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Forum: Pentax SLR Lens Discussion
04-23-2011, 01:23 AM
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And that's another point -- I didn't mention it above because 1) I'd written about it on other threads and 2) I got lazy. Yes, all camera lenses (that aren't utter trash) gain flatfield sharpness when reversed. The PRO: All that sharpness, for no extra money! The CON: Working distance for primes is around 4.5cm, under two inches. That's OK for studio shooting, but kinda cramped for field work. Bother.
But wait! There's more! Reversed zooms act a bit differently. I diddled-around the other day with my lowly A35-80, arguably one of the crappiest lenses Pentax ever sold. I reversed it, using a simple 49mm-PK mount-reversal ring. At 35mm it reaches 2:1 magnification at about 5cm distance. At 75-80mm it focuses out past infinity, and reaches 1:2 down at about 15cm distance. And it is quite sharp, reversed! A bit of fringing at extreme high-contrast edges, but otherwise pretty decent.
And that's with a crap lens. Better zooms should give better results. So I tried my Promaster-Tamron 28-70 (FF-AF) on a 58mm-PK reversal ring plus 52-58mm step ring. It didn't reach infinity focus at 70mm -- that step ring adds enough extension to pull far focus down to about 27cm -- but I don't see any fringing! I also tried a couple older push-pull zooms, but they are sloppier to use than more modern zooms with separate zoom rings. Just make sure your zoom has an aperture ring, and it'll make a dandy macro lens! As with any lens, more extension gives more magnification.
NOTE: You can use CIF (catch in focus) with mount-reversal rings. Don't try the metal tape trick. The tape adds enough thickness to jam the adapter on the camera mount. Instead, scrape or file away the adapter's black paint in the appropriate location, to safely short the contact pins on the camera mount. And where is that location? Just opposite the red dot (index mark). Looking at an adapter: With the red dot at 12-o'clock, remove paint between 5-6-o'clock.
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Forum: Pentax SLR Lens Discussion
04-22-2011, 11:55 AM
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To summarize a bit: Real macro camera lenses are usually exceptionally well-built, and are designed for edge-to-edge flatfield sharpness. Virtually NO "macro-zooms" meet those criteria. Many non-macro camera lenses also don't qualify. If your subjects are rounded, and/or edges aren't critical, then no matter. If you're shooting postage stamps, microcircuits, other flat stuff, then it matters.
Macro camera lenses --
PROs: Construction, image quality, ease of use (aperture automation and flash, etc).
CONs: Money, money, money; macro camera lenses aren't cheap.
Camera lenses on extension --
PROs: Flexibility. And money, money, money; simple extension is cheap.
CONs: Money, money, money; fancy extension isn't cheap.
You could mount an AF lens on AF tubes (or de-glassed AF teleconverters). Those aren't cheap, and AF isn't necessary with CLOSE macro work. You could mount AF or A-type lenses on cheaper A-type tubes or deglassed A-type TC's. Either of those options retains aperture automation and thus allows stopped-down metering and shooting, and easy flash.
You could mount any lens with an aperture ring on cheap simple tubes or bellows. Or even lenses without aperture rings, if you don't mind shooting wide-open. These include camera lenses, enlarger and projector lenses, or any optical material that will fit. I like cheap enlarger lenses (EL's) for their edge-to-edge flatfield sharpness, and cheap projector lenses and lenses scavenged from old medium-format cameras for their character.
So, a great advantage of tubes (or bellows, for more flexibility) is that you're not limited to the constraints of an expensive macro lens. You can use good camera lenses close-up. Some cheap lenses are legendary here, such as the Industar-50/3.5. You can use whatever cheap lenses you have. If they are enlarger lenses, you'll get results no worse than expensive camera macro lenses. You just need to take responsibility for the lighting.
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