Canon CLS clip filter question

[nmoushon]

So I finally bought myself a CLS clip filter for my 450D the other week and went out to test it out. Went to M31 and took test shots and all seemed well. So continued with my session. Took 150sec exposure with flats and darks to match. Plugged them into DSS and out popped an EXTREMELY blue M31. Was shocked at first and went back and looked at my singles. They had a tint of blue but thought I could remove that in PS then looked and my flats and they were solid baby blue. So I took the flats out and restacked. Better but still obviously blue tinted and I cant figure out a way to remove it PS. So:

What am I doing wrong?!

A couple things came to mind.

1) Does the filter have to be facing a certain way out? I had the logo facing out presuming it was the right way but also thinking it shouldnt matter.

2) I see how the flats effected my image a lot so I'm guessing I have to remove the clip filter every time I go to take flats? Doesnt that defeat the purpose if I remove/move the camera?

3) Do I need to change the white balance or some other setting inside the camera that would fix this?

4) Or is there something else that I'm doing wrong?

Thanks in advance for any help and advice.

[Steve Ward]

I would have a look at the histogram of the output tif first , DSS has a tendency to produce results that at first glance look terrible.

You have a LOT of adjustment available at the end of the DSS program , colour balance , saturation and luminance can all be tweaked .

Steve.

[nmoushon]

Well the fact that I looked at a RAW flat and it was blue(instead of white) tells me that the filter is adding the blue tint not DSS. Unless I'm doing something wrong. I have also adjusted the histogram and saturation. Nothing to a level that would do this to an image without the clip. I did the same thing to this image as i did all my older images. Move the RGB histogram to have the all over lap as much as possible and the boost sat. to about 15%. Thats all I do. And it came out extremely blue with the flats and better but still quite blue without.

[GlassWalker]

That sounds normal for a CLS filter. Flats with the filter in place is right. I think this is a processing issue, but I'm not familiar with DSS to help there... you probably need to work the colour channels individually to re-balance it.

[swag72]

This filter does create a blue cast - I remember my flats always coming out tinged blue! But it can be processed out in CS, it just requires lining the blue histogram up with the red and green. My DSLR images certainly never stayed blue.

[nmoushon]

I guess I'll have to go back and try processing it again. Thanks everyone. Will post pics when I get off work.

[AndyUK]

This filter does create a blue cast - I remember my flats always coming out tinged blue! But it can be processed out in CS, it just requires lining the blue histogram up with the red and green. My DSLR images certainly never stayed blue

Ditto for me too - It is a little disconcerting at first to have baby blue flats that these filters deliver, but as Sara's said, once you've stacked the lights and callbration frames in DSS, you can always process them out by using levels and selecting the separate R, G and B channels to line their black points up. You can also do something similar in DSS at the end of the stacking process (by moving the peaks of the RGB curves so that they're all in the same place...)

[Steve Ward]

IRMC.

[Auntystatic]

The best thing to do is a custom white balance on your camera to get a near normal colour (see your manual), then in dss tell it to use the custom white balance when processing your images. Its under options/settings/ Raw/FITS DDP settings

Its always better to start with a good raw than have to work harder in PS later

[jgs001]

You can have DSS create a custom white balance during the stacking stage, and that removes the blue cast of the CLS without having to shoot a custom WB or mess about with levels and curves...

In the RAW/FITS, set

In the light stacking tab set RGB Channels Background Calibration

My images with camera lenses are shot with a CLS and I do not have to process the colour cast out of it, even the DSS stretch does not show the blue CLS cast. The colour does not effect the flats, as I believe they are processed in greyscale anyway.

[nmoushon]

Thanks for all the help everyone! Its good to know my small freak out was shared by a lot of people the first time too. I'll have a go at it this weekend. Will be getting more data (hopefully) this weekend to add to it also.

[jgs001]

If you still have the original raws, you should be able to restack and eliminate the blue cast.

[nmoushon]

I do still have them John. Will try your suggestions this weekend. Thanks again for the help.

[Gina]

I use a CLS clip filter with my 1100D all the time to reduce any LP though it's quite low here. Yes, it does produce a blueish cast but that's all taken care of in the processing. It only shows with broadband objects and I simply balance the colours in PS after stacking in DSS.

[Velvet]

My filter on 40D does exeactly the same, blue cast. But processing normally removes this.

Velvet

[nmoushon]

Just to update: I did what John suggested and the auto white balance did the trick! Thanks guys! Now just to get a couple more hours of data so I can post a decent pic!