An action finder can be really useful for situations where it is hard to look into the viewfinder – like when you are wearing a space helmet. Or oversized Italian sunglasses. This is a picture I took with my DA-20 on a recent vacation.
This article  came about because everything I have seen about accessory viewfinders seems to have been cut and pasted from manufacturers’ literature. This article will (hopefully) help you determine whether you should use one or more of these. Remember: Nikon sold one accessory finder for every 1,000 F-series bodies. Although this is a convenient excuse for why the F6 has a fixed prism, it also should tell you that most people learn to live with the standard pentaprism that came with their camera bodies.
Action Finders: DA-2, DA-20, DA-30
The action finders are all huge and heavy (so not for wimps), but they give you some flexibility – like not having your camera jammed in your face.
In an SLR system, eye relief and magnification are closely related concepts. The higher the eyepoint, the greater the distance the entire frame can bee seen from the eyepiece. The greater the eye relief, the lower the magnification. The Nikon action finders are designed around an eye relief of 61mm (2.5 inches); the magnification is 0.6x. Contrary to popular myth, an action finder does not produce a big, “TV-like” image. It simply lets you see the whole viewfinder from a little bit further back.
Can you use an action finder all the time? Yes and no. Because it lowers magnification, the action finder makes it a little more difficult to use telephoto lenses. If you are relying on focusing screen aids (such as split-image rangefinders, microprisms, etc.) or autofocus, the lower magnification won’t have much impact. If you use groundglass focusing, life gets a little harder.
Do you need the expensive rubber eyecup? Yes. Beware of all the action finders missing this useful part. Your eyeglasses are not in danger from the action finder eyepieces; rather, the rubber eyecup keeps your eye at roughly the right distance from the viewfinder.
Every viewfinder really has only one eyepoint: the eye position where the whole viewfinder is visible. Nikon’s high-eyepoint pentaprisms are designed to focus when eyeglasses are pressed up against the eyepiece.
This means that diopter correction is relatively simple: you just pick the correction lens (or setting on an F4, F5 or F6) that works in one position. You may notice that you use different viewfinder corrections for glasses and contact lenses with the same prescription; part of this is the difference in distance from the camera’s viewfinder system.
With an action finder, your eye could be anywhere in the range from right against the eyepiece to the magic 61mm from it. Although this does not seem like a very big range, your eye works very hard to see the focusing screen as the distance increases and diminishes – much the same way that a camera lens needs to extend or retract much more when it is focusing on a close object. The rubber eyecup keeps your eye at the “right” distance: the one where the average eye can focus comfortably. If you don’t use the eyecup and press your eye up to the finder, you might find your eyes a little bit fatigued after a while. Unfortunately, the usual solution for this problem is absent: the action finders have no built-in adjustment and there are no accessory diopters.
The F3 action finder (DA-2) meters the same way that the F3 standard one does – it doesn’t. On the F3, centerweighted ambient metering and centerweighted TTL flash are measured by a sensors in the camera body. The body of the finder is made of brass. The eyecup is rectangular and snaps on over a large rectangular plastic frame on the back.
The F4 action finder (DA-20) gives you a choice of centerweighted or spot metering via a switch on the side of the prism (like the DP-20). The DA-20 outer housing is plastic. It features a normal TTL hot shoe (no locking pin). The DA-20 has a similar eyecup to the one on the DA-2. The DA-2 provides an abbreviated viewfinder information display (the lower display is actually part of the DP-20, not the F4 itself)
|Exposure mode||Small window (left)||ADR window (center)||Focus ind.|
|P or P HI||“P” + auto-selected shutter speed||Minimum aperture of lens (or other aperture and “fEE” in left window)||Minimum aperture of lens (or other aperture and “fEE” in left window)|
|S||Auto-selected aperture||Minimum aperture of lens (or other aperture and “fEE” in left window)||Minimum aperture of lens (or other aperture and “fEE” in left window)|
|A||“A” + auto-selected shutter speed||Aperture set on lens||Minimum aperture of lens (or other aperture and “fEE” in left window)|
|M||Shutter speed + reading of how off from normal exposure (e.g. +2.0)||Aperture set on lens||Minimum aperture of lens (or other aperture and “fEE” in left window)|
One variation of the DA-20 (which I assume was made for underwater work – and which I stupidly returned to KEH) has a built-in illuminator for the lens aperture ring. It comes on whenever the meter is on, so watch your batteries.
The F5 action finder (DA-30) gives you matrix (not 3D or color), centerweighted or spot via a similar switch to the one on the DP-30 (standard F5 finder). Its body is made from a crinkle-painted l.ght alloy. It has a locking hot shoe. Given its functionality, I suspect the DA-30 shares its electronics with the DP-20 (the F4’s standard finder). The DA-20 also has a similar eyecup to the one on the DA-2. You get all of the same viewfinder information that you get with with the DP-30 (standard F5) prism.
Magnifying Finders: DW-4, DW-21, DW-31
Magnifying finders are fun. They eliminate the light loss from the pentaprism and give you a magnified (6x) view of the whole focusing screen. Distortion is very low. These have very low eyepoints and are designed to be used without eyeglasses (precisely why the Nikon magnifying finders have correction from +3 to -5 diopters built in. Once you press your eye all the way in, it’s a revelation. These have three (by my count) multicoated elements.
Magnifying finders are very useful with standard groundglass focusing (D-screen) and with astrophotography (M-screen). You can actually use them for anything with the sole exception of (1) situations where you need to keep the camera high (at eye level) and (2) situations where you lose track of left-to-right movement. The latter is related to the fact that all magnifying finders reverse the view left to right.
The DW-4 (F3) gives you centerweighted ambient and TTL flash metering. The DW-21 (F4) and DW-31 (F5) give you spotmetering for ambient and for flash. The F4 and F5 magnifying finders require the oddball SC-24 TTL cord, which plugs into an eight pin connector on the back of the finder. I am not sure why the first flash needs eight pins, since the hot shoe only has five pins (three dedicated, one hot shoe contact, one shoe). The SC-24 terminates in a standard Nikon TTL hot shoe.
Magnifying finders (and waist-level finders) seriously impede taking vertical shots.
Waistlevel Finders: DW-3, DW-20, DW-30
First it killed the Rolleiflex. Now it’s killing me. 35mm SLRs started with this type of finder; thank heavens it didn’t survive in the mainstream. The pentaprism displaced the waist-level finder – and the fact that a pentaprism shows everything correctly, right-side up and correct left-to-right, and not brightness, carried the day.
Today, the waistlevel finder has only three real uses: shooting above crowds, shooting from low angles, and shooting on a copystand. The DW-3 (F3), DW-20 (F4) and DW-30 (F5) are essentially the same thing: just a popup hood through which you look at the top of the naked focusing screen from a foot or more away. This makes manual focusing difficult and pretty much defeats any focusing aid in your focusing screen. Things are better with the autofocus cameras.
Each has a small 5x magnifier that provides a small, highly distorted view of the center of the focusing screen. While this is sufficient for copy (and some macro) work, it is pretty unpleasant for general use. This is no different from a standard Rolleiflex TLR viewfinder. The only reason people tolerated it on Rolleis was that in the olden days, medium format pentaprisms were so dark as to be useless.
Metering and TTL flash are similar to the magnifying finders. The F4 and F5 versions use the same TTL connectors that the magnifying finders do.
The principal virtue of the waist-level finder is that it is cheap, simple, compact, and lets you do a couple of unique things. If you don’t do those things, skip this type of finder.