The OCI (Octopi Camera Interface) lets you adjust your back focus, camera tilt and centricity in the light cone. It utilizes precision screws to make it perform at a accuracy of 0.001" with a 5 minute turn of the clock dial/knob in the coarse mode and is available up to 13 times that accurate.
The OCI is to help alleviate camera issues. If you have image train issuses between the filter wheel and the telescope then the GERD CTU would be more appropriate.
To address justusliebig's concern "I understand this setup increases the distance from filter to sensor. I can't believe that's good", I needed actual numbers to put his concerns in numbers that show the actual difference in filter diameter in relationship to sensor distance. I used the Astronomy tools calculator and you can check the numbers yourself if you feel so inclined. https://astronomy.to...ccd_filter_size
While looking at this page: https://astronomy-im...5-x-2″or-7-x-2″
I saw this snippit:
"When connected to ASI6200, the distance from the filter to the sensor is about 18mm"
Using these numbers run though the astronomy tools calculator and again at 8mm extra distance between a ASI6200 camera and a ASI filter wheel to account for the extra distance added by the OCI when set at the center point With the OCI set in the center position, there is 3mm inward and 3mm outward for a total of 6mm of adjustment, for precisely adjusting the back focus or tilt without having to remove anything from the telescope.
These filter diameters are the minimum recommended and larger are always better.
Tak FSQ-106EDX4 F/5 with a ASI6200mm attached to a ASI 2" filterwheel: distance between filter and camera sensor = 18mm and needs a filter with a diameter of 45.41mm and after installing a OCI at center point the minimum filter diameter goes from 45.41mm to 46.36mm, a difference of 0.95mm.
With a A-P 175 f/8 the numbers are 44.97mm dia. to 45.73mm dia. after accounting for the OCI. A 0.76mm difference.
Askar FRA600 F/5.6, the numbers are 45.22mm without a OCI and 46.08 with for a differnce of 0.86mm.
For fun I ran a RASA11 just because it is F/2.2 and it was about 3mm difference but I doubt anyone would use a 2" filter wheel on one.
If you are using a QHY camera with a dovetail then you replace the QHY tilt plate with the OCI and you will only have to add about 2mm to the factory distance from the filter to the camera sensor. For the newer QHY camera's that don't use the dovetail, use the numbers above for the ASI cameras.
The question is: Are you willing to give up less than 1mm of filter diameter to have the ability to adjust your back focus, your tilt and your centricity with precision?
Edited by bugbit, 03 April 2021 - 02:35 PM.