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Forum: Pentax SLR Lens Discussion
04-23-2011, 04:11 AM
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Here's a trick you can use to position the kit lens aperture where you want it for macro work: use a short piece of plastic or rubber tubing over the aperture lever. Friction between the tube and the aperture lever protection shield will hold the aperture in place. Then you can focus with the lens wide open & close it down a bit for the exposure to get better dof & image quality.
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Forum: Pentax SLR Lens Discussion
04-23-2011, 02:21 AM
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I have seen no evidence that a lens designed and and marketed as a macro lens performs any better that a good prime lens on a tube for macro photography of natural subjects.
If such evidence exists I'd love to see it!
The "for macro photography of natural subjects" qualification is as important as the "I have seen no evidence" qualification. There is a really good chance that field flatness issues may be an important distinction between high quality special purpose macro lenses and regular lenses used for macro work; even so it hardly matters for non-flat subjects because depth of field is so thin that natural (non-flat) subjects will be out of focus at the edges regardless of lens field flatness.
RioRico makes a reasonable case that reversed lenses may have better flatness characteristics for macros because the subject will be positioned where the lens designers thought a flat film plane would be. However, those same lens designers also assumed the flat image requirement was needed when the subject was quite far from the lens - certainly not as close to the lens as in the case of a reversed lens.
Pacerr addresses the same flatness issue well.
Flatness will be an important issue for certain subjects like integrated circuits, stamps, ground & polished technical materials etc. If flat subjects are of interest to you then perhaps you should think about seeking lenses designed for the purpose.
This forum has a long thread showing superb macro images taken with Raynox brand close-up adapters on a variety of lenses. See: https://www.pentaxforums.com/forums/lens-clubs/74221-raynox-macro-club.html here's an example http://img41.imageshack.us/img41/3838/004sb.jpg
But here's a test that looks at the effect of the Raynox 150 lens on the flatness and sharpness at the edges of the field when it is on a good macro lens (without the Raynox the edge-edge focus is excellent):
As you can plainly see the poor edge definition probably caused by the Raynox for the Bee photographer had no practical effect on the image of the Bee shown above.
In conclusion I think the tube/prime lens approach may work as well as a dedicated macro lens for natural 3D subjects but maybe not for flat subjects.
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