LRGB Imaging, exposure lenghts and Darks

[Zakalwe]

Hi guys and gals,

I'm entering the world of LRGB imaging and I need to ask a question about darks. I intend to take the RBG data using 2x2 binning to speed up the collection of the colour information. How should I judge the exposure length of the RGB lights? 2/3 of the Luminance exposure time?

Second question. Do I need to take a bank of darks for the RGB lights as well? I presume that I cannot use the unbinned darks on the RGB lights?

Third: If I use dithering (PHD and Nebulosity) do I need darks at all? The camera is an Atik 428.

Thanks in advance!

[ollypenrice]

2/3 binned will give a similar saturation to unbinned, I guess. I tend to shoot slightly shorter colour than L because I want the L to pull out the faint stuff but I will generally remove the L from the stars. These can be kept smaller and more colourful without the L layer burning them to white and bloating them. There is a price to pay for binning colour. It doesn't give such good stars and they may need the L layer retaining to keep them a decent shape.

You need the darks to have the same bin mode as the lights.

A bad pixel map, if your stacking software supports them, works very well instead. In AstroArt 5 you can use a bias and a BPM instead of darks, for instance. Generally you just need to see what works best for a given camera.

Olly

[Zakalwe]

Thanks Olly. I use Nebulosity for image acquisition and it supports Bad Pixel Mapping. I'm going to try dithering too (assuming this blooming cloud ever clears). Perhaps with dithering and BPM there wont be that much need for darks?

Have you tried scaleable darks?

[martin_h]

I use Nebulosity/PHD for dithering....works well if you set the dither to medium and the settle to about <0.3...if you have it any higher it takes an age to re acquire a good guide position. I also use Neb to produce a BPM and stack the result in DSS using a Bias in the place of a dark.

[Zakalwe]

Thanks Martin......if I can get results half as good as yours then I'll be happy!

If these damn clouds ever clear I'll have a bash at dither guiding with Neb.

[ollypenrice]

We couldn't get Neb/PHD to dither. Or rather we couldn't get it to stop dithering. It would spend all night dithering over whether or not it was time to start the next capture...

Olly

[fwm891]

We couldn't get Neb/PHD to dither. Or rather we couldn't get it to stop dithering. It would spend all night dithering over whether or not it was time to start the next capture...

Olly

That's why I dropped Nebulosity and now use AA5 for capture and either PHD or a second instance of AA5 for guiding

[ollypenrice]

That's why I dropped Nebulosity and now use AA5 for capture and either PHD or a second instance of AA5 for guiding

Aha, I do guide in AA5 with my own rigs and could capture in it as well, I guess. I just love Artemis Capture but it would be good to dither. Better go and read the AA5 capture manual...

Olly