LRGB and binning

[MarkF]

A quick question.

Just to make sure I have got this right, I took 20 180sec Lum subs for the detail along with 20 Bias and 20 180sec Darks at the same temperature. (took the camera off capped it and left it running on a cushion under the tripod whilst clearing up.)

I took 5 2x2 bin 180secs of each colour (RGB) making another 15 lights. (Binned gives four times the sensitivity of the camera so 25% subs of the Lum subs?)

Is that the correct ratio?

Then when stacking, do I need to do more darks and bias for the binned subs as they are a different size or not worry about darks and bias for RGB?

Spent all day trying to work out the processing for LRGB on M13, just want to make sure I have captured enough of everything and I am not trying to learn to process with the wrong data. Although a fair bit of high thin cloud last night.

This what I have come up with so far based on this method of capture. (took me a while to realise how to reference a fit to get the RGB aligned with the Lum)

Now I am basing my perception of colours for M13 on other images I have seen and they all look a bit blue/whiter than this.

[themos]

Now I am basing my perception of colours for M13 on other images I have seen and they all look a bit blue/whiter than this.

You could use a planetarium program to find a G2 star (or similar) in your image and make that White.

[Ben Ritchie]

20 Bias and 20 180sec Darks at the same temperature.

You don't need to take bias if you're taking darks at the same exposure length as the lights - darks are effectively bias plus thermal noise. The main reasons to take bias are (a) if the thermal noise of your CCD is very low (e.g. the ICX285 chip in the Atik 314L, SXV-H9 etc.) so you can forget darks completely, or ( if your dark exposures are a different length to your lights, as bias allows the darks to be scaled.

[MarkF]

Thanks Ben, so I don't need to take the same length Darks as lights all the time I can use the Bias to let the stacker sort it out, just make sure the ambient temp is the same? Also what tolerances are there in degrees either side ie. will 11 degree darks be okay for 5 degrees either side?

Cheers for that Thermos, methinks that is for a cloudy day to sort out

[roundycat]

you don't need bias unless you are using non dark subtracted flats, then you should subtract bias from the flats.

Your gain does not go up by a factor of four with x2 binning, more like x1.4 but it depends on the camera. You should shoot plenty of L to go with the RGB or the colour will be diluted. You picture looks ok, maybe a bit less saturation. Doing the colour by eye works ok, G2V is a lot of work for little return. One thing at a time!

Dennis