Quote:
Originally Posted by miketoll
Given two lenses of the same 'speed' and focal length one sometimes seems to focus better than the other which I have always put down to one lens having better contrast than the other. Any thoughts on that?
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Mike,
I do not have two similar A/F lenses to check out the lens resolution bit but I guess when you reach the boundarys
everything counts.
So I have just looked at Photozone reviews of the Sigma and Tamron to look at the MTF charts and the Tamron has it by a nose.
Now going back through the thread to crazee horse second post and he says " we both put the cameras on auto and then program and focused on the same thing. ". In this case that may also have relavence.
What auto/program mode was used ? From my experience of the 350D then if it is on basic program ALL A/F points are live just the same as the D50. In this case his friend may have set Vari program on the D50 and that would allow him to set a single central A/F point.
From a specs point of view ( DPR ) the 350D A/F range is EV -0.5 to + 18, D50 range EV -1.0 to + 19 so the D50 has it by 0.5 EV
Lenses from photozone MTF at 300mm, Sigma on the 350D MTF centre 1676 edge 955, Tamron on the D50 centre 1849 edge 1489. Advantage the Tamron on the D50
The unknown is then selected focal length. As these are both variable aperture lenses if the guy with the D50 was at less than 300mm and crazee horse at 300mm then it would be advantage D50. Could have been f5.6 on the 350D and say f5.25 on the D50.
Hardly scientific, but add all these factors up and the result would be as described.
Don