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EXTENSION TUBE ( Autofocus Extension Tube for Pentax?)

R Togog , Dec 03, 2007; 11:44 p.m.

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

Responses


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Matthew McManamey , Dec 04, 2007; 12:04 a.m.

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.

Johannes Borgström , Dec 04, 2007; 03:37 a.m.

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.

Nick White , Dec 04, 2007; 07:17 a.m.

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.

Kari Vierimaa , Dec 04, 2007; 07:40 a.m.

One more: AF in macro work with extensions doesn't feel useful, it's more likely to be annoying if works at all.

Deb Mayes , Dec 04, 2007; 01:10 p.m.

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.

Chris Kresser , Dec 04, 2007; 11:14 p.m.

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.

Tommy Lee , Dec 05, 2007; 12:43 a.m.

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.

Chris Kresser , Dec 05, 2007; 10:26 a.m.

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

Chris Kresser , Dec 05, 2007; 12:52 p.m.

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.


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