Extension Tubes


Arthur Dent

Link Posted 01/10/2005 - 22:20
I have beeen researching extension tubes for my MX and *st D. Pentax makes "extension tube set B" but I get the impression that they don't have all the contacts to let the lens talk to the caera.

There is a well-regarded brand called Kenko whose tubes claim to maintain all functions (including autofocus, which I find a bit hard to beleive).

Has anyone here had experience with these brands of tube and what does each set actually allow you to do? I don't really care about autofocus but I'd like to use them with the excellent 100mm f/4 macro (that I bought from
George. Thanks, George, it's exactly what I wanted!). So any information would be appreciated. Thanks in advance!
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Kim C

Link Posted 01/10/2005 - 23:55
Hi Arthur,
None of the Pentax tubes have the electrical contacts though the 1.7x AF adaapter works very well as an extention tube .

I suspect the reason is the the electrical contacts are mainly for auto exposure. The depth of field is so critical that most use manual exposure as Pentax recommend. I haven't tried any independants as I always use manual settings usually with the LX. If you do intend to get one, I would try it very carefully first for compatibility.

Kim

Anonymous

Link Posted 02/10/2005 - 12:27
To retain full auto and program metering on the *istD you need extension tubes with seven electrical contacts. As there are no optics involved, non-brand tubes will be just as good as any others. I have a Jessops branded set which work fine. Be careful though: many extension tubes described as KA or KAF only have six electrical contacts and will not support auto/program modes on the *istD or some of the more recent film cameras. You can, of course, use any old K-mount tubes without electrical contacts, but you'll be restricted to manual exposure and stop-down metering.

I've not used any extension tubes which retain autofocus, but for macro work manual focus is pretty much essential anyway.

Steve

http://www.siblog.co.uk/
http://www.siblingmedia.com/

Arthur Dent

Link Posted 03/10/2005 - 14:58
I don't think it would be possible to transmit autofocuis through the tubes unless the motor is in the lens, which would make for some prettty costly lenses. But other functions, like metering, are useful since it avoids having to do calculations for exposure compensation because of the extension.

I beleive the Kenko tubes will transmit all data. They claim aurofocus, but that has to be for brands that use a motor in the lens.
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Kim C

Link Posted 03/10/2005 - 15:26
Arthur Dent wrote:
I don't think it would be possible to transmit autofocuis through the tubes unless the motor is in the lens, which would make for some prettty costly lenses. But other functions, like metering, are useful since it avoids having to do calculations for exposure compensation because of the extension.


Even with tubes that have no contats, you will still get the correct manual or aperture priority exposure without calculations. You only need to do this when using a hand held meter. All the Pentax cameras measure the light level either off the focus screen or off the film plane like the LX. You only need the contacts for shutter priority or programed exposure. Neither of these is very good for macro work.

Kim

George Lazarette

Link Posted 03/10/2005 - 23:16
My "auto" extension tubes have nothing more than the lever to stop the lens down, and I find them perfectly satisfactory.

G

MattMatic

Link Posted 04/10/2005 - 06:19
I had a set of Pentax extension tubes, but manual stop-down metering was a bit of a pain. So I ebayed them
Got hold of a cheap set of second hand "Teleplus" extension tubes which have the electrical contacts. This allows auto matrix metering, and all the other modes. Focus is manual, but that's no problem for macro work.
I also have the Pentax 1.7xAF adaptor, and have used this with the extension tubes for some seriously close macro work!
Matt

Kim C

Link Posted 05/10/2005 - 09:37
stevo wrote:
To retain full auto and program metering on the *istD you need extension tubes with seven electrical contacts. As there are no optics involved, non-brand tubes will be just as good as any others.
Steve


One point to bear in mind is that although there is no glass involved, the optics are still important. Depth of field and the focus plane is very critical in macro work and unless both faces of the tube are absolutely parallel, you will get degraded results. I did have a set of independant tubes and at the time was happy with the results. I came across a set of Pentax ones at a bargain price and got them mainly because the lengths matched the tables in The Pentax Way and so the calculations were easier. What did surprise me was that the results were much better. I may have had a rogue set and most independant tubes will probably be OK but it is worth checking.

Kim

Arthur Dent

Link Posted 05/10/2005 - 14:19
Well, I bought the Kenko set. It has seven contacts, plus the little stop down thingey so you can still use them on M cameras.

They're solidly built, the one thing I was worried about. But they are metal, and feel solid as anything. I think this is the best set available, not too cheap but you get your money's worth!
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