Make a K into a KA mount extension tube.

Started Nov 14, 2011 | Discussions thread
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brandrx
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Make a K into a KA mount extension tube.
Nov 14, 2011

Hi folks,

Since we Pentaxians have such a hard time finding KA mount extension tubes, I think it is time we figured out how to make a K mount into a KA mount extension tube. So, put on your thinking caps.

I already know this will work but I just can't figure the best way to implement it.

If you have a K mount extension tube (has an aperture lever), you can make it act as a KA mount by doing the following:

Go to http://www.robertstech.com/matrix.htm to get the pin layout.

First, even though the K mount is solid metal, the A pin on the camera is recessed just enough that it does not make contact. Therefore the A pin is not shorted.

Short the A pin to ground (the metal mount) using aluminum foil. Install your K mount extension tube. If you are using an "A" type lens, you should be able to leave the lens in the "A" position. If you are using a K lens set the lens to minimum aperture (for instance f22 if that is the largest number on your lens). Now you can control the aperture from the camera in the Av mode. The apertures you read in the camera will probably be wrong. So, you need to figure out which pins to open between the camera and the extension tube by the use of tape and looking on the robertstech link I provided above. Or you can try to live with just shorting the A pin and experiment for best aperture setting for your shots. For instance I used a K mount 100mm extension tube and a Tamron SP 200mm f3.5 Adaptall 2 lens, However, with just shorting the A pin between the camera and the extension tube my wide open reading at the camera is f1.2. However, I know that the taping of certain pins will change that so I read f3.5 as wide open at the camera.

EDIT: Shorting pin A and taping pin 1 and 2 on the combination above gives me aperture control from the camera from f3.5 to f22.

This is really difficult for me to explain. It is best if you can do it yourself and see it in action.

What I would really like to figure out is how to be able to short the A pin without the use of taping aluminum foil to the camera when using a K mount extension tube. Perhaps some kind of tiny spot weld at the point that the A pin could make contact with the metal of the K mount.

Anyway folks, the above method will work when using just a K mount attached to the camera or with a K mount extension tube between the lens and the camera.

My brain hurts now. So, I have to give this up for now.

Cheers.

Ron

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Ron - 'We don't have time to go take pics this afternoon Carl.'
Carl - 'What do you mean? It will only take 1/1000s.'

'Keep your eyes looking forward. However, glance back now and then to see where you've come from. It will put a smile on your face.' ~ brandrx

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