Nd filters versus stopping down

[Jody_S]

One other factor to consider is color cast. Not all ND filters are truly neutral. The editor of On Landscape, an online landscape magazine published in Britain, looked at a handful and found significant color cast in some of them. As I recall, the resin filters were the worst, and one of the best was a glass ND filter from China. This may not be a big issue for B&W photographers, but for color film users is concerning.

Are the results of his test available online?

[BrianShaw]

I find I'm now using ND and grad filters for maybe 75% of my outdoor shots, sometimes more if I'm using barrel lenses with a Packard or Galli shutter. I also find the designations confusing, not to mention a 0.9ND might not be exactly 3 stops. I've solved this rather easily by spot metering through the filter.

I’ve read a thousand times that metering through a filter is wrong and inaccurate but I’ve always found it to be close enough. My SLRs do that successfully and so do my external meters... or at least it’s not so far off as to cause noticeable errors.

[LabRat]

So use a film with bad reciprocity failure characteristics. That will significantly darken the landscape and light pollution.

I've used that, and it works, and would work with a ND to enhance LIRF effects...

Even better for very long B/W exposures is to use a #29 red, as there is a good amount of red in starlight that passes, but holds back bluish light well for a dark background (but light pollution from red/orange streetlights and moon still enters in, but somewhat reduced)...

Steve K

[LabRat]

I’ve read a thousand times that metering through a filter is wrong and inaccurate but I’ve always found it to be close enough. My SLRs do that successfully and so do my external meters... or at least it’s not so far off as to cause noticeable errors.

Yea, I tested ND's to work fine metering through, though there's a point where LIRF kicks in, even in daylight with very heavy ND's, so don't forget to use the filter factor when calculating exposure for LIRF (but reading the base exposure through the ND is OK)...

Steve K

[Oren Grad]

I've deleted a bunch of griping that descended into an ad hominem food fight.

Please make your substantive point, no matter how critical, without framing it as personal attack. If in the heat of the moment you're feeling too frustrated to do that, please take a break and simmer down until you can.

[Drew Wiley]

Meters are not color neutral, so metering colored filters through them can be misleading, not to mention the spectral unevenness of pan films. ND filters are supposed to be color-neutral, as their name implies, but do often have a minor bias. I've measured them using an instrument at least a hundred times more accurate than either a handheld or TTL light meter, and the quality ones are typically within .05 density - a sixth of a stop.

[Jody_S]

... the quality ones are typically within .05 density - a sixth of a stop.

My cheapo plastic Chinese ones are off by way more than that. In fact, reading through the filter is the only way to get acceptable exposures with them.

I don't know if they have a color cast because I've never used them with color film, but I doubt it's enough to affect metering (@ a dozen readings in different areas to calculate exposure) or color shots that are to be scanned for processing (beyond what can easily be corrected in Photoshop). I expect the processing of color film introduces more color variation than the filters, especially since there are no more labs batch processing for commercial photographers. I doubt a Jobo with small chem kits of dubious vintage (no matter if they were just purchased, at least some of the chems could be years old) is anywhere near as precise as the old pro labs were (I know, we all have horror stories of poorly processed E6 somewhere, once upon a time, which is why we also had our favorite labs that didn't screw up our film).

[Two23]

Funny this topic should come up. In the past I've rarely used ND filters. When I do, it's usually to slow the shutter speed way down (like to 1/2s) when using ancient lenses that have no shutter and I have to use my hand. However, the past several weeks I've been photo'ing a genre new to me--ice racing! It's blinding bright out there on the ice. To minimize DoF so I can make my subjects pop out from a very distracting background, I need to stop down wide open. However, even with f2.8 Nikon lens that's not nearly enough! And often I can't stop down that far because even with ISO 100 I need a shutter speed faster than 1/8000s and my Nikon camera just doesn't have it. So, I bought a Hoya 3-stop ND filter to tame things down. With that I can slow shutter down just enough (1/300s) to allow me to pan a little. So while not large format shooting here, I did explain why stopping down won't work as well as using an ND I think.

Below shot: ice racing on Brant Lake, SD.

Kent in SD

[Doremus Scudder]

Funny this topic should come up. In the past I've rarely used ND filters. When I do, it's usually to slow the shutter speed way down (like to 1/2s) when using ancient lenses that have no shutter and I have to use my hand. However, the past several weeks I've been photo'ing a genre new to me--ice racing! It's blinding bright out there on the ice. To minimize DoF so I can make my subjects pop out from a very distracting background, I need to stop down wide open. However, even with f2.8 Nikon lens that's not nearly enough! And often I can't stop down that far because even with ISO 100 I need a shutter speed faster than 1/8000s and my Nikon camera just doesn't have it. So, I bought a Hoya 3-stop ND filter to tame things down. With that I can slow shutter down just enough (1/300s) to allow me to pan a little. So while not large format shooting here, I did explain why stopping down won't work as well as using an ND I think.

Below shot: ice racing on Brant Lake, SD.

Kent in SD

You do mean "opening up" to maximum aperture don't you?

[Pere Casals]

I'd like to add something about color shifts from ND filters.

Taking a look to datasheets we realize that quality filters have a really flat spectrum, ND filters only changes colors in case of bad filters in their denser version, in special with some variable density filters based in cross polarization.

...but there is another effect, long exposures on their own may change colors, color film have different reciprocity failure for each layer, we all know the need of M filters for Velvia 50 long exposures... but color shifts may also happen with long exposures and any color film.

...this is well known, just pointing that (IMHO) there is a myth around saying that strong ND filters changes colors when it's about different reciprocity failure of color layers.

This can be seen in a single image: say we expose for 4 seconds (with ND filter ), while "Zone-V" is neutral it may happen that shadows (that would require 32s, for example) would have a color cast. This cast disapears if we can open up the diafragm (with ND filter still in place) by 3 stops.

For BW film it also may happen that spectral sensitivity changes with exposure, but I'm not sure about that...