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Archibald wrote:
I had a look at a couple of my Canon lenses with and without the Canon 500D closeup lens. Just from peering in the front, the entrance pupil appears to increase with the supplementary lens when using my Canon 100mm and 55-250mm lenses (the 55-250 at 250mm). The increase with the 100mm is marginal. It is hard to judge, though, and maybe I'm not determining the property correctly. I'm thinking that once everything has been taken into account, that the increase might be quite small.
At any rate, even if we assume no change in the entrance pupil, the shortening of the focal length will give the combo a lower f number.
The upshot is that when using a closeup lens, the effective aperture becomes bigger. So one should stop down more for equivalent DOF and diffraction....Show more →
Thanks. I'm happy to let you work with those issues. When it comes to a given shot, I work empirically, adjusting the aperture to get an appropriate DOF in the viewfinder. A numerical value of some sort is a useful reference:
a) To inform the viewers of the final image
b) For me to reproduce or alter the DOF in future images
Any small diffraction effect can be dealt with by PP software.
If an effect such as you suggest exists when using the Raynox in a given situation, there is nothing I can do about it. Awareness of it is something I can take into account when my chosen aperture seems not to give the DOF I expected.
It remains to be seen whether the MSN-202 is the best tool I have for photographing less-static subjects and/or larger ones. In macro in general, I like to give myself plenty of working distance, which some of my other lenses can offer but at the loss of full aperture framing and focusing.
Harold
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