[pearsaab]

I honestly did not realize they made variable ND filters and was curious what people thought of them. In looking at top of the line ND filters would you buy one over the other and why?
Thanks!
Amy

[BigMackCam]

I've tried them, albeit only low and medium cost models, and I found them of limited utility in stills photography. At stronger settings, most of them introduce a sort of "X" shape shadowing to the captured images, rendering them almost unusable.

Apparently, NiSi will soon release a new variable ND that somehow avoids this common "X-effect". Check out this article on PetaPixel:

NiSi's Latest Variable ND Filter Avoids the X-Effect Problem

[Bruce Clark]

My admittedly cheap versions are now gathering dust on a shelf in my study.. I found the "X" to be markedly worse on wide angle lenses. I did post some samples on this forum some time ago. If the the new model eliminates the problem then I could perhaps revisit the use of these things.

[MadMathMind]

Variable ND filters don't help me personally. Fixed ones do.

I use ND filters only for reducing shutter speed so I can stay below the flash sync (because HSS really crushes your power in most circumstances). To use my light meter for correct exposure, I need to know exactly what kind of filter compensation I'm applying. I've never met an NDX filter that tells you the stop settings (and even then, it would move too easily), so fixed ones are by far the right call for me.

[mikec100z]

I have had two variable ND filters, a cheaper Cameron brand and a medium prices Tiffen. Both have proven to be of limited use. The Cameron produced the X effect well within the range of its adjustments. I thought it was because it was a cheap filter and I bought the Tiffen. If is better but is really usable only on standard to telephoto lenses. The X effect if quite pronounced on wide angle lenses, and is worse when you near the maximum capacity of the filter.

These limitations have resulted in the Cameron being given away and the Tiffen being largely left in the bag. I now generally use fixed ND strength filters when I want one.

[Bob 256]

The variable ND filters consist of two polarizers which adjust the light transmittance depending on one's rotational position relative to the other. They freely transmit infrared light at all settings so no good for IR photography, and they interact with polarized light from the scene (sky lighting), hence the patterns in photos taken with them. Another problem is there is no guarantee that the color transmission will remain neutral at all (or any) settings so scene coloration can result. Four air to glass surfaces so that's another negative. Best to stay with a good fixed ND filter if an ND filter is needed.

[SoloJoep]

Because of the X issue with variable ND filters and (to me) the hassle of changing fixed filters (plus both options being pretty costly) I’ve successfully resorted to screwing 2 CPL together and voilà, a DIY variable ND filter!

No X problems whatsoever, and since I had a bunch laying around due to my LBA it didn’t really cost me ‘anything’.

I’m using this setup mainly for outdoor portrait flash photography, and I can’t complain really.

However, the filters are somewhat stiff to turn, but this doesn’t bother me. And also there’s obviously no indication at what ND value you’re at, but if you’d really want to it could be figured out and added manually.

I guess there’s a risk of additional reflections from adding 2 layers of glass in front of the lens, but so far I haven’t noticed much or any issues.

[pearsaab]

Thanks everyone for the excellent feedback. Makes my decision easy.