Hi John
I know is not a CCDAP related question, but it is in regard to the optimum sub-exposure page on the CCDWARE website...perhaps you can help.

I worked through the procedure described and acquired all of the necessary data for all of my filters. I have to redo the exposures for my narrowband, as the background value did not get over 100 counts after 3 minute exposures.

But the results for the other filters are as follows:
L – 30mins
R – 65 mins R 2x2 – 26mins
G – 89 mins G 2x2 – 36mins
B – 114 mins B 2x2 – 45 mins

I guess from these figures that the Luminance optimum sub-exposure time might be about right, but the RGB values are huge! It seems to me, that if I were to take a 114 minute blue subexposure that I would totally saturate the stars. This is an STL11K camera....do you think that these values might be wrong? I am pretty certain I followed the guidelines.

thanks
martin

(Moved to this forum)

Martin,

These values are not unreasonable. The concept is to use the sky glow noise to overwhelm read noise. Color filters block a considerable portion of the energy in sky glow. Therefore you must expose considerably longer to get the sky glow signal high enough. Note that 2x2-binned color sub-exposure times are considerably lower than unbinned ones.

That being said, most color data is read noise limited and subsequently blurred either in PS or via subsequent processing.

Hi John..and sorry for the slow response here....I was looking for where my post had moved to...found it now!

Thanks for the reply.....I guess the recommendation to shoot colour unbinned is somewhat flawed when you think how many 114 minute subexposures you might have to throw away! I think I will stick with 2x2.

tks
Martin

I thought so too, Martin but consider. We generally smooth the color information in post processing anyhow. I did some experiments with unbinned color on an evaluation U16M with a KAF16803 sensor. Maybe it was me but I thought the color went together easier. It might be worth an experiment at your end to check it out.

I use 10 min. sub-'s for clear and used the same for color. The U16M is very balanced with a color combine ratio of 1.03/1/1.07 which may help. And it is a lot more sensitive than a KAI11002.