Subs or binning ... are they the same ??

[Jeffkop (Jeff)]

Hello to the community once again.

And once again Im after some help ... well point of clarification really.
I have been imaging M104 and my camera telescope combo is such that in full frame mode the object appears too small to me. So the night before last I imaged it using the 2x2 bin mode. OK ... but the resolution was down I thought.

So last night I played with something called sub frames, where I can select a half size and use 1x1 binning. I expected that the image would just be a cropped version of the full frame but it wasnt, the galaxy was bigger. So I took all these pictures in LRGB and then found out I cant dark frame subtract because the calibration procedure in CCDSoft expects full frame not subs, and so I cant use the dark frame I took in the calibration setup.

So I am confused .. wots a sub? ... I hear people taking about taking 10 minute subs ... are these binned images just being called something different ?? .. If not how do they apply some dark frames to them.

Sheeeeeeeze ... Lots to learn.

Thank you

Jeff

[[1ponders] (Paul)]

Generally "subs" is referring to a collection of images taken to combine together to produce a single image either through adding, median combine, averaging or similar. Binning refers to on chip combining of pixels. Instead of using single pixels to catch the light they are "joined" together to make a super pixel. 2x2 binning combines 4 pixels into one. This give the advantage of increased sensitivity and greater well depth. The down side is it reduces your image size by 1/4.

From memory in CCDSoft a sub frame is a section of a frame being taken. It is normally smaller than the original and is used to get a faster download for focusing, or as you have done, for selecting only one area to be imaged (ROI region of interest). Strange though that it would give a larger image view. You don't have some form of auto-fit to window ticked somewhere do you?

[Bassnut (Fred)]

Dark frames must be identical in size to the sub frames for them to calibrate correctly. A cropped sub (or any other size/position manipulation) will not align correctly with a dark, making it useless.

The CCD soft stacks subs and the manual explains how it all works.