Re: hyperfocal

[Tom Deering <tmd@xxxxxxxxxxx>]

>Here's a zipped DOF routine you can play with.

I don't know how other feel, but I'd prefer that attachments not be 
sent to the entire list.  While I am interested in DOF calculations, 
I use a Macintosh which cannot easily use a ZIP file.  Others may not 
want to wait for the download or care about DOF.

>It came up with a
>hyperfocal distance of 25 feet for a 75mm at f/22 at a resolution of 30
>lines per mm. Remember that if focused at infinity, the circle of
>confusion increases towards 25 feet where it reaches the selected limit.
>If focused at the hyperfocal distance of 25 feet, the circle of
>confusion increases from 25 feet to the selected limit at 12 and a half
>feet AND FROM 25 FEET TO INFINITY. Thus, while the image remains at or
>under the selected circle of confusion, more of the image will be at a
>larger circle of confusion than if focused at infinity. Moral of the
>story - you will get a better image if you focus at infinity at just
>don't include anything closer than 25 feet.

It's funny.  I use a programmable calculator to do stereo math in the 
field.  And I find I use the optimal focus formula more often than 
any of the others.  This is a formula that makes the near and far 
point equally sharp (or equally blurry.)  While I can guestimate my 
near point limitations from experience, I can't estimate optimal 
focus accurately.

I used it several times today at the New York City Marathon.  I had 
only ASA 100 film, and was using F11 to get the right exposure. 
Since I don't shoot at F11 very often, the DOF is foreign to me. 
Even once I know the near and far limits of the DOF, I can't figure 
out where to focus to maximize it.

I'll let you know tomorrow if it was worth the trouble.  :^)

Tom