Looking For Advice/Info On ND Filters

Started May 26, 2009 | Discussions thread
submagination
Senior MemberPosts: 1,078
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Singh-Ray Vari-ND Review
In reply to submagination, Jun 7, 2009

Some people had questions about the Singh-Ray vari-nd filter and I wanted to put together a quick set of images for those interested.

First, how the test was done:

All images were shot on a 5D mark II with the 35mm f1.4 lens. I have a 72mm-77mm step-up ring to attach the vari-nd to the lens. Since I have some lenses with a 77mm front end, this is in no way a problem for me since I could find myself in situations in which I might need to shoot with the vari-nd on them. I didn't experience vignetting with this configuration. 35mm isn't all that wide (even on full frame) and I didn't expect any problems even with the extra space the step-up ring added. If you have to go really wide, it might be worthwhile to get the 82mm filter.

The camera was set to manual and I kept a constant f16 @ ISO 100 for all shots. I did not use a cable release or mirror lock-up because I didn't really care about sharpness, just exposure and the effect on image quality at higher densities. Given some light clouds, the base exposure (without the filter) was 1/25s. I wanted to make sure I wasn't blowing out all of the sky and mostly exposed for the highlights there and let the rest of the light levels fall where they may. After taking a shot, I'd dial down the shutter a full stop (3 clicks) and then dial the filter until I was at the right exposure level as given by the meter. Since the vari-nd doesn't actually mark the light loss (there's a basic scale, but this is just for reference - the dots don't actually mean anything in particular), this was the only real way to go about this.

All images were shot RAW and opened in ACR. I set them all to the same white balance and made no other changes to processing. AWB did have some slight variation between the different shots but it was very minor. There was a larger swing between the first image (without the vari-nd) and those with it. This should be obvious to most when looking at the images.

Here's what I found:

1) There appears to be a warming or polarization effect with the vari-nd. I don't dislike it, but it's there and worth noting.

2) Singh-Ray states

"The Vari-ND is capable of densities of more than 8 stops. Results at these densities, however, may be unpredictable."

  • and they're absolutely correct. At > 8 stops, the ND effect was not even throughout the frame. Minor adjustments over the 8 stop mark "moved" this effect around. This likely has something to do with the way the different polarization layers interact at their highest level, but I don't know the specifics. Either way, it's pretty easy to spot and you know once you get to the "Max" mark on the filter that you should probably dial back a bit.

3) At higher densities (somewhere between +6 and +7), it looks like you start to lose a bit of contrast. While you can likely recover a lot of this in post, it's again worth noting.

4) You can NOT use the vari-nd with a CPL. Well, you "can", but the results are undesirable in all but the weirdest circumstances. The following shots were made with the vari-nd at its lowest setting and I had exposures on both at ISO 100, f/16, 5s (not a typo - a full 5 seconds). I also set the vari-nd + CPL shots to the same white balance that I processed the original shots with and did no additional processing.

If a CPL usually costs at most 2 stops and the vari-nd is 2 stops at its lowest setting, then we would expect about a 4 stop light loss (in the shooting conditions of this test, this would be close to ISO 100, f/16, .6s. Clearly there's some magic with how a CPL and the vari-nd interact that's not only giving the crazy colors but a ton of additional light loss. It's also worth noting that the different colors were achieved by spinning the front element of the CPL.

You can also notice that with the step-up ring, vari-nd and the CPL that the 35mm f1.4 is getting the CPL in the corners. Easy to crop out, but again worth noting if you're considering stacking filters.

5) All the weirdness above said, the images between +2 to +8 stops look really good to me and this is a great item to keep in my bag. While on the expensive side, this one filter can take the place of multiple ND filters and quickly justifies the price tag.

I would definitely recommend this to anyone interested in the sort of shooting that ND filters lend themselves to.

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