As promised, the results of my lens testing program.
Tests run on something like a PDML resolution test rig (array of USAF
targets, t-max 100 B&W film, good tripod, cable release, roughly 50 focal
lengths focus distance, 10x loupe, etc) with the intention of producing a
subjective rating rather than a supposedly accurate objective lines/mm
rating. Note that these tests at best only show sharpness/contrast, not
bokeh, color rendition, distortion and abberations, etc.
I didn't test past f/8 because it saved film and I rarely get the option
of shooting even that far stopped down in the real world. Some lenses may
continue to improve in performance at f/11. All supposedly decline at
f/16 and smaller due to diffraction.
Unfortunately, I couldn't get far enough back to test anything longer than
85mm. Pity, because I'd love to see how the screw-mount teles hold up
against the more modern internal-focusing low-dispersion-glass versions.
CRITICAL NOTE! I tested ONE sample of each lens. With the exception of
some of the 50s I only have one sample. One is NEVER a statistically
significant sample of the population of lenses out there, and it is very
possible that my single sample of any given lens was defective from the
factory or has suffered optical or mechanical damage since being made and
is not performing as well as the design is capable of. Other than the
manufacturers themselves, I doubt anybody ever tests a statistically
significant number of lenses given the number that are made.
My findings line up very well with user-community opinion of the lenses
tested, which gives me confidence in my methods and results, but my
findings are only really valid for MY particular lenses.
It is worth noting that:
-all lenses were better in the center than the corners at large apertures,
especially ultra-wides
-wide angles all show the weaknesses of retrofocus design in poor
corner performance. (Rangefinder wideangles are better, but struggle
with poor corner illumination instead)
-no lenses were great wide open; the fast ones were particularly bad
-lenses got worse the more they differed from 50mm
-most lenses were excellent by f/5.6, almost all by f/8.0
-expensive modern zooms can outperform primes, especially at the corners
-average zooms are a bit weaker than primes
-bigger, more expensive lenses do perform better
Grading is center/corners, as follows
A) noticeably sharp and contrasty
B) sharp and contrasty, with a little less fine detail/resolution than A
C) still good, but noticeably less sharp and contrasty.
D) much less contrast, more fuzzy or mushiness, words and lines resolvable
but don't look quite sharp. OK, but no better.
F) smeary, blurry, low in contrast. Words and lines hard to resolve.
I'd say that I could have varied my evaluations by half a letter grade
overall, so fine distinctions are only so valid. I didn't attempt
to resolve A+s, which means that a lens which is superbly sharp doesn't
get credit for it. Primarily I was looking at degradation of performance
in each lens across the frame and through the aperture range.
What do these grades mean in real world picture taking? It depends
on your standards, uses, etc. I can SEE a difference in photo results
between letter grades, even in real world use. I still USE lenses at
settings that are marginal because sometimes the widest aperture is more
important than maximum optical quality.
20MM LENSES
Best lens tested was 17-35mm f/2.8 Nikkor AF-S, by a wide margin.
It's better at the corners and as good in the center as any prime I
tested. It's also $1400, and the size and weight of a grenade launcher.
Super Takumar 20mm f/4.5
f/4.5 C / F
f/5.6 B / D
f/8.0 A / C
Gerjan says it is bad in the corners, and it is. Nikkor AI 20mm f/3.5 is
a bit better in the corners and equal in the center. Nikkor 20mm f/2.8s
are better overall, as is the 20mm f/2.8 A/FA Pentax I'm sure.
This was, of course, far and away the widest thing Pentax made at the
time (1968), until the SMC 15 and K 18 came along.
24MM LENSES
Weak as a group, especially in the corners. I'd love to test the 24mm
f/2.0 FA AL Pentax, expecially given the lousy corner performance of the
equivalent Nikkor 24mm f/2.0 AIS.
Super Takumar 24mm f/3.5
f/3.5 B / D-
f/5.6 A / D+
f/8.0 A / C
Shows that 24mm was still a tricky thing to design in its day.
