I started using Lee filters once I moved to the 5D and found them a big improvement over the previous cheaper filters I used.
I recently got a 0.9 ND filter to help slow down the shutter speeds. I then started to notice a magenta type casts in the clouds, the following gallery is an example;

http://gallery.mac.com/john.ahern#100229&v...lor=black&sel=1

Sometimes I like the cast, but most times I think it just looks weird and un-natural and reminds me of the cast I used to get all the time with the cheaper filters I had in the past. I can remove the cast in Photoshop but I want to minimize the time I spend on the computer.

I don't know if this is due to the normal graduated filters, the new ND filter or something I am doing wrong.

I know Lee do a Proglass 0.9 ND filter that is designed for DSLR due to them being more sensitive to IR, I wonder is this the solution, anybody with some experience to share?

John

Firstly - are you shooting RAW or jpeg?

I have noticed this as well. I went to the Lee website and downloaded their PDF. The examples (page 20, 28 and more) of landscapes with a 0.9 ND filter all have a magenta cast. They show these examples alongside an explanation of their ND filters which says they do not affect color balance. Hmmm. If I was using these for a lot of images, I guess I'd just shoot RAW files and process all the images with a conservative correction.
...I do wonder where that cast comes from.

I shot RAW, then process in Lightroom. I can take the image into Photoshop and use a colorbalance layer on highlights to remove the cast.

John

I contacted Lee about this and got the following responce withing a few hours;

"You are correct, the magenta skies are caused by excess IR getting to the sensor, or rather an imbalance of IR to visible light reaching the sensor. This will only happen in certain conditions and usually only when you use multiple ND filters ( usually grads and standards ) on the same image on a digital sensor. The Proglass product was developed to prevent this as they absorb the IR, so as long as you have at least one of those in front of the lens then this will not happen.

We have tweaked the resin filters over the years to absorb as much IR as possible, and even with Velvia we did not see the problem, but with digital it has arisen again and if you commonly use multiple NDs then I think a proglass would be a worthwhile investment"

Will get a Proglass filter in the next while once I have bit of money spare and report back.

John

Are there Proglass graduated ND filters?

As far as I am aware they only do Proglass ND filters, as mentioned in their email they have tweaked the graduated filters to adsorb more IR.

John