Variable ND filters, color cast & correction

MooseKiller · February 2, 2013

Greetings Grinners!

So, I am looking around at variable ND filters, and one of the common comments is that some tend to impart a color cast... My question is: Is there an easier color cast to correct for, and what is generally the best way to correct for it in post? This will be for both stills and video, so if there are suggestions for both... :wink

And since we're on the subject, any suggestions on the filter itself? I am planning on going with a single, larger filter, and then use step up rings for using on a variety of lenses.

I will cross post to video as well, but mods, please feel free to adjust as needed...

Thanks everyone!

DavidTO · February 3, 2013

Don't get a variable. They cause too many problems. On a recent workshop I had the opportunity to see them in action as we reviewed images. So many of them looked horribly funky. Really awful. Sure, you can get good results, but it's just not worth it. They seemed to be good up to about 6 stops, and then completely fell apart.

The real point is you just don't need a variable, I don't think. Between aperture and ISO adjustments you should be able to get as much variance as the filter would give you and still be in an acceptable range for either.

I recently got the Lee Big Stopper and a square polarizer to go with it. Advantages: works with very wide lenses and no vignetting, easy on/off for composing/metering while shooting, great optics. Cons: expensive and bulky.

MooseKiller · February 3, 2013

Thanks for the feedback, DavidTO!

thegridrunner · February 4, 2013

I have a variable ND filter that I use for filmmaking. They are indispensable for filmmaking because they allow you to have a low shutter speed and wide open aperture with a lower iso to achieve a shallow depth a field with a clean noise structure. It is much easier to carry than several ND filters and to make quick adjustments. But as you mention, sometimes you will have a slight color shift that will have to be fixed in post production.

tsk1979 · February 4, 2013

What if you are a RAW shooter. The color shift should be somewhat correctable, right?

DavidTO · February 4, 2013

tsk1979 wrote: »

What if you are a RAW shooter. The color shift should be somewhat correctable, right?

What I was seeing over 6 stops wasn't a minor color cast, it was horrible and inconsistent across the frame. Not fixable. It was color and contrast that was varying in a way that rendered the shot unusable. Singh-Ray was the brand.

DavidTO · February 4, 2013

thegridrunner wrote: »

I have a variable ND filter that I use for filmmaking. They are indispensable for filmmaking because they allow you to have a low shutter speed and wide open aperture with a lower iso to achieve a shallow depth a field with a clean noise structure. It is much easier to carry than several ND filters and to make quick adjustments. But as you mention, sometimes you will have a slight color shift that will have to be fixed in post production.

I don't know about video and nd filters. The Lee has a color shift, too, and yes, when shooting RAW an overall and consistent cast is easy to fix.

thegridrunner · February 5, 2013

DavidTO wrote: »

I don't know about video and nd filters. The Lee has a color shift, too, and yes, when shooting RAW an overall and consistent cast is easy to fix.

In Video, you have to keep a smaller shutter speed to avoid a strobing effect. I usually set my shutter speed to 1/50th of a second. Also, if you want a shallow depth a field, you have to shoot wide open. So that only leave an iso adjustment. ISO 100 or 50 is not slow enough to darken a sunny day shooting at 1/50 a second at f2.0. That is why ND filters are so important. It is the only way to darken a scene enough on a sunny day. But as you mention, there can be color shifts that need to be addressed in post and many times secondary color correction for the same scene. The price you pay for shooting video on a sunny day.

DavidTO · February 5, 2013

This is the kind of issue I was seeing and why the variables are a non-starter for me. http://photo.net/filters-bags-tripods-accessories-forum/00aItm

For still photography I would never consider using one.

CatOne · February 5, 2013

I have the Singh-Ray Vari-ND and I don't have the color shift problems that David notes.

One important thing to note, though: I think they advertise it as 1-10 stops. You can crank it farther, like to 12 (it may be more). Beyond 10, stuff gets bad, so you wouldn't want to do that. It's possible that's what David saw.

So it's usable. However, if I had to do things again, I think I'd just get a 10-stop. Reason being, I pretty much NEVER use it at anything other than 10 stops. You have a lot of latitude in today's cameras to adjust exposure with the ISO, so pretty much the only reason for one of these is when you really need to cut out light, and 10-stops is a good ticket (and has good optical quality). Thus, that's what I'd get, and if I needed 8 stops I'd either tweak my camera aperture or ISO to get the right shutter speed.

I think the Vari-ND is more a product from the film days when you had no option to tweak the ISO. It's mostly an anachronism today.

angevin1 · February 5, 2013

thegridrunner wrote: »

That is why ND filters are so important. It is the only way to darken a scene enough on a sunny day. But as you mention, there can be color shifts that need to be addressed in post and many times secondary color correction for the same scene. The price you pay for shooting video on a sunny day.

Nope. Thank God you're wrong otherwise we'd never be able to actually shoot any movies without 40kw of interior light. For film-shooting-Camera's, stacking ND filters in a matte box was the typical way. Also ND-film comes on rolls that can be had, for putting over windows and so forth to reduce incoming light. Scrims, another useful tool for reducing light.

I would NEVER use something that caused me more work. I have to have the cleanest image into the camera as is humanly possible. You can go fix your stuff, not me. Besides, if you're shooting with a DSLR, or anything other than a Pro-res or RAW file, there ain't near enough room in the resulting media to fix much color cast.

To the OP. Yeah. I use as many ND's as needed, stack 'em, and use those adapter rings also!

DavidTO · February 5, 2013

This.

CatOne wrote: »

I pretty much NEVER use it at anything other than 10 stops. You have a lot of latitude in today's cameras to adjust exposure with the ISO, so pretty much the only reason for one of these is when you really need to cut out light, and 10-stops is a good ticket (and has good optical quality). Thus, that's what I'd get, and if I needed 8 stops I'd either tweak my camera aperture or ISO to get the right shutter speed.

Variable ND filters, color cast & correction

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