Stacking problems

Tandum (Robin) · #1 04-07-2009, 01:08 AM

I finally got some images out of my little starlight express mono camera with a set of trutek filters attached to the tak. I don't understand why there are halos around the big stars in the attached image. I captured, calibrated, stacked and colour converted this image in maxim.

I'm was just looking at image scale tonight and this was shot at 820mm, I'm shooting it again now at 632mm to compare.

I do have a badder IR filter on the nose of the filter wheel but I am yet to do a G2V test on the filters and I'm thinking that's the problem. Any other clues?

Gama · #2 04-07-2009, 02:03 AM

Are the filters Parfocal, and IR Block ?.

This will stuff things up for you..

Theo

Tandum (Robin) · #3 04-07-2009, 03:22 AM

They are supposed to be parfocal but not ir block. The set came with a clear filter and a 1.25" IR filter but I can't get that into the chain so I'm using a 2" badder on the nose of the wheel. Looking at these Red and Green channels they don't seem to be very parfocal at all and the blue channel looks bloated like the green. However, maxim gives them similar FWHM values in the quality section when stacking. It tries to throw out 1/2 the luminence subs

.

Try again tomorrow night I guess

At least I can see the little starlight has the scale I'm after for galaxies, which is all I really want from it

.

jjjnettie (Jeanette) · #4 04-07-2009, 09:25 AM

Sorry to tell you this Robin, but it's your optics that are letting you down here.

I hate seeing you have all this trouble.

Tell you what, I'm willing to swap your Tak for my 120mm Sky Watcher.
No seriously, I don't mind at all. A straight swap, I don't expect anything extra for the extra aperture either.

Tandum (Robin) · #5 04-07-2009, 10:42 AM

What a generous soul you are Jeanette and here I thought you'd be after the Vixen.
It's been patiently sitting in it's box waiting for someone to take it out at night

jase (Jason) · #6 04-07-2009, 06:58 PM

If your RGB filters are not UV/IR blocking, you're going to have some troubles in nailing the right G2V colour balance. The UV/IR signal "poisons" the visual wavelength data. Certainly keep the IR blocking filter in place.

Tandum (Robin) · #7 04-07-2009, 09:04 PM

The filters are parfocal, ran through all of them with the mask on the front and they all have exactly the same focus point. Checked collimination of the scope and it's perfect as far as my eyes can tell. Found a G2V star and the figures don't look ridiculous, 1.475-1-1.087 (RGB). That IR filter in the nose is an Astronimiks filter I got off Doug, not a badder.

It looks like the camera is Blue and Green sensitive and those colours cause star bloat on bright stars, Red and Ha are fine. I have it shooting 60 second subs on Blue Green and 5minutes on Red. I'll try mixing that with some Ha from last night.

I'm sort of out of ideas now

rat156 · #8 04-07-2009, 09:12 PM

This happens a lot with my camera too. I believe that it's atmospheric scattering of the blue channel. Stuff all you can do about it except in processing. Download CCDSharp from the SBig website (it's now free), and run your blue channel through a deconvolution routine, then recombine.

Cheers
Stuart

Tandum (Robin) · #9 04-07-2009, 09:15 PM

It's actually all channels except red

but I'll give it a try.

Here's the short exposure run. That's a lot closer but too much red now, it's causing halos

[edit]
Using the Exposure Calulator it looks like my exposures on M8 are way longer than they need to be and my G2V figures are wrong. I need to do that G2V check again but here's an M83 manually corrected with new figures. Not perfect but getting there.