Any Pentax MX or Olympus OM users out there??

[excalibur2]

I think it's for use with cameras with shutter priority or Program (P) mode that allow control of the aperture from the camera. There's be something at the bayonet end that you wiggle to adjust the aperture, I think. However, I don't have a P-mode SLR to try it out. I'd guess it potentially makes the lens more useful to digital camera users, if they have an appropriate adaptor...

Is that a one-touch or two-ring zoom? The M version is a lovely one-touch, 70mm when short and 35mm when zoomed "out". I damaged mine by dropping it on some rocks while falling over, and replaced it with a similarly lovely but somewhat lighter Vivitar 35-70 that works in the same fashion (but also has an A setting. IIRC).

My Pentax 24-35 is 2 touch and the 35-70 and 75-150 is one touch..no creep with these two as they are quite stiff to slide in and out to focus. Plus other zooms and 2Xs converter, some primes Rikenon 28mm and 50mm and the Pentax converter to M42, so that lot should give the ME super a work out

 

[ChrisR]

When attached to a suitable body, the aperture should remain open for composing and focusing and only close when you press the shutter release.

All the K-mount lenses work like this on any Pentax SLR: K, M, A etc (many earlier M42 screwmount lenses did not do this automatically). The A mount has the additional controls to set the aperture from the camera as I described.

 

[excalibur2]

All the K-mount lenses work like this on any Pentax SLR: K, M, A etc (many earlier M42 screwmount lenses did not do this automatically). The A mount has the additional controls to set the aperture from the camera as I described.

Canon have something similar whereby you set the lens on "A" and it allows the camera to control the lens apertures, and my Nikon F90x if you don't set the lens on f22 you get an error message irrc it's for AV mode.

 

[Petrochemist]

I think it's for use with cameras with shutter priority or Program (P) mode that allow control of the aperture from the camera. There's be something at the bayonet end that you wiggle to adjust the aperture, I think. However, I don't have a P-mode SLR to try it out. I'd guess it potentially makes the lens more useful to digital camera users, if they have an appropriate adaptor...

Is that a one-touch or two-ring zoom? The M version is a lovely one-touch, 70mm when short and 35mm when zoomed "out". I damaged mine by dropping it on some rocks while falling over, and replaced it with a similarly lovely but somewhat lighter Vivitar 35-70 that works in the same fashion (but also has an A setting. IIRC).

Yes the A setting on the lens allows the camera body to control the lens aperture. This isn't just in P mode, but also works in A & M with suitable cameras. All Pentax's AF bodies & the latest of their manual bodies will work (My original ME didn't but the ME Super did). Of course if the camera can't control the aperture you can use the other settings instead. AFAIK none of the adapters available for Pentax lenses make use of the A setting properly. I have a DA adapter for lenses without an aperture ring, which basically uses a ring in the adapter to adjust the levers on the rear of the lens - there's no indication of the true f-number being used.

There is apparently a slight difference in the way the rear linkages worked in A series & later lenses to the earlier models - IIRC one moves proportionally with the aperture diameter & the other with aperture area.. This change means later bodies should be metered with earlier lenses shut down rather than wide open. I've not noticed the difference myself, but it might be responsible for the odd poor exposure I've had over the years..