Sigma 35mm f/1.4 user feedback needed

Started Jun 10, 2013 | Discussions thread
Mais78
Contributing MemberPosts: 596Gear list
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Focus and recompose vs using outer points
In reply to HarryLally, Jul 8, 2013

Focus and recompose is quicker and generally works very well with lenses at f2.8 or slower.

With a f1.4 lens things change. A 35mm lens has a c.54 degrees angle of view, assuming you focus on the subject and then recompose to have it on the rule of thirds you are rotating by about 9 degrees (54/3/2). The shift of the focus plane is the difference between the cosin and the distance from the subject given a certain degree. Assuming the subject is 1m away the shift of the focus plane for a 9 degree movement is 1.25cm (assuming you can rotate perfectly without moving the camera forward or backward). With a DOF calculator, if you assume circle of confusion at 0.006mm (c. pixel size of a 5DMkIII, to define DOF as sharpness at pixel level, 100% view), your DOF at 1m is 1.32cm at f1.4, so no margin for error. I would say at f1.4 to be safe you should not recompose if your subject is closer than 2-2.5m.

 Mais78's gear list:Mais78's gear list
Olympus OM-D E-M5 Canon EOS 6D Tamron SP 24-70mm F/2.8 Di VC USD Canon EF 40mm f/2.8 STM Sigma 35mm F1.4 DG HSM +5 more
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