Difference between m and a

Looking into purchasing a smc 50mm in the next few days for portraiture but can't seem to find the difference between smc 50 M and smc 50 A. I know it's not auto focus. What is the difference

Is it aperture priority?

The M50 is manual exposure only and you would need to do stop down metering whilst the A50 is fully automatic exposure.

Jeff

Both are superb lenses (assuming you're talking about the f/1.7 versions), they have the same optics. The A version communicates the aperture to the camera when the aperture ring is in the A position, which means all exposure modes can be used. The M version can't do this so you will need to use manual mode and use the green button (or guess) to get the exposure right. The M version is better built though - all metal as opposed to the plastic of the A.

If you're just starting to use manual lenses, remember to enter the menu and set the camera to allow the use of lenses without an A mode. If you don't do this then old manual lenses will not work.

Good luck with whichever you choose.

There are no electronic contacts on the M series lenses, and no "A" on the aperture ring. This means they cannot do some programs such as Tv and will only work in M and Av modes. Stop down will also have to be manually set.

The A series will work with almost everything, apart from not being autofocus of course. Just set the aperture ring to "A" and let the camera control things.

Ok. Clean as crystal. Thanks everyone

You're really restricted to M mode only with the original smc lenses. Even in Av mode, as there's no contact electronic contact the camera does not' know' what aperture is set on the lens and cannot control the lens aperture. As said above, you set the aperture on the lens first, point at where you want to meter primarily then press the green button ... The lens stops down and the meter reads the light and sets an appropriate shutter speed. You can then change the speed in order to make it darker or brighter.

It's really two extra steps in practice ... You get quick with practice, but the A type lenses eliminate these steps, which can be more convenient.

Very important..... The 'A' lens details are recorded in the
Exif data along with the aperture + speed used if the lens
is set on A.

PhotoMe shows ...
smc PENTAX-A 50mm f/1.7 or 135mm f/1.8

The 'M' lens just shows M Lens and the speed. No aperture.

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If this link is permitted, you can read all about them here:

http://www.pentaxforums.com/lensreviews/

Cheers.
Philip

Thanks everyone for your help. By the way, anyone selling a 50mm by any chance?

There's a K 55mm f/2 for sale here:

https://www.pentaxuser.com/forum/topic/fs--pentax-smc-k-55mm-f2-0-50667/p-0#comm543412

The K will work in the same way as the M. It's a very good lens and I'd say this is a very good price for it.

I've got about 4 Pentax-A 50mm f/1.7's mostly on bodies.
All of them are in excellent condition and if you want one
I could sort out a good one for £39 posted. Both caps included
but they won't be Pentax originals.

Let me know by PM if interested.

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Thanks for the posts guys. I am currently bidding for 1 on eBay at the moment. If I am not successful I will get back to you

The way I've worded that could be confusing The £39 is just for a lens not lens
and body. I ran out of body caps so I put lenses on until I get some. One of the bodies
is an MZ-S

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Just pointing out that these limitations only apply to bodies with crippled mounts (all of the DSLRs and some of the MZ series film cameras). I usually use HyperManual so I don't really notice the extra step. Otherwise 'K' & 'M' lenses work fine in M and Av on film bodies. A future FF with non-crippled mount would be very interesting!

When using my K-5, the only real drawback when using M lenses is that because you need to use Manual mode, you lose the horizontal spirit level in the finder (it becomes the exposure +/- indicator).

John.