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10-15-2013, 05:22 AM   #1
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extension tubes

Are auto extension tubes available for Pentax K mount DSLRs from any vendor?

10-15-2013, 05:45 AM   #2
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yes, and they all work. The more expensive, the better the construction quality. estension tubes pentax
10-15-2013, 06:01 AM   #3
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QuoteOriginally posted by carrrlangas Quote
yes, and they all work. The more expensive, the better the construction quality. estension tubes pentax
Wow, the only one I could find on that list you posted was upwards of $500. That is a lot to pay for a set of extension tubes!
10-15-2013, 06:03 AM   #4
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?? this is the first one when you search "extension tubes pentax" Fotodiox Pentax K Macro Extension Tube Kit for Pentax K Cameras, Extreme Close-ups: Camera & Photo

10-15-2013, 06:38 AM   #5
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Just get a couple of cheap 2x converters and remove the glass. You are not going to need auto focus for macro, just get some with A contacts and aperture control. Also look on ebay for Vivitar AT-22 tubes, they have aperture control but no contacts, but hey manual all the way for macro is the way to go.
10-15-2013, 06:55 AM   #6
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QuoteOriginally posted by carrrlangas Quote
That is NOT an auto extension tube set. As far as I can see from the pictures on the site there are no electrical contacts at all. And it doesn't look like there are tabs to support step down metering either.
I would like to repeat what another poster said regarding auto focus, it is much easier to get good macro shots with manual focus because then you can chose what's in focus rather than letting the camera do it. Unless you use focus stacking (and you need manual focus there too) the key to macro photography is not only what's in focus but what is OOF.

NaCl(look for electrical contacts on any ext tube set you buy)H2O
10-15-2013, 08:57 AM   #7
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For extension tubes "auto" usually just means that there is a linkage to the lens's diaphragm actuator. On a Pentax DSLR such tubes will only work with lenses with aperture rings, and then with the usual restrictions for M-type lenses (stop-down metering only, etc.). These tubes are easy to find used, on eBay or from used camera stores such as KEH.

A-type tubes, i.e. with the diaphragm actuator plus the 6 electrical contacts the tell the camera the aperture range of the lens, are much rarer. As bluestringer says, you can convert A-type 2x teleconverters to A-type tubes by removing the glass. This operation is easier on some tubes than others. There are some proper A-type tubes out there, but are very hard to find.

Extension tubes with autofocus are rarer still; AF isn't generally useful once you put a lens on extension anyway.

Sorry if you knew all this already, but "auto" naturally causes some confusion.
10-15-2013, 10:30 AM   #8
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Auto means different things to different people. The most common seems to be simply having an auto diaphragm linkage and an aperture lever (the latter useless on DSLRs since they don;t use it).
That will let you do stop down metering (green button) and also avoids the inconvenience of stopping down manually by turning the aperture ring just before shooting. BUT you cannot use lenses that don't have an aperture ring as you will end up shooting with fully closed aperture. In fact even just switching to live view will fully close the diaphragm.

Next step up you will have contacts so that the lens can relay its focal length and aperture details to the camera. That gives you auto exposure, assuming of course that your lens also has the contacts.

Then you can get tubes having also the screw drive for AF - but as already mentioned that is not much use anyway as with tubes the lens's focus range is very limited and in any case the AF sensoir will probably not work anyway due to the effective reduction of aperture. If I'm not mistaken an F2.8 50mm lens with a 50mm extension tube becomes F8 or thereabouts with the result that there is not enough parralax for the AF sensor.

The auto diaphragm linkage on extension tubes is often troublesome if you mount more than one tube. Each tube adds friction and inertia which will easily slow down or even stall the actuator. The result will be erratic exposure. You can probably mitigate it somewhat by using the 2 second timer with mirror lockup if, as I think, the aperture lever is actuated on mirror lift rather than just before opening the shutter. I also don;t like using extension tubes with the linkage because I think it wears out the actuator mechanism in the camera.

As for myself whenever I use extension tubes it is with a reversed lens so the auto diaphragm lever is of no use anyway. For 'normal' macro shots I use a Tamron 90mm and only use extension tubes when I need more than 1:1 magnification and for that I use old lenses with the aperture ring which I set to full open while focusing and composing and then close to the required aperture just before shooting. I have managed to get some very high magnification images with an old K-mount 28mm F2.8 and 150mm extension tubes.

I think if you want to get the full benefit out of extension tubes then you really should be using them with a reversed lens, which means also that any any linkages or contacts will be of no use. The only important thing you need to consider in an extension tube is that it is a good tight fit with no looseness, and that its interior has a good matt black coating to avoid reflections. Even the slightest reflectivity inside the tube will severely degrade the contrast, the effect being worse at high magnification.

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