# Help: preset focus via distance settings.



## photo1234 (Mar 12, 2007)

Hello,

I was reading the latest edition of "Understanding Exposure by Byran Peterson". On page 38-39, he talks about how distance settings have replaced depth 0f field scales. He also gives an example of a picture and says that "the distance of two feet is aligned directly above the center mark near the front of the lens". What does that mean?
If I need a great depth of field, I use higher fnumber setting (f22 for example) and then focus 1/3rd into the scene and click. How do I do this through distance settings. I don't see any such setting on my camera.
I have a Canon Rebel XTi which I purchased recently.
Any help will be greatly appreciated.

Thanks
Photo1234


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## snappin (Mar 12, 2007)

Haha now thats odd. I just read that passage and was wondering the same thing. I haven't gone to inspect my camera yet, nor read further to see if he explains it any more, but I am very interested in everyone else's response also.


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## fmw (Mar 13, 2007)

In the old days, lenses had a depth of field scale. Surrounding the index mark on the lens barrel were colored lines in spread out in either direction. You could read the depth of field by choosing the colored lines that corresponded to your aperture and see the distances that would be in acceptable focus between them. Those are gone on most modern camera lenses. I can't tell you why. The current lenses have the same distance markings but do not have the array of colored lines. I have a kit lens that doesn't even have distance markings. You can use the distance markings to preset the point of focus but there is no longer an indication of depth of field.

Depth of field does extend beyond the point of focus about twice as far as it extends closer than the point of focus. If you want to set a hyperfocal distance at the far end of depth of field, then you can focus at the near point that you want in focus and the distant point and read the distances on the scale. 1/3 of the way into that range of distances would set the focal point to include the the distant part of the subject at the hyperfocal distance, assuming you have a small enough aperture to cover it. 

Since you no longer have a depth of field scale, you don't know what aperture will cover it, however, except by experience or by using the DOF preview feature on the camera. I'm pretty sure the author is explaining how to set the hyperfocal distance and probably trying to show you how to get along without the DOF scales by just stopping down as far as you can. I realize this is a pretty sketchy response because I didn't read what the author wrote but I hope it is pretty close to what he meant.


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## Torus34 (Mar 13, 2007)

It's possible to set up a DOF table of distances for any lens.  One site, and a table for a 50mm lens, is at:

http://www.dofmaster.com/doftable.html


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## jwkwd (Mar 13, 2007)

Pretty much what Torus had posted, just a different format: http://www.dofmaster.com/dofjs.html


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