Filters in my Bag

My new Hoya CP filter came in yesterday. It was overcast, so I didn't have a good opportunity to try it out. It's has multi-layer AR coatings on each face, so it should have less ghosting than the Tiffen I've been using, and the filter is only 5mm thick, so I might not even get the vignetting I sometimes got with the Tiffen. Time will tell.

As I tucked it into my KAP bag and put the Tiffen back in the DSLR bag, it got me to thinking: The filters I keep in my bag have sure changed!

When I started off with 35mm, I kept UV filters on the ends of my lenses. I thought it a necessity, a way to protect my lenses against smudges and scratches, and at that stage it probably was. But over time I learned how to be paranoid about my lenses, and the UV filters did little more than filter out UV light. Eventually they came off, and spent more time in the filter bag than on the lenses.

Early on I got a circular polarizer. That Tiffen CP I used for KAP is the same one I got back in '95 for 35mm. It's probably time to change it out since the optical surfaces aren't what they once were, but it's still in use. Case in point, I keep one in each camera bag. The only bag that doesn't have a CP is my 4x5 bag, and I'd be interested in changing that.

I shot enough B&W film through 35mm cameras that I got a fairly good set of Wratten gel filters for B&W work. #25 red, #47A blue, a #90 viewing filter (for me, not the camera) were my main ones. I also got a #12 deep yellow, #8 yellow, and #58 green which didn't see as much use, but were good to have. When I started shooting more 4x5 B&W than 35mm, these moved to the 4x5 bag. It turns out the #58 green is good for shooting black lava rock beaches, so it will probably find its way into the 4x5 KAP bag.

In the days of film, you couldn't white-balance to correct for color shifts. I kept filters for fluorescent and tungsten lighting to shift their white point closer to outdoor conditions. I shot a lot of color slide film, balanced for outdoor shooting. So for the lab shots I did at the time this was a big boon. With digital cameras, they're really not necessary any more. And with my film work now being only B&W, they went in the filter bag with the UV filters, probably never to be seen again.

One set of filters I haven't removed is the split ND filters. These are rectangular pieces of acrylic that are clear at one end, and have a neutral density tint at the other, with a transition between the two in the middle. Slide film has about five stops of dynamic range. If you're shooting a scenic, and the sky is three stops lighter than the foreground, metering the foreground puts it in the middle of your dynamic range, and puts the sky at a blown-out white. Pop a two-stop split-ND filter on the end of the lens and slide it down until the transition puts the ND over the sky and the clear over the foreground, and the sky will come out one stop lighter than the ground. Neat stuff!

"But with digital, you don't really need to do that!" Well, yes you do. Or rather you should consider it. True, you can dodge and burn in programs like Photoshop and Gimp, but you only get so many bits per pixel. Even if you have any texture left in the sky at all (which at three stops you wouldn't), chances are it'll look posterized by the time you're done with it.

"But with HDR, you don't need to do that, either!" True, and the next time you try to do an HDR wildlife shot of a running deer, let me know how it turns out. I'm not pooh-poohing HDR. I think it's a great technique. But to say that one technique invalidates another one is the wrong way to look at it. Each has its place, and the split-ND filters still live in my DSLR bag. (Heck, I can't wait to try HDR with split-ND!)

Why use filters at all? That's actually a really good question. Everything you stick in front of a lens will affect the final image quality. Filters are planar-planar optics, which when stuck in a converging beam will introduce spherical aberration into the optical system. Unless you have a really good reason to use one, a filter only degrades your image. In one of John Shaw's books he posed a really simple test: Unless you can vocalize a particular photographic reason to use a filter, don't use one.

For example: "The reflection off the vegetation in this shot is washing out the color, and de-saturating the image. A circular polarizer will let me cut the reflections and bump the color in the leaves."

Another: "My digital camera has seven stops of dynamic range. The foreground in this shot is three stops darker than the sky. Metering off the foreground will blow out the sky. A 2-stop ND filter will bring it within the range of the camera's sensor, and bring out the texture in the clouds."

But here's the worst: "My friend always said to keep a polarizer on your lens." Errr...

Each time I use a filter, it's a conscious choice to address a particular photographic problem I'm facing. Daylight balanced film under fluorescent lighting used to be one I had to deal with. I don't now, so that filter has gone by the wayside. Flying my KAP rig over a reef and wanting to cut the surface reflection is one I deal with these days, so keeping a circular polarizer in the bag is entirely justified. B&W and the Wratten gels are as natural a choice as when Ansel Adams was using them decades ago. Be aware of what you're doing when you choose to use a filter, and make sure it does what you intend.

Tom