The 300mm lens I rented gave me a bit of a scare. I recently purchased a program, Reikan FoCal. This is a focus adjustment and performance evaluation tool that is actually pretty handy for its low price. I originally purchased it to fine tune the focus of my Canon EF 100-400mm f/4.5-5.6 L IS lens, which has been focusing soft on my 7D. FoCal is capable of automatically determining which AutoFocus Micro Adjustment (AFMA) setting will produce ideal results, which is extremely handy. I purchased the Pro version of FoCal in order to get some additional features, such as an aperture test series that will tell you which aperture produces the highest resolution. I decided to run a quick aperture test on the 300mm f/2.8 lens tonight, and its a good thing I did! (read more…)