CLS Filter advice needed

[Carole]

When I do long exposures with the CLS filter I get a light blue sky and I am finding it very difficult to process the image in order to get a normal looking dark sky.

Does any-one else have this problem and how do they overcome it?
Or should I be using different settings on my DSLR?

Currently using manual 800 ISO, Raw, Bulb and Daylight white balance, 5 min subs. 

It didn't happen at Kelling Heath as the skies were dark. 

Carole

[Mike]

Try different white balance settings.

[Carole]

I'll give that a go Mike.

Thanks

Carole

[Mac]

Try different white balance settings.

Wont make a blind bit of difference, as the image is RAW.
The image saved is just the raw data, the white balance ect is just stored as data and is not applied to the image.
JPG yes, as this is a finished image.

The white balance is adjusted post processing.
When you open the raw images in your canon software
Just click through the different white balances.
You can change it to anything you like.

Mac.

[MarkS]

I get different background sky colours depending on what combination of light pollution and filters I am using.

I simply choose an area of background sky and set it to be the black point.  Easy to do in IRIS.  Might be easy to do in Photoshop as well (but don't ask me how!)

Mark

[Carole]

Hi Mark, yes you showed me how to do this in Iris, but I suppose I was trying to find out whether any-one else had the same problem.  Preferably I'd like to be able to sort it out in Photoshop, but will re-visit Iris if I can't.

It's a black sky until I start to stretch the image to show the detail, and then it goes blue.

Have also had a fair bit of advice on UKAI so will plough through all the suggestions and see what works.
As you remember I did not have this problem at all at Kelling Heath, so it's to do with too much light which increases with the long exposure.

Carole

[Rocket Pooch]

Hi Carole,

Everyone else with these filters has the same problem, look here http://www.astronomik.com/en/cls/astronomik_cls_transmissioncurve.html its the light curve of the filter, a CLS is a very heavy light pollution filter.  It cuts out a lot of Red and Green which is why you think the image if Blue, the blue is there just mainly the red has gone.

By increasing the Red you are adding the Red back, its not there, you are balancing the other channels so they look ok.   A long time ago Robert and I decided a Neodium filter was probably better for our skies because it is less agressive and also lets through a lot of light in the right areas and we could put up with the light pollution.  Talking of which I have a brand new 2" CLS I have never used?

If you get your colour balance looking ok you will be missing a lot of Red and Green from the source.

Chris

[Carole]

Thanks Chris, I can't say I fully understood the graph, but I got the jist of it. 

So it looks like everyone has the same problem in light polluted areas using a CLS filter, and it's just a question of learning to process it so it looks OK.

Thanks every-one.