- SCTs are not Rich Field Telescopes
- A C6 / Evo 6 / NexStar 6SE has a narrow back opening (27mm) that limits the maximum TFoV.
- With an F6.3 reducer, the max true field of view of the C6 can be had with a 1.25" eyepiece (32 Plössl, 24ES68, or similar) using the Celestron prism diagonal.
- Using a focal reducer with a C6 SCT might mean you are giving up a couple millimeters of aperture.
- Focal reducers shift the focal plane towards the objective. Add the longer light path of 2" diagonals, and you might not even reach focus.
- Even if you reach focus with a big 2" eyepiece in a C6 SCT, it'll probably be vignetted, and the larger the field stop, the more severe vignetting will be.
So, with that said, I just want to share the following:
I just got a GSO 2" 99% dielectric SCT diagonal, for my C6. When I use it with my Meade 4000 F6.3 (China) Focal reducer, plus my Meade 82° UWA 20mm eyepiece, the following happens:
- It does reach focus
- The field stop (black edge) is still visible, and clearly defined (sharp)
- I don't notice any evident vignetting. There might be a small illumination fall-off but I didn't see it.
- The view is much nicer than with a 32mm Plössl (same TFoV but more majestic in the 82° vs the 52° Plössl)
- I like the ergonomics of the 20mm UWA much better than the 32mm Plössl (I'm fine with short eye relief and don't wear glasses)
With my 34mm Meade SWA, the field stop gets blurry, vignetting is evident and the view just feels wrong, it's is nowhere as nice as what the same eyepiece provides in my 10" dob.
I'm posting this in case anybody is wondering about possibilities of mixing 2" eyepieces with focal reducers. I already had the 20mm UWA and am quite happy to use it instead of a 32mm Plössl, and I didn't feel like getting a 24ES68 (a third eyepiece with a ~27mm field stop felt wasteful).