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04-22-2009, 02:57 PM   #1
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Pictures showing how to convert a TC to an ext.

Extension tubes with A contacts are rarer than hen's teeth, some of us are converting old cheap (~$25-35) TC's into ext. tubes. These are identical to the TC's sold as ext. tubes.

I had to destroy the first one trying to pry open the whole thing, but now I have learned the proper technique and it is as easy as unscrewing the center element.









Hope this helps.

04-22-2009, 03:16 PM   #2
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Wow, cool!

Will this method work with any TC, ex: Tamron 1.4x, or Vivitar Macro 2x TC ?

Now, how is the photo looks like without the glass element? Will it be the same or even better?

Thanks again.
04-22-2009, 03:25 PM   #3
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QuoteOriginally posted by HermanLee Quote
Wow, cool!

Will this method work with any TC, ex: Tamron 1.4x, or Vivitar Macro 2x TC ?

Now, how is the photo looks like without the glass element? Will it be the same or even better?

Thanks again.
It should work with all types of TC's, I have tried three differnet brands including vivitar. However, the 2X TC's will give you a 25mm ext. tube, where as the 1.4's would be narrower.

The second photo above was taken with the FA77 and a 25mm ext. tube converted from a TC. It's an uncropped image, so yeah it can get close. I am planning to make a 100mm tube for the sigma 100-300 F4 and use it with the Pentax 540 flash (The subject to lens distance will allow for this flash).

The TC's deteriorate the IQ, the ext. tube barely changes the IQ, just a fall in light, but with the sigma 100-300 and the 540 flash it should be irrelevent. Hopefully someday, I'll have time to take some shots and psot.

Last edited by pcarfan; 04-22-2009 at 03:32 PM.
04-22-2009, 03:44 PM   #4
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If you make sure the TC's A pin is extended & shorted out, the camera will think all mounted lenses are in A mode. Therefore A's will continue to function correctly in A mode, and M42's and K's will also meter properly in stop down mode (e-wheel turned to minimum f-stop.)

Iowa Dave

04-22-2009, 03:50 PM   #5
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Pcarfan,

So if I mount an FA 50mm macro/2.8 on this "Modified" 2x TC,
what will my lens be? 100mm macro/2.8 with 2:1 magnification ratio? or else?

Thanks,
04-22-2009, 04:13 PM   #6
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QuoteOriginally posted by HermanLee Quote
So if I mount an FA 50mm macro/2.8 on this "Modified" 2x TC,
what will my lens be? 100mm macro/2.8 with 2:1 magnification ratio? or else?
Not exactly.

If you combine your FA 50mm macro/2.8 with an unmodified 2X TC, you'll have a 100mm macro/5.6 with 2:1 magnification ratio. IQ will suffer, however.

If you combine your FA 50mm macro/2.8 with the modified 2X TC, you'll have a 50mm macro/2.8 with about 1.5:1 magnification ratio. IQ remains more or less the same.
04-22-2009, 04:16 PM   #7
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QuoteOriginally posted by newarts Quote
If you make sure the TC's A pin is extended & shorted out, the camera will think all mounted lenses are in A mode. Therefore A's will continue to function correctly in A mode, and M42's and K's will also meter properly in stop down mode (e-wheel turned to minimum f-stop.)
(Scratching my head....) I thought the problem of incorrect exposure with M42- and K-mount lenses was the function of the focusing screen (at least with the K10D and K20D). How is it related to the A pin?
04-22-2009, 05:01 PM   #8
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With a 50mm lens and a 25mm ext. tube, you have to get very close to the subject to get the image in focus. With my FA77, the distance is ok. With the sigma 100-300 (As sharp as most of my primes), will have a very good lens-to-subject distance even with 100mm ext. tube.

I've tried it with my 50mm and didn't like it. I will get a TC with AF and modify it for my FA77 to do macro. I will experiment with 2-4 25mm A tubes for the sigma 100-300 ( 50mm to 100mm ext. tubes in early tests are very prmising), the image can be easily focussed by the focus ring and by changing the focal length. If the IQ doesn't deteriorate much, it will be a stunning combo.....300mm 1:1 macro (100mm ext. tube...with the US stamp test) , can't beat that.....

04-22-2009, 05:11 PM   #9
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QuoteOriginally posted by pcarfan Quote
I will experiment with 2-4 25mm A tubes for the sigma 100-300 ( 50mm to 100mm ext. tubes in early tests are very prmising), the image can be easily focussed by the focus ring and by changing the focal length. If the IQ doesn't deteriorate much, it will be a stunning combo.....300mm 1:1 macro (100mm ext. tube...with the US stamp test) , can't beat that.....
Note that the far end of the zoom lens is 300mm only when focus at infinity. At macro range, the focal length is not really 300mm.

