Flats using a light panel

[PeterCPC]

I have just aquired a new A3 light panel for my C8 and I have an issue.

I also got a A3 size Opal Acrylic sheet to diffuse the light. However, the flats image still has lines, presumably from the LEDs in the panel. My question is - will these flats work ok or do I somehow need to diffuse the light still further and, if so, what do you suggest?

I have attached a part of the flat image and exaggerated the lines a bit so you can see what I mean.

[scotty38]

You'll need to get rid of those lines as they won't be in your normal lights I'm afraid.

What about sheets of A4 or even A3 rather lol?

Edited May 26, 2022 by scotty38

[Stuart1971]

As @scotty38 says, the flats need to show the same abnormalities that are present in your lights, so no, these will not work at all….☹️

You can’t beat an EL panel for flats, I have never had much luck with LED type ones….

Edited May 26, 2022 by Stuart1971

[ONIKKINEN]

2 hours ago, PeterCPC said:

I have just aquired a new A3 light panel for my C8 and I have an issue.

I also got a A3 size Opal Acrylic sheet to diffuse the light. However, the flats image still has lines, presumably from the LEDs in the panel. My question is - will these flats work ok or do I somehow need to diffuse the light still further and, if so, what do you suggest?

I have attached a part of the flat image and exaggerated the lines a bit so you can see what I mean.

Looks far too detailed for a flat. Did you have focus in infinity? Looks almost like you have focused on the panel itself, with the panel out of focus and any diffusing layers between even a sparsely LED populated panel would work.

[vineyard]

Yes I've noticed horizontal bands in my flats as well (with an artist's light panel, so I guess that's LED) - and they definitely affect the final image.  You can post-process them out more or less, but it's not ideal.  I haven't got round to it yet, but will test a t-shirt over the objective facing the light panel to see if that diffuses it enough as per @ONIKKINEN suggestion above.

[PeterCPC]

58 minutes ago, scotty38 said:

You'll need to get rid of those lines as they won't be in your normal lights I'm afraid.

What about sheets of A4 or even A3 rather lol?

This is what I got using 8 sheets of paper on the panel. looks much better I think.

[PeterCPC]

13 minutes ago, ONIKKINEN said:

Looks far too detailed for a flat. Did you have focus in infinity? Looks almost like you have focused on the panel itself, with the panel out of focus and any diffusing layers between even a sparsely LED populated panel would work.

I took this with the camera resting on the panel so no focusing was involved.

[Stuart1971]

3 minutes ago, PeterCPC said:

I took this with the camera resting on the panel so no focusing was involved.

Hmm, it really does look like it’s focused on the panel, you need the focus at the same setting as you use for your Astro shots….also how long is the exposure…you should be aiming for around 25,000 to 30,000 ADU…

[ONIKKINEN]

7 minutes ago, PeterCPC said:

I took this with the camera resting on the panel so no focusing was involved.

Ah, throw the panel on the scope with the scope in infinity focus (the same focus as when imaging stars) and im pretty sure the patterns go away.

[PeterCPC]

3 minutes ago, Stuart1971 said:

Hmm, it really does look like it’s focused on the panel, you need the focus at the same setting as you use for your Astro shots….also how long is the exposure…you should be aiming for around 25,000 to 30,000 ADU…

I wouldn't have the first idea about ADU but the exposure was 0.0005 secs gain 120 offset 50.

[Stuart1971]

1 minute ago, PeterCPC said:

I wouldn't have the first idea about ADU but the exposure was 0.0005 secs gain 120 offset 50.

So are you using a telescope, if so the panel should be on the end of that with it focused for nightime use…?

[PeterCPC]

2 minutes ago, ONIKKINEN said:

Ah, throw the panel on the scope with the scope in infinity focus (the same focus as when imaging stars) and im pretty sure the patterns go away.

Great. I will give it a try but will have some paper ready just in case 🙂

 

Just now, Stuart1971 said:

So are you using a telescope, if so the panel should be on the end of that with it focused for nightime use…?

