Deminishing returns.....

Started 3 months ago | Discussions thread
jasonm10 Regular Member • Posts: 172
Re: Deminishing returns.....

Astrozoid wrote:

Alen K wrote:

Astrozoid wrote:

When you use LENR you get a double whammy hit because not only have you lost half the signal you could have recorded, you are adding noise in each dark that you shoot in the camera. You would add a lot less noise with a good master dark.

I don't understand this. Please elaborate. If I take N light frames with LENR on (generally a bad idea, I agree), I will be using N dark frames, one for each light. Mathematically, there should be no difference between averaging N frames, each with a dark pre-subtracted, and averaging N frames then subtracting the average of N dark frames (the master dark).

Yea, except for one thing.

I can construct a master dark out of as many subs as I like when I shoot darks in my garage.

I don't have to limit it to the same number as the number of lights.

If you shoot 16 lights with 16 darks, you will inject X amount of dark-frame subtraction calibration noise. With 64 darks, I will only inject 1/2 as much.

So, separate darks vs LENR darks will inject less noise to the final stack.

Jerry

Hi Jerry. I'm getting confused with seems to be the cross over nomenclature about processing calibration frames.

Subs= sky image? Some astro process people say lights perhaps meaning sky images too.

Lights also = sky image? Or does 'light' refer to the calibration frame of shooting pure white exposures as one of the four needed calibration frames most software looks for?

Bias is the frame with closed lens cap at fastest shutter speed while in the field to get same temp and other info on the camera as well?

Darks are easy, that's shooting maybe at least 50 exposures exactly what you've shot the sky at but with the lens cap on to get as black as possible for the sensor.

So,

Subs ... lights = sky image @ hundreds of exposures. (no cap on of course, unless your trying to emulate dark matter.)

Darks = black frames with lens cap on @ 30+ exposures per photog prefs.

Bias = well, biased fastest shutter cap on @ 50+?

?Lights? = pure white exposure in field usually @ 50?

I'm sure this is all on your and others websites and I will get there, but trying to read this very good thread I keep getting mixed up. I usually will shoot all 4 calibration frames at the time of the shoot.

Thanks so much for what you do and sharing your knowledge here and on your website.

Stay safe.

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