Also, by the time you add enough tubes to achieve 1:1 at 300mm, the effective aperture will be so small focusing will be difficult, AF may not work, and you will put so much strain on the in-camera AF motor (unless the camera body and the tubes and the lens support HSM).
04-22-2009, 05:20 PM   #10
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QuoteOriginally posted by SOldBear Quote
Note that the far end of the zoom lens is 300mm only when focus at infinity. At macro range, the focal length is not really 300mm.

Also, by the time you add enough tubes to achieve 1:1 at 300mm, the effective aperture will be so small focusing will be difficult, AF may not work, and you will put so much strain on the in-camera AF motor (unless the camera body and the tubes and the lens support HSM).
AF is useless, as most of the focusing will be done by changing the focal length. I tried with some non A ext tubes totaling 100mm and it works fine. Just a rough shot of the US stamp with 100mm tube and the sigma 100-300 at 300. (I read somewhere that a 1:1 lens will cover a US stamp), and this is an uncropped image. I can get much closer than this if I reduce the focal length from 300 to something less....



It's a pain to do non P-TTL flash and changing the aperture manually, that I am waiting for my other TC's with A contacts to arrive prior to proper testing.

Another image with a lower focal length and closer subject to lens distance (still far enough to use the 540 flash).



I need to clean my sensor, yikes!

Last edited by pcarfan; 04-22-2009 at 05:32 PM.
04-22-2009, 05:25 PM   #11
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QuoteOriginally posted by SOldBear Quote
(Scratching my head....) I thought the problem of incorrect exposure with M42- and K-mount lenses was the function of the focusing screen (at least with the K10D and K20D). How is it related to the A pin?
When the A pin makes ground contact, the camera thinks the lens is a type A; therefore it thinks it can stop down the lens at exposure time using the lens' lever.

Then, if you use the e-wheel to tell the camera that you want the lens wide open (instructing the camera to NOT stop down the lens) it meters the light & times the exposure according to how the lens is actually stopped down (ie. according to how much light is coming thru the lens.)

You may also have to short out the DATA pin depending on the camera but I'm not certain of this....the K100D wants the DATA pin shorted.

Iowa Dave

Last edited by newarts; 04-22-2009 at 05:32 PM.
04-22-2009, 05:29 PM   #12
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QuoteOriginally posted by newarts Quote
When the A pin makes ground contact, the camera thinks the lens is a type A; therefore it thinks it can stop down the lens at exposure time using the lens' lever.

Then, if you use the e-wheel to tell the camera that you want the lens wide open (the camera has been instructed to NOT stop down the lens) therefore it meters the light & times the exposure according to how the lens is actually stopped down (ie. according to how much light is coming thru the lens.)

You may also have to short out the DATA pin depending on the camera but I'm not certain of this....the K100D wants the DATA pin shorted.

Iowa Dave
I've used my M42 lens like this with proper metering and P-TTL flash. With the 1.7 AFA the M42 lens can AF, meter and use P-TTL flash, pretty neat indeed. But shorting the pins with the aluminum foil always leaves foil pieces ripping off and falling into the camera a body. Is there any tricks to short all the pins (including the sunken one)? scarping the lens ring to expose metal still misses the sunken pin.
04-22-2009, 05:37 PM   #13
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QuoteOriginally posted by pcarfan Quote
I've used my M42 lens like this with proper metering and P-TTL flash. With the 1.7 AFA the M42 lens can AF, meter and use P-TTL flash, pretty neat indeed. But shorting the pins with the aluminum foil always leaves foil pieces ripping off and falling into the camera a body. Is there any tricks to short all the pins (including the sunken one)? scarping the lens ring to expose metal still misses the sunken pin.
I shorted the A pin on the camera side of the mount. Remove the mounting plate, put tin foil over the A pin, and replace the plate (doing this is not risky or complex.)


The squished foil shorts the A pin.

Iowa Dave
04-22-2009, 05:49 PM   #14
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Dave

Thanks. Where do I get these sticky-back aluminum foils ?
04-22-2009, 06:42 PM   #15
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QuoteOriginally posted by pcarfan Quote
Where do I get these sticky-back aluminum foils ?
Home Depot, near duct tapes.

Buy a roll and you have enough to fix the A connection ball for the whole Pentaxian population
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