Re: Pre-order: Sigma 24-70mm f/2.8 DG DN E-mount for $1,099!
MAubrey wrote:
It isn't about tested vs. theoretical (thought the Nikon S addition is certainly theoretical!). It's about two entirely different systems for measurement that produce different results.
It's just not a responsible comparison.
This is so, so true and leads to so many useless arguments online. A quick summary of what you're looking at, annotated.
All manufacturers except Zeiss and Leica: Computer generated 'theoretic best possible' MTF at infinity.
Variables: which program used for calculations, what type of light used, frequencies calculated
Zeiss and Leica(in-house, not just labeled): actual MTF results done on Zeiss K-8 and K-9 machines at infinity, average of 20 to 80 copies of prototype lenses.
Variables: none
Lensrentals: Trioptics Imagemaster HR MTF bench at infinity
Variables: none
All other test results: computer analysis of target chart.
Prime variables: Imatest or DxO
Major variables: Target chart size, target chart resolution, choice of 'corner' and 'mid' targets (this is actually 24 choices using Imatest), lighting (a 20% variation in results possible), camera used, 'acceptable angle' standards, use of RAW vs JPG, RAW converter used for RAW images.
Any comparison between two sites using numbers is absolutely positively invalid.
Comparison within a site is generally valid, although with computer analysis sites you need to make sure methodology hasn't changed over time (changes in cameras or charts) or with focal length (many use different charts and lighting for wide-angle vs telephoto).
So it's never valid to say Joe show the XRay 85 is sharper than Bill shows the Wonderbar 85 to be. It's never valid to comapre Nikon's MTFs to Sigma's MTFs.
It is valid to say Joe shows the XRay 85 is sharper than the Wonderbar 85.
And it's valid when someone else says Bill showed the Wonderbar 85 is sharper than the XRay 85.
And these days, when differences are slight, Bill and Ray could well have both shown the absolute truth. Not just copy variation, but Bill might be testing in-camera jpgs at 12 feet and Ray testing RAWs at 26 feet, both with different lighting.
Nov 17, 2019 at 12:49 PM
Previous versions of RCicala's message #15048105 « Pre-order: Sigma 24-70mm f/2.8 DG DN E-mount for $1,099! »
