Flats calibration

[wimvb]

17 hours ago, david_taurus83 said:

it looks like OSC, or my DSLR anyways, is very fussy as to the light source for flats

Have you looked at your deBayered flats? They can have a colour bias. A minor colour bias shouldn't be a problem, but it shouldn't be too strong (what ever too strong means).

[david_taurus83]

3 hours ago, wimvb said:

Have you looked at your deBayered flats? They can have a colour bias. A minor colour bias shouldn't be a problem, but it shouldn't be too strong (what ever too strong means).

No, I don't debayer until after the lights are calibrated. All calibration is done with raw files.

[wimvb]

5 hours ago, david_taurus83 said:

. All calibration is done with raw files.

Of course. I was thinking you could deBayer the flat to see if it has a colour bias.

[david_taurus83]

Yes , there's a considerable blue bias in the tracing pad flats. Think I will just have to lump the Artesky round with me in future.

 

[ollypenrice]

Have you tried twilight natural sky flats? I would switch the drive off and leave a few seconds between exposures. (I've never done this myself but people do make it work.)

Olly

[powerlord]

Does a blue bias really matter? You can correct that surely?  I find the same thing with my cheap sketch pad, but as the point of flats is getting rid of dust, spots, vignetting.. Does it really matter?

[david_taurus83]

On 29/07/2021 at 08:28, ollypenrice said:

Have you tried twilight natural sky flats? I would switch the drive off and leave a few seconds between exposures. (I've never done this myself but people do make it work.)

Olly

I'm in bed long by then Olly! This is taken with my mobile setup, Redcat, 6D, star tracker mount etc. No way of leaving it all connected until near dawn.

[ollypenrice]

3 minutes ago, david_taurus83 said:

I'm in bed long by then Olly! This is taken with my mobile setup, Redcat, 6D, star tracker mount etc. No way of leaving it all connected until near dawn.

If you have focus you can shoot flats in the evening twilight. It doesn't have to be perfect focus. A known point on the drawtube would do.

Olly

[david_taurus83]

16 hours ago, powerlord said:

Does a blue bias really matter? You can correct that surely?  I find the same thing with my cheap sketch pad, but as the point of flats is getting rid of dust, spots, vignetting.. Does it really matter?

No, it doesn't matter in the respect that it calibrated out dust artifacts perfectly but over corrwcts the vignetting! What I don't like is the LED tracing pad is clearly doing something to the colour balance before any processing starts. Flats shouldn't do this at all. I've always used the Artesky panel and I've never had to struggle with flats. I bought the tracing pad as a cheap option that can be powered off a 5v power bank as I didn't want to: 

A: lug around my big 12v leisure battery just for the Artesky panel or

B: spend £££ on one of those lighter LiFePO 12v batteries.

Guess I'll just have to lump it with either A or B. Theres also a small demon on my shoulder whispering things like if I have a 12v supply on hand I might as well have a 12v camera...😈

Edited August 1, 2021 by david_taurus83

[david_taurus83]

6 minutes ago, ollypenrice said:

If you have focus you can shoot flats in the evening twilight. It doesn't have to be perfect focus. A known point on the drawtube would do.

Olly

Not a bad shout that. This issue for me is my DSLR has a tendency to suffer from immigrating dust particles that move around each session so need to shoot flats on demand!

[Xiga]

David, if you already own a tablet you could give that a try. I still use an old iPad for doing my flats and it works great. Back when I used my modified DSLR with an IDAS-D1 filter, my flats were also unbalanced. I'm not sure it was even an issue for my setup, but for peace of mind I found an easy solution, which was to use a simple full screen colour app which had 3 sliders for RGB (0 to 255) which allowed me to set the colour so my flats would have a balanced histogram in all 3 channels. Could be worth a try, especially if you already have a tablet lying around somewhere, and would save you some £££'s. 

[powerlord]

Ive been using a cheap sketch thing too, mayne best use the tablet then - it's a decent samsungso should have a decent colour temperature when set to white.