FRA400 with small pixel Full Frame camera? Askar FRA400 · GTom · ... · 6 · 339 · 0

I am thinking on adding a grab and go scope, besides the William GT71, the FRA400 is the other candidate.
However, the expectations are high, I need great performance in the corners with small pixel, large sensor cameras also when using the reducer!

How does the FRA400 fare in this league?
Tried to find the glass they used, no info - that didn't make me optimistic.

Hi GTom,
here is a exsmple with 6my pixel full-frame: https://www.astrobin.com/y5ehhw/?q=Tralfi

The stars in the corners are elongated but for wide field very usable.

The scope produces also ring reflections from bright stars outside the field of view which needs to be treated in post.

CS
Tralfi

I use my FRA400 with an APS-C sized sensor OSC camera (IMX571, 3.76 μm[b] [/b]pixels), both with and without a reducer.

When used with the reducer, even on an APS-C sized sensor, there is very noticeable chromatic aberration and some slight star shape distortion towards the corners and along far left/right edges. When using just a UV/IR Cut filter, BlurXterminator mostly has no problems fixing the stars, so I would not consider it too much of an issue.

It's different when using a dual-narrowband Ha+OIII filter. In that case I get clear separation of red and cyan signal of individual stars, separated enough that BlurXterminator by default tends to 'correct' red and cyan shapes separately, resulting in double stars. It can be fixed though, it just takes a couple extra steps - splitting RGB channels, running BlurX in Correct Only mode on all channels, star aligning the separated channels and then recombining them. This process mostly corrects chromatic aberration, it just leaves a little residual colour noise around the brighter stars. The distortion of star shapes on the other hand is not an issue, BlurX handles that without problems in either case.

Without the reducer I've found the performance much better, while there's still some chromatic aberration, it is much better then with the reducer.

Considering my experience with an APS-C sensor, I definitely wouldn't recommend this particular scope for use with a reducer and a full frame OSC camera. The chromatic aberration can be worked around as described above, but it would definitely be nicer to not have to deal with it in the first place.

I use the FRA 400 with IMX571 color and I am satisfied with that, but I did not buy the reducer because I saw many images with degraded performance (elongation, CA) compared to no reducer.