 Stephen |
Understanding Depth of Field Better I was using my lens on my camera to determine what is the best depth of focus to use for shart images, and here is what I have came up with, so if I am wrong let me know, if I am right let me know, because I want to get the best possible landscape pictures possible for my vacation. If I was focusing on something about 16 feet away, I would set my apeture to f/16, instead of f/22, or f/32 to get the sharpest results. If I was focusing on a main subject between 8-12 feet away, I would set my apeture to f/9.5 (my camera has that setting :D). Am I right so far? Another question I have is, when I use the depth of field preview, the screen is either dark, or bright, and it seems the smaller the opening the darker it is, so how do you determine how much of the final shot is going to be in focus. Please help me.
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Jeff S. Kennedy |
As to the first part of your question, it all depends on what lens you are using. As far as DOF preview the more you stop down, obviously, the darker the image in the view finder. You can see the actual DOF but the darker it gets the harder it is to see. It's just something you have to get used to. Learn to use the DOF scale. It is pretty accurate.
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Jon Close |
With respect to your first question, it sounds as if you're confusing the way the f-number is used. For flash photography, the maximum useful range of the flash is determined by it's Guide Number divided by the f/stop. In the case you're describing where you want sharp images and great depth of field, the proper f/stop is not directly related to the subject distance. In general a lens's peak sharpness and contrast will be at 1-2 stops from maximum aperture, regardless of the subject's distance. For an f/2.8 lens that would be at f/4 or f/5.6. For an f/3.5-4.5 zoom that would be at f/5.6 or f/8. Maximum depth of field is acheived at the smallest apertures. However, the smallest apertures introduce diffraction errors. If you want both great depth of field and sharpness you (in general) would not use an aperture smaller than about f/8 to f/16. On Kodak's Web site, there are explanations on setting the aperture for maximum sharpness and getting maximum or minimum depth of field and determining the hyperfocal distance.
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John A. Lind |
The second URL has an interesting method for finding the hyperfocal distance on lenses that have DOF markings, with a good example to show how it works. If you use lens DOF markings, be aware that you are relying on the lens maker's definition of the maximum diameter for the "circle of confusion." This determines where the boundaries lie for the front and rear of the DOF. A smaller allowable circle of confusion will narrow the DOF markings and a larger one will make them wider. A miniscule point in space that is out of focus on film will create a circle, not a point. The more out of focus the point is, the larger the circle on film. This is a "circle of confusion." The maximum circle of confusion is is how big a point can be on the film before it can be detected as being out of focus in a print by the average human viewing the print from a normal distance (for the print size). Because it is established using "average humans" and "normal print viewing distances" the exact CofC value is somewhat subjective. For 35mm film, I have seen definitions for the maximum circle of confusion range from 0.025mm to 0.045mm. I use the conservative 0.025mm for building hyperfocal distance and DOF tables. When I first noticed seeming differences between camera lenses and various books a spreadsheet revealed the following: CofC camera/lens/book What does all this mean? -- John
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