Maintaining star color on long exposures

[cventer]

When doing long exposures ie 5 - 10 minutes.

What is the best way to maintain good star color around the object of interest ?

Does eveyone take shorter RGB exposures and blend into the long exposure image ?

If so what sort of exposure lengh do you use for your starfield RGB exposures?

[cventer]

Bump. No one ?

[Octane]

Hi, Chris,

I guess it depends on the camera you're using and its well depth.

I know with my STL-11000M on the FSQ-106N that I can expose for ten minutes without loss of star colour. Mind you, I've been binning 2x2 and exposing for a maximum of 5 minutes per colour.

I think you'll find the concensus is that, perhaps you expose for a quarter of the duration as your luminance to regain star colours again, and, then add them back in with a simple luminance mask limited to the stars.

Cheers.

H

[Peter Ward]

Depends on camera, well depth, aperture, seeing, transparency, etc.

In short there is no simple exposure time.

That said, a 5 minute RGB can capture much without saturating.

Add luminance to taste ;)

[gregbradley]

Chris, I have found with the KAF8300 on fast scopes 5 minutes is the go.
On slower scopes 10 minutes seems fine. Well depth is 25,500 electrons versus say KAI11002 of around 60,000 and KAF16803 of around 100,000.

Over 5 minutes you start getting some overexposed stars and larger FWHM values in general. There can even be a couple of ugly bloated large stars from some sort of spillover. Once the wells are full its saturated and antiblooming kicks in which is not 100% effective.

I have gone with 5 minute subs with my 8300 camera and I like the results better. Others use slower scopes and haven't seen that problem.
They would if they tried 20 minute subs with a few bright stars in the field.

Greg.

[Paul Haese]

Just to add to the mix.

TSA 102 with reducer f5.76 or there abouts. 20 minute subs in L and blue. 15 minute subs in R and G and no over saturation. No need to take shorter subs either. Taken on a 8300 sensor.

[cfranks]

I think I'll have to go shorter than 5min for RGB. Attached is 5min Luminance of NGC2070 and stars are getting 'blown out' already. 10" f7.3 KAF8300. I have no luck generating a star mask for a field like that either.

Charles

[RobF]

A lot depends on how you process too, although you don't really wan't to start with lots of blown out stars or only the star halos will show true colour. Depending on the object, you might want to mask the stars as you stretch out faint objects, increase saturation, etc. Lot of ways to skin the cat. A lot more mucking around if stars are processed separately of course.

Pixinsight has a nice masked stretch routine that protects the stars a little as the FOV is stretched.

[gregbradley]

Here's an example of what I am talking about.

Look at the bright yellow star in between the 2 galaxies and there is a bright blue one to the left of that.

I processed this a fair bit and I corrected a lot of the bloat but it still looks ungainly. But it is 500% better than the original:

http://www.pbase.com/gregbradley/image/134561608/original

This is with a TEC180FL at F7 and a Microline 8300 at -40C.

So speed of the system and aperture comes into it. With an FSQ106ED it may not become an issue as Paul has pointed out.

But with a 10 inch Newt or a 180mm refractor it is.

Same with my CDK17. It was noticeable better with 5 minute subs over 10 minute subs where bloat had already occurred.

Greg.