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03-26-2009, 09:48 AM   #1
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Photozne May Not Be so Impartial

Why is it that a lens on a Nikon is considered "very good" at 1650LWPH and "excellent" at 1950, but on Pentax it has to be 1750 for very good and 2050 for excellent. Canon standard is even lower at 1550 for vg and 1850 for ex. I was comparing the Sigma 50-150 and the DA* 50-135 and it seemed from just looking at the bar graph that the sigma was quite better, then I looked at the actual numbers. Hmmmmmmmmmmm. I checked the Nikon, Pentax, and Canon 50mm 1.4s; same thing. A lens has to be more than 10% better to be rated excellent on a pentax than it does on a Canon!

Sigma AF 50-150mm f/2.8 EX HSM DC (Nikon mount) - Review / Test Report

Pentax SMC-DA* 50-135mm f/2.8 ED [IF] SDM - Review / Test Report

Nikkor AF-S 50mm f/1.4 G - Test Report / Review

Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report

Canon EF 50mm f/1.4 USM - Test Report / Review

03-26-2009, 09:51 AM   #2
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Shall we guess which firm(s) supply the most ad revenue?
03-26-2009, 09:52 AM   #3
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simple...

We "pentaxians" have higher standards..... Isn't that why we selected Pentax in the first place???
03-26-2009, 10:05 AM   #4
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From the Photozone FAQ:
QuoteQuote:
Q: Are the figures comparable between cameras or different systems ?
It depends on the similarities between the image sensor system. A sensor SYSTEM contains the image sensor with or without micro-lenses, an IR filter, a low-pass (Moire) filter and the signal processing. As you can imagine the output quality is largely dependent on the whole chain on not just on the amount of megapixels. The different output quality between the Canon EOS 350D and the Olympus E-300 is a good example (despite a 8MP sensor). The tests are a good guidance for the lens quality as long as you compare the results WITHIN a test group (e.g. Canon).

Here're a few tendencies:
  • the Pentax results are a bit steeper (sharper and softer results are more pronounced). The tangentially resolution is a bit favored due to the extremely weak vertical AA filter.
  • the Canon results tend to be a bit better at the extreme borders due to the smaller sensor
  • the Olympus results are comparatively weak due to the aggressive AA filter on the E-300
This and the other info in the FAQ may address the issue... or maybe they're biased .

03-26-2009, 10:09 AM   #5
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EDIT: The response above me is much better.
03-26-2009, 12:10 PM   #6
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QuoteOriginally posted by heliphoto Quote
From the Photozone FAQ:
QuoteQuote:
Q: Are the figures comparable between cameras or different systems ?
It depends on the similarities between the image sensor system. A sensor SYSTEM contains the image sensor with or without micro-lenses, an IR filter, a low-pass (Moire) filter and the signal processing. As you can imagine the output quality is largely dependent on the whole chain on not just on the amount of megapixels. The different output quality between the Canon EOS 350D and the Olympus E-300 is a good example (despite a 8MP sensor). The tests are a good guidance for the lens quality as long as you compare the results WITHIN a test group (e.g. Canon).

Here're a few tendencies:

* the Pentax results are a bit steeper (sharper and softer results are more pronounced). The tangentially resolution is a bit favored due to the extremely weak vertical AA filter.
* the Canon results tend to be a bit better at the extreme borders due to the smaller sensor
* the Olympus results are comparatively weak due to the aggressive AA filter on the E-300


This and the other info in the FAQ may address the issue... or maybe they're biased .
That explains why a particular lens may perform differently on different platforms. I t doesn't explain why the standard is different. It seems like their system would be like a teacher grading differently based on hair color. Brown haired kids need 90% or better on the test to get an "A", but blond kids only need 88 to get an "A", and those with red hair only need 86.
03-26-2009, 12:14 PM   #7
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Just a thought - if expressing the lens resolution figures as % of the maximum sensor resoluition would explain this somewhat.
03-26-2009, 12:17 PM   #8
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QuoteOriginally posted by Parallax Quote
That explains why a particular lens may perform differently on different platforms. I t doesn't explain why the standard is different. It seems like their system would be like a teacher grading differently based on hair color. Brown haired kids need 90% or better on the test to get an "A", but blond kids only need 88 to get an "A", and those with red hair only need 86.
Recently, Popular Photography changed their resolution ranking. It looks like, only full frame cameras will be able to score "excellent," now.

