Olympus Pen F: solving problems no one had?

The Olympus Pen F series of cameras is unique. And “unique” has many connotations in English, some not so complimentary. The Pen F, FT, and FV are variants of a half-frame SLR body that takes a variety of lenses. They deviate from conventional SLRs in ways that are apparent – and maybe not immediately so. These cameras are lovable but also irrational.

Size and weight: zero sum

It’s not really small. The first thing that people need to get out of their heads is the idea that a Pen F-series camera is smaller than a 24×36 camera. Not by a long shot. The Pen is far larger than a Contax T, a Minolta AF-C, or a Rollei 35S. In fact, it’s only 10mm narrower (side-to-side) and 4mm shorter (top-to-bottom) than a Canon VL2 rangefinder with a 35mm f/2 lens that shoots a frame double the size of the Pen’s “single frame” and has at least six times as many lenses that fit it. A Pen is, however, smaller than typical 35mm SLR.

Why is the size not smaller? What kind of gets lost in all of this is that the major dimensions of a camera, especially an SLR, are dictated by the frame size and whether it has a mirror. A “half frame” is half the area of 24×36, but its linear dimensions are only smaller by 30% (18×24). The picture below provides some scale; that width difference is indeed just 1cm.

Also not shocking is the fact that even with the frame scaled down, the 35mm cassette and takeup mechanism are the same size as a 24×36 camera. Smaller 35mm cameras manage to get the canister and the takeup immediately to either side of the film gate; the Olympus, weirdly, has this (because, oh, yeah, we forgot – a rotary shutter has to retract to somewhere).

No, the lenses aren’t really that small either. Compared to a 35mm SLR, you could make this argument. Compared to a 35mm Leica thread-mount camera, this is false. a 35mm f/2.5 Voigtlander pancake has the same diameter and half the height of the 38mm f/1.8 Pen Zuiko (in no small part because the VC lens sits partially inside the camera body). The 90mm Pen lens, likewise, is very similar in size to a 100/3.5 Canon LTM lens.

Pornoprisms and the rotary shutter club

Porroprism. The Pen uses a porroprism (no, not pornoprism) to deliver the viewfinder picture. Porroprisms are derived from binocular design and allow an optical path to be twisted on its axis to get around corners. You might know this same general idea as a periscope. The Pen uses this to get light from a side-flipping mirror, up the right side of the camera across the top deck, and into your eye. The byproduct is that the top of the camera is flat. Olympus penned this as “revolutionary” and derided “old style pentaprisms.”

The reality was that the porroprism was the only way to solve for a situation where the reflex mirror flipped to the side rather than flipping up. This, in turn, was the byproduct of a frame that was 24mm high and 18mm wide: if you reflected straight up into a pentaprism, the mirror box of the Pen would have been just as deep as a full-frame 35mm SLR – because 24mm worth of mirror height would have to flip up (because the image height is the same as a full-frame camera.

The porroprism system is not bright. Sorry. I have a bunch of Pens, and even the FV has nothing on a full-size 35mm SLR. Why? The porroprism system has many more parts and many more air-glass surfaces. For light to get into the eyepiece on a Pen, it passes through:

• A main reflex mirror (1 front-surface)
• A focusing screen (2 air to plastic surfaces)
• A lower prism (2 air to glass surfaces)
• Another front-surface mirror (on metered models, with a 50% light loss)
• A 2-component condenser lens (2 air to glass surfaces)
• A second prism (2 air to glass surfaces)
• An ocular lens (2 air to glass surfaces)

On a conventional SLR:

• A main reflex mirror (1 front-surface)
• A focusing screen (2 air to glass)
• A condenser (maybe)
• A pentaprism (2 air to glass surfaces)
• An ocular lens (2 air to glass surfaces)

On top of the insanely complicated porroprism system in the Pen that unavoidably degrades brightness and contrast, a most conventional SLRs do not compromise the entire viewfinder brightness for the sake of a meter. Some feed off the roof of the pentaprism and some look though semi silvered spots in reflex mirror. But it’s rare that there would be a first-surface mirror that had 50% reflectance/50% transmission.

The porroprism concept would not have worked on a full-size 35mm SLR, nor would it actually work on anything that did not have a “portrait” frame orientation relative to film travel. It might have done something to mitigate the awful size of 6×4.5 SLRs, but no one actually tried that. But at the end of the day, the porroprism was an artifact of an arbitrary choice of film format. It was the one way that Maitani could design a small half-frame SLR, and it is not portable to most other formats.

