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Color of diffuser for flat Frames

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#1 Seven007

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Posted 16 June 2021 - 12:09 PM

Hello everyone,

I was wondering if the colour of the diffuser will effect my final image.

Until now I am doing sky flats with T-Shirts as diffusers.

With a white diffuser the single channels are much more separated and I have to be more careful not clipping one.
With a yellow one the channels are much closer together.

My question will there be difference in my image depending on the colour of the diffusor?

Best Regards
Sven

#2 DubbelDerp

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Posted 16 June 2021 - 01:52 PM

I've been wondering this myself. With a white t-shirt and using a dim light source, the three histogram peaks get very far apart. I don't see how keeping the peaks in the channels closer together could be anything but a good thing. Interesting idea to use a yellow source, I'm going to have to try that! 


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#3 galacticinsomnia

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Posted 16 June 2021 - 06:50 PM

Flexible Cutting boards, cover the optical tube, point towards any bright area.
Keep histogram in the middle.  Keeping colors even doesn't matter, what matters is the capture of the gradients from center to edges.

There is no replacement for a good diffused light source.  Thansluscent polypropelene plastic has wonderful characteristcs. 
3 bucks at wally world, or buy a bunch on amazon. 

Do an experiment if you don't believe colors don't matter, much, take your flats, and make them all black and white or grayscale.
Will have no effect unless you have really messed up in taking the flats.

Clear Skies !!


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#4 limeyx

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Posted 16 June 2021 - 07:19 PM

I've been wondering this myself. With a white t-shirt and using a dim light source, the three histogram peaks get very far apart. I don't see how keeping the peaks in the channels closer together could be anything but a good thing. Interesting idea to use a yellow source, I'm going to have to try that! 

Interesting. I have some yellow paper. I might try that if I can pry it out of the kids hands


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#5 whwang

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Posted 16 June 2021 - 09:50 PM

I use daytime or twilight sky or a light panel as the light source for flat.  All these sources are blue.  So I always use a yellow or brown T-shirt or diffuser to make the color in my flat frames brown, more or less matching the color of the night sky.

 

In principle, the color of the flat frame should not matter.  In reality, cameras can have some nonlinear behavior.  Matching the color (and brightness) of your light and flat frames as much as possible has the potential advantage of minimize of nonlinear effects.


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#6 galacticinsomnia

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Posted 16 June 2021 - 10:53 PM

Matching the color (and brightness) of your light and flat frames as much as possible has the potential advantage of minimize of nonlinear effects.

This is also true, there is potential.

Clear Skies !!


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#7 Seven007

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Posted 17 June 2021 - 04:52 AM

Great thank you everyone for your input!

#8 colinrm

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Posted 18 June 2021 - 01:01 PM

I've been using a sheet of acrylic with window tint on it to reduce the brightness of my flat panel.  It gives the slightest green hue to it.  I haven't noticed any problems with it.  I've also used T-shirts and other cloth of varying colors to try to "balance" the channels in the flats.  It never seemed to make a difference to the final image quality.

 

I also typically balance the channels of my master flat by splitting the CFA, linear fitting to one green channel, then merging back to a full image.  This makes the flat not change the color balance of the lights.

 

The only problem I've really encountered is if one channel is significantly dimmer than the others, this can cause it to be more noisy in the master than the others.  This is fixable, though, by combining channels at different exposures so their SNR is about equivalent.


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