06-16-2011, 08:10 AM
Personally I wouldn't trust the infinity scale unless you have checked it and proved it yourself that it is right. For example, I have manually adjusted my Samyang 8mm fisheye as the lens scale was way out when I got it. The other time I might guess at infinity is if I am using small apertures so the depth of field will mask any errors.
Given even small shifts in the focus setting can affect the sharpness greatly, a focus on the subject at the time is always safest.
Note the lens characteristic changes with temperature. What is at infinity at room temperature might not be when it is freezing. I have observed this in my early astrophotography days. I took out and set up a lens, focused it exactly, and set a sequence of exposures off. When I looked at them, I could see the slowly defocus as time went on, due to the temperature changes. Now I make sure the lens cools down before I start and it has not happened again.
Given even small shifts in the focus setting can affect the sharpness greatly, a focus on the subject at the time is always safest.
Note the lens characteristic changes with temperature. What is at infinity at room temperature might not be when it is freezing. I have observed this in my early astrophotography days. I took out and set up a lens, focused it exactly, and set a sequence of exposures off. When I looked at them, I could see the slowly defocus as time went on, due to the temperature changes. Now I make sure the lens cools down before I start and it has not happened again.
<a class="bbc_url" href="http://snowporing.deviantart.com/">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.