I thought I saw someplace a "real" number for and infinity equivalent, as perhaps a multiple of focal length. Yes I DO know that infinity is not a quantity, but at some point there is distance that might as well be. Most accounts that I can find now say things like "Focus on infinity, something a mile or two away" In order to apply some hyperfocal arithmetic, I'd like to know if there is a good enough minimum numerical equivalent, please.

Quote:

On 2004-11-01 10:05, Ed Workman wrote: I thought I saw someplace a "real" number for and infinity equivalent, as perhaps a multiple of focal length. Yes I DO know that infinity is not a quantity, but at some point there is distance that might as well be. Most accounts that I can find now say things like "Focus on infinity, something a mile or two away" In order to apply some hyperfocal arithmetic, I'd like to know if there is a good enough minimum numerical equivalent, please.

please explain what you're trying to compute. I ask because the rule of thumb is that if you focus on the hyperfocal distance, everything from half that distance to infinity (forever, as it were) will be in focus.

Cheers,

Dan

For critical work 2000 x the focal lenght.

For most of what I do anything from 1000x to 1500x is just as good.

so for that 65mm Optar, focusing from one end of a football field to the opposite goal post is plenty. But for that 14" lens, you 'll need a 1/4 mile minimum.

<blockquote> Hi,</blockquote> in the immortal words of my physics professor, infinity is defined as: <blockquote> Big enough </blockquote> He'd go on to explain that "big enough" meant that increasing the quantity grossly would have no effect on the calculation. For optics, you can go with the "focal length x 2000" and be big enough.<blockquote> <blockquote> Dan </blockquote> </blockquote>

Thanks very much for the replies. I have been collecting parts to build a hand held 8x10 "Self Casing Field Camera" and I want to be able to use scale/hyperfocal focusing.
I spent part of Tuesday afternoon and Wednesday morning in the desert with my Kodak 2D discovering just how much focus is affected by small movements (advertent and inadvertent) at "long" distances, and with a 10 inch lens. hmmm, this may not work.....