Purple Streaks from ND/Pola?

[Steven Dean]

I have a few shots that have purple streaks in them. I am thinking that the culprit is a variable nd/pola, which I use when one-man-banding it in the woods, etc. (on the shortlist to be replaced). I never had anything like this with MX, but obviously Dragon is a new camera... Any opinions on this? 1 second exposure, frame averaging, proper blackshade, camera was up to temp. I jacked the saturation, and modified curves on this to make it more apparent (streaks to right, and left of center)... Any thoughts on this?


Thanks!

 

[Nawaf Alsabhan]

Post a R3D snapshot, also, what was your f/stop on the lens?
Which OLPF are you using? (Low light? Skin Tone?)
Phil Holland did lots of tests with ND and Dragon, and Dragon is better with ND's than MX, so I don't think it's that.

It could also be a blackshade issue, that's what I first thought.

 

[Phil Holland]

There have been some other examples posted around. And I'm seeing it on other camera systems too, particularly with Variable NDs.

I'm not getting this on my Dragon with a Circular Polarizer, but it is hard to recreate all potential possibilities with various brands and all that.

I don't think anybody is experiencing this with regular NDs. Just Variable NDs and potentially Circular Polarizers.

 

[Bob Gundu]

Lots of discussion on those rainbow artifacts. Conclusion seems to be the polarizers used.

 

[Steven Dean]

Thanks for the replies everyone! Decided to just sell the vari nd...

 

[Mike P.]

You could have also done a lens cap test -- just shot a the back of the lens cap (or maybe an 18% frame) with the same settings but without the fader, jack the ISO up and see what kind of noise pattern you get. Presuming it's the fader, the resulting pattern wouldn't be anything like what you're seeing in the image. Conversely, if you end up seeing a similar pattern (purple & green waves in the same areas of the frame) even without the fader, you could need to re-blackshade (or the inherent pattern is being exaggerated/exacerbated by the pola).

Other than IR contamination, the only anomaly I've seen with cheaper faders is a giant "X" when you push the strength too far.