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Lens focus The place to talk about your camera's glassware.

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  #31  
Old 17th March 2019
MikeOxon MikeOxon is offline
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Re: F1.2 pro glass

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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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  #32  
Old 17th March 2019
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drmarkf drmarkf is offline
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Re: F1.2 pro glass

Quote:
Originally Posted by MikeOxon View Post
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?
I was using the Depth of Field Calc iOS app, and settings for 15’ - yes, as you say, this will depend a lot on how you define dof (which isn’t a set quantity visually anyway, gradually fading away and also depending on a lot of light and subject variables).

Yes, I thought I’d covered the two sorts of image I mainly take - one picking out a single person (for which f1.2 is ideal) and the other covering a group (all of which one wants in acceptable focus).

In the past I have fiddled about in PP trying to get a believable enhanced fall-off of focus with distance, but I gave up trying quite quickly. Maybe others have better PP skills than I, but after getting the 17 f1.2 I was able to stop worrying about it.
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  #33  
Old 17th March 2019
MikeOxon MikeOxon is offline
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Re: F1.2 pro glass

Since drmarkf mentioned an iOS App, I might also point out that the Focos App, which works far twin-lens iPhones, can produce the effect of a wide-aperture lens automatically.
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