Pentax Spotmatic F SMC Takumar Auto-Manual Slider

A number of these have passed through my grubby hands. The M49 screw SMC Takumar lens has additional levers etc to enable open aperture metering, also on the Pentax ES.

 

The question - they all came with the Auto - Manual slider in the Auto position, which is correct for normal use. The slider I'm referring to is the crescent shaped thing seen in the right hand picture. But when I tried to move it into the manual position, it just won't budge.

 

I think I've had four of these SMC lenses, three 55mm and one telephoto, and they ALL had the A/M slider jammed in the auto position. I wonder if this is a common problem, or is there something I'm missing?

 

Here's the lens. Thanks in advance for any comments.

 

It has to be mounted to move.

I have the same lens (but no M42 camera). Mounted in my adapter for use on Nikon Z it moves freely - otherwise it is locked.

On your picture of the mount - at 2 o'clock you see a little pin that has to be depressed.

Sorry, I just notice mine is not the same, it is a SMC 50/1.4 but it should work the same way regardless.

On your picture of the mount - at 2 o'clock you see a little pin that has to be depressed.

 

Thanks for the prompt reply Niels. I removed the lens and located and pressed down the pin. Yes, it does release the slider, enabling it to move freely between settings. But upon replacing the lens firmly on the camera, the slider is still locked on my example. I can only assume that the pin is not being depressed fully, perhaps due to wear to the lens pin or to its mechanism.

 

It begs the question, why did Pentax only enable the auto / manual facility with the lens mounted?

 

Thanks again.

Edited January 8, 2022 by John Seaman

According to the owner's manual, the "Auto/Manual" switch should always be set to "Auto" when used on the Spotmatic F (see page 23):

 

pentax_spotmatic_f.pdf (cameramanuals.org)

 

I believe this also applies to other Spotmatics with full aperture metering. Unlike the stop-down metering only bodies, the lens mounts on FA metering bodies have a recessed groove that prevents the pin from being depressed when the lens is mounted, locking the A/M switch in Auto. My guess is that setting the switch to Manual can result in metering problems. Quirks such as this were unavoidable when updating existing mounts for newer technology such as FA metering and auto exposure, while maintaining compatibility with older models. If you mount a SMC lens on an older stop-down metering only body, the mount will depress the pin and the A/M switch will slide as on older lenses.

FA metering bodies have a recessed groove that prevents the pin from being depressed when the lens is mounted

 

Yes, I see the groove! So the pin only comes into play when mounting an SMC lens on to an older non-F M42 body.

 

No wonder the various adaptions to make M42 lenses support full frame metering were short lived and the companies who introduced them (Pentax, Olympus, Praktica?) quickly moved to bayonet mounting.

My guess is that setting the switch to Manual can result in metering problems.

 

The Spotmatic F, ES (Electro-Spotmatic), and ES II were all designed for open-aperture metering. According to Pentax, in the ES II user's manual: "CAUTION: All SMC Takumar lenses up to 300mm [except the 85mm f/1.9 and SMC Takumar Zoom 85mm-2l0mm] are designed for open-aperture reading. When directly mounted on the ES II, they will give correct exposure readings at full aperture. Do not try to take meter readings at stopped-down aperture, as this will indicate different shutter speeds." The locking auto/manual switch on these lenses prevents incorrect readings by inadvertently switching the lens to manual aperture.

 

There were a few Super-Takumar lenses with this feature also before the introduction of the SMC/Super-Multi-Coated series, but they are uncommon.

Edited January 8, 2022 by m42dave