difference between pentax-a and pentax-m lenses

i have been searching for more lens for my k200d camera and have found several on ebay, but not sure what is the difference between lens which state pentax-a and pentax-m, they both state they are k mounted bayonet fittings,

They are both K mount

the Pentax K mount has a very long history, this is an excelent sourse of information http://kmp.bdimitrov.de/

Hi Karen,

(Probably simplifying but it will answer the question well enough...)

Pentax M lenses were designed for the M-series cameras (MV, MX, ME Super etc) which offered manual and/or aperture priority only. The aperture is set with the aperture ring.

A series lenses were introduced to go with the Super-A/Program A and later cameras that offered shutter priority and full program modes and the aperture can be set to "A" allowing the camera to set the aperture, or for the user to set the aperture from the camera (where the model allows that).

Due to metering problems with the M series lenses and the new digital bodies you are better off getting A series lenses if you can. There was a long thread on this last Thursday.

Hope this helps, Kris.

The A mounts have the "A" position on the aperture ring allowing the camera to "talk" to the lens and, therefore, work in all picture modes. The M's don't have this feature and so will only work in Manual and Aperture Priority modes with stop-down metering.

The A's - needless to say - fetch more money, however, the M's are probably just as good optically so represent more of a bargain if you're comfortable with using your camera manually.

Beaten to the punch

Well at least we were both singing from the same song sheet...

For the digital SLRs it's much easier to use the A series and later lenses. I moved totally onto doing this as, despiye there being all sorts of great K and M series lenses; it just wasn't worth the hassle, not to me anyway.

These days I just use the FA and DA lenses, simply because it's the most efficient way to work.

Which of these various older lens require an adaptor to be used on the current dslr's , ie k10d. :
Thanks in advance for any replies.

None of the lenses mentioned above require an adaptor - all Pentax bayonet lenses will fit just fine on a DSLR as-is.

You'll need an adaptor if you wish to use older (pre-1975) M42 screwmount lenses (cheap adaptors available but genuine Pentax recommended). Pentax adaptors can also be bought to allow you to use Pentax 645 and 67 (medium format) lenses - although probably only worthwhile if you have an existing collection of these.

Hope that helps!

Thanks for reply and clarifying re Lenses,wasn't sure if M42 & M were same fitting as I got caught out with an older lens my Son had on his old Pentax that looked same as std kit lens but when I tried it on, could not get it back off. Had to send camera to UK to have it removed. So the essential factor is K mount
Regards
EddieD

The ones to watch are Ricoh lenses, which can have extra pins that jam on the K mount proper.

K mount = Bayonet
M42 = screw

you wont confuse the two to look at! as long as it's a Pentax lens, K mount will always be fine with any DSLR, except for certain metering issues with M series and earlier lenses. As John mentioned there are problems with certain lenses designed for Ricoh bodies. This is not entirely limited to Ricoh lenses so it's wise to be careful when using older non-Pentax glass.

It is worth taking this a bit further. M = male 42 = 42mm diameter 1mm pitch thread. Theer is also T-mount that is M42 but 0.75mm pitch, but usually if the lens is T-mount is is described as such.

Also note that there is no connection between the diaphragm on an M42 lens and a digital body so you have to use stop down metering. This is no great issue because it means that you can use Av (and, of course M). For K and M lenses there is one-way connection between the digital body and the lens. Before the shutter opens the camera stops down the lens to the setting on the aperture ring. The camera does not know the setting