Pentax-K bajonet inexpensive zoom lenses test

with the Pentax K-50 - 16MP DSLR, APS-C
I am looking at the performance of three zoom lenses for Pentax cameras.
They are somewhat different animals, if not for the fact that they come for cheap:

* according to the best about-Pentax online sources, at the time the "Takumar" lenses were similar or equivalent to the Pentax-F, where the "Takumar" brand was used to mark cheaper versions that lack the multi-coating of the better siblings. You must specify "at the time" because the Takumar brand has been previously used for other purposes, also for first-class lenses

PREAMBLE

I admit that I don't have the time to perform this sort of tests properly, so some of the results may be wrong for a number of reasons.
In spite of the fact that I took some precautions and all of the shots have been taken with Shake Reduction ON, a few may suffer from a bit of shaking. Let me remind everyone that Shake-Reduction is sensor-based on the Pentax K50 (as in all Pentax DSLR, for what I know), so it applies to all lenses, no matter their age.
The targets have been shot twice for each test; for the manual-focus lens (the Cosina), I focused once with Live View and once with my eyes only; for the other two lenses I once relied on autofocus and once on Live View.
As for the borders, everytime I have selected just the best one out of the eight available (4 per each of the two shots); same applies for the two available center spots.
The numbers and scales on the targets are meaningless because I didn't use them properly, so I'm just basing my judgement on what I see; all samples are at full resolution.
Sorry, you cannot judge fall-off from these shots because the targets were not evenly illuminated. I know, I've been lazy.

I'd like two share some more few considerations.

It may be obvious, but I don't want to take for granted that only skilled photographers may read this page, so...: remember that I'm working with APS-C here, hence the "real borders" of the lens input are cut out. If you are going to attach any of these lenses to a full-frame camera, you don't know what quality to expect at borders through this evaluation.
Most lenses are not perfectly aligned and borders are not avenly at focus. This is, sadly, a very common issue, well known to those who seriously test photographic equipment: there is nothing odd in the fact that one border, e.g. the one on the top-left, appears much better than the corner on the (e.g.) bottom-right.
Also, tests on targets at a given, relatively short distance may not tell the whole story. It is a very good idea to shoot at infinity and see what comes out; some lenses may behave better or worse in comparison to what target-based tests say.
That is why I am also adding some outdoor shots, and I will likely based my personal choice on the images taken outdoor instead of doing otherwise.




80mm (Cosina), 70 mm (Takumar and Tamron)
at 70-80mm (the smallest focal length), f4/4.5 (max aperture), the Cosina is doing surprisingly fine in spite of being the oldest lens, likely surpassing the other two both in the center and the borders, where the advantage on the Takumar is less evident.
The Tamron is badly suffering in the border.
Actually, the Cosina does very well also at the other apertures, where it is on par with the Takumar (the latter maybe slightly better at f5.6), while the Tamron needs f8 to catch up with the competition at the borders.

Cosina at 80mm

Takumar at 70mm

Tamron at 70mm

f4,
f4.5 for the Cosina
center

f4,
f4.5 for the Cosina
border

f5.6
center

f5.6
border

f8
center

f8
border

f11
center

f11
border





135mm, more or less
at 135mm, the story changes a bit.
The Cosina is not that good at full aperture, while the Takumar is, just by a bit, the weakest at times.
The Tamron performs very consistently in the full range but in the end the three trade blows at each other here.

Cosina at 135mm

Takumar at 135mm

Tamron at 135mm

f4.5,
center

f4.5,
border

f5.6
center

f5.6
border

f8
center

f8
border

f11
center

f11
border





200mm, more or less
at 200mm, the Tamron is doing quite fine, definitely better then the Takumar. The Cosina trails the most recent optics (the Tamron, in spite of being more recent, likely relies on a scheme from the Takumar times).

Cosina at 200mm

Takumar at 200mm

Tamron at 200mm

f5.6
center

f5.6
border

f8
center

f8
border

f11
center

f11
border





Click here and proceed to the second part of the test, where I check the performance of the three zoom lenses in outdoor, real-world shots.

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