Where to line up infinity symbol?

[sooner]

Hi Folks,

This may seem silly but I often focus my rangefinder cameras with the hyperfocal method by lining up the desired range as denoted on the lens itself. But I catch myself wondering where exactly to line up the infinity symbol across the line by the desired f/stop. Is the middle of the infinity symbol the right place, almost like it's perfectly balanced on the line, or should it be the right-hand side of the infinity symbol? Hey, that "flat eight" usually represents a fair amount of play in the lens, so it makes sense that there is a significant focusing affect depending on whether you line up the line with the left, middle, or right side of the infinity symbol. Your thoughts are welcome.....John.

 

[rbiemer]

John,
I do this: Turn the lens to "infinity" and see where the symbol lines up with the focus mark, then I sue that position to line up to the f stop mark.
Rob

 

[sooner]

Thanks, Rob, that makes a lot of sense. --John

 

[sooner]

Rob, for what it's worth, when I did as you suggested, the focus line matched up with the middle of the infinity symbol, so now I know where to line it up to the line for whatever f/stop I'm shooting at. Thanks again for indulging a dumb question....John.

 

[rbiemer]

Not so dumb, John. As you said, the infinity symbol can take up a significant fraction of the lens rotation. I honestly don't know how critical the position might be at small apertures but better to err on the side of precision, I think.
Rob

 

[Al Kaplan]

The old rule of thumb for setting hyperfocal distance was give yourself one f-stop safety factor. Line it up for f/5.6 when shooting at f/8 for instance.

BUT -Big But! - no matter how you figure it, a lot of your picture will still be "out of focus". Only the exact plane of focus is truely in focus. What we're playing with here is the concept of "acceptable sharpness". This will vary with print size and viewing distance. A high speed grainy film will mask the effects of image unsharpness so it appears to give you more depth of field.

The image doesn't suddenly go from tack-sharp crisp to complete and total fuzziness once it gets past that distance marker on your lens barrel. Now that I have you completely confused your best bet is to shoot your own tests with your lenses, take notes, and come to your own conclusions.

 

[john_s]

Al's warning is correct. The degree of acceptable unsharpness assumed in the calculations of depth of field is far too unsharp for many purposes. I try to go one stop further than Al's suggestion and go for the marks for two stops wider than the actual aperture in use. It appears that you're getting "less depth of field" than you thought, but you never had it in the first place.