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02-16-2010, 09:05 PM   #1
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ME Super and aperture <-> light meter

Hi,

I've just started shooting on my grandfather's old Pentax ME Super using a Sakar k-mount lens and noticed that aperture changes aren't reflected in the light meter.

Apparently the ME Super sports a "Pentax K with fully automatic diaphragm linkage". I'm not sure if this means a Pentax KA mount, but probably not since the ME Super ran from 1979-1984 and the KA mount was introduced in 1983 (according to wikipedia).

I also have a Tamron 35-80mm f/2.8-3.5 (either Adaptall or Adaptall-2, hard to tell since the labelled lens caps/covers could have gotten switched around during all these years) that I use with what's probably an Adaptall-2 custom mount labelled "for PENTAX K.M." (once again hard to tell since most likely nothing is in the original packaging). I also have the same aperture/light-meter problem with this lens.

There are also several M42 screw mount lenses for which I lack adapters. The Sakar lens is an MC Auto Zoom/Macro UV 35-200mm F3.5/4.8.

I would like to know if there are any adapaters that will allow me to use either the Sakar k-mount lens, the M42 screw lenses, or the Tamron lens with the aperture/light-meter functionality between the body and the lens.

I know Tamron produced Adaptall-2 KA mount adapters, but I'm not sure if they will solve my problem: either the Pentax ME does not have a KA mount, or my Tamron lens is simply an Adaptall lens. (Adaptall lenses and Adaptall-2 mounts are interchangeable minus lacking some features, right?)

Apparently the only M42 <-> k-mount adapters that preserve the flange focal distance (whatever..) are Pentax originals and Bowen, and only the Pentax are worth it. Once again, will these adapters allow me to use the light-meter with the aperture?

As for the Sakar lens, are Sakar k-mount to Pentax k-mount adapters available?

I've tested some store ME Super lenses which work fine, so I know there is nothing wrong with my camera's built-in light meter.

Also, hand-held light meters are waaaay more expensive than I expected. (although only incident light-meters were in stock).

02-16-2010, 09:54 PM   #2
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The ME Super has a basic K-mount. What I would do is test the connection between the lens and light meter. Take the lens off the camera and look at the mount. On the upper right side, there's a spring loaded tab that moves down in an arc. That tab follows the position of the lens's aperture ring and tells the light meter where it's set. You can look through the viewfinder with no lens on, activate the light meter by pressing on the shutter button, and move the tab down. The light meter should change. If it doesn't, the variable resistor that the tab connects to is not working, or the ambient light is too bright and the meter is pegged. Try setting the ASA dial to its lowest number and doing it again.

Any K-mount lens with an aperture ring should be capable of moving that lever. You can look at your lenses and see something like this:

The arc slot at the bottom has its own tab that moves the camera's tab. You should be able to move the aperture ring and see that tab follow along. There might be something wrong with the Adaptall installation but the Sakar sounds like it should work. The Adaptall PK-A adapters wouldn't do anything extra for you with this camera. If there's no tab or it doesn't move when the aperture ring moves, the lenses have problems. I suppose a lens with a stuck aperture might act like this.
The M42 lenses will work with adapters. The adapter will shove the camera's metering tab all the way down when you install it. The camera can't read the aperture ring position on M42 lenses. To use the camera's meter, you have to set the lens's Manual-Auto (or M-A) switch to Manual, then set the aperture ring on the lens. The meter reading should change as you move the ring.
02-17-2010, 01:23 PM   #3
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After taking off the lens I was able to test the spring-loaded tab on the
camera mount by moving it along the arc. It worked fine. In manual mode the
light-meter recorded over- or under-exposure, and in automatic mode the
shutter speed adjusted accordingly.

Now with the Sakar lens. When I move the aperture ring the tab in the arc
slot rotates accordingly, and the light diaphragm contracts or expands.
Opposite there is an extruding "bayonet" tab that overrides and opens the
aperture completely. It looks almost exactly like your picture.

When mounting the lens on the camera this "bayonet" tab is rotated and the
aperture is forced completely open. When looking down the barrel of the
mounted lens I notice that rotating the aperture ring no longer
expands/contracts the diaphragm in either manual or automatic mode. This
might be a problem.

I also noticed that if I mount the lens preset to its smallest aperture,
the camera detects an increase in aperture, but not vice versa: i.e.
reducing (then increasing...) the aperture again is not detected. Possibly
the inset lens tab is too thin and allows the camera's corresponding tab to
"slip" by. I've attached some pictures, best I can do, what do you think?

Otherwise, thanks for the good news. I'll see if I can get my hands on a
Pentax M42 adapter. I'll also take a closer look at the Tamron lens. Not my
highest priority though - the rings are very sandy/gritty, apparently it's
been to the Sahara.
02-17-2010, 07:04 PM   #4
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Images not previously attached. Hopefully here...

Attached Images
   
02-17-2010, 08:51 PM   #5
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I just realized that the lever sticking out of the Sakar lens mount is used for open-aperture metering, explaining why the aperture did not appear to change.

So as you mentioned the M42 adapters must use stop-down metering.
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