Pentax K 24mm f/3.5
f/3.5 C+ / D-
f/5.6 A / D+
f/8.0 A / C
Performs much like its predecessor, and is probably the same optically.
Nikkor 24mm AF f/2.8 better in the corners, Nikkor AIS 24mm f/2.0 is
unusually better in the center and worse in the corners.
Pentax M 24-35mm f/3.5 @ 24mm
f/3.5 B / D
f/5.6 B+ / C
f/8.0 B+ / C+
Never great but never awful. As good as primes in the corners.
a hair better wide open than the Nikkor AF 24-50 f/3.3-4.5
28MM LENSES
Best 28mm lens tested was the 28mm f/1.4 AF Nikkor, as it darn well
ought to be at $1600! 28mm f/2.0 Pentaxes are well thought of and
could give the 28mm f/2.0 AIS Nikkor a run for its money--if I could
find and/or afford one.
SMC Takumar 28mm f/3.5
f/3.5 B / C+
f/5.6 A / B+
f/8.0 A / B+
A little weaker in the corners than the best Nikkors, otherwise
as good as any 28 I tested.
Pentax K 28mm f/3.5
f/3.5 B / C
f/5.6 A / B
f/8.0 A / A
AI Nikkor 28mm f/3.5 is a hair worse in the corners wide open, otherwise
about equal.
Optically a hair worse than its SMC predecessor, although it could be
sample variation. I remember the K lens being fairly long and big, which
the SMC is not so perhaps it is not the same design.
Pentax M 28mm f/2.8
f/2.8 C / D-
f/4.0 B / D
f/5.6 B / C
f/8.0 A / B
Upholds its poor reputation as the worst of the 28s I tested. As with
other M lenses held in low esteem a fine performer well stopped down.
Like many M lenses apparently weaker in the corners due to Pentax'
effort to miniaturize.
Pentax K 30mm f/2.8
f/2.8 B- / C-
f/4.0 B+ / B-
f/5.6 A / B+
f/8.0 A / A
Why did Pentax not make this an M lens? It's a lot better than the M 28
f/2.8 and not that much bigger.
It is better than the SMC 28 f/3.5 which is quite good, competitive with
the 28 f/2.0 AIS Nikkor which is widely held to be Nikons best MF 28, and
only topped by the much bigger and more expensive 28 f/1.4 AF Nikkor.
Perhaps the odd focal length didn't sell, or it was too expensive.
It looks like perhaps the 18 f/3.5, 30 f/2.8, and 200 f/2.5 form a kind
of K* or K Limited series of new designs of excellent quality and slightly
odd specs.
Pentax 24-35mm f/3.5
f/3.5 B / D+
f/5.6 A / C+
f/8.0 A / B
at least as good as most 28s, weaker in the corners than the best.
This lens has noticeable barrel distortion but is quite a good performer
overall
35MM LENSES
Best 35mm in the corners was the 35mm f/2.0 AF Nikkor, or perhaps the
magnificent 17-35mm f/2.8 again. Best in the center was the 35mm f/2.0
A pentax, although the 35mm f/2.0 FA AL by reputation should be as good.
Super Takumar 35mm f/2.0
f/2.0 C+ / D
f/2.8 B / D+
f/4.0 B / C
f/5.6 A / B
f/8.0 A / B+
As good as the 35mm AF Nikkor in the centers, weaker in the corners.
Super Takumar 35mm f/3.5
f/3.5 B / D
f/5.6 B / C+
f/8.0 A / B+
About the weakest tested. This has always looked like a "beginner"
lens to me. Even the SMC version didn't have a fully coated front element.
Slow Nikkor 35s have mediocre reputations as well.
Many people have come to the defense of this lens, so I could have a bad
sample.
Pentax A 35mm f/2.0
f/2.0 C / D-
f/2.8 A / D
f/4.0 A / B
f/5.6 A / A
f/8.0 A / A
The sharpest center performance at wide stops of any lens I tested,
challenged only by the 50mm f/1.7 A pentax.
