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Author Topic: P25 versus P45  (Read 3888 times)
Gary Ferguson
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« on: March 17, 2006, 11:34:50 AM »
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This link shows a comparison between a P25 back and a P45, both shot with a Hasselblad 80mm at f16.

I can't see much additional information from the additional pixels. It seems to support Michael's assertion that to really squeeze the benefit from a P45 requires better lenses, and it must signal caution about the improvements we could expect if Canon ever release a 22MP successor to the 1Ds II.

http://www.captureintegration.com/comparis...P45-vs-P25.html
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ddolde
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« Reply #1 on: March 20, 2006, 02:35:59 PM »
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No doubt the lenses are a factor.

One thing to remember though, 39 mp ain't twice the resolution of 22 mp or even close.  To double the resolution you would need 88 mp, ie both pixel dimensions need to be doubled.  

Here we are going from 4080 pixels in the short dimension to 5428 pixels.  That's 1.33x the resolution.  Thats one reason why the Canon 5D looks almost as good as the 1DsII.  The linear resolution factor for these two is only 1.14x.

Also these are just jpgs and I wouldn't put too much stock in what can be seen here.  I'd need a raw file to really see for myself.  But the P45 does look quite a bit better to me anyway.
« Last Edit: March 20, 2006, 02:38:57 PM by ddolde » Logged
BJL
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« Reply #2 on: March 20, 2006, 03:47:21 PM »
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Quote
This link shows a comparison between a P25 back and a P45, both shot with a Hasselblad 80mm at f16.
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Diffraction probably means that f/16 is too small an aperture to use with the 6.8 micron pixel spacing of the P45, at least if you want maximum sharpness; f/16 is about at the diffraction limit of the 9 micron pixel spacing of the P25 sensor, so diffraction might prevent any lens or sensor giving resolution significantly better than the P25 already does at that aperture. The rule of thumb seems to be avoiding aperture ratios more than twice the pixel spacing, like Thom Hogan's observation of needing to stay at f/11 or below with the D2X and its 5.5 micron pixel spacing.

The Olympus E-1 has a Kodak FFT CCD related to that of the P45, with the same 6.8 micron pixel spacing, and the E-1 will not automatically choose an aperture beyond f/11 in S or P mode, I believe due to diffraction effects.
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