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M42 lenses with Pentax K-bodies exposure metering?
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PostPosted: Fri May 24, 2019 7:16 am    Post subject: M42 lenses with Pentax K-bodies exposure metering? Reply with quote

Can it be done somehow?

Are there adapters that tell the body aperture?

edit: fixed the title, the question is below expressed more clearly (I hope Smile )


Last edited by kansalliskala on Sat May 25, 2019 6:06 am; edited 2 times in total


PostPosted: Fri May 24, 2019 1:22 pm    Post subject: Reply with quote

Tell what to what? Smile "that tell the body aperture" can mean "to tell the body aperture" set on lens, or, "to tell the lens the aperture" set on the body. Smile

Later Asahi and Pentax M42 and K-mount lenses have a lever which position is monitored by body. Adapter chips some can register the aperture set by camera (for exif) but lens must be set manually.


PostPosted: Sat May 25, 2019 3:03 am    Post subject: Reply with quote

I'm assuming that, since kansalliskala mentions M42 and K bodies that he's not referring to anything as hitech as exif and what have you.

Just to be sure about nomenclature, when aperture is mentioned, usually we're referring to the iris mechanism on a lens. So it's lens aperture, not body aperture. The body houses the shutter (obviously) so it is the body's shutter speed that is one of the two components of exposure that a camera's exposure meter measures -- or evaluates. The light value recorded by the meter is actually the quantity that is measured. The camera then determines the proper shutter speed and aperture for correct exposure to occur. In the case of the old-school mechanical cameras, the correct exposure is arrived at by centering the needle(s) of the aperture ring and shutter speed dial, each keying off the exposure value recorded by the meter.

Now, if you already know all this, then just what the hell are you talking about? Er, writing about?


PostPosted: Sat May 25, 2019 6:03 am    Post subject: Reply with quote

cooltouch wrote:
In the case of the old-school mechanical cameras, the correct exposure is arrived at by centering the needle(s) of the aperture ring and shutter speed dial, each keying off the exposure value recorded by the meter.

Now, if you already know all this, then just what the hell are you talking about? Er, writing about?


Sorry for being too cryptic. Very Happy

I have some m42 lenses I would like to use with a Ricoh K-5 body.

Exposure meter needle moves when you set the aperture of a K-mount lens, so it can be centered to the ring that moves when you move the exposure time selector.

I wonder if there are m42 adapters that you can fix so that the aperture lever or connector was positioned like f/4. Then I could use the lenses at f/4 (135 and 200 mm lenses, that would be just good).


PostPosted: Sat May 25, 2019 6:06 am    Post subject: Reply with quote

Well AFAIK for any bayonet film camera that can take a M42 lens adapter there is no mechanism which pushes the pin at the back of the m42 lens that operates the iris, so only M42 lenses that have a auto\manual switch or preset for aperture are useful...all the others without, would have to be used wide open.
So M42 lenses that can be stopped down, select the aperture and take the exposure reading...some older M42 lenses are handy in that once you have selected your aperture there is a ring on the lens that swivels to fully open to stop down, this is handy for focussing.


PostPosted: Sat May 25, 2019 9:40 am    Post subject: Reply with quote

Late model Super, Super-Multi-Coated, and SMC -Takumars lenses have the aperture-coupling lever for letting body know the setting, as do Ricoh lenses. This was improvement made by Pentax to M42 mount, carried into K-mount lens/camera design. I don't know of any M42 Takumar or M42 Ricoh adapters which couple the lever to Ricoh K-mount body.

Edit: Oh! Wait! Pentax M42 to K-mount should work for coupling M42 lenses with aperture lever to Ricoh K-mount bodies -- the Super, Super-Multi-Coated, SMC, and Ricoh M42 lenses.


PostPosted: Sat May 25, 2019 2:55 pm    Post subject: Reply with quote

No, anything earlier than Pentax-A can only be used as dumb lens. I think there is (may be not on all bodies) some roundabout way to use -K and -M lenses in aperture priority, but definitely not M42.