Pentax M 24-35mm f/3.5 @ 35mm
f/3.5 B / D+
f/5.6 A / D+
f/8.0 A / C
Corners are weaker here at its longest setting than elsewhere, but
center sharpness is excellent throughout its range
Pentax A 35-70mm f/4.0 @ 35mm
f/4.0 B / C+
f/5.6 B / B
f/8.0 B+ / B+
Never great, but very consistent performance
50MM LENSES
The best performers of the lot. Most held an "A" rating until f/4.0
and a "B" rating until f/2.0. All were "C"s at widest aperture
but none worse than "C" at any point. Pentax A 50mm f/1.7 a standout,
as its reputation suggests. All very good.
SMC Takumar 50mm f/1.4
f/1.4 C / C
f/2.0 B / C
f/2.8 B+ / C+
f/4.0 B+ / B+
f/5.6 A / A
f/8.0 A / A
Strangely weak at fairly wide stops but competitive wide open.
Pentax M 50mm f/1.4
f/1.4 C+ / C+
f/2.0 B / C
f/2.8 B / B
f/4.0 B / B
f/5.6 A / A
f/8.0 A / A
Apparently the best performer of the lot wide open, but weaker at fairly
wide stops than most. This is credible as the SMC 50 f/1.4 shows similar
characteristics.
Pentax M 50mm f/2.0
f/2.0 B / C
f/2.8 A / C
f/4.0 A / B+
f/5.6 A / A
f/8.0 A / A
The equal of the 50mm A f/1.7 in the center, weaker in the corners.
Better in the center than the 50mm f/2.0 AI Nikkor, but weaker in
the corners.
Pentax A 50mm f/1.7
f/1.7 B / C+
f/2.8 A / B
f/4.0 A / A
f/5.6 A / A
f/8.0 A / A
Upholds its stellar reputation. Makes me wonder how good the 1.4 A is.
85MM LENSES
I wish I still had my 85mm f/1.4 A* to test against the equivalent
Nikkors, which are not impressive at wide stops. Really none of the
85s are great at wide stops and in general are only on par with 50s
when closed down an extra stop.
Best lens tested at this focal length was the Nikkor 80-200mm f/2.8
AF-D zoom, which is intriguing because Nikkon has put out two more
recent zooms in that focal length range which are supposed to be BETTER.
Of course this is one of the zoom ranges receiving the most aggressive
development for pro use because it is so popular.
On the other hand, most "average" 28-80 or 80-200 zooms don't get much
better than "B" at this focal length, with "C" or "D" corners.
I'm curious how the 80-200mm f/2.8 FA Pentax measures up.
SMC Takumar 85mm f/1.8
f/1.8 C+ / C
f/2.8 B / C+
f/4.0 A / C+
f/5.6 A / B
f/8.0 A / A
I understand why these sell for more than $400 used in excellent
condition, whereas the 85mm f/1.8 AF Nikkor sells for about $350 new.
This lens outperforms every other 85mm prime I own, and is only challenged
by the the legendary 105mm f/2.5 Nikkor which is a full stop slower and
by expensive pro 80-200 zooms which are much bigger and a stop and a half
slower.
The Nikkor AF 85mm f/1.8 is competitive at middling stops, weaker at
larger stops, and noticeably bigger.
Pentax M 85mm f/2.0
f/2.0 D+ / D
f/2.8 B / C
f/4.0 B / C+
f/5.6 B+ / B+
f/8.0 A / A
Lousy wide open--worse than anything else except the 85mm f/1.4 Nikkors
wide open. Competitive at f/2.8 and a little weaker than average at
f/4.0. Fine at smaller apertures. This performance could account for the
mixed reviews I have seen for this lens.
The 85mm f/2.0 AIS Nikkor is marginally better, especially at wide stops.
Interestingly, Nikon also replaced a reputedly very sharp 85 f/1.8 with a
reputedly less sharp but smaller 85 f/2.0.
DJE
