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Re: How to determine DOF
In reply to Hugowolf,
3 months ago
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Hugowolf wrote:
Seems more likely to be due to changes in the actual focal length of the lens at MFD. Any significant change in actual focal length will change the relative aperture. The only lens for which I have measured this is the Canon 100 mm f/2.8 USM macro lens. At MFD it has a focal length of 68 mm, so the reported f-stops are way off.
Brian A
You might be on to something here. Your macro does that to avoid too much extension ("internal focus"), these are normal lenses that aren't concerned with that. Magnifications in this case are about the same (about 1:6) but will have to think about this.
Thanks!
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