03-26-2009, 12:43 PM   #9
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QuoteOriginally posted by asdf Quote
Recently, Popular Photography changed their resolution ranking. It looks like, only full frame cameras will be able to score "excellent," now.
Just as it should be.
03-26-2009, 01:18 PM   #10
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QuoteOriginally posted by Parallax Quote
That explains why a particular lens may perform differently on different platforms. I t doesn't explain why the standard is different.
It does for the AA filter reason. They're using a K10D for all testing which will measure higher LP numbers compared to stronger AA filters. Now, if they switched to the K20D which has a more typical AA filter, then they would probably lower the LP ranges...

If you upgraded from a K10D to a K20D, you'd understand...the first thing I noticed was the K20D images looked a lot softer when pixel peeped. I'm fairly certain it's because of the AA filter...
03-26-2009, 03:22 PM   #11
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QuoteOriginally posted by kenyee Quote
It does for the AA filter reason. They're using a K10D for all testing which will measure higher LP numbers compared to stronger AA filters. Now, if they switched to the K20D which has a more typical AA filter, then they would probably lower the LP ranges...

If you upgraded from a K10D to a K20D, you'd understand...the first thing I noticed was the K20D images looked a lot softer when pixel peeped. I'm fairly certain it's because of the AA filter...
O.K., I think I'm starting to get it. My common sense was telling me that there was something that I was overlooking. I couldn't really believe that they would be that blatantly biased. I did upgrade from K10D to K20D last year, but on the K10 I had a Tamron 28-75 that FF terribly, so I don't have any shots from both cameras with a common lens (that focused properly) to compare.
03-26-2009, 04:08 PM   #12
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Photozone can tell you a lot about a lens,but it doesn't tell you everything. but I don't base my lens purchases based on only one report.

Photozone has panned quite a few lenses that I know are very very good...though If I ever released my families Lens test data that has been accumulated over 40+ years I think there would be a new round of holy wars.

the Leica Summilux-R 50mm f/1.4 is much better than klaus would have you belive, except when it comes to flare.

The canon 70-200mm f/2.8L IS isn't anywhere near as good as a prime.

The Zeiss ZA 135mm f/1.8 is sharp...but when it's used wide open it has so much LoCa if you tested the Pentax 135mm f/1.8 against it The sony would lose, badly.
03-26-2009, 04:13 PM   #13
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QuoteOriginally posted by kenyee Quote
It does for the AA filter reason. They're using a K10D for all testing which will measure higher LP numbers compared to stronger AA filters. Now, if they switched to the K20D which has a more typical AA filter, then they would probably lower the LP ranges...

If you upgraded from a K10D to a K20D, you'd understand...the first thing I noticed was the K20D images looked a lot softer when pixel peeped. I'm fairly certain it's because of the AA filter...
Just to add to what you're saying: The "softness" is probably caused by the combination of the AA filter, the sensor out-resolving the lenses as well as vibrations being magnified and more noticeable on account of the higher pixel count. Pixel count does affect MTF results positively; the photozone FAQ answer above only states that there are other factors as well. I don't think you can blame only the AA filter on the difference between MTF results for the same lens on a 8MP Canon and a 12MP Sony when the Sony always wins. The perception of sharpness is affected by (1) contrast and (2) resolution. Anti-aliasing affects contrast (EDIT: here, I'm talking about "acutance") first (i.e., between a black diagonal line and the white background).

Here's something TL/DR about contrast vs. resolution:

Understanding Lens Contrast

Contrast (EDIT: read "acutance") you can increase with post-processing, but details lost due to lower resolution you can't recover.

EDIT: Here are two images (one converted from raw and scaled; the other one with an unsharp mask applied in Gimp):



(with unsharp mask to increase acutance: )

Last edited by asdf; 03-26-2009 at 07:30 PM.
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