Yes, I can see what you're pointing out. I'm sure this is due to different alignment of the camera for the Inside/Outside pictures. I need a better camera mount or a least more care in handling the camera.
Here's a retake on the DPAC for this Vixen FL-80Sfrom today. I took more care in keeping the camera position exactly the same, and I carefully observed transition Inside/Outside without being able to notice any rotation or deviation from straight.
For comparison I've juxtaposed ½ Inside + ½ Outside. see below.
I agree with you, that this objective is a true 1/10 wave in green, and very probably better, but I think it will take more precise measuring and more careful modelling to get any closer to an exact wavefront rating. Anyway my purpose with this test has been accomplished, as I think DPAC to rating categories of 1/2, 1/4, 1/8, and 1/10 wave is plenty for at least my practical purposes. I think that's what you're advocating too.
Yes! I'm certainly happy to have this optically excellent objective for my astronomical explorations, and on top of that, in a lightweight package that's perfect for my grab/go setup. I have another FL-80S in our cottage in the woods, and I think this will test just as good.
My smaller FL-55S scopes do show some line bowing, I estimate ~1/8, but I'd like to model it for a better approximation. My FL-102S is not 100% perfect with respect to color crossing, but the small deviation is due to the spacers having been compressed through the years, and I'm not going to tamper with that.
Edited by AllanDystrup, 25 February 2018 - 04:45 AM.