How can I estimate how far back to move and crop to increase depth of field?
Asked 5/23/2012
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2 answers
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I’m photographing close-up subjects and my depth of field is too shallow. Since the images are only for web use, I’m considering stepping farther back and then cropping instead of shooting so close.
For example, if a subject fills the full 4000 px image width at one distance, but I only need that subject to end up about 640 px wide in the final image, how should I estimate how far back to stand? Is there a practical rule of thumb for this, especially for close-up work?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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Why work so hard? I think you are making this much harder than it has to be.
Getting something to be exactly 640 pixels in the image will be difficult, require careful measurements and accurate calculations and is very error prone (and for something really close the internal construction of the lens makes a huge difference and this will be impossible to calculate)
But Getting something in the ballpark with a nice safety margin and than downscaling the rest of the way is ridiculously easy.
just move back until the subject covers approximately 1/3 of the frame than crop and after that downscale the rest of the way.
Why 1/3? You want 640px out of 4000, that is approx 1/6, I want to make it a little bigger to be on the safe side and 1/3 is really easy to judge by eye compered to 1/5 or 1/4.
At that distance hopefully you already solved the DOF problem - and even if the image is still a little bit blurry downscaling will make it less blurry.
By the way, the fact that downscaling reduces blurriness also let you use a smaller aperture, the blur caused by diffraction will be reduced.
Originally by user2481. Source · Licensed CC BY-SA 4.0
user2481
14y ago
0
Generated from our catalog & community — verify before relying on it.
For close-up work, an exact distance calculation is often unreliable because lens behavior at short distances can vary, especially with internal focusing. A practical approach is easier and safer:
- If the subject fills 4000 px now and you only need about 640 px, you need it to occupy much less of the frame.
- 640/4000 is about 1/6 of the frame width.
- In practice, don’t aim that tightly. Move back until the subject covers roughly 1/3 of the frame width, then crop and downscale the rest.
That gives you a safety margin and is much easier to judge by eye than trying to hit exactly 1/6.
If your real goal is more depth of field, the better method is to use a depth-of-field calculator and choose a camera-to-subject distance that gives you the depth of field you need, then crop as needed for the final web image.
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