Good flats?

Questions and answers about processing in StarTools and how to accomplish certain tasks.
Carles
Posts: 48
Joined: Thu Jul 30, 2020 5:06 pm

Re: Good flats?

Post by Carles »

mgutierrez wrote: Sat Mar 13, 2021 6:20 pm Well, actually my problem is that I don't know how to take flats with this filter. I was told that good flats should have an equilibrated histogram, quite centered. Without filter I managed to get that. But with the filter the channels are quite separated so I don't know how to center them in the histogram
As far as I know you shoul only be concerned abot the luminance histogram , not the RGB. The right histogram for flats usually is around a 1/3 of the histogram on the left. but that depends on the camer and bit depth too. in my case I usually aim for between 19k and 23k . Color shouldn't matter for flats as it corrects illumination in the frame and dust bunnies and vigneting and so on.. don't think they're are applied in RGB. Actually just loaded my master flats in DSS as a file, and it is black and white.
Stefan B
Posts: 41
Joined: Sat Oct 31, 2020 8:59 pm

Re: Good flats?

Post by Stefan B »

Hi Carles,
Carles wrote: Sat Mar 13, 2021 8:18 pm ...but certainly the dark flats and flats have to be taken with same exposure time.
if you used the old dark flats they're not gonna work with the new flats.
yes, dark flats and flats were shot immediately after each other with the same exposure time... But as already mentioned, applying the dark flats even increased the issue. :confusion-shrug:
And is weird about the NiNa problems you're encountering. Did you try playing with the % of brightness needed or the minimum and maximum exposure times?
Think I did so. Maybe I should have increased the tolerance... Worth trying.
But with the filter the channels are quite separated so I don't know how to center them in the histogram
@mgutierrez: This is also the case with my flats which worked so I wouldn't bother about that. Does applying the flats do the job, i.e. flatten the image? If yes, I guess everythin is fine...

Best regards
Stefan
Carles
Posts: 48
Joined: Thu Jul 30, 2020 5:06 pm

Re: Good flats?

Post by Carles »

Stefan B wrote: Sat Mar 13, 2021 9:24 pm yes, dark flats and flats were shot immediately after each other with the same exposure time... But as already mentioned, applying the dark flats even increased the issue. :confusion-shrug:
Hi Stefan,

But, applying flats keeping the Bias too? because I don't think that they're meant to be used together. if you were using; lights, darks, dark flats and flats WITHOUT bias and it got worse...then I don't know. :( For me the "trick" was to substitute Bias for Dark flats, not include both.

Regards

Carles.
Burly
Posts: 310
Joined: Mon Aug 31, 2015 7:06 am
Location: Northamptonshie uk

Re: Good flats?

Post by Burly »

You use bias or dark flats not both , if using a dslr best to drop darks and load bias or dark flats as darks.
jackbak
Posts: 3
Joined: Sun Jun 14, 2015 3:38 pm

Re: Good flats?

Post by jackbak »

Burly, et al -

When you say dark flats without bias are you meaning take a dark flat without setting eg. my ASI533MC's hardware bias, just set its gain?

Thanks,
Jack
Stefan B
Posts: 41
Joined: Sat Oct 31, 2020 8:59 pm

Re: Good flats?

Post by Stefan B »

Hi Carles!
But, applying flats keeping the Bias too? because I don't think that they're meant to be used together. if you were using; lights, darks, dark flats and flats WITHOUT bias and it got worse...then I don't know
Here's the status quo:

Good: new lights, old flats, old dark flats, old bias
Bad: new lights, new flats
Worse: new lights, new flats, new dark flats

I didn't bother doing bias during the last session. Maybe that would have been good for testing another combination. But it appears that something is wrong with the flats... will have to look at histogram, APT vs NINA, combination of calibration frames...

Best regards
Stefan
Carles
Posts: 48
Joined: Thu Jul 30, 2020 5:06 pm

Re: Good flats?

Post by Carles »

Stefan B wrote: Sun Mar 14, 2021 9:10 pm Hi Carles!
But, applying flats keeping the Bias too? because I don't think that they're meant to be used together. if you were using; lights, darks, dark flats and flats WITHOUT bias and it got worse...then I don't know
Here's the status quo:

Good: new lights, old flats, old dark flats, old bias
Bad: new lights, new flats
Worse: new lights, new flats, new dark flats

I didn't bother doing bias during the last session. Maybe that would have been good for testing another combination. But it appears that something is wrong with the flats... will have to look at histogram, APT vs NINA, combination of calibration frames...

Best regards
Stefan
Hi Stefan!

uh...that's weird. But, that only happens when you use NiNa ? So the "good" is using APT and the "worse" doing all lights, flats and dark flats with NiNa ?
it is strange indeed... you do the Dark flats from the Flat wizzard? If so, at least in mine, NiNa doesn't change the name of the files.. just in case you had added a dark flat as a flat or the other way around. Another way is to create a sequence selecting Darks Flats as type, and also giving it a Name so it makes its own Folder.

I can not come up with anything else really. As mentioned, I am really happy with NiNa and all works fine. Flats included.

Carles.
Stefan B
Posts: 41
Joined: Sat Oct 31, 2020 8:59 pm

Re: Good flats?

Post by Stefan B »

Hi Carles,

so far all the flats created in NINA did not work, even if they had the same parameters (exposure, ISO) like the ones taken with APT. But I'll have to do a direct comparison between the two apps on the same night with the same parameters.

In NINA the flat wizard just gave me an error message telling that 50% histogramm could not be reached within 15 sec exposure. That can't be true since the ISO has been 1600 and the light source has been a light pad with the highest illumination possible. I am sure that you get clipping if exposing for 15 sec with ISO1600 on this light source. But as already said, maybe the 10% tolerance has been too low. I will also look into this when I have the opportunity to...

Best regards
Stefan
Carles
Posts: 48
Joined: Thu Jul 30, 2020 5:06 pm

Re: Good flats?

Post by Carles »

Hi Stefan,

sure, better do a side by side comparision, but not sure what is going on.
I've downloaded your master Flats, APT flat looks a lot darker than NiNa flats.
Also the brightness is different, perhaps a camera tilt? How are your light vigneting
profile without flats? That could be it too.. NiNa flats seem tilt way up, wheather APT
flats look more centered.

You should open one light frame, and stretching in a way to see the vigneting, and compare
with those two master flats. Maybe the camera was tilted when taking flats but not when
taking lights? That could explain why APT worked better.

Regards

Carles.
Attachments
Flats NiNa vs APT.png
Flats NiNa vs APT.png (332.66 KiB) Viewed 201 times
Stefan B
Posts: 41
Joined: Sat Oct 31, 2020 8:59 pm

Re: Good flats?

Post by Stefan B »

Thanks for pointing that out, Carles! :bow-yellow: Not sure how a tilt could snug into the process (certainly, I haven't touched the camera between lights and flats). Maybe by slewing to the zenith... Or it's something different. Could be i moved the light pad too much, so the lighting wasn't even. I try to rotate the pad during the flats session in hope of averaging out the noise and potential uneven lighting coming from the pad. Not sure if I've done that during all sessions. So many potential sources of error ;)

Best regards
Stefan
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