California Nebula - Kelling Heath Ha and DSLR

[Carole]

Yes please Robert.

carole

[Carole]

OK I have checked the subs and re-stacked.
I have done two slightly different versions, but neither of them have had any post DSS adjustments to the RGB.

Version A. I used the recommended settings in DSS as follows:
AHD debayering
Reset all white balance settings
BIAS set black point to 0
Masterdark - Sigma clipping median combination
Bias - Median combination
If background colour is hard to fix tick background calibration (I chose this in the A version).

The RGB sliders were on top of each other at the end.
Version A link:
https://dl.dropbox.com/u/5730788/Califronia%20stack%20A%20RGB%20ticked.TIF

Version B: I used the same settings as above but tried bayer linear interpolation instead of AHD which I normally use.
I did not tick the Background colour is hard to fix option and the RGB sliders were separate at the end.
Version B link:
https://dl.dropbox.com/u/5730788/California%20stack%20B%20RGB%20NOT%20ticked.TIF

Increasing the saturation early on in the processing is producing better star colour.  I think I left this too late previously.

If any-one would like the actual RAW files, I will have to link those to an E mail address, let me know if you would like this as I'll have to PM it to you as you can't link to a folder of files in Dropbox in the Public folder.  If I don;t have your E mail address please PM it to me.

Carole

[MarkS]

Version A "felt" the easier to process but I didn't have time to perform a quantitative assessment.  I'd like to do so, to understand precisely what are the differences between all 3 versions.

There seems to be something odd with the stars at the top right in all three versions - they have a reddish fringing.  Was this the corner of the original image - possibly with a slight optical aberration?

[Carole]

Not quite sure which stars you are referring to Mark, there is a very slight dither overlap, but only right at the edge.  Again will examine closer when I get home from work today.

Meanwhile this is my re-stack and process of Version A I didn't really get much difference between A & B, and both of them are suffering with horizontal banding (tried Noel's actions horizontal banding redution 3 iterations but it's made no difference), and this is one of the reasons I decided to get a CCD camera as this is becoming a real problem - that and noise.

I have managed better star colour by increasing the saturation at an early stage.

[MarkS]

Star colours are much better!  It's a big improvement.

[Carole]

Thanks Mark, I think I've worked out how to keep the star colour now, do an initial levels followed by an increase in saturation before going on to any more stretching. 

Carole

[MarkS]

I've taken all 3 of the TIFF files you have posted, subtracted one from another, divided one into another and have come to the conclusion that Version B is the least adulterated.

In your original image, you had manually scaled the RGB before the background had been subtracted, I guess it's using the black and white points selected by DSS.  This scales the data in a non-linear manner which I don't think is ideal.

Version A has done an RGB auto scale and come up with something different to what you did manually in the original image.  It seems to have scaled RGB in such a way as to make the background uniform grey whilst preserving the white point. This is preferable to the original.

Version B is my favourite because it seems to have completely left the stacked data unadultered (though I'd like to verify this against one of the original subs).  This allows you to make all your processing choices post-stack.  Definitely my preferred way of doing things!

Mark

[Carole]

Many thanks for all your effort and analysis Mark, that was certainly worthwhile. 

Does any-one have any ideas how to deal with horizontal banding in Photoshop?

(though I'd like to verify this against one of the original subs).

Mark would you like me to post up one of the RAW subs in dropbox, or indeed do you fancy stacking the whole lot in Iris? 

Thanks

Carole

[MarkS]

Mark would you like me to post up one of the RAW subs in dropbox, or indeed do you fancy stacking the whole lot in Iris? 

I'll bring a USB memory stick to the meeting tonight.  Do you have the flats and darks and maybe the bias frames also?

[Carole]

Hi Mark,

Unfortunately I can't come to the meeting this evening, I have to pick up a friend from Gatwick airport.  I'll drop the subs in dropbox for you and send you the link.  I'll include Lights, darks, flats and bias.

Carole

[RobertM]

That's a better result for star colour but the nebula now has a really strange colour hue.

Robert

[Carole]

I'm more concerned about the awful sky background and horizontal banding Robert.  However I now have my LRGB filters for the CCD camera so I think I will put my energy into getting used to using those for the time being when the skies allow. 

Should I be using an additional LP filter as well as the LRGB when imaging from Bromley.  I asked Bern and he said "see how it goes". 

Carole

[MarkS]

Should I be using an additional LP filter as well as the LRGB when imaging from Bromley. 

In my opinion, stick to narrowband from Bromley.

[Carole]

You're probably right Mark, but I would like to at least see what they will produce from Bromley, even if it's just to practice using and combining them and to get some comparison to using them at a dark site.

Carole

[Fay]

Carole, please can you send me the files of California?

Thanks