Thread: F1.2 pro glass
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Old 17th March 2019
MikeOxon MikeOxon is offline
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Re: F1.2 pro glass

Originally Posted by drmarkf View Post
......for me doing street photography of small groups of people around 12-15’ away, 17mm at f1.2 gives around 18” dof, while f1.8 is around 5’. In terms of subject isolation that’s usually closer to ‘major’ than ‘slight’ in my view.

I was surprised to read of such a large difference, so I checked with the Cambridge in Colour DoF calculator. Of course, DoF is not a 'hard and fast' calculation and depends a lot on how you define 'sharpness' but, using their rather strict criteria of viewing a 20" print from 25 cm (less than a foot away), the results I got were:

17mm at f/1.2, subject at 12': DoF= 2.95'

17mm at f/1.8, subject at 12': DoF= 4.5'

Significant, yes, but not as 'major' as you suggested. Also, if you were photographing a 'group' of people, might not the greater depth of field be considered more useful?
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