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12-03-2006, 08:47 AM   #1
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SMC-A vs. SMC-M

Hello, I'm new here and new to pentax. and I'm planning ona k10d soon.

I'm a fan of primes and manual focus, can someone explain the diff between the SMC-A and SMC-M lenses and how they will operate on the new digiSLR?

many thanks, MIke

12-03-2006, 08:53 AM   #2
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Welcome Mike,
The A lens will have all the exposure options of the later F,FA,and DA lenses, you just MF with it. The M lenses lack the electrical contacts to do so. They are used in what I call semi-manual mode. The camera will meter them, but the lens needs to stop down first. The camera will handle that for you at the push of a button. Not all that inconvenient.

Hope this helps
-Alan
12-03-2006, 09:24 AM   #3
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Thanks Alan,
is this the same as the M42+adapter lenses? or does that add a layer of complication?

Thanks, mike
12-03-2006, 11:20 AM   #4
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I use both A and non-A older primes. The only difference is that with K and M lenses camera has no control over the lens aperture while with A lenses it does, allowing you to use your camera in other than M modes (P, Av, Tv...).

But since I use K, M and A lenses in M mode only anyway with my *istDS the only practical difference to me is that there is no continuous meter reading, so you'll have to hold DOF to explore the scene (using spot metering of course) while with A this is not required.

Also, in M mode I always use AE-L button to set initial shutter speed based on aperture (custom menu: "Tv shift") so the only difference is this: with A lenses there is immediate Tv shift, while with K and M lenses you can hear/see aperture briefly closing down before Tv shift occurs. The workflow is the same though.

Finally, if M lenses are used EXIF info does not have aperture information.

12-03-2006, 11:22 AM   #5
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QuoteOriginally posted by triplefinger Quote
Thanks Alan,
is this the same as the M42+adapter lenses? or does that add a layer of complication?

Thanks, mike
no it's not mike. with the SM w/adapter you will have to close down the aperture manually. the cam has no way to use the pin that is on the lens. in other word when you make your shot you will have to manually close the lens down. if you are shooting at f11up the image is starting to get pretty dim in the VF.. my 50mm is a bayonet but it's not meter coupled. on a tripod i'll focus and set the shot up viewing at f4.5 then set it to f11 just when i shoot the shot.
12-03-2006, 11:25 AM   #6
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forgot to say that you use the cam in Av mode when using the screw mounts because the cam is metering with the actual amount of light coming in.
12-03-2006, 01:01 PM   #7
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Thanks very much, I'm excited to get all this together.
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