EXTENSION TUBE ( Autofocus Extension Tube for Pentax?)

Discussion in 'Pentax' started by rtogog, Dec 3, 2007.

  1. Hi, Any one here use AF Extension Tube? Is it valuable item for macro phothography? Does Pentax make it? I like to find one from third party but still can't find one. Many thanks, RTogog
     
  2. I have never seen such an animal. Macro photography with tubes or bellows is a very delicate setup and usually requires a tripod or some other type of bench anchor. DoF is so thin when doing this it is EXTREMELY difficult to maintain focus handheld. Stopping down the lens to improve DoF usually gets you to a shutter speed that you can't hand hold either. The point is, by the time you get everything else set-up, AF is no real advantage. In fact, you'd be more likely to get mad at the AF and turn it off anyway.
     
  3. I don't know of any AF extension tubes for in-body AF motor systems; they do exist for Canon EOS. Having used them, I agree with Matthew.
     
  4. Kenko (Teleplus) make a set for Pentax AF - http://www.warehouseexpress.com/?photo/camextens/kenko.html#PC304510 I have a set of these in Nikon mount. They don't get used very often since I also have two macro lenses. As others have said you will probably want to focus manually most of the time; the AF is however very useful when you use them to alter the close focusing ability of longer lenses.
     
  5. One more: AF in macro work with extensions doesn't feel useful, it's more likely to be annoying if works at all.
     
  6. dkm

    dkm

    Kenko work fine, especially the PZ-AF 25. I use mine with my 100mm 2.8 macro lens. As for how useful it is, it depends on what you shoot. Since it's also useful for closer focus on longer lenses, as noted above, it's handier than you might think.
     
  7. bdb

    bdb

    How funny, I just came to the forum to ask a question about extension tubes. Mine is a bit more specific: I know that extension tubes reduce the minimum focusing distance of a lens, but they also reduce the maximum focusing distance. However, I can't find any information about HOW MUCH the maximum focusing distance is reduced with each tube (12, 20 & 36). Does anyone know? I have an FA77 and sometimes I'm frustrated by the minimum focusing distance. I shoot portraits with it, and I'm wondering what the minimum and maximum focusing distance would be with the 12mm extension tube.
     
  8. I don't have a 77mm FA to check maximum distant for you. For what you what to do, you may want to check out a pentax T183 close up lens instead (step down to 49mm from 52mm). Your maximum working distant would then be 1.82 meters and allow you to focus closer for a tighter portrait.
     
  9. bdb

    bdb

    Tommy, Thanks for the tip! That sounds much better for my needs. Where would I find one of those? And do you know what the minimum focusing distance would be with such a lens? Does is degrade the IQ of the lens it's used on? Thanks again, Chris
     
  10. bdb

    bdb

    Okay, I found this description of the Pentax close-up lenses: http://kmp.bdimitrov.de/misc/macro/index.html I don't see how the T183 would help me, because according to the link above the minimum focus distance with that lens would be 42 inches. That's larger than what the FA77 is normally! However, the T80 would apparently give me a minimum focusing distance of 19 inches and a maximum focusing distance of 36 inches. That's a pretty narrow band of working distance, but I guess that's how close-up lenses work? Thanks for your help.
     
  11. I have the Kenko late model and it works fine on film or digital bodies. It is only 1 ring but it covers an acceptable area for my use.
     
  12. bdb

    bdb

    Jeff, Do you have the 12mm or the 25mm ring?
     
  13. Hello, Is KENKO AUTO EXTENSION TUBE DG SET (12,20 & 36 mm) for Prntax have an auto fucus capability? I read on other forum, some of Kenko Telepluss DG (1,5X or 2x)are used for macro works with macro lens (Pentax DFA 50 or DFA 100) . Is it not degrade the quality of images compare with dedicated Extension Tube? Kenko also offer KENKO UNIPLUS TUBE 12 & 25. What are the main different compare with Auto Extension above other? Thanks, RTogog
     
  14. Unlike a macro (e.g.: FA100/2.8) lens, which give you a contineous focus range from infinity to 1:1 (~12 inches). Close up lens and extension tube just move the max to min focus range closer. For example, on a 85/1.8, it's normal focus range is infinity to .85m (32 inches). By puting a T183 (+0.55 achromat) on it, it became (183cm + lens to sensor) ~6.5 feet to 26 inches. This is a gain of about 7.5 inches closer while still maintaining a workable close portrait focus range. You can of course get closer with a +2 achromatic (ie. Canon 500D), but your focus range now become 1.6 feet to 17 inches. This mean you will have to take your close up lens on and off while you switch between portrait to tight close up focus range. The 85mm + 500D combo will also have a non-focusable hole between ~33.5 inches (the minimum of the 85/1.8 without the +2) to 24 inches (the max of a 85/1.8 when a +2 close upis attached). A 12.5mm extension tube will woek also. It will yield a much smaller non-focus able gap but still have the issue of having the need to take the tube on and off when the focus distant transit accross the ~29" focus point.
     
  15. On" Does it degrade the IQ of the lens it's used on?" Pentax's T183 is a high quality dual element achromatic close up lens. On my copy, the center degrade very very little. The corner as with any close up lens will soften a bit when use wide open. This should not be an issue with portriat application. To me, it is actually a plus.
     
  16. bdb

    bdb

    Tommy, Thanks for your replies - they are much appreciated. Do you have any tips on where to find a T183 lens? I've searched high and low and can't locate one anywhere.
     

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