[grandit]

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I am trying to figure out how to remove the glass in a Pentax Rear Converter - A 2x-S without wrecking the lenses. It seems that there are two parts to the glass assembly, nested together and I can unscrew the outer piece from the inner piece but can’t do anything with the inner piece. I have not attempted to dismantle the entire thing as I figure there must be a simple way to do this and of course I expect that there are a lot of small parts that may go flying if I try to dismantle the whole thing. Ultimately I want o be able to put it back together to use as a converter. I am doing this to use it as an extension tube.
Any help would be appreciated!

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Last edited by grandit; 03-18-2022 at 08:21 PM. Reason: Did not finish the post the first time

[pepperberry farm]

I am trying to figure out how to remove the glass in a Pentax Rear Converter - A 2x-S without wrecking the lenses. It seems that there are two parts to the glass assembly, nested together and I can unscrew the outer piece from the inner piece but can’t do anything with the inner piece. I have not attempted to dismantle the entire thing as I figure there must be a simple way to do this and of course I expect that there are a lot of small parts that may go flying if I try to dismantle the whole thing. Ultimately I want o be able to put it back together to use as a converter. I am doing this to use it as an extension tube.
Any help would be appreciated!

would it not be simpler to just buy an extension tube?

[luftfluss]

would it not be simpler to just buy an extension tube?

Are there readily-available extension tubes that have auto-aperture capability?

[pepperberry farm]

Are there readily-available extension tubes that have auto-aperture capability?

I thought there were some available:

^ Vivitar 2x Macro Focusing Teleconverter MC For Pentax K Mount [EX+++] | eBay

https://www.ebay.com/itm/384775797056?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=...53.m1438.l2649


(or am I missing the point?)

[luftfluss]

I thought there were some available:

^ Vivitar 2x Macro Focusing Teleconverter MC For Pentax K Mount [EX+++] | eBay

[Exc+5] Kenko 2X KAX Macro TELEPLUS MC7 Teleconverter Pentax K Mount From JAPAN | eBay


(or am I missing the point?)

What you're pointing to is a teleconverter, though, not an extension tube... although I'd probably rather disassemble the Vivitar than the Pentax A 2x-S.

[pepperberry farm]

then I'm misunderstanding those two advertisements - they both claim 'macro-focusing' and have the contacts on the mount for auto-aperture control, etc....

[luftfluss]

then I'm misunderstanding those two advertisements - they both claim 'macro-focusing' and have the contacts on the mount for auto-aperture control, etc....

If you look at the product photos, you can see there is glass in there, so that will degrade the image. No glass in an extension tube.

But maybe these things would provide greater magnification than similarly-sized extension tubes...?

Last year I was looking for an extension tube with "A" capability for my Tamron 180/2.5 63B, couldn't find one but managed to snag the Adaptall extension tube intended for the 90/2.5 Macro, so now my 63B also does 1:2 close-ups

[Joetitch]

There are a few different brands of ext tubes with "a" contacts.
Mine are Teleplus.
Some have AF in their names but this doesn't mean auto focus. It means they have the aperture follower function for non crippled mounts.

[UncleVanya]

Don’t dismantle the 2x-s it’s pretty high quality - although 2x is a bridge too far often. Try to get the Takumar 2x A series, they are cheap. I have one already deglassed and another is stubborn and I need to get my spanners out to remove the glass.

[grandit]

Thank you all for the replies. Extension tubes are a strange new world for me and all I am trying to do is to get one with auto exposure as I am launching into digitizing all of my favourite old film negative with my DSLR and need to bring the focus point much closer to the lens. I cannot find any tubes with KA mounts anywhere but I can find a Tokina 2x KA teleconverter at a reasonable price and from what I can see on DPReview is the glass on these ones can be removed without too much fuss. I shall keep my Pentax teleconverter in one piece.

[kypfer]

For a relatively repetitive job like negative digitising, once the kit is set up and calibrated, a set of totally manual tubes, albeit with at least an aperture linkage, should be perfectly adequate.
Set the camera in Manual, close down a stop or two to eliminate any slight mis-focussing, (Catch in Focus will help here) and just use the Green Button to fine-tune the exposure as needed.
FWIW, my auto tubes are Kenko branded, with a full set of 7 Pentax AE contacts (and a non-problematic Ricoh pin), but no a/f linkage or power contacts, also a Super Paragon branded set with no contacts at all.

[dtrego]

The Kenko Pz-AF Uniplus extension tube has all the contacts (including the two for power zoom/SDM inside the barrel), screw drive, and aperture lever - but they very rarely come up for sale. I've been watching for one for at least a couple of years on the big auction site, local stores, craigslist, etc., and finally snagged one this past week.

Kenko Pz-AF UNIPLUS TUBE 25 reviews - Pentax Camera Accessory Review Database

[grandit]

For a relatively repetitive job like negative digitising, once the kit is set up and calibrated, a set of totally manual tubes, albeit with at least an aperture linkage, should be perfectly adequate.
Set the camera in Manual, close down a stop or two to eliminate any slight mis-focussing, (Catch in Focus will help here) and just use the Green Button to fine-tune the exposure as needed.
FWIW, my auto tubes are Kenko branded, with a full set of 7 Pentax AE contacts (and a non-problematic Ricoh pin), but no a/f linkage or power contacts, also a Super Paragon branded set with no contacts at all.

Thank you kypfer. That’s a logical approach and the light bulb finally went on! As usual simple is best.

[UncleVanya]

For a relatively repetitive job like negative digitising, once the kit is set up and calibrated, a set of totally manual tubes, albeit with at least an aperture linkage, should be perfectly adequate.
Set the camera in Manual, close down a stop or two to eliminate any slight mis-focussing, (Catch in Focus will help here) and just use the Green Button to fine-tune the exposure as needed.
FWIW, my auto tubes are Kenko branded, with a full set of 7 Pentax AE contacts (and a non-problematic Ricoh pin), but no a/f linkage or power contacts, also a Super Paragon branded set with no contacts at all.

With an aperture ring… Without an aperture ring this won’t work as the camera can’t control aperture.

[kypfer]

With an aperture ring… Without an aperture ring this won’t work as the camera can’t control aperture.

Sorry, yes, my oversight … if there are no auto-exposure contacts on the extension tubes you will need a lens with an aperture ring, though this could even be an old M42 lens, (+ suitable adaptor), in which case even the aperture linkage would be redundant and one could use a set of the really cheap tubes … probably somewhat cheaper than the usual selling price of fully-auto tubes