Hi all

Given the little discussion that Steve, Marcelo & I had in response to Steve's question on a 35mm rectilinear lens, I thought that I would throw this one in.

Very recently, people have been coming out with complaints about the open aperture performance of P67 lenses. The comment is that P67 lenses might be great at f11 but wide open they are pretty poor compared to say blad. Steve in his tests has also reported various open aperture problems with some of his lenses.

My view is that a lens will always perform worse, wide open than stopped down a little. I've also noticed that at f2.8/4 that depth of field on a 67 is very limited - focusing errors, shake etc are going to be factors. For black and white portraits (I don't do colour printing), the smoothness and tonal range of my 67 prints give me the feel that I'm after. Why would photographers like John Swannell, Bob Carlos Clarke and Terence Donovan accept poor lenses (all P67 users).

My question is - are P67 lenses worse at wide apertures than other makes and is it possible for them to be better without a huge increase in price.

Tapas

-- Tapas Maiti (tapasmaiti@hotmail.com), April 19, 1999

Answers

Tapas & Marcello: I did an experiment with my 300mm on a bright day using Velvia hand held to see just how good or bad this lens really was wide open. My prior test was on a tripod but that combination could jade opinions on sharpness. The experimental shots were at 1/250 second hand held. I was a bit surprised to find that the results were better than my tripod tests. At f/4, the work was just slightly soft but still sellable. At f/5.6, the slides were sharp and nearly as good as f/11 through f/22 work. I've done some hand held f/4 work lately with my 200mm as well and admit that wide open, it is a bit soft. But again, at f/5.6 it is much improved and commercially acceptable. David Muench also uses this camera besides his Linhof and Leicaflex. He has sold much work using it, so this has got to tell us something. The lens tests that I've seen between Bronica, Pentax, Mamiya and Hassy have shown only minor differences in performance at the different apertures. Leitz is the only optics producer that I know of that has almost no image degradation at full aperture. For Pentax to improve its full aperture performance, it would involve improving the off axis aberration(coma, lateral color, astigmatism, field curvature) correction as well as axial aberrations(spherical, longitudinal color, spherochromatism). Not only would this require more elements but it would require exotic glass like the new fluorides and titaniums. The cost would resemble Leitz. Ouch! The only cheap solution might be using lenses that are long proven for their off axis capability; view lens technology. Use Plasmat designs! Cheers, Steve

-- Steve Rasmussen (srasmuss@flash.net), April 19, 1999.

Nearly 20 years ago "Modern Photography published a lens test book comparing all 35mm and MF lenses at the time. Most lenses were best 2 stops in on each end of the range. Pentax lenses were as good or better than all other MF lenses though I think there was one Hassy lens that did slightly better wide open. Wish I hadn't thrown it away 14 years ago though some of the technology has changed.

-- Tom Goodrick (tgoodrick@earthlink.net), May 14, 1999.

I might be recalling a different "Modern Photography" data book, but I don't believe they tested ALL the lenses, especially not those in medium format. If I recall correctly, they tested the P6x7 200mm, 150mm 105mm, & 75mm. All lenses received excellent results, and like most lenses, the wide open results are usually "good" or "acceptable", and you dont hit "excellent" til your at 5.6-8.0. Worth noting is that the 75mm lens is the only lens in the Pentax line which scored "Excellent" at almost EVERY aperture, and at BOTH center and edge [f22 center was just "very good", if I recall correctly]. Contrary to popular belief, based on tests like these, it is the sharpest lens in the P67 line [most people tell the 55 is, but based on only my experience, I swear my 75 is just a tad better]. As for why lenses can be soft wide open, there is another factor which you should consider in real-world tests, and that is film flatness. A lens can be outstanding, but if the film is not flat, you cant take full advantage of the lens. The first frame on 220 in a P6x7 is not always satisfactorily flat, nor is the subsequent frame after a camera has been sitting for days without being advanced for the next shot. Basically, this was the old concern with TLR cameras -less the Minolta Autocord which transports differently than the Rollei & Rollei copies [is the softness due to the lens or a less than perfectly flat film frame?]. If you stop down a to 5.6, you can basically "hide" a less-than-flat film, assuming it is off only a hair. I am not saying this is the problem, but it is a factor to consider any time you have a 6x6, 6x7, 6x9 plane to cover. 120/200 presents a unique problem in that the film is so thin and flexible - unlike 35 & 4x5. Keeping it flat requires better engineering - hence the different designs you see, like the Mamiya 23 6x9 backs, etc.

-- Miles Stottard (p67shooter@yahoo.co.uk), August 15, 2001.