Will stacked ND filters perform as well as a single 10 stop ND filter?

Question

I have the Tiffen 0.9 ND filter which gives me approximately 3f stops reduction. I like to really slow things down and although it's sufficient in low light it just won't do in daylight.
Should I get a pair of 2 more 0.9 ND filters to stack or should I would a single say 10 stop filter be a better solution?  Will the stacked ND filters perform as well as a single 10 stop filter?
I would like to be able to slow things down to the point where I get similar results to this photo, but in daylight. It was shot at f4, ISO 200 and 75 seconds, at night.

jrista · Accepted Answer

From a functional standpoint, yes, you could essentially achieve the same effect with multiple stacked filters as a single high-density filter (say a 10-stopper.) There are a variety of concerns to be aware of, however, regarding stacking multiple filters.

Filter quality:

The Lee "Big Stopper" 10-stop ND filter is pretty high quality glass filter
There are two Lee ProGlass filters (0.6 and 0.9) of the same quality
The full range of standard Lee ND filters, (0.3, 0.45, 0.6, 0.75, 0.9) are resin
Many third-party filters are resin, a very few are glass (UPDATE: Since this answer was posted, many more third-party manufacturers are using "optical resin" (CR-39) or optical glass for filters. They are expensive, but Lee is no longer the only good source of glass filters.)

Color cast:

Stacking lots of resin filters can cause strange color casts
With digital, color cast is usually an easy post-process fix

Vignetting:

Stacking enough resin filters means a pretty thick hunk of junk on the end of the lens
At least four resin ND filters (0.3/1stop, 0.6/2, 0.9/3, 1.2/4) are needed to match a single 10-stop filter
On wider-angle lenses, you can barely get away with two stacked filters let alone four without vignetting

Flaring:

Any additional optical device added to the light path adds the potential for flare and ghosting
Stacking four ND filters adds a total of 8 additional surfaces which can reflect
To my knowledge, no 4x4/100mm filters are multicoated, so their chances of flaring/ghosting are high

Versatility:

A single 10-stop filter still leaves you some room to also stack on a graduated ND filter to balance contrast

If you want to do some serious ND work, such as 5 minute exposures of sunset along the coast, you should get a 10-stop filter. You'll probably also need at least one GND to normalize scene contrast if you are photographing a sunset/sunrise, which would usually require a setup like the Lee base filter kit with a tandem adapter and an additional independent filter holder (for a total of up to 8 filters)...that is pretty much guaranteed to add vignetting on anything other than a telephoto lens.

Chris Wuestefeld · Answer

If you're stacking filters, you're liable to get vignetting around the corners of the photo. Plus, there's the danger of internal reflections, and other optical issues.

My preferred solution is a single, variable ND filter, with which you can dial-in the amount of light you want.

EDIT responding to comment:

A variable ND filter is one that can vary its density. By twisting it, it gets lighter or darker, so -- depending on the filter in question -- you could adjust from, say, 1 stop to 10 stops, all in a single accessory. Obviously this is more expensive, even than buying a couple of regular filters, but I find it a big help.

As I understand it, this is basically built of two thin CPL filters, so twisting it alters the angles between the polarization, letting in more or less light. But when I tried to do that myself, with two of my own CPLs, the results just didn't work at all.

EDIT 2: I only just looked at your sample image. I don't think that you can do this photo with ND filters alone. I'm pretty sure there's also multi-exposure HDR going on in there as well.

Paul Cezanne · Answer

Just in case you want to see what kind of color cast and vingetting you can get with stacked cheapo ebay filters here is the before shot:

and here is the post processed shot. I did crop a lot of the vingetting away but not all of it and had to use Lightroom to undo some of it.

This was a 240 second (4 minute) exposure at f8.0 (17mm, full frame, ISO 100)

Will stacked ND filters perform as well as a single 10 stop ND filter?

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