Neutral density filters

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    Does anyone here use them? If so, what for?

    I’m thinking of picking up one or two. I like using parabolic umbrellas as light modifiers, but they’re really efficient – especially the silver ones. That means I have to turn down the power even on a lowly 160ws light and stop down to f/8 (or smaller). It doesn’t help that my D90 has a base iso of 200.

    So I’m thinking of putting a one-stop ND filter in front of my lens. Only I have no idea as to whether this is a smart idea or a dumb noob trick. Most of what I’ve been able to find about using them involves shooting at a wider aperture in sunlight.


    Hi Lurker,

    I don’t use them often, but when you need them, they’re invaluable. As you’ve found, studio flash can be just too damn powerful sometimes.

    There are alternatives- notably buying some ND or diffusion gel and putting it in front of the flash can work. I do this sometimes, because I have a stack of gels for colour temperature effects and it didn’t cost much to buy a sheet of ND as well. I just clip it up between the umbrella reflector and the dome of the flash head with wooden clothes pegs. If you can find somewhere to buy a sheet of ND as a one off this will probably be your cheapest option, too. You could even try a very poor man’s version by putting some tin foil with a hole in it in the way to try to cut down a bit of light.

    If buying ND for the front of the lens, I’d consider getting something like the Cokin filter holder system which will let you use the same filters on multiple lenses. In particular this is very useful for ND grad filters which are very useful for subtly taming too-bright skies. Not something it sounds like you’re concerned with at the moment, but worth considering for the future. You have to take good care of these plastic or resin square filters but kept in their boxes they last decades- I’m still using ones I bought to go with my Pentax P30 20 years ago!

    If you’ve only got one or two lenses with the same front filter screw diameter a screw-in filter might be worth considering but they tend to be expensive and (paradoxically) in my experience they’re actually more prone to scratches and destruction than the resin squares are, perhaps because they’re more likely to get unfastened and thrown into a bag. They tend to be more expensive.

    If you want to go to more extreme filtration (like 3 or 4 stops) I gather it is worth investing in ND filters which also reject infrared. These are more expensive but otherwise you can get into problems with IR contamination causing bad colour shifts especially in the shadows and on man-made fabrics.

    I have a couple of ND filters and a couple of graduated ND filters which are quite useful for shooting outside especially for video. If we ended up doing that regularly I’d probably go for the ultimate in filter technology and buy a matte box, which has slots for filters. That circumvents the issues with flare and glare you can sometimes get by putting a sheet of not very optically clever dark stuff in front of a nice expensive anti-flare multi-coated lens…

    In your position I’d definitely try clipping ND gel to the flash head before messing around with filters on the lens. It is likely to be cheaper and less likely to compromise the quality you get at the camera.

    Cheers, Hywel.




    Thanks for the advice; as always it’s helpful.

    I’ve considered putting a gel on the flash, but the design makes doing so difficult – not impossible, but just difficult. The modifier I’m particularly trying to tame is this one, with the on-axis (“cage”) mount, on an Alien Bee light.

    I hadn’t considered the Cokin filter holder system, mostly because I never have heard of it before. I’ll have to check that out. I was thinking more of a screw in filter for the lack-of-hassle factor. Given my current small number of lenses, and the fact that I only want to lose one stop, I didn’t think the cost would be too bad.

    Of course if I wanted to throw money at the problem :mrgreen: I could buy a new camera with a base ISO of 100 instead of 200, and/or upgrade my Alien Bee strobes to Einsteins for the ability to turn the power way way down when necessary.



    Why not just stop your lens down further (assuming you can)? Does that give you unwanted depth of field?



    Having ND filters lets you choose your aperture, as you say, rather than being forced into the choice by the amount of light. Sometimes one wants control over the depth of field, and lenses are generally at their sharpest
    around f/5.6-f/8. By the time you stop down to f/16, diffraction effects start to soften the image which may not be what you want.

    That can be a particular problem shooting video where shutter speed is constrained to 1/50th of a second for natural looking cinematic motion, but outside on a sunny day shooting at 1/50th of a second might force you to be at f/16 when you really wanted to be at f/4.

    Cheers, Hywel.



    I’m already at f/8 and I’d rather not stop down any further. Not so much because of depth of field (although I probably should worry about that more than I do), but because going beyond f/8 gives up sharpness.



    I know what diffraction is, and that it’s a limiting factor in every radio antenna and in many telescopes. But I hadn’t really realized that it can be such an issue with photographic lenses stopped down beyond f/8 or so. I guess that’s true; it’s something I’ll have to watch for.

    I guess it should go without saying that before you start throwing light away, you should decrease your sensor sensitivity to its minimum. Problem is, I don’t think it goes below ISO 100 on our Canon DSLR cameras. In the old days I’d shoot the slowest film I could in outdoor shots, usually Kodachrome 64 and sometimes Kodachrome 25.

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