Rotary shutter. Olympus did not exactly invent this; the rotary shutter was long in use on cine cameras and even some full-sized 35mm, like the Unisex, er, I mean, Univex Mercury. This is a questionable innovation, and its use is really driven by the body-consuming porroprism path. Most 35mm SLRs are built around something like the Copal Square S shutter. The shutter is a flat unit; the mechanical drive is a box affixed to one side. None of this impedes the optical path, which goes straight up into the pentaprism. On the Pen, you can’t use that space because part of the viewfinder is there. The rotary shutter hardware in a Pen sits fairly flat. The advantage of a rotary shutter is that it can synch at all speeds; the disadvantage is that it can only spin so fast. Consider also the sensitivity of something whose timing relies on sheer speed. A conventional metal SLR shutter runs mechanically as fast as its synch speed. So it may sweep the frame at 1/125 of a second, but the effective speed is 1/1000 because only a fraction of the frame is being exposed at a time. This is one of the reasons why the Copal was one of the most popular focal-plane shutters of all time. It isn’t high strung.

The optics of optics

Lenses. One of the big draws for the Pen are its tiny lenses (compared to full-sized 35mm SLRs). That said, it’s a fairly closed universe. Lenses run from 20mm (~30mm in 35mm format), and conventional primes maxing out at 250mm (~375mm). Most primes take 43mm filters, which is convenient.

But there is nothing that wide-fiends would recognize as more than a moderately wide lens. The two zooms are constant aperture but do not really save much space.

In retrospect, Maitani’s decision to put the lens mount lock on the lens (and not the camera bayonet) was a poor choice. In theory, you should be able to fit any SLR lens to something with a register distance within .15mm of a Leica M. But the locking mechanism in the rear apparently has made this unattractive. So your choices are adapting M42 lenses (of which super-wide is rare), or Nikon or Olympus super-wides, which are generally so big that you may as well use them on full-size cameras.

Perhaps most infuriating is the inability to mount Leica lenses. The register distance of a Leica thread mount lens is 28.80mm; the register of a Pen is 28.95. It should have been possible, in theory, to put most (but not all) LTM lenses on the table. In theory, though – Leica-mount lenses still have rangefinder cams that project behind the lens mount, and some wides have protruding rear ends. So at best, maybe 50mm and up, plus retrofocus wides.

Those gripes aside, the Pen lenses are fantastically sharp. Having tested quite a few of these out, here are some short takes:

20mm f/3.5 – awesome wide-angle (like a 28mm or 30mm).

25mm f/4 – a sleeper of a wide, sold for very little, the equivalent of a 35mm lens. Fairly dim viewfinder image on the FT but passable on the F and FV. Unlike the 2.8 version, this is tiny, about the size of the 38mm.

38mm f/1.8 – the base lens on the FT and the normal bundled lens with an FV, this lens is small and sharp. It does not give up much in terms of speed to the 40mm f/1.4, and it is a touch shorter.

40mm f/1.4 – the “upgrade” on the FT, this is actually super-bright on the FV. It does not have great bokeh, and it does have lanthanum glass that will need bleaching every now and then.

100mm f/3.5 – surprisingly sharp and cheap 150mm equivalent. Not much smaller than a 35mm rangefinder 100mm lens.

50-90mm f/3.5 – a strange and wonderful fixed-aperture zoom, this actually has remarkably low distortion. The rotating front is not great for grad or other filters that themselves rotate, but this deserves far more play than people give it.

Replacing some old problems with new ones

The Forever War Roll. The Pen series actually exacerbates one problem: the roll of film that never ends. This was originally sold as a feature. In the long view, it is probably actually a bug. It is pretty much a given that you lose interest in a roll of film when it is about 80% done. Search your feelings. You know this to be true, no matter how long or short the roll. On a 24×36 camera, that might mean frame 19 on a roll of 24 or frame 29 on a roll of 36. Unfortunately, when your roll of film could be 72 frames, as on a Pen, that means you could be in the pain zone with fourteen frames to spare.

Scanning. Half-frame was never a favorite of photofinishers; even in the minilab era, 18×24 wreaked havoc on printing to normal sizes. For scanning, Pen negatives are manageable with a Pakon x35 series scanner (since you can tell it an arbitrary frame size and it does all 72 frames in one continuous process). They are not so manageable with higher-resolution film scanners because very little scanning software is designed around anything outside of “mainstream” formats (24×36, 6×4.5, 6×6, 6×7, 6×9).

Optical printing. One thing to bear in mind is that optically printing half-frame usually benefits from shorter enlarging lenses than 50mm; for 18×24, they are typically 40mm. You should also be aware that most brands of enlargers don’t make (and in many cases never made) negative carrier inserts in 18×24. That said, without the urge to pixel-peep, you might actually enjoy the prints.

We still love the Pen F

None of this is to say that the Pen F is a bad camera – in fact, it is an extremely cool platform that is fun to use and actually manages to make very sharp, well-exposed images. It is, however, a system whose marketing hype outruns the utility of its innovative features. In the end, if this piece sounds like razzing, just bear in mind that we only do it because we know the Pen can take it!