I recently acquired a second hand Yashicamat 124G and noticed immediately
that my photos varied in sharpness depending on the aperture setting. Photos
shot at f3.5 - 4 were a little soft, while photos shot at f11 just about leaped
off the page. Being of an experimental bent and since it was raining like hell
one weekend, I decided to burn a roll of film in pursuit of some quantitative
My 124G is in LN- condition and has no faults in the optical system. The
taking lens is a four element Yashinon 80mm / f 3.5. This lens is generally
thought to be a copy of the Zeiss Tessar, although I have no way to confirm
To accomplish my test, I set up several USAF 1951 style resolution targets (thanks go to David Jacobson for his terrific post script file, available at http://photo.net/photo/optics/USAF1951.ps) on a vertical wall with the camera supported by a tripod 3.2m away, measured to the front of the lens. A 500 watt halogen shop lamp was used to illuminate the target and the camera was fired via the self timer. Focussing was done in the normal fashion with the view finder and built in magnifier. Kodak T400CN (C-41 process) B&W was used as the test film -- something like tech pan or Tmax 100 would be a better choice, but that's what I had available. Films were read under a stereo microscope with diffuse transmitted light.
Magnification factor was determined directly by measuring the length of the
image of one of the photo targets on the negative. This magnification factor was
then applied to the line pattern that was resolvable as three lines separated by
Tests were run at all apertures at D = 3200mm. The view finder field of view
was also marked out on the target wall in black tape, so that view finder
coverage could be determined.
Resolution, Distance to target = 3.2 meters,
magnification factor 1/39.6 Resolution (lines / mm)
f center corner 3.5 35 25 4.0 44 29 5.6 63 32 8 63 44 11 79 50 16 71 50 22 56 44 32 35 35
Exposed negative size: 56.1mm tall by 56.9mm wide, width of exposed negative
outside viewfinder field of view at 3.2m: 4.5mm top, 4.1mm left side
(photographer's left, facing subject), 4.1mm right side, 2.1mm bottom. This is
about 86% coverage left to right, 88% coverage top to bottom, 76% of total area.
The view finder's field of view at 3.2m is 203cm tall x 198cm wide.
There is a 12% "step size" between successive resolution targets, which is
pretty coarse. This should tend to yield errors that are conservative rather
than strictly random. There is a clearly visible difference, for example, in the
films from f5.6 and f8, although the best resolution is reported in both cases
as 63 l/mm at center. At f8 I would guess it's probably closer to 67 or 68 l/mm,
but not quite good enough to split the next target (71 l/mm).
Measured length of the image of a 11" (27.9cm) sheet of paper (the center
resolution target) on the negative was 0.706cm, which yields an apparent
magnification of about 1/39.6.
My exposures were a little on the low side throughout -- I used the built in
light meter and the subject was a white wall with a few photo targets. Doing it
over again, I'd increase exposure a stop or two. Increased exposure would make
the film a bit easier to read and might have made have tipped one or two of the
measurements above into the next higher bracket. Exposures were dead even across
the field at all apertures.
Overall, I would use caution in the comparison of these results with those
that have been recorded and published elsewhere. Test methods and individual
cameras, interpretation of film, etc. will all vary. My specific purpose here
was to develop a quantitative feel for how resolution varied with aperture
setting, not to make any particular claims about the quality of the optical
system in this make of camera. As others have pointed out, there is also a hell
of a lot more to a good camera that the ability to split resolution test
The results back up my observation that the photos I shot at f8 - f22 were
noticeably sharper than at 3.5 - 4.0. Others have commented on this
characteristic of Tessar - formula lenses as well. Clearly, where maximum
sharpness and detail is required, shooting at f11 and f16 will be beneficial.
Where a slightly softer focus is preferred (e.g. portraits), one can work toward
either end of the aperture range, depending on depth of field and shutter speed
requirements. What was surprising to me was both the very high maximum
resolution and the very wide range of variation with aperture. Given that the
usual driving force for MF over 35mm is better resolution for bigger
enlargements, this is very useful information to have.
Comments from a reader regarding lens tests:
Thanks for posting your results.
I read your description of the tests. I'm not certain that it said anywhere
in it that you varied the focusing.
I recently did a similar test (two weeks ago) for an old 1930s Baldax 645
folder with a Meyer-Gorlitz F4.5 Trioplan scale-focusing lens.
I carefully measured the distance to resolution chart (in this case 4 meters)
and exposed a roll of FP4+ using a cable release at speeds of 1/25 and 1/50 at
F4.5 and F5.6 with the camera mounted on a tripod. In exposing the roll, I
bracketed the scale focusing just slightly. If I had gone only by the negatives
scale focused at 4 meters, I would have gotten rather mediocre readings of about
28 lines per millimeter. But negatives shot with the focus set at 3-3/4 meters
(even though the tape-measured distance to the chart was 4 meters) produced
readings of 48 lines per millimenter wide open!!
I learned two things: that the lens was sharper than I would have thought if
I had relied only on results with the focus set at 4 meters; and, more
importantly, I learned exactly where in practice the scale focusing actually
With a TLR there is the temptation to assume that sharp focus on the ground
glass equals sharp focus on the film plane. Not necessarily so. Slight variances
between the two, in film plate pressure, etc. can make them not quite the same.
Finally, I believe in my own case that I would have seen an even higher
resolution (possibly) with a finer grain film like Agfa25, but since I was
conducting the test more for the purpose of determining exact focus (I had had
the lens apart for cleaning and had remounted it) numbers weren't that
The point of my long-winded story is that it is just possible that the
softness you note at F3.5 - F4.5 has more to do with an imprecision in focusing
which is masked by greater depth of field at smaller aperatures than it does
with the lens underperforming wide open.
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