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comment on lenstip / optyczne article
#1
Sylvain has forwarded this article to me:[size="2"][url="http://www.lenstip.com/index.php?art=127"]http://www.lenstip.c...dex.php?art=127[/url][/size]



I reckon there's a need to comment on this:

If you folks removed the AA filter the results would be completely different. So far for "true measuring". Have you folks noticed that AA filters have different strengths ? Are you aware that this causes a variable amount of de-sharpening depending on the specific camera ?

A lens test which does not try to reverse (to be reprecise "recover") the effect of an AA filter has little meaning. Optical systems are linear. The USM sharpening procedure is linear as well. We try to "normalize" the sharpening by reaching max. LW/PHs near the sensor limit (unless it exceeds default USM settings). Whether this is too much or too little may be debatable but applying none at all is invalid. Regarding the recent discussions about the K5 a fellow (PhD in Physics) has actually proofed mathematically that a sharpening of 100%, 0.5px is actually lossless on the K5 in terms of effective resolution or in other words - only if you apply some sharpening you will approach the effective limit. If you measure K5 data without sharpening at all you actually wouldn't measure the amount of "existing details" but something much lower that that.

Just to mention Imatest again: "[size="2"]A camera with little sharpening will have an MTF50 that doesn't indicate its potential."[/size]

You mention that Nyquist is the limit by citing "Sensor response above the Nyquist frequency is garbage. It can cause aliasing, visible as Moire patterns of low spatial frequency.". Yes, this is true. This is about the -visible- response on a real sensor. So ? We do not oppose this. We just cite that Imatest can MEASURE a bit beyond Nyquist: "this allows analysis of spacial frequencies beyond the normal Nyquist frequency". You may note the difference between "sensor response" vs "analysis" here ?



[size="4"] [/size]
#2
What does this mean in laymen's terms?



1. A body with a thick AA filter not only requires but also allows for more sharpening and, therefore, it would be unfair to compare it with a body that does not have an AA filter, if the test procedure is based on unsharpened files?



2. If the test procedure is based on RAW files differently sharpened for each body, the amount of sharpening is probably not exactly right and, therefore, grants an unfair advantage to one of the bodies?



3. If the test procedure is based on jpeg files, mainly the quality of the jpeg engine (and not the sensor) is tested?



If so: wouldn't it make sense to make the RAW files of the test shots available for download so that each reader can also try to develop the RAWs with his or her personally preferred RAW converter in order to figure out whether there are any relevant differences?
#3
In simple words: an AA filter softens an image in order to avoid moire/aliasing effects. The softening can be (pretty much) reversed via a certain amount USM due to the linear nature of optical systems. Thus a very defined amount of USM is recovering (most of) the original amount of "resolution" information (at cost of sensor noise though). Frankly that's just what most of you do with your RAWs. Nobody uses completely unsharpened RAWs except maybe in very high ISO images where noise is more critical than "resolution".

Just to mention - we don't apply any aggressive sharpening (I strongly opposed that approach in the recent K5 discussion) anyway. However, even if we did this would have an impact on the scale only but not on the qualitative validity of the results. A sharp center would still be sharp and a soft corner would still be soft - that's just a matter of the presentation of the resulting values.

We have always mentioned that the results are technically not cross-comparable. They are not comparable because of different AA filters, different sensor resolutions and different post-processing (both internal and external). The processing chain is simply different.



As far as publishing RAWs is concerned - we are generating multiple gigabytes of data per test. There's a natural limit to the bandwidth of our service ... our budget. :-)

[quote name='Tiz' timestamp='1291274521' post='4673']

What does this mean in laymen's terms?



1. A body with a thick AA filter not only requires but also allows for more sharpening and, therefore, it would be unfair to compare it with a body that does not have an AA filter, if the test procedure is based on unsharpened files?



2. If the test procedure is based on RAW files differently sharpened for each body, the amount of sharpening is probably not exactly right and, therefore, grants an unfair advantage to one of the bodies?



3. If the test procedure is based on jpeg files, mainly the quality of the jpeg engine (and not the sensor) is tested?



If so: wouldn't it make sense to make the RAW files of the test shots available for download so that each reader can also try to develop the RAWs with his or her personally preferred RAW converter in order to figure out whether there are any relevant differences?

[/quote]
#4
[quote name='Klaus' timestamp='1291276283' post='4675']

In simple words: an AA filter softens an image in order to avoid moire/aliasing effects. The softening can be (pretty much) reversed via a certain amount USM due to the linear nature of optical systems. Thus a very defined amount of USM is recovering (most of) the original amount of "resolution" information (at cost of sensor noise though).[/quote]

I'm not sure if I would refer to it using the terms "reversing" or "recovering". It's like you get milk (optical image), out of which you get cheese (AA-filtered image) and you turn it in to something else by putting it on a pizza (sharpening in post) <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />



GTW
#5
[quote name='genotypewriter' timestamp='1291278494' post='4677']

I'm not sure if I would refer to it using the terms "reversing" or "recovering". It's like you get milk (optical image), out of which you get cheese (AA-filtered image) and you turn it in to something else by putting it on a pizza (sharpening in post) <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='Big Grin' />



GTW

[/quote]



Yep, correct.
#6
Does it mean that AA-filtered images are cheesy then? :-)
#7
[quote name='Lomskij' timestamp='1291280916' post='4681']

Does it mean that AA-filtered images are cheesy then? :-)

[/quote]

Yup... but it's better on an USM pizza ;-)
#8
<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/sad.gif' class='bbc_emoticon' alt='Big Grin' />

I don´t like what I am seeing here (and there).

Photozone and Lenstip are two highly regarded photoreview sites with a slightly different approach, BUT with mainly the same verdict for lenses. I worked in 3 different countries and in offices with more then 10 nationalities. What I learned is, there are always many different approaches for the same problem, especially with different backgrounds. None of them are right or wrong as long as the outcome is certifying . Just different. So we should respect that everyone has there own reasons for choosing a certain way.



How about you guys send each other an email or just a quick ring before it gets out of hand and move on?

I am pretty sure the guy on the other side is a decent bloke with the same hobbies <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='Smile' />.

(I believe the guys from Lenstip will read this as well)



Regards
#9
At the end of the days who cares

If pizza tastes good I don't care how it's made.
#10
Actually I was more than surprised to read this article. There was no discussion under the hood prior of the publication.

However, you can't simply expect that this article can stand as is without being commented.

That said I will not start a similar front page article on this - at some stage it's getting too silly.





[quote name='Bjoern' timestamp='1291282988' post='4687']

<img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/sad.gif' class='bbc_emoticon' alt='Big Grin' />

I don´t like what I am seeing here (and there).

Photozone and Lenstip are two highly regarded photoreview sites with a slightly different approach, BUT with mainly the same verdict for lenses. I worked in 3 different countries and in offices with more then 10 nationalities. What I learned is, there are always many different approaches for the same problem, especially with different backgrounds. None of them are right or wrong as long as the outcome is certifying . Just different. So we should respect that everyone has there own reasons for choosing a certain way.



How about you guys send each other an email or just a quick ring before it gets out of hand and move on?

I am pretty sure the guy on the other side is a decent bloke with the same hobbies <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='Smile' />.

(I believe the guys from Lenstip will read this as well)



Regards

[/quote]
  


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