Help. Aside from photo stacking how do I get more in focus

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Originally Posted by DanK

That's not all there is to it.

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I disagree. That's all there is to it when taking into account the context that Brian requested we take into account. If we throw in a lot of other requirements and parameters into consideration, that then becomes a completely different subject for discussion. You're contemplating Brian's need to enlarge the subject when he didn't explain that need. Even so, as Grahame and I explained, the subject can still be enlarged subject to the limitations already mentioned in previous posts.

As I understand it, the maths is the following. Unless the magnification is quite large, the DOF is approximately inversely proportional to the square of the magnification. This means that if you move back to twice the distance, you increase the DOF by a factor of 4. If you now crop and enlarge by a factor of 2 to bring the subject back to its original size, you double the blurring. The net effect is thus an effective increase in the DOF by a factor of 2.

That's interesting, Tony! I don't remember ever seeing that explanation. On the other hand, when you explain the same thing two months from now, I'll probably mention that I don't ever remember seeing it. :D

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Originally Posted by rpcrowe

I expect that your point of focus was about 1/3 of the way into the flower...

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http://i63.tinypic.com/e5i4pv.jpg

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Originally Posted by Mike Buckley

I disagree. That's all there is to it when taking into account the context that Brian requested we take into account. If we throw in a lot of other requirements and parameters into consideration, that then becomes a completely different subject for discussion. You're contemplating Brian's need to enlarge the subject when he didn't explain that need. Even so, as Grahame and I explained, the subject can still be enlarged subject to the limitations already mentioned in previous posts.

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I try to crop to no less than 1600 and then scale to 1200. I can't remember up-scaling.

Mike--if Brian were to move back, the image flower would constitute a smaller share of the frame. Cropping to get the same framing magnifies the cropped area, if the image size on the screen is held constant. I wasn't adding anything more.

Tony--This is helpful, but I am still puzzled. Again, assume that one keeps the image to be the same fraction of the frame. One is magnifying by cropping exactly the same amount one is reducing by moving back.

So I am still puzzled. I suspect that the key is the different AOV in the two cases, but I haven't sat down to read more and then try the math.

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Originally Posted by JBW

I try to crop to no less than 1600 and then scale to 1200.

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Was the image of the rose 1600 pixels across? If it was not, you could have backed back a little to have a bit more DOF. If the cropped image was already about 1600 pixels, there is not much room for manoeuvre.

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Originally Posted by DanK

So I am still puzzled. I suspect that the key is the different AOV in the two cases, but I haven't sat down to read more and then try the math.

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Tony is spot on with his explanation. This is just a property of DOF. You double the framing, the DOF goes up by a factor of 4.

Same thing in portraiture. If a half-body shot has DOF of about a foot, a full-body shot at the same aperture will have DOF of about 4 feet.

Unlike portraiture, when you shoot macro close to the diffraction limit, by moving back and using a tighter crop you might deteriorate the overall sharpness of the image. I wonder if it would be better for Brian, instead of scaling down from 1600 to 1200 pixels, open up aperture to say f/11 and step back even more so the final image does not have to be scaled down.

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Originally Posted by dem

Tony is spot on with his explanation. This is just a property of DOF. You double the framing, the DOF goes up by a factor of 4.

Same thing in portraiture. If a half-body shot has DOF of about a foot, a full-body shot at the same aperture will have DOF of about 4 feet.

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But this example also includes cropping to return the framing to the original, hence magnifying more.

I think the answer dawned on me. stepping back and then cropping to get the same framing is equivalent to capturing the image with a smaller sensor, which does increase DOF. In the case of FF and 1.6x crops, the difference is about one stop, if I recall.