No. I am just conducting a test indoors with just the camera and the panel - no optics involved.

[ONIKKINEN]

5 minutes ago, PeterCPC said:

Great. I will give it a try but will have some paper ready just in case 🙂

I have a toy-quality amazon A4 light panel and used to use printer paper in between the scope and panel to act as a diffusion layer. One night i decided to try without the paper and saw no difference whatsoever except for faster exposures needed to get a good flat, so i just never put the paper back in again. Your mileage may vary of course, but the panel is so far out of focus that it should act as its own diffusion layer so to speak.

[The Admiral]

Since you are taking flats in order to correct for non-uniformity of the light pattern produced by the scope, it follows that the camera has to be attached to the scope as if you were imaging when you take flats. You can take darks with the camera off the scope because there is no light involved.

Ian

[Stuart1971]

1 hour ago, PeterCPC said:

Great. I will give it a try but will have some paper ready just in case 🙂

 

No. I am just conducting a test indoors with just the camera and the panel - no optics involved.

So there lies the issue….👍🏼

[PeterCPC]

14 hours ago, The Admiral said:

Since you are taking flats in order to correct for non-uniformity of the light pattern produced by the scope, it follows that the camera has to be attached to the scope as if you were imaging when you take flats. You can take darks with the camera off the scope because there is no light involved.

Ian

Yes I know. I was just trying to establish if the light panel was going to be suitable.

[PeterCPC]

15 hours ago, ONIKKINEN said:

I have a toy-quality amazon A4 light panel and used to use printer paper in between the scope and panel to act as a diffusion layer. One night i decided to try without the paper and saw no difference whatsoever except for faster exposures needed to get a good flat, so i just never put the paper back in again. Your mileage may vary of course, but the panel is so far out of focus that it should act as its own diffusion layer so to speak.

This makes perfect sense and I wonder why I never thought of it. Thank you. 🙂

[The Admiral]

1 hour ago, PeterCPC said:

Yes I know.

Yes, sorry I should have guessed that! I just hadn't picked up on that!

Ian

Edited May 27, 2022 by The Admiral

[michael8554]

18 hours ago, PeterCPC said:

exposure was 0.0005 secs gain 120 offset 50.

Which camera Peter ?

Just guessing, that's a very fast exposure, wouldn't say 1 second be better ?

Will require a PWM Dimmer and/or lots of ND filter or A3 printer paper.

Michael

[PeterCPC]

3 minutes ago, michael8554 said:

Which camera Peter ?

Just guessing, that's a very fast exposure, wouldn't say 1 second be better ?

Will require a PWM Dimmer and/or lots of ND filter or A3 printer paper.

Michael

ASI294

[The Admiral]

If I recall correctly the ASI294 has peculiarities when taking flats. The recommended exposure time is 2-3 secs. There are numerous posts around on taking flats with this camera.

Have you successfully taken flats before with this camera?

Ian

[Stuart1971]

19 hours ago, PeterCPC said:

I wouldn't have the first idea about ADU but the exposure was 0.0005 secs gain 120 offset 50.

At that shutter speed, they are not flats but pretty much bias frames … try to get around 2-4 second flats..👍🏼

[Anthonyexmouth]

11 minutes ago, The Admiral said:

If I recall correctly the ASI294 has peculiarities when taking flats. The recommended exposure time is 2-3 secs. There are numerous posts around on taking flats with this camera.

Have you successfully taken flats before with this camera?

Ian

Yeah, over 2 secs for the 294 and matching dark flats. It's a great camera but you have to get the calibration frames right. 

[PeterCPC]

Noted all.

[PeterCPC]

Just to conclude this. I have found that, if I use the light panel on the lowest setting with the Opal Acrylic diffuser and 4 shhets of white paper, I can get 2 secs exposures with the histogram looking good. In case it helps anyone else out with a similar issue. This is with the camera installed on the C8.

Edited May 28, 2022 by PeterCPC