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Photography Question 
Bob P. Grattan
 

Macro shots


I own a Canon 35mm EOS Rebel S. When using my close-up (+1, +2, +3) lenses to do close-up shots like the center of a flower, the depth of field is shorter than I wanted it to be. How can I get it to be longer as I've seen in some other macro shots of a similiar type.

Thanks,
Bob


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8/8/2002 8:19:25 AM

 
Jon Close
BetterPhoto Member Since: 5/18/2000
  With all lenses, the DoF shrinks with closer focus. To get greater DoF you need to set a much smaller aperture (higher f-number).

You can use the Near Field/Far Field Focus calculator at
http://www.outsight.com/hyperfocal.html
to determine the f-stop you need to set to get your desired DoF with your lens.


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8/8/2002 10:28:29 AM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Bob,

Jon's generally correct about using a DoF calculator. However, don't consider the answers you get from them to be highly accurate at very close macro distances. These calculators are generally intended for distances at least 7-8 times the focal length of the lens. Their math tends to lose accuracy at very close focusing distances.

The primary problem is definition of "focus distance." Is it to the front of the lens? Is it to the film plane? Is it to the rear lens node? All three are different locations, and at extremely close distances the differences among them become significantly large. There are secondary issues as well, including the DoF model's definition of the acceptable circle of confusion diameter, which directly defines where the DoF boundaries are. A proper DoF model will either allow the user to set these, or will explain what they are as assumptions. Take what you get from them as a starting guideline and work from there. It's been my experience any errors from the models are in the direction of showing more DoF than what is realized in the photographs. If the model shows it's very close or not enough, it's not enough.

Jon is very correct about needing to use tight apertures. Some recent photographs of african violets made on 35mm film were about 2/3 life-size _on_the_film. I shot them at f/11 and f/16. For me, the "eyes" of a flower are the anther and stigma (pollen bearing pods and small stem in or near them). For frame-filling photographs of a single blossom I set critical focus on them and work to get the DoF to encompass the petals.

-- John


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8/11/2002 8:41:25 PM

 
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