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09-06-2010, 10:20 AM   #16
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Whether there is an aperture ring or not is immaterial. To prefocus any lens with a distance scale, you line up the desired distance on the scale with the center line just below the distance scale. It's as simple as that.

The numbers that may or may not be present to either side of that center line are the DOF scale, and they have nothing with how one actually sets the focus. Those numbers are there just to tell you want the DOF would be, and that can be useful information if you are trying to figure out what aperture to use or what focus distance to use. But if you already know what aperture and focus distance you want, I can't why you'd care to find out what the lens tells you DOF would be. Of course, that does beg the question, *how* did you figure out what aperture and focus distance you want? I guess if it's because Peterson said to use some particular aperture and focus distance, that's useful as a starting point, but that's about all I'd take it for.

09-06-2010, 10:50 AM   #17
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QuoteOriginally posted by yoon395 Quote
Hello all,
I had a question regarding front to back sharpness for a landscape photograph. I'm reading Understanding Exposure by Bryan Peterson and see him continually referring to "presetting the focus via the distance settings on the front of the lens" while using an f/22 aperture to ensure sharpness from a few feet out to infinity.

What exactly is meant by presetting the focus via the distance setting? Is this a feature with particular lenses? I have my Pentax K-x kit lens and a Pentax-A 50mm/1.7 and can't seem to figure out what he's referring to.

Any other tips for front to back sharpness would be appreciated.

Thanks!
You are describing what is know as 'Hyperfocal Distance' used mainly in landscape photography. Easier to demonstrate than explain. When you focus on a subject, a third of the scene in front will be in focus, while two-thirds behind will also be in focus - the point of focus is known as hyperfocal distance. focusing here will give you the maximum possible depth of field. This is best achieved in manual focus of course.
There are charts that offer the hyperfocal distance for a given focal length at a specific aperture, but manually focussing a third of the way into a scene will give you the maximum depth of field.
09-08-2010, 01:30 PM   #18
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I've played around with manually pre-focusing, using Peterson's tips, and just using autofocus, and it's really hard to tell the difference. Is manually focusing landscapes by using infinity focus with a point 1/3 of the way into your picture really the best way to take a deep landscape shot? Or can you achieve the same result by using autofocus and just picking a point 1/3 of the way into the picture, with an f-stop of 11 or 16? Or would you focus on the infinity point in your picture?
09-08-2010, 04:33 PM   #19
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There would be no difference whatsoever between manually focusing 1/3 of the way in and autofocusing 1/3 of the way in - focus is focus. As for aperture, you should see a pretty clear difference between f/11 and f/22. Not at the point where you focused, but in the extreme foreground and extreme background. You'd probably have to view pretty large to notice, though.

I also focus on something in particular - I never just aim 1/3 of the way in and take whatever I get. If I can't identify a center of interest in a scene that I'd like to focus on, I find it's not worth taking the picture.

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