Newbie question

The light source can matter. Many people use light panels that are originally meant for drawing on, like tracing things. The problem I've had in the past trying to use the one I have, is that if I try to dim it too much I can see lines or like a flicker from the frequency of the light. You may have to cover the tablet with a thing white t-shirt or something to be able to get your exposure how you want.

As for your histogram, I always aim for 1/4-1/3 from the left. You don't want anything clipped to black, and you really don't want it clipped to white.

you don't have to worry about that; it just needs to be a moderately bright light source

but,

as others have mentioned, your tablet probably has a strobing pattern coming from the display; you might be able to see this with a slow-mo camera

that can affect your flats in a negative way

I recommend, for someone who doesn't have dedicated flat panels, to just put a white T-shirt on the scope, remove ripples in it, in front of the objective lens, using rubber bands maybe, or paracord (or if you want to iron it beforehand also), and point at the sun/daylight sky through a window or outside, or even at an evenly illuminated wall inside your house, like, one that the sunlight is hitting; these will give you the best budget flats

Oscar:
you don't have to worry about that; it just needs to be a moderately bright light source

but,

as others have mentioned, your tablet probably has a strobing pattern coming from the display; you might be able to see this with a slow-mo camera

that can affect your flats in a negative way

I recommend, for someone who doesn't have dedicated flat panels, to just put a white T-shirt on the scope, remove ripples in it, in front of the objective lens, using rubber bands maybe, or paracord (or if you want to iron it beforehand also), and point at the sun/daylight sky through a window or outside, or even at an evenly illuminated wall inside your house, like, one that the sunlight is hitting; these will give you the best budget flats

So my tablet has a high refresh rate screen. That should lower the flicking the camera will see right? And when I say high I mean 120htz

I honestly am not sure

I never really learned about flat panels or tablet flats because the sun served my purpose

I just know that any strobing is bad

if you want me to guess, I think you would see double the strobe lines of 60 hertz, but it's just a guess

Hello, as someone getting into astrophotography using a DSLR, lens, and tracker, I have a possibly stupid question lol. 

When taking flats. Is there a certain brightness to target, for the light source specifically, if I was using a tablet with a white screen? I know I have to adjust my camera shutter speed to hit a certain spot on the histogram, but does the light source matter? 

Thanks.

Using an LED panel is where I ended up after many other attempts - so you are starting in a perfect spot, especially as you have a controlled setup you can replicate any time and place!
(white T-Shirts also work well, but tuning it to fit for different filters always needed some tweaking)

Regarding exposure time/light intensity I would look out for
a. make sure you exposure time much longer than refresh rate of LED screen - and not too short, otherwise you wil get moiree effect artefacts
b. aim for histogram peak to be between 30-50% of your total range
c. take flats every single time for each filter - any shortcut of usings last nights flats might work but often does not 

Arny

I have had that happen too, even when shooting narrowband flats well after sunrise. It really surprised me the first time I saw it. Certainly something to be aware of.

The flickering is indeed the biggest problem I see with drawing panels. But my solution is to increase the number of flats I take. Unless you hit the exact frequency of the flicker with your exposure time, the dark and bright stripes are always at different positions (btw, I never saw the flickering while using my tablet screen, though). I build a DIY adjustable panel and I am trying to keep the exposure time of the flats as long as possible to prevent the flickering effect. This works well with NB filters. For LRGB (especially L) it doesn't work all the time. But there you can lower the ISO speed of your camera if needed. It won't have a huge impact on the flats, if the flat sensor gain doesn't match the light frame's gain.

However, it is just a matter of the statistics. Taking more flats will even out the strobing effect on the master flat. I typically use 30 flats to get an even master frame. Sometimes I go even higher to 50. I never had issues this way. There are so many things to me that are more important and have much more impact on the final image quality than the possible left over pattern in the master flat using this method.

I know, that not all of you may agree with me, but this is what I experienced.

CS

Christian