CLS filter processing help, Have a go!

[JB80 (Jarrod)]

Hey all,

I have never quite got the hang of processing widefield shots with a cls filter in, infact it comes up somewhat of a disaster. Truth be told it just shows how much I need to learn to get the hang of processing.

Anyway I took a bunch of 5 minutes subs last night, 11 to be precise and 4 darks(it was set for a run of 10 but the camera went flat and I fell asleep anyway) and stacked them in DSS so the final image is 55 minutes worth.
Here is the finished .tif with no adjustments made.....

https://www.dropbox.com/s/26r56ddpy61gq79/dbox.TIF

Now I had a couple of attempts today to try and get a better result but just can't manage anything with colour to come from it. I was following a tutourial but it had things in it that PS wouldn't let me do for whatever reason like setting limiting locks so I figure the best bet is to take a breather and start again maybe trying something different.

At the same time I start to wonder though if it's maybe the subs? Have I done things right in the stacking? Maybe it's my camera? etc, etc.....
I'm fairly certain it's my rubbish skills though.

So if people want to have a go with the .tif I have inculded it in the dropbox link above.
Maybe you can do better than I can, it can't be hard.

Here is my dodgy attempt.

[joecool (Mark)]

hmmm, maybe no flat frame? Shocking vignetting... And a weird inner ring (from the lens?)

I have a CLS. Here is how I go about editing the weird white balance out in photoshop. (Oh, also, during capturing I set the 450D to ISO400 (best noise to bit depth) and force the white balance to Daylight).

Before you edit anything in photoshop drag the layer to a new layer and use Image->Adjustments->Curves and drag the line over to the left until you can see the black on the top and the left of your image from the stacking amd a thin green bar on the right. Now use the rectangular marquee tool to mark a selection which only has the clean part of the image. Now un-tick the layer visibility eye button next to this new layer and select the old original layer. Choose Edit->Copy.
Choose File->New. Create with defaults. Then Edit->Paste.

To fix the seeming lack of flat frames I saved this cropped image out to a tif file and used MaximDL to Auto flatten background...

Then opening it back in photoshop-
Now you can do Auto Tone, Auto Contrast, Auto colour.
Now Image->Adjustments->Colour Balance. You need the histogram open and showing All Channels View. Now (usually) leaving the setting on Midtones drag the sliders until the 3 colour bumps overlap.

I find this gives pleasing colours when using the CLS filter. I don't think I will use mine again though. It requires twice the expose time with my 450D which is a big negative, and the skyglow can be removed with Noel Carboni's Astronomy Tools Light Pollution Removal action.

Edit - I just tried Light Pollution Removal with Enhanced Flatten and got almost the exact same image as with MaximDL for removing the vignetting and skyglow. Hey look - more stars, less vignetting!

There is star colour in here. But no nebulosity?

Mark.

[h0ughy (David)]

i use the rgb channels and adjust until it looks normal

[joecool (Mark)]

David, having a look at your M83 you just took, expand your histogram and you will see that it's colour bands are all over the shop. The galaxy is far too red. Galaxies are too far away so see much if any nebulosity so they should be mostly white from the stars. Using the histogram is the trick. A simple Auto Tone, Auto Contrast, Auto Colour will get you close. and then do some twiddling with the Colour Adjustments.

With dedicated astronomy software more can be done but I only have Nebulosity and Photoshop with Noel Carboni's tools at the moment... Here is a 2 minute re-edit to show you what i mean. This is an excellent example of how the CLS filter messes with the colours.