Question on shooting flat frames - Forums

Topic starter

Oct 1, 2023

Hi,
I've been using a dedicated cooled camera in combination with NINA for 2 months. The flat wizard is really handy, and my lights have always been calibrated correctly.
As a flat field generator I use a tablet and a piece of paper to diffuse the light, but since I have a UVIR cut filter and a dual narrowband filter, I have to change the screen brightness or otherwise exposure times are very different.
Is there any app that let me set the screen brightness to a specific value? I could set, for example, 20% brightness for the UVIR cut and 75% brightness for the dual narrowband and have correctly exposed the histogram in both cases with 2 sec.

Helpful Concise Engaging

Danny Lee

Oct 1, 2023

I would be interested in an app like that too, I take my flats in the same way, using a tablet and a simple white screen app.

The tricky part, as you say, is getting the brightness right so as not to over expose the flats.

Well Written

andrea tasselli

Frequent contributor

Oct 1, 2023

It depends on the flat panel you're using, some allows for something like it I suppose. The point is however that you shouldn't worry about the exposure lengths of the flats since NINA takes care of correctly expose the flats.

Daniele Borsari

Topic starter

Oct 1, 2023

I know that, but having the same exposure every time is more convinient since I can reuse darkflats

andrea tasselli

Frequent contributor

Oct 1, 2023

Darkflats are automatically generated by NINA so what's the issue? Soon enough in my experience you should get enough baseline darkflat masters to cover all your flat exposure range. That's what I have.

dkamen

Oct 1, 2023

Daniele Borsari:
Hi,
I've been using a dedicated cooled camera in combination with NINA for 2 months. The flat wizard is really handy, and my lights have always been calibrated correctly.
As a flat field generator I use a tablet and a piece of paper to diffuse the light, but since I have a UVIR cut filter and a dual narrowband filter, I have to change the screen brightness or otherwise exposure times are very different.
Is there any app that let me set the screen brightness to a specific value? I could set, for example, 20% brightness for the UVIR cut and 75% brightness for the dual narrowband and have correctly exposed the histogram in both cases with 2 sec.

You can set display brightness to 100% and use images with different shades of gray, e.g. created with a paint program or even with a flat background generator like this one. #ffffff is 100% brightness, #808080 is 50 %, #404040 is 25% and so on.

Helpful Concise

Quinn Groessl

IOTD Staff

Oct 1, 2023

Daniele Borsari:
I know that, but having the same exposure every time is more convinient since I can reuse darkflats

if you control all the variables, you should be able to get away with using the same exposure time for flats every time per filter. The ambient light is the most awkward variable to control, especially if you’re outside, but easily done with a sheet or blanket or something.

So if your flats are always 1 second with the UV/IR filter, and they’re always 3 seconds with the dual narrowband, then you can make master dark flats that will last a long time the same way you can make a dark library for your lights.

Well Written Helpful Insightful Concise

Ped

Oct 1, 2023

If it's an iPad, there's this. I've not used it, so not sure how well it works, but seems interesting.

Daniele Borsari

Topic starter

Oct 1, 2023

@Ped It's an Android tablet.
@dkamen Your idea is really good!

Related discussions

New to narrowband (SHO). Suggested exposure times? Calibration frames, etc?

Hi! Stepping into narrowband with a 183GT, shooting SHO and need some tips. My setup is a ZS73 scope on a HEQ-5 Pro Mount with ZWO guide system, etc. How long should my exposures be? How many calibration frames (darks, flats, bias) should I need and ...

Directly addresses calibration frames (flats) question relevant to author's setup.

Apr 8, 2022

Review: ToupTek 36mm LRGB and SHO Filters.

Thought I'd share my thoughts about the ToupTek Astro filters I've been using. Brilliant budget friendly filters. ToupTek Astro 36mm LRGB + SHO Filter Review. Introduction.We all know how expensive astronomy can be. Further to that, we all kn...

Filter-specific flat calibration challenges with budget-friendly filter options.

Mar 27, 2025

Flat acquisition no longer sufficient for broadband only

I can't seem to fix this problem, but all my broadband stacks are coming out like this now, flats are no longer fully correcting them. Not a problem with narrowband at all. I have been imaging for over a year, and this just started happening. It ...

Troubleshooting flat frame acquisition issues with broadband filters.

Jun 10, 2025

Issue with flat frames

Hello everyone, I need some advice about flats. A few months ago, I switched to a monochrome camera with an IMX571 sensor (ToupTek ATR2600M), paired with a ToupTek filter wheel and Antlia LRGB filters. As my main telescope, I use an Askar 103 APO. I ...

Flat frame problems with monochrome camera and filter setup.

May 6, 2025

Flat frames made easier

I've always had problems with flat frames, especially using MaximDL with my CCDs. The main issue was finding the correct exposure time, because a poor flat frame is worse than no flat frame at all ! Therefore, I often skipped flat frames and used...

Discusses flat frame shooting techniques and tools relevant to author's workflow.

Apr 4, 2022