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03-31-2013, 05:22 AM   #1
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Exposure metering using extension tubes with a K-X

I am trying to use automatic metering on my K-X using cheap extension tubes.

I have set up the camera to allow aperture ring setting as follows:

Press the Menu button
Press the left button on the four-way controller to get to the Custom Settings menu
Press the down button on the four-way controller and select Using Aperture Ring
Press the down button on the four-way controller, select Permitted and press the OK button.
Press the Menu button to exit the Custom Settings menu

I then set the camera to Manual exposure setting and press the +/- button which is supposed to set an appropriate shutter speed. However, it is much too fast so the image is almost black.

Any clues on what I am missting?

Thanks

Chris

03-31-2013, 05:52 AM   #2
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https://www.pentaxforums.com/forums/pentax-dslr-camera-articles/100260-manual...ic-lenses.html
03-31-2013, 06:05 AM   #3
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Did you change this setting also?

Press the Menu button
Press the left button on the four-way controller to get to page 4 of the Rec. Mode menu
Press the down button on the four-way controller, select Green Button
and press the right button on the four-way controller.
Press the down button on the four-way controller, select Action in M Mode
then press the right button on the four-way controller and select Tv SHIFT. Press the OK button then the Menu button twice.

(This setting allows easy and accurate exposure metering using older lenses without an "A" setting on the aperture ring. When the Green button is pressed in Manual exposure mode, the lens "stops down", the camera's meter measures the light passing through the lens, and an appropriate shutter speed is automatically set based on that measurement).

Using Older Lenses with the PENTAX K-x | Pentax Support
03-31-2013, 07:27 AM   #4
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If you are using the cheap extension tubes, then they have no aperture control. When you set the aperture on the lens, that is what you see through the viewfinder, it will be very dark if you use a small aperture. I'm assuming the tubes are painted black where they mount to the camera, if so you can try sanding off the black and see if that will make the green button metering work. Macro with tubes need a lot of light, and my advice is to use a flash either a ring flash or off camera flash on a bracket, then you can set exposure according to the flash output, either auto or manual, keeping the shutter at 1/180.

03-31-2013, 09:17 AM   #5
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Thanks for all the suggestions - unfortunately I am still not able to set automatic shutter speeed.

I have made the changes to the Menu settings.

When I turn on the camera it asks me for the focal length. I am using a 50mm lens from an old SLR with the extension tubes so I enter 50mm.

I set to Manual, the image through the viewfinder is OK, light enough to focus.

When I press either the green button or the +/- button the shutter speed does not change when I change the aperture.

Any more suggestions?

Chris
03-31-2013, 10:31 AM   #6
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Try sanding off the black paint on the tube where it meets the camera contacts. Or you could slip a piece of tinfoil between the tube and contacts to see if that is the problem before you do the sanding.

I just checked my old cheap tubes that I haven't used since I got the Vivitar AT-22 tubes, and yes I had to sand off the paint to make them work with the metering. In fact I had to sand the Vivitar tubes to make catch-in-focus work.

Last edited by bluestringer; 03-31-2013 at 10:41 AM.
03-31-2013, 03:47 PM   #7
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I have tried sanding off the black paint where the camera contacts touch the extention tube but it does not seem to have done anything.

I have now discovered that the exposure is correct when the aperture is wide open but when I stop it down the exposure time does not increase so I can only get automatic exposure with maximum aperture which does not give me much control (or depth of field!).

Anyone got any thoughts on what is going one?

Thanks

Chris
03-31-2013, 04:25 PM   #8
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Try the tinfoil trick. If that works, then you may need to sand more. Only other thing I know is to use a flash and meter with the flash exposure.

03-31-2013, 04:26 PM   #9
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With the K-10D in order to use manual metering with non-A lenses the DOF preview has to be set to optical. When I activate the preview (on the K-10D it's on the Power Switch) the lens will stop down and the bar meter activates. From the bar I can "needle match" the exposure by adjusting the shutter speed (from the e-dial) or the aperture from the ring. This is the procedure for using K, M and M42 lenses or with extension tubes without contacts. This is not covered in either the manual or the support topics on the Pentax websites. I found this out from blogs and trial-and-error.

WIth 'A' type lenses the EV bar is active as soon as I switch to manual mode and I can adjust the aperture from the e-dial too. The lens doe not have to stopped down to calculate the correct exposure.

On the K-X you can assign the optical DOF preview to the Green button. Perhaps this will also enable stop-down manual metering (activating the EV bar)?
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