How seeing and cooling affect the result. In comparison FC100DL & Mewlon 180c on Jupiter

[Fedele]

28.09.2021
In the same evening of just enough seeing, I performed recordings of jupiter with both Mewlon 180c and Barlow 2x, and FC100DL with Barlow TV 2x + PowerMate 2.5x.
the telescopes were put out at the same instant and shooting began shortly thereafter (20 min). The FC100DL was just acclimatized (not perfect), the Mewlon I guess not

[vlaiv]

Best F/ratio for ASI224 is around F/15, with both of your setups you pushed F/ratio quite a bit beyond that (F/24 and not even sure I can calculate effective F/ratio for FC100DZ).

What capture parameters did you use (exposure length, duration of recording, number of stacked subs and so on)?.

[Fedele]

I know that for ASI224 best F/ratio is  f20 / f22. Anyway not matter 

[vlaiv]

5 minutes ago, Fedele said:

I know that for ASI224 best F/ratio is  f20 / f22. Anyway not matter 

It does matter. Using higher F/ratio means that you either need to use longer exposures - which is bad because you want to freeze the seeing or read noise becomes too significant and you end up with noisy recording (especially in poor seeing when you can only stack hand full of subs).

Using F/24 instead of F/15 spreads light over (24/15)^2 = x2.56 larger area - hence signal per pixel goes by factor of x2.56. In order to reach same signal level per exposure you need to increase exposure length x2.56. Instead of using say 5ms exposures - you'll end up using 12ms + exposures and that makes all the difference in freezing the seeing.

You are trying to compare two very different setups for results and if you don't control other variables - you might conclude that above result is down to seeing or cooling or whatever - but in reality, it might be because of improperly chosen exposure length or something else entirely.

[CraigT82]

Those Jupiter images are almost identical apart from a little rotation, how sure are you you haven't mixed up the recordings or stacks and both images are from the same scope? 

[Fedele]

25 minutes ago, CraigT82 said:

Those Jupiter images are almost identical apart from a little rotation, how sure are you you haven't mixed up the recordings or stacks and both images are from the same scope? 

uhm....uhm....

i will CHECK!!