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Re: [OM] ( DZ OM ) Value for money?

Subject: Re: [OM] ( DZ OM ) Value for money?
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Tue, 14 Jul 2009 10:20:46 -0400
The lens resolution is not tested with the sensor.  It's tested with 
DXO's measuring gear and the results are plotted against the Nyquist 
frequency of the sensor.  It appears that you did not actually look at 
the test data I referenced or you would have seen that lens resolution 
did indeed exceed the sensor at some points.  That would not have been 
possible to measure using the sensor.

I can't talk about your results with the 70-200/4 since that's a 
different lens and I have no idea how well it performs or how any 
individual sample performs.  The test I linked was for the 70-200/2.8 L 
IS.  It did resolve more than the 5D but not as much as the 5D Mk II or 
1Ds Mk III.  But the Canon 50/1.4 and 85/1.8 primes do resolve to and 
beyond the resolution of these 21 MP cameras but not by much and not 
consistently across the frame.  But different lenses (such as a hand 
picked OM 24/2) might do much better.

Film is definitely the limiting factor on the Modern Photo tests.  Most 
color films are in the 50-80 lpmm range with commonly used films around 
50-60.  Actual resolution between lens and film is termed the "system 
resolution" and can't exceed the smallest component.  Norman Koren 
discusses this here as well as the "old" system math and the new MTF 
math  <http://www.normankoren.com/Tutorials/MTF.html>

Chuck Norcutt


C.H.Ling wrote:
> I don't understand how dpreview test the lens' "Nyquist frequency" with a 
> low res 5D. But any day I will take a higher resolution camera if I can 
> justify for the cost, storage memory and processor power, I think I need 
> 40MP at least.
> 
> Have a look on this test site with 70-200/4 IS, even at F11 I see the result 
> of 1Ds Mark III better than 1Ds Mark II not to mention the 5D.
> 
> http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?FLI=0&API=0&Lens=404&FLIComp=0&APIComp=3&LensComp=118&CameraComp=9&SampleComp=0&Camera=453
> 
> I remember people mentioned the 'aerial resolution' (?) of lenses can over 
> 200lp/mm. And the guy in a Tamron lens site mentioned he seen 100 lines per 
> mm (I'm pretty sure he mean line pair) with a Tamron 24-48 while Modern 
> Photography only seen 50 lines per mm with film, he believe the different is 
> limitation of film.
> 
> http://www.adaptall-2.com/articles/Resolution_and_Contrast.html
> 
> I'm with Ken, I believe we need much higher resolution sensor to resolve the 
> details then 2 pixels per line pair consider the details may not be 
> perfectly aligned with sensor. I have a strong feeling that my 24/2 can do 
> better with higher than 21MP sensor.
> 
> C.H.Ling
> 
> ----- Original Message ----- 
> From: "Chuck Norcutt"
> 
>> What got me on this point to begin with was DPreview's test of the Canon
>> 70-200/2.8L which is one of the more revered zooms in Canon's stable.
>> Check this page which is the test of that lens on a 5D body.
>> <http://www.lenstip.com/115.1-article-Polarizing_filters_test.html>
>> Use the aperture slider and watch the resolution graph change. Only at
>> f/5.6 to f/11 is the 70-200 able to equal or slightly exceed the 12.7
>> megapixels of the 5D sensor (represented by the line labeled "Nyquist
>> frequency").  Below f/5.6 some irregular things start happening and
>> above f/11 diffraction begins its steady toll against resolution.  So,
>> if this lens can just barely handle a 5D it certainly can't handle the
>> pixel density of a 50D (15 MP on an APS-C size sensor).  At f/5.6 to f/8
>> the 5D Mk II will pull a bit more out of the lens than the 5D but not a
>> great deal.  To utilize the resolving power of the 5D Mk II you need
>> very good primes.  Here you can see that the 50/1.4 can resolve to the
>> level of the 1Ds Mk III (21 MP, like the 5D Mk II) at f/5.6 to f/8 (but
>> not elsewhere).
>>
>> Quite apart from noise, one reason to want a camera with larger pixels
>> is to be able to find a lens that can resolve to the level of the
>> sensor.  Little pixels just make the job harder on the lens.  That said,
>> it's also easier to make a lens that resolves little pixels if the
>> sensor is small and the lens doesn't have to cover a large area.
>>
>> Chuck Norcutt
>>
> 
-- 
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