Nikon F Prisms

Prisms for the Nikon F

Subtitle: Why have aliens attacked my camera?

Those of you who have seen the big metering prisms for the Nikon F probably suspect that Nikon had a fine time watching photographers all over the world lug these huge, lumpy beasts all over the world in the 1960's. Those of you who have the big metering prisms are probably calling for my blood -- I use an F with the eyelevel prism, so I can't really comment on the weight of the camera, although at least one book that I've glanced through calls the F/FTn combination "the weightiest 35mm camera ever." It's not just weight, it's ... solidity ...

Eyelevel PrismThis prism was standard issue until the early 60's, when the first Photomic prism appeared. It's a basic pentaprism finder. There are those who regard the Nikon F/Eyelevel combination as "the" classic SLR shape. Unfortunately, it took Nikon another twenty-three years to introduce a finder with the high-eyepoint, something that I wonder about every time I scratch my glasses on the eyepiece's frame and the wind lever (I'm also left-eyed, more's the pity ...)
Model I MeterThis meter was the first one introduced with the F; from a top view, the dial-side end is round, but it is otherwise similar to the Model III Meter. It is quite scarce.
Model II MeterThis meter is similar to the one found on the Nikkorex F cameras, and is distinguishable by a large selenium photocell window.
Model III MeterWhile this wasn't exactly a prism, it was a slip-over selenium cell meter for the Eyelevel Prism, thus providing a very inconvenient method of metering. My guess is that this was a holdover from the rangefinder days and is similar in operation to the MR meter for Leicas (and undoubtedly similar meters for the Nikon S's). Judging from a grainy photograph, it looks like it has ASA coupling from ISO 6 to 4000 and uses the pin-coupling that all non-AI meters do (and presumably also has the ring resistor).
Photomic Prism (1962)This was the first metered prism, although the metering itself was done through a Cadmium-Sulfide (CdS) cell behind a round window on the front of the prism -- in other words, it was not a through-the-lens (TTL) metering system. It came with a special little "Incidence Acceptor" that screwed into the front of the prism, over the metering window, and limited the angle of light that the CdS cell received. Basically, without the little tube, the meter accepted light approximately equal to a 35mm lens field of view; with the tube attached, it because about a 135mm field of view. In other words, the angle of acceptance goes from 75 to 15 degrees. You could also put an opaque disc on the window to make it into an incident (rather than reflected) meter, which is nice, but sort of useless (with incident meters, the general philosophy is to point the meter towards the camera, but when it's part of the camera itself, well, you get the picture). It can also be set to compensate for filter factors up to 4x. It had a ASA range of 10 to 1600 and used what I call a "fully manual indexing system" (FMI, isn't jargon wonderful?). The meter has a prong that sticks into the little meter-coupling fork at f5.6 on most Nikkor manual-focus lenses. There are marks around the ASA dial which can be set to compensate for a filter on the lens, based on the filter factor in use (which is something like log10(filter factor) + 1 = number of stops lost to the filter). The ASA dial is the dial on top of the stack covering the shutter-speed dial, which needs to be lined up properly to mount the prism ... There were two versions of this prism available, an earlier one with a "flag" switch, and a later one with a button switch similar to the later Photomic (TTL) prisms; the "flag" versions have some value to collectors. There is a long slot on the bottom edge of the prism's front which shows the position of the prong/slider.
Photomic T Prism (1965)This was the first TTL metering prism. It used two doublet lenses to average the readings from the entire screen onto a CdS cell. It, too, uses the FMI system to meter, with an ASA coupling of 10 to 1600. Note that the FMI system works fine with any lens that has the meter fork, since there's no tab on the meter to break off when you mount a non-AI lens. Incidentally, this was the first metered prism to require modifications to the top plate, resulting in contemporary F/eyelevels to be sold with Red Dot markings (see the special models page). It looks quite similar to the original Photomic prism, except that it lacks the round window. This prism is activated by pushing in a button on the side of the prism (which causes an indicator/switch on the top of the prism to pop up; turn the prism off by pushing the indicator back down).
Photomic Tn Prism (1967)This prism is essentially the same as the "T" prism, but with a single aspheric lens to "centerweight" the meter reading. It uses the FMI system and couples to ASA from 10 to 1600. It may be distinguished externally from the T by an engraved "N" behind the indicator/switch.
Photomic FTn PrismThis prism is the same as the "Tn" prism but with a different twist, quite literally. Instead of the FMI system, it uses the "semiautomatic indexing system" (SAI), in which you set the lens to f5.6 before you mount it to the camera, and then cycle back and forth between the minimum and maximum apertures on the lens; some spring-loaded gizmo in the finder automatically sets the maximum aperture of the lens. This finder is also the only F finder that displays the shutter speed along with the aperture in use. It couples from ASA 6 to 6400. It has a much shorter slot on the front of the prism, which indicates the maximum aperture of the lens in use rather than the actual position of the slider.
Action FinderThis finder provides about one inch of eye relief (distance from your eye to the prism), and with a true image, I think. Then again, digging up one of these beasts at about $500 somehow doesn't seem worth it, just to see what it does; tell you what: you send me the Action Finder and I'll tell you if it's reversed or not ... or you could just tell me, Action Finder (or DA-1 or DA-2 or DA-20 or DA-30) owners.
Waist-Level FinderThis is just a standard WLF; two different versions were made, one with three sides, and one with four sides. Both (I think) had a pop-up 3x magnifier. The top folds down to protect the finder when not in use. I guess that these finders are most useful for either crawling about on the ground or holding the camera high above your head. On the other hand, you can use the cheap person's WLF: take off the prism. Granted, the resulting image is small and dim, but at least you didn't have to spend $100 and lots of time tracking down a WLF for the F.
6x Magnification (Stovepipe) FinderThis finder appeared late the the model run, when the F2 was on the scene. It's probably most useful for microphotography, although I hear that some people use it as a loupe (lupe). Note that microphotography is taking pictures of really small things, while photomicrography is taking small pictures of bigger things. Microfiche are produced by photomicrographs, while you can take nice pictures of brine shrimp (micro-fish, in a sense) through microphotography. Or maybe I have that reversed; where did I put that dictionary?

I am most grateful to Hayao Tanabe for providing much-needed knowledge regarding the Model I and II Meters, and truth to dispel rumors swirling about the Nikon F Red Dot. Phil Ducor corrected my misguided thoughts about the Photomic prism.

Take me back to The F and F2 page