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10-29-2011, 08:43 AM   #1
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New Camera, new lens, old TC

Hi

I have a K20 and a new DA* 300 mm as well as the 18-55 kit lens. My old Pentax lenses work well and I read the excellent article by Robert Donovan, but not one fills the bill for using a CPC 2x TC. It has what looks liike a KAF mount without autofocus and six contacts in a row. I used it on my K1000 with a manual lens, but cannot get a way to meter with DA lens ( NO aperture ring ). Tried using it on Av and M with the green button after setting shutter speed, but really have to take a picture, check the exposure on the LCD and adjust the speed. I would like the lens to stop down for hopefully better IQ and use the camera metering. Any ideas?

10-29-2011, 11:45 AM   #2
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Your CPC 2x TC has a black anodized base and the body cannot communicate with your lens with the TC mounted in between. You need to scratch off the anodizing to create a short between the body contact and the TC. If you look at the TC with the lens release button at 12 o'clock, the six contacts are lined up to the right. You need to scrape away the anodizing next to the last contact (2 o'clock) with an exacto knife, or similar. This should allow you to control the aperture via the rear dial.

I found CPC 2x TC quite poor as a lens extender. I've removed the glass elements from the TC to use as a PK/A extension tube.
10-29-2011, 11:35 PM   #3
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QuoteOriginally posted by excanonfd Quote
You need to scratch off the anodizing to create a short between the body contact and the TC...

...I've removed the glass elements from the TC to use as a PK/A extension tube.
Here's what it looks like:

10-30-2011, 11:55 AM   #4
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You guys and this forum continues to amaze me. How on earth did you figure that one out? I works and I must agree with excanonfd that the image is not that good. I have not loooked at it with the K20 yet ( it is dark here where I am now), but do remember not being impressed with the CPC on my K1000. Will confirm whether it is worthwhile since it was a birthday present many moons ago from my good wife. Does it work well as extensive tubes? I am sure she will not know the difference if I put it to good other use. I must say that the DA* is so good that I hoped it will make up for loss of IQ

Thanks again for both your replies and the posting of the picture SOldBear


10-30-2011, 01:24 PM   #5
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QuoteOriginally posted by Basie Quote
You guys and this forum continues to amaze me. How on earth did you figure that one out? I works and I must agree with excanonfd that the image is not that good. I have not loooked at it with the K20 yet ( it is dark here where I am now), but do remember not being impressed with the CPC on my K1000. Will confirm whether it is worthwhile since it was a birthday present many moons ago from my good wife. Does it work well as extensive tubes? I am sure she will not know the difference if I put it to good other use. I must say that the DA* is so good that I hoped it will make up for loss of IQ

Thanks again for both your replies and the posting of the picture SOldBear
All credit to SOldBear for assisting me with this sometime ago, I couldn't remember which thread this subject was under - better to simply describe the process. Deglassed TC as an extension tube works great for macro retaining the AE function with your PK/A macro lenses, best TC I found is the Pentax F 1.7x AFA but it's expensive.
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