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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 which was shot at f4, ISO 200 and 75 seconds.

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2  
I would like similar results to that too! – dpollitt Apr 18 '12 at 13:46
Shouldn't be too difficult; camera, filter, location and light... – Jakub Apr 18 '12 at 14:00
Stacking too much filter is not a good idea. See petapixel.com/2011/06/16/… where the get horrible pictures just by stacking UV filters... – floqui Apr 18 '12 at 14:55
LOL! I wonder how long it took him to put that together. Better yet to undo it as many filters suffer from thread locking... – Jakub Apr 18 '12 at 15:38

3 Answers

up vote 12 down vote accepted

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.

  1. 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.)
  2. Color cast:
    • Stacking lots of resin filters can cause strange color casts
    • With digital, color cast is usually an easy post-process fix
  3. 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
  4. 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
  5. 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.

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Excellent as always! Thanks @jrista. I've been looking at the Lee big stopper already but it's a square filter that requires an adapter. Is there a comparable round 77mm filter you would recommend? – Jakub Apr 18 '12 at 15:42
Just came across this, not something I want to do but interesting nonetheless. – Jakub Apr 18 '12 at 15:46
I think I am starting to understand why in this case the square is better; 10 stops will be too dark to focus so having the adapter allow me to focus and set things up then i just slide the glass into the adapter... I guess – Jakub Apr 18 '12 at 15:52
2  
@Jakub: Yup, that is exactly it. Lee actually has a chart on their BigStopper page that lists original to new shutter speed conversions for a lot of useful shutter speeds. You do everything without the filter, configure exposure in manual mode, adjust by x10 stops (preferably with shutter), then (at least with Lee), you can simply clip the filter holder onto the lens already set up with all the filters you need. Once the filters are on, just trigger exposure (preferably with a cable release.) – jrista♦ Apr 18 '12 at 16:58
up vote 4 down vote

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.

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Thanks. Good point about the internal reflections. What do you meant by variable ND filter? Single glass or a filters that slide into a mount such as the Lee holder? – Jakub Apr 18 '12 at 13:59
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@Chris: Your "EDIT 2" seems incorrect. According to the photographer: "None of my photos are HDR or blended images, they are taken from just one shot". I don't think there are any multi-exposures, however there does appear to be some post-process tone mapping and maybe a bit of effects work on the far-distance point light sources going on. – jrista♦ Apr 18 '12 at 14:56
@jrista - good point. Here's my theory on how the picture was taken, then. This is pre-dawn or post-sunset blue hour picture (to get the stars). The flare in the middle isn't the sun, but a cluster of artificial lights that are together quite bright. The sharpness of the shadow in the foreground is cast by a flash in the water, to camera right. But even at that, it seems to me like there's still too much shadow in the greenery to the left. – Chris Wuestefeld Apr 18 '12 at 15:02
@Chris - This foto is in fact a single exposure, not an HDR. You can tell by the silky smudged skies and by the statement beside the photo itself. I am wondering if this is a 10 stop filter with a CP filter to saturate the colours. There is undoubtedly some post processing going on but that's beside the point, the fact remain that the image is pretty well taken in daylight at f4 and ISO 200 and the exposure is still 75 seconds... – Jakub Apr 18 '12 at 15:34
Regarding saturation, that can be done in about 20 seconds in post...unlike film, digital color is not as dependent on the hardware as it is on the software. I wouldn't consider an ND filter a primary means of saturating colors with a digital camera. – jrista♦ Apr 18 '12 at 15:54
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up vote 0 down vote

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:

enter image description here

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.

enter image description here

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

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