the 16200 than the 163. Aside from the OAG, how much spacer do you have between the OAG and the 163? If you get the reducer to sensor distance the same between both cameras the focus point should be the same. I know they can be pretty touchy, fiddling around with spacing increments when setting up my old ED272, 1mm spacing corrector to sensor change made a much bigger difference to the focuser travel. COmparing the two cameras, it is possble the 163 was not quite at the ideal spacing, the abberations will show up in the corners first and the APS-H sensor of the 16200 will show them up with a smaller spacing discrepancy than the 4/3.


How does the corrector attach to the drawtube? If it is a lack of "out" travel can you add a spacer there?

[stephen2615 (Stephen)]

I think I have figured out a problem but I can't see any solution.

My Sesto Senso autofocuser seems to be the issue. It has lost its way and doesn't know where it is anymore.

I calibrate it (on three different computers just to be sure) and the settings are 0 to 135143 (give or take a few numbers). So 0 is as far back as the focuser will go and 135143 is as close as it will go. 66000 should be half but it is not. I put the setting to 100 but it firstly ends up on 10 mm (instead of around 0 mm) on the focuser scale and then if going back to 66000, it is no where near half way and if I go to 100 again, it ends up about 18 mm on the focuser.

So it is to blame. When I changed the focus trying to get focus, it kept losing the area towards 0 (extended fully). So 100 was about midway in the focus length. It just (obviously randomly) seemed to happen when I put the 16200A on my mount. I was not able to use half of the focus.

Just one more set back in a comedy of errors with the 16200A. I have to see if it can be completely reset back to factory default.

[The_bluester (Paul)]

Is the focuser a rack and pinion or a Crayford type? If it is a crayford style and you run it "past" 0 on the focuser scale the focuser will slip and your step count looses it's reference point.

I think from memory you can reverse the focuser direction in the software? (I have never had my hands on a Sesto Senso but If so, set it so that position 0 is with the focuser fully racked in, it is usually easier to visualise that way, a bigger number racks the focuser out further. Given you can manually focus with a Sesto Senso still attached it makes calibrating easier too, you can just rack the focuser in all the way then in the software, set it to 0 steps.

If you have a rack and pinion focuser then the step count should not change unless the focus motor actually slips on the drive shaft under power, or you move it manually with the power off.

[stephen2615 (Stephen)]

I think I might have figured something out. The speed settings were changed just to slow it down to a crawl. That involves reading the current settings, then send the settings and then save the parameters.

That seems to have solved the problem of the focuser getting lost with its position. It now knows where zero is so I wonder if overwriting the config somehow sorted it all out.

Wish me luck. And typically, we have high cloud around. I really want to capture NGC 6188 in SHO!!

[The_bluester (Paul)]

Of course there is cloud!

I was hoping to help out the Vic astronomical society tonight with some EAA type images to zoom screenshare for the monthly deep sky meeting, queue up 100% cloud cover. Maybe next month!

[stephen2615 (Stephen)]

I bought the QHY 16200A in March and waited and waited and waited for the filters to arrive. Nothing seems to be coming out of China without really long lead times. Even cheap items like spacers are not available and of course, that 5 mm spacer might be the difference between using and not using your gear. I was trying to use my WO Z61 as a guide scope just for fun but nope, no 1 and 1/4 inch spacers in Australia with no idea when they will arrive. Back to normal my butt.

[The_bluester (Paul)]

Know that pain, I am waiting on a new camera and a new mount, about all I can do is wait and hope.