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Hyper focal distance


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#1 Mathew Collins

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Posted 27 August 2017 - 10:15 PM

Hi,

 

I have seen the following calculation in a book.

 

"For example, for a 50mm lens at f/8 with a circle of confusion of .0001", the hyperfocal
distance is 40 feet. Thus, if you set the focus distance at 40 feet,
everything from 20 feet to infinity will be in focus."

 

If i calculate using the formula

H = F x F / (f x Cc)

   = 50mm x 50mm /(8 x 0.00254mm)

   =123031.5mm

   =403.64ft

 

Anything wrong with my calculation?


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#2 Dom Jaeger

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Posted 27 August 2017 - 11:24 PM

A more typical CoC figure would be 1/1000 of an inch: 0.001" or 0.0254mm. Looks like an extra zero slipped in after the decimal point.


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#3 Gregg MacPherson

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Posted 28 August 2017 - 02:13 AM

Does anyone still use the old style Kelly wheel type DoF calculator?  I mean the physical rotating disks that work like a slide rule.  They're a great way to get a more global feeling for the variables,  and so simple,  reliable.  


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#4 Simon Wyss

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Posted 28 August 2017 - 09:08 AM

I just missed slide rules. At school we were the first class allowed to have an electronic calculator, that was in 1977, a TI-59. But I got well drilled in mental maths before gym. As a rule of thumb I reckon with a third of the real distance as HD. In general news gathering people and everybody on quick and dirty jobs set focus too far. TV is full of such hyperfocal shots.

 

It should be hypofocal distance.


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#5 Mathew Collins

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Posted 29 August 2017 - 04:41 AM

A more typical CoC figure would be 1/1000 of an inch: 0.001" or 0.0254mm. Looks like an extra zero slipped in after the decimal point.

 

I quoted from 'Cinematography - Theory and Practice' by Blain Brown page 278. If CoC is 0.001, then the calculated hyperfocal distance would be 20 feet.


Edited by Mathew Collins, 29 August 2017 - 04:42 AM.

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#6 Robin R Probyn

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Posted 29 August 2017 - 05:51 AM

Does anyone still use the old style Kelly wheel type DoF calculator?  I mean the physical rotating disks that work like a slide rule.  They're a great way to get a more global feeling for the variables,  and so simple,  reliable.  

 

 

Those white plastic ones..? I had one when I was a focus puller.. short lived career ..   even easy, arse holes to infinity shots I would whip out that calculator and make it look really difficult in front of the make up ladies I fancied ..  never worked.. and usually shot out of focus too..


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#7 Dom Jaeger

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Posted 29 August 2017 - 06:50 AM

I quoted from 'Cinematography - Theory and Practice' by Blain Brown page 278. If CoC is 0.001, then the calculated hyperfocal distance would be 20 feet.


Try it again, using 0.0254 (mm) as the CoC figure in that formula, instead of 0.00254. You'll get the same answer as before, only divided by a factor of ten, which is about 40ft.
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#8 Mathew Collins

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Posted 29 August 2017 - 01:37 PM

Try it again, using 0.0254 (mm) as the CoC figure in that formula, instead of 0.00254. You'll get the same answer as before, only divided by a factor of ten, which is about 40ft.

 

That was a mistake. Please read

 

"I quoted from 'Cinematography - Theory and Practice' by Blain Brown page 278. If CoC is 0.001, then the calculated hyperfocal distance would be 20 feet."

 

as

 

I quoted from 'Cinematography - Theory and Practice' by Blain Brown page 278. If CoC is 0.001'', then the calculated hyperfocal distance would be 40 feet.


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#9 Mathew Collins

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Posted 30 August 2017 - 11:27 PM

Thank you all.


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