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06-06-2011, 07:41 AM   #1
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Confused about reviews

I have a question regarding two lenses I own. Namely the FA 50mm f1.4 and the DA 35mm f2.8 macro limited.

From the beginning, I was always under the impression that the 35 was sharper then my 50mm. But recently I saw the reviews on Photozone, and there it turned out the the 50mm outresolves the 35 at most apertures:

The DA35ltd:
Pentax SMC DA 35mm f/2.8 Limited macro - Review / Test Report - Analysis

And the FA50:
Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report - Analysis & Verdict

But the Pentaxforums reviews are the other way round. The DA35ltd is rated as super sharp, while the FA50 as not so sharp. Which does make more sense, and confirmes the findings of my own eyes.

The DA35ltd:
Pentax-DA 35mm F2.8 Macro Review | Pentax Lenses | PentaxForums.com

And the FA50:
Pentax-FA 50mm F1.4 Review | Pentax Lenses | PentaxForums.com

So... What do I trust? I know I should not care, both lenses outresolve me. I mean, I'm more limited by my own lack of creativity then by the issue I'm adressing above. But still... I want to know.

06-06-2011, 08:10 AM   #2
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Congratulations, you've discovered that reviews of the same things can be different and that they can leave you puzzled. Been there, done that. I think any review that has some (or a lot) of testing results in it is apt to have more credibility than general impressions by humans. While it still always comes down to you and what you see and think, reviews are best treated as guides rather than as absolutes. In this case, if you can't see any difference in sharpness, and if you are satisfied with their performance, does it really matter what reviewers say?
06-06-2011, 09:13 AM   #3
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I always assumed the reviewers had some way of objectively measuring the resolution.
06-06-2011, 09:13 AM   #4
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QuoteOriginally posted by Clavius Quote
So... What do I trust? I know I should not care, both lenses outresolve me. I mean, I'm more limited by my own lack of creativity then by the issue I'm adressing above. But still... I want to know.
I'm not sure they contradict - consider this statement from the review of the FA 50mm f/1.4: "Typical for such lenses the results are a bit soft at f/1.4 and less so at f/2 but still usable." The Pentax DA 35mm Macro has no f/1.4 or f/2.0, so in a sense it has an advantage starting at f/2.8, i.e. it's 'starting resolution' is higher, and it will never produce a picture as soft as the FA 50mm f/1.4.

Also keep in mind there aren't strict guidelines on how users write their reviews on pentaxforums, so there's a lot of factors that can affect a review. A user who has shot with film on a lens like the FA 50mm f/1.4 can consider how the lens performs on a full-frame film body, where it will have different corner resolution and vignetting. Or maybe they just shoot with it on a digital APS-C digital body, where the image area will be cropped and the lens will perform differently, i.e. more in it's 'sweet spot'. Or maybe they shoot both and consider both.

When people use the word 'sharp' here in the forums to describe a lens, they don't always share what f-stop they are considering, and that can have a great impact on lens resolution (and perceived sharpness of that lens). One person could shoot with the FA 50mm at f/1.4 all the time and declare it a soft lens, and another user could shoot with it at f/2.8 all the time and call it sharp, and since they don't have to disclose what f-stops they're shooting with, they are both right.

06-06-2011, 09:49 AM   #5
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Photozone provided absolute number measured in a controlled environment but from a single copy (??).

Reviews are very subjective and based one's perception on sharpness but from multiple copies.

So both are right and useful IMO.
06-06-2011, 09:53 AM   #6
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QuoteOriginally posted by Clavius Quote
I always assumed the reviewers had some way of objectively measuring the resolution.
They can measure MTF (modulation transfer function) which is essentially the capacity of the lens to preserve the contrast at the frontier between a pure white and pure black area. This is one measure of sharpness. It is not the only one, however.

However, resolution is linked to the sensor, and any measurement is thus dependant on the sensor and how it interacts with the lens (angle of incidence of the light rays, wavelengths that pass through, etc).

Still more confusion : perceived sharpness is also influence by contrast, colour rendering, optical aberrations, and much more.

So in short, there is no single way to measure sharpness, and other parameters influence your perception of an image. so measuring is always subjective.
06-06-2011, 10:10 AM   #7
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In this particular situation, one of the differences between the FA 50 and the DA 35 is that the DA is a macro lens. Detail captured is not only related to sharpness of a lens, but also distance to the item being photographed. The FA 50 doesn't focus particularly close, while the DA 35 can photograph stuff that is at the end of its lens hood.

I like the way the DA 35 renders colors, contrast better than I liked the FA 50.

Anyway, the reviews here are going to be almost entirely opinion based. Those opinions will be influenced both by lenses the person has used before as well as their own skill level and ability to take advantage of a particular lens's attributes. Finally, since cost is a factor in lenses, need to remember that a (formerly) cheap lens like the FA 50 is going to tend to get better reviews than a relatively expensive lens like the DA 35.
06-06-2011, 10:11 AM   #8
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Thanks guys. This does make things a lot clearer. I should believe my eyes.

06-06-2011, 10:12 AM   #9
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I think another problem is that there is no "defined" standard for such observations. Different testers might "rate" the same lens with a different score from another. The reviews here were done by different people.

As bdery notes the sensor can influence things in a far more critical way than used to be the case with film. I find that such reports can be useful as an initial guide but I find these days that the character of a lens, it's colour rendition, bokeh and other trait matter more to me than an absolute measure of how sharp it is.

Kim
06-06-2011, 10:28 AM   #10
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And one other review, only of the 50mm:
Pentax smc FA 50 mm f/1.4 review - Introduction - Lenstip.com

and:
Pentax SMC FA 50mm F1.4 Lens Review: 1. Introduction: Digital Photography Review

You can read on forever.

There is also MTF50 and MTF20, maybe someone can explain the difference?
06-06-2011, 02:30 PM   #11
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QuoteOriginally posted by RonHendriks1966 Quote
There is also MTF50 and MTF20, maybe someone can explain the difference?
MTF50 is about sharpness, MTF20 about resolution. I never bothered to find out more about these indicators because this is all I actually need to know, but if someone has more theoretical knowledge on this, feel free to share... for forum's sake
06-06-2011, 09:54 PM   #12
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The proof is before your own eyes. You're considering new lenses. BUY THEM! SHOOT THEM! JUDGE THE RESULTS YOURSELF! And if you don't like a lens, RETURN IT! (Make sure you've bought from a reputable dealer with a no-questions return policy.)

Lens tests are like standards -- many exist, and they aren't necessarily compatible. And copy variation exists, so test results of one copy may not be valid for another copy. User reviews reflect experience with more than one copy and thus may better rate a lens model in toto. I've read many technical reviews, with detailed testing, that proclaim a camera or lens to be GREAT, while the user ratings say it sucks. Murphy's 3rd Law: Any device that tests perfectly in the lab will fail in the field.

Tests and reviews are merely indicators. You need to analyze and judge such 'information' critically. Nothing is simple nor certain. Everything is foggy. Alas.

Last edited by RioRico; 06-06-2011 at 10:09 PM.
06-06-2011, 10:50 PM   #13
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trust your feelings, you know that it is true. but I'm not your father.
06-06-2011, 11:00 PM   #14
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QuoteOriginally posted by Pentaxor Quote
trust your feelings, you know that it is true. but I'm not your father.
Shoot, that's going to make that Father's Day card really awkward now...
06-06-2011, 11:19 PM   #15
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There are also good and bad copies of lenses, so one copy of a particular type can vary. Someone has one bad copy of any lens and the results are skewed.
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