[maucard]

I just noticed that the lens performance tests on the ephotozine web site show very different results for the supposed Pentax/Tamron siblings: (1) Pentax HD FA 15-30 F2.8 vs. Tamron SP 15-30 F2.8, and (2) Pentax HD FA 24-70 F.2.8 vs. Tamron SP 24-70 F2.8. In both cases, the Pentax lens seems to have a much more even performance than the Tamron equivalent, with small difference between center and border also at f 2.8; on the other side, the Pentax lenses show a more than double amount of chromatic aberration with respect to the Tamrons... Here are the links:

HD PENTAX-D FA 15-30mm F2.8 ED SDM WR Review
Tamron SP 15-30mm f/2.8 Di VC USD Review
Pentax HD Pentax-D FA 24-70mm f/2.8 ED SDM WR Review
Tamron SP 24-70mm f/2.8 VC USD Lens Review

Of course the differences may be explained by errors made during in the procedure of the lens performance tests, but... what do you think, is it possible that the Pentax/Tamron siblings are not siblings indeed? Would it be possible, for example, that the optical design is the same (Tamron in origin) but slightly modified by Pentax for its own Tamron-derived lenses?

Maurizio

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Last edited by maucard; 09-28-2016 at 02:22 PM. Reason: typo

[clackers]

The glass and coatings are different, but the optical design is the same.

These tests are presumably evaluations of single copies though and do not take into account sample variation, as Lens Rentals warns.

[Na Horuk]

Of course the differences may be explained by errors made during in the procedure of the lens performance tests,

and lens sample variation, and differences in camera. CA, resolution and some other things are affected by the camera sensor, since a higher MP sensor will "record" more CA than a lower MP sensor. The cameras used for these tests were different cameras (brand, sensor), you cannot really do valid comparisons.
Finally, the lens construction itself can have effects - if the inside is less or more reflective, if the aperture blades are too shiny, if the lens hood is better optimized, etc.

Interesting to see such big differences, but I think there would have to be a special comparative test done, with multiple copies of each lens on just one camera (likely adapted to a Sony, because it can take various mounts), to truly answer your question.
Until then, all we have is various lab reviews (from magazines, websites) and user reviews.

[maucard]

Thank you Clackers. Ok... so, the copy-to-copy variation can be an explanation, but if you look to the above cited reviews the differences seem quite huge and in the same directions for the two couples of lenses (both Pentax lenses are more even in wide-open performance, both are more aberration-prone than Tamrons), so it does not seem (albeit it cannot be excluded) the result of a random variation in lens quality. As you said, the glasses used in the Pentax version of the lenses are different, so (perhaps, but I'm not an expert in the field) it is possible that the exact quality and type of the used glasses may produce quite different performance on a same lens design, and that Pentax engeneers chosen the type of glasses used for these Pentax lenses in order to maximize the uniformity of performance (at the expense of a worse control of optical aberrations)...

---------- Post added 09-28-16 at 03:16 PM ----------

and lens sample variation, and differences in camera. CA, resolution and some other things are affected by the camera sensor, since a higher MP sensor will "record" more CA than a lower MP sensor. The cameras used for these tests were different cameras (brand, sensor), you cannot really do valid comparisons.
Finally, the lens construction itself can have effects - if the inside is less or more reflective, if the aperture blades are too shiny, if the lens hood is better optimized, etc.

Interesting to see such big differences, but I think there would have to be a special comparative test done, with multiple copies of each lens on just one camera (likely adapted to a Sony, because it can take various mounts), to truly answer your question.
Until then, all we have is various lab reviews (from magazines, websites) and user reviews.

I agree with you, Na Horuk, these are all additional good explanations for a different performance of lenses having a same lens design. Hence, we may conclude that (this is my point) for what we know these lenses are not simply "Pentax rebranded Tamron lenses" (as often they are referred in the web forums) but Pentax manufactured lenses wich, albeit sharing a same basic optical design with the Tamrons, could have (for what we know) a quite different optical performance.

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Last edited by maucard; 09-28-2016 at 03:18 PM.

[Na Horuk]

True. They also have some different features. The Pentax versions are WR. The Tamron versions have AF switch and in-lens stabilization. But they do look very similar. Lens world is complicated, with many things being outsourced, collaborated, and traded
Pentaxians mostly complain when the same optical design with Pentax brand name costs more

[FantasticMrFox]

True. They also have some different features. The Pentax versions are WR. The Tamron versions have AF switch and in-lens stabilization. But they do look very similar. Lens world is complicated, with many things being outsourced, collaborated, and traded
Pentaxians mostly complain when the same optical design with Pentax brand name costs more

That's the thing - as far as I know including optical stabilisation in a lens usually negatively impacts on its image quality (after all there are additional parts connected to the optical elements, taking up space etc.). So if Tamron and Pentax went as far as having to put seals into the lens, did they maybe remove the entire in-lens stabilisation rather than just disabling it?

That would be interesting to see - disable the Penrons and see whether the stabilisation is still in there. Because if it isn't, that could be at least part of an explanation of why the Pentax versions are doing better optically with ePhotozine.

[Digitalis]

The glass and coatings are different, but the optical design is the same.

If the glass used in the two versions of this lens are different, the design would have to be altered.

I think there would have to be a special comparative test done, with multiple copies of each lens on just one camera

I'd prefer to take the cameras out of that equation, I will be doing a bench test - the only problem is acquiring a decent sample size to reach an effective conclusion as to why the lenses are performing differently.

[CDW]

ePhotozine.com tested both versions of the 15-30 2.8 and the results were similar. The Pentax version was more uniform in sharpness from center to edge over a wide range of F stops. CA is easily correctable but you can't recover loss of sharpness. I would side with Pentax and a decision to go for sharpness and uniformity, although at twice the cost of the Tamron version is a bit hard to swallow.

[clackers]

If the glass used in the two versions of this lens are different, the design would have to be altered.

Since the optical design seems unchanged, the only way Asahi Man can be right when he says the glass and coatings are the same is if both Tamron and Pentax order glass from the same supplier.

[Rondec]

ePhotozine.com tested both versions of the 15-30 2.8 and the results were similar. The Pentax version was more uniform in sharpness from center to edge over a wide range of F stops. CA is easily correctable but you can't recover loss of sharpness. I would side with Pentax and a decision to go for sharpness and uniformity, although at twice the cost of the Tamron version is a bit hard to swallow.

Twice the cost? The Tamron 15-30 lists on B and H for 1199 and the Pentax 15-30 lists for 1440. That is a couple hundred dollar mark up, but it isn't exactly twice the cost.

[ffking]

It should be noted that the two ephotozine tests of the 70-200 f/2.8 differ considerably - that might be as a result of withdrawing the lens and then issuing it later - might be inherent variation?

[Digitalis]

the only way Asahi Man can be right when he says the glass and coatings are the same is if both Tamron and Pentax order glass from the same supplier.

IF asahi man doesn't cite his sources, i'm calling them into question. I have only a small sample size to go on between the Tamron/Pentax versions of the 15-30mm f/2.8 - barring sample variation, there is a deviation between them in the test scores in MTF testing, but of the lenses I have tested so far...I need more copies of these lenses to test so I can arrive at a conclusion that can completely eliminate sample variation*. From what bench test results I have so far the Tamron/Pentax 24-70mm f/2.8 the test results are showing a similar pattern. The Pentax 70-200mm f/2.8 is indeed a unique design. Among the Tamron/Pentax re-branded lenses all I can say at this point is that pentax has done something to these lenses....as to what they have done is as of yet, unclear.

* But I also have to get my test bench re-calibrated as I have moved house yet again, so I can't do anything right now...which is very frustrating. But at least I don't have to worry about the trains causing vibrations and (literally) fuzzing up my test results.

[FantasticMrFox]

It should be noted that the two ephotozine tests of the 70-200 f/2.8 differ considerably - that might be as a result of withdrawing the lens and then issuing it later - might be inherent variation?

But that's because Pentax withdrew the lens as they were unsatisfied with its performance, and worked another year (?) on it. So it's not surprising the tests differ, because the lens was tweaked.

[noelpolar]

Twice the cost? The Tamron 15-30 lists on B and H for 1199 and the Pentax 15-30 lists for 1440. That is a couple hundred dollar mark up, but it isn't exactly twice the cost.

$700 more here...

[FantasticMrFox]

Twice the cost? The Tamron 15-30 lists on B and H for 1199 and the Pentax 15-30 lists for 1440. That is a couple hundred dollar mark up, but it isn't exactly twice the cost.

In Germany Tamron €970, Pentax €1,700. Not twice as much, but quite the difference.