Could i ask a late question to the group. Is it better to max out the resolution when collimating? I have 8”SCT with focal reducer but i also go native with a 2.5 Telemate for lunar imaging. Should i use the full resolution of my scope or does it make no real difference to the tri-B?
I have now had my tri-Bahtinov mask 3D printed by a friend but have not yet had an opportunity to use it!
However, from my understanding, the tri-B design depends on the aperture and focal length of your telescope.
My 8" SCT is an LX200 Classic F10 which has a native FL of 2000mm. If your NexStar 8" is similar, in native mode it will have a focal length of 2000mm but when using your powermate, it will increase the FL to 5000mm. Your focal reducer will have the opposite effect and reduce the FL by whatever factor the reducer has on it, usually F6.3. This will therefore result in an effective focal legth of 1260mm on your NexStar..
In fact, when using APT to plate solve on my Meade LX200 Classic, once it suceeds in plate solving, it tells me that my scope with camera has a FL of 2140mm, presumably due to the back focus required due to my Strarlight Xpress AO unit which puts the camera some 120mm behind the focal back of the OTA. So when I desinged my T-B I specified an FL of 2140mm.
However, I have been informed that FL does not make a huge difference to the T-B design. Unfortunately I have not tested mine yet.
I am no expert, so it would be good to get some other feedback from guys who undertsand the physics of what goes on!