Orion 10 inch Dobsonian on Equatorial Platform, and my imaging setup.
Processed version of my B&W photo M42 Orion Nebula from 4/1/2020 – lights and darks – I didn’t have any flats to hand.
This image has been taken with ca. 30 light frames only 5 secs long, showing how much more sensitive the Altair 183M mono camera is than my QHY10 one shot colour camera!
This post follows on from previous post below:
I’ve changed focal reducer for the dedicated Sky Watcher one – it came up on AB&S second hand. Reason for doing this is that the Equinox had great difficulty gripping the Tele Vue TRF-2008 field flattener and it kept slipping – this isn’t problem with TRF but rather with this particular combination. New field flattener grips tightly and daytime tests suggest comes to focus but I don’t have far enough away tree to know for sure whether enough back focus so I will find out next clear night……if not enough back focus then I will need to cope with TRF which will focus. Mind you this is the dedicated SW one so it should work!
I have connected the field flattener to the telescope using a bespoke 2″ nosepiece purchased from First Light Optics. I think the end of the focuser tube might unscrew to allow direct connection by screw thread of flattener to scope but I can’t get it to budge and I am worried that I might damage the scope if I try harder to get end off the draw tube on the focuser.
I would like to use a light pollution filter with my QHY10 camera for nebulae as my location is badly light polluted and the situation is getting constantly worse due to new estates and industrial units being built around Lichfield. However such filters are not always ideal for all targets such as galaxies and I would therefore like to be able to move the filter in and out of the front of the camera without affecting the orientation of camera and telescope/field flattener. Doing this would mean that I can take series of flat frames with filter and without filter and then rotate it in or out as needed.
In my previous post, I have attached the instruction manual for the Tele Vue TRF-2008 field flattener that I use with the QHY10 camera.
Here it is again (PDF):
This manual states that the optimal distance from flattener to camera sensor is 56mm.
Teleskop Service do a manual filter wheel for 2 inch filters.
The specifications of the filter wheel are as follows:
These show that the filter wheel requires just under 30mm from M48 thread to M48 thread.
However this now means I would need 2 x M48 to T2 adapters, one each side of the filter wheel.
First Light Optics sell such adapters:
So if I used the First Light Optics adapters above then I would add 2 x 10mm into the optical path giving a total of 30mm for filter wheel and 20mm for adapters = 50mm.
Although this appears to be small enough to fit within the optimal 56mm distance from field flattener to camera of 56mm, the page reproduced from the QHY10 camera instruction manual below shows that the QHY10 adds a back-focus requirement of 20mm meaning that the total back-focus requirement would be 70mm when optimal distance is 56mm.
However, if I can find a filter wheel with similar front-back width as the one above buy with T2 threads rather than M48 ones so that I don’t need adapters then it should work OK.
I was very concerned that only one thumb screw on focuser tube for Sky Watcher Equinox Pro 80mm OTA- my QHY10 and field flattener kept becoming loose risking it would all fall out and affecting focus and flats. I was going to drill and tap extra holes for more thumb screws then noticed this hole directly opposite the thumb screw, virtually invisible because it has a grub screw in it. I replaced that with a more robust bolt and now have a very secure connection for my camera that i don’t think will loosen….Just need to take another set of flats now!