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05-31-2011, 06:22 PM   #16
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QuoteOriginally posted by geekette Quote
With m42 lens, in manual mode, the +/- button doesn't meter. If a Pentax-M or Pentax K lens is in it and I press the +/- it does stop down metering fine. I cannot get the camera to meter through the m42 lens in manual mode at all. So I make a guess and snap and look at histo.. it's wasteful but the best I can do atm.
Then you need to set the green button to Green Button and Action in M mode to P Line. I forgot the AV button doesn't work with screw mount lenses.

Last edited by boriscleto; 06-01-2011 at 04:20 AM.
05-31-2011, 07:09 PM   #17
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+/- button should meter on an M42 lens in the manual mode. The switch needs to be pushed to cover up the word 'auto' assuming you have a Takumar lens. Some folks have thought that pushing it toward auto was auto mode, but it is the opposite.

If the lens is not a Takumar then it might be auto only which will not work.
05-31-2011, 09:12 PM   #18
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Interesting the Av +/- button in manual mode is now working, metering through my M42. (scratches head)
06-01-2011, 04:20 AM   #19
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QuoteOriginally posted by geekette Quote
Interesting the Av +/- button in manual mode is now working, metering through my M42. (scratches head)
Perhaps you had the camera in AV mode instead of M mode. They are right next to each other on the dial, sometimes I get mixed up.

06-01-2011, 07:04 AM   #20
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The M and K lenses are auto lenses as they were called in the day. They meter wide open and stop down when the shutter is pressed. They do that by mechanical means. That was the state of technology in the day. You set the aperture with the aperture ring and the lens stopped down. The A lenses came along much later and they stop down by means of the electrical contacts. With Pentax being the only company to have compatibility with all it's old lenses with all DSLR models, we see it discussed quite a bit. You can meter with all the lenses although the procedure is slightly different and non A lenses tend to be off slightly. The best way to use an M42 is in Av and let the camera choose the shutter speed. If you leave your Tak in auto position on the lens, the aperture will remain wide open as K mount cameras have no mechanical means of stopping down. With a Tak, I set the camera in Av, focus wide open with the lever in auto and move the lever to manual and shoot. If you can see good enough to focus stopped down, you can forego moving the lever and leave the lens in manual.

It sounds complicated but it really isn't, at least to those of us who have used them for years. On my SP1000 which only had stop down metering, you had to move a lever on the camera body to meter and then turn either the aperture ring or the shutter speed knob on the top of the camera to center the meter needle which was visible in the viewfinder, focus and shoot all at the same time. For myself, I'm not too excited about adding to my manual lens collection and would much rather use auto focus modern lenses and I am slowly changing them over as I get the money to do so. It is nice that Pentax users can still use their old glass. None of the other manufacturers have that compatibility although Nikon's high end cameras have pretty much full compatibility but not on their lower priced bodies.
06-01-2011, 08:04 AM   #21
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your description is not quite right.

If we start at the beginning.

All lenses were what they called either Manual aperture, which meant that you changed the aperture and the lens stopped down instantly, making the viewfinder dark, or Preset which had 2 aperture rings one where you preset the desired aperture with hard clicks, and a second much looser "operating" ring that actually was used to open and close the aperture. the operating ring was next to the focusing collar, so that you set your aperture, then with the lens wide open, focused on the subject, and just before hitting the shutter, you would move your hand forward and stop the lens down using the operating ring.

The next innovation was auto aperture, with a mechanism in the camera that would operate the spring loaded aperture in the camera, holding it open to focus and letting the lens stop down to the desired preset aperture to shoot.

With all of the above lenses, you needed to stop down to meter with the camera (assuming it had a built in light meter)

Then came open aperture metering, where a second mechanical coupling in the camera that told the body where the aperture ring was set, or more specifically how many stops from wide open, so that the camera meter could be calibrated for open aperture metering. this was introduced in to some later S-M-C Takumars as well as the K mount lenses.

The A series lenses retained the aperture setting coupling, and also included electrical contacts that told the camera the aperture range of the lens, i.e. min and max aperture. the aperture activation lever also changed in function, from an open close function to a scaled operating lever with the aperture area linear with lever displacement. these lenses could be used on older K&M bodies because they retained the aperture setting lever, but on A series or program bodies, the camera could read the max and min aperture and control the lens through the activation lever.

It was at some point around 2000 that some pentax bodies dropped the aperture setting lever coupling (so called crippled K mount) and had to use only A lenses or the stopped down metering like we have today.

It is really all about saving a little cost on the lens and body, and nothing more.
06-01-2011, 10:07 AM   #22
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As an aside, I wish Pentax had been able to do what Fujica did! The are 2 types of M42 adapter for the Fujica X mount. The simpler one will allow you to use any M42 lens and it will auto stop down when you take a picture. The other one also allows full auto control on some of the AX cameras with the Fujinon M42 lenses!


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