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01-21-2013, 01:23 PM   #1
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Depth of Field / Infinity Focus Question

Is infinity always in focus past a certain point when a manual focus lens is set at infinity? or is the far focus point limited by the smaller aperture even when set at infinity?

According to my depth of field calculator it says my hyperfocal at f/2.8 on my 28mm is 45 feet....does that mean that focused at infinity everything from 45 feet and farther is in-focus?


Thanks!

01-21-2013, 01:38 PM   #2
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QuoteOriginally posted by godwinaustin Quote
Is infinity always in focus past a certain point when a manual focus lens is set at infinity? or is the far focus point limited by the smaller aperture even when set at infinity?

According to my depth of field calculator it says my hyperfocal at f/2.8 on my 28mm is 45 feet....does that mean that focused at infinity everything from 45 feet and farther is in-focus?


Thanks!
Yes, if focused at infinity. It also means if you set the lens to focus at 45 feet, you'll get everything from 45/2 = 22.5 feet to infinity.

But keep in mind that means "acceptable focus" which on a crop sensor might be more stringent than a full-frame. It is a good idea to calculate the hyperfocal distance as one stop wider than you are actually using when using a crop sensor. Same with any distance scale on the lens. Fudge it one stop tighter and you'll like the results better.
01-21-2013, 01:41 PM   #3
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QuoteOriginally posted by vonBaloney Quote
Yes, if focused at infinity. It also means if you set the lens to focus at 45 feet, you'll get everything from 45/2 = 22.5 feet to infinity.

But keep in mind that means "acceptable focus" which on a crop sensor might be more stringent than a full-frame. It is a good idea to calculate the hyperfocal distance as one stop wider than you are actually using when using a crop sensor. Same with any distance scale on the lens. Fudge it one stop tighter and you'll like the results better.
10 feet is the last finite focusing distance on the lens, and then the infinity symbol, so how can I set focus at 45 feet?

What does infinity represent as a near focus point?
01-21-2013, 01:57 PM   #4
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QuoteOriginally posted by godwinaustin Quote
10 feet is the last finite focusing distance on the lens, and then the infinity symbol, so how can I set focus at 45 feet?
Well, you can't I guess, but on a longer lens (or a lens with a longer focus throw) the hyperfocal point will be available so just something to keep in mind.

QuoteQuote:
What does infinity represent as a near focus point?
In this case 45 feet (and beyond) -- there is essentially no distance past 45 feet if that makes sense. If you want the maximum sharpness that far out, you'd focus on infinity, and so something 45 feet away would show the same sharpness as a shot of the moon. But if you want maximum depth-of-field to also get "acceptable focus" on objects 22.5 feet - 45 feet away, you'd focus on the hyperfocal point instead on the lens (if you could) and now something 45 feet away will show maximum sharpness, but the moon would be ever so slightly softer but still "acceptable", as would objects say 30 feet away (which would be very soft if you focused on infinity instead).

01-21-2013, 01:59 PM   #5
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awesome Von, thanks so much!


QuoteOriginally posted by vonBaloney Quote
Well, you can't I guess, but on a longer lens (or a lens with a longer focus throw) the hyperfocal point will be available so just something to keep in mind.

In this case 45 feet (and beyond) -- there is essentially no distance past 45 feet if that makes sense. If you want the maximum sharpness that far out, you'd focus on infinity, and so something 45 feet away would show the same sharpness as a shot of the moon. But if you want maximum depth-of-field to also get "acceptable focus" on objects 22.5 feet - 45 feet away, you'd focus on the hyperfocal point instead on the lens (if you could) and now something 45 feet away will show maximum sharpness, but the moon would be ever so slightly softer but still "acceptable", as would objects say 30 feet away (which would be very soft if you focused on infinity instead).
01-21-2013, 03:58 PM   #6
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One caution regarding the hyperfocal. All things are relevant and that includes DOF. The hyperfocal is based on an assumption of moderate viewing distances and moderate enlargement to yield "acceptable" focus (as noted above). Enlarge enough or look closely enough (as in pixel peep) and even extreme DOF evaporates into thin air.


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01-21-2013, 04:32 PM   #7
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Also above I was ignoring the effect of atmosphere -- in real life something a mile away (or even a few hundred yards away depending on the air quality) is not going to be sharp as something 50 feet away (even if the scale was such that they appeared the same size in the frame) just because of the air, haze, heat, etc...
01-21-2013, 05:23 PM   #8
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Yes. When it doubt, stop it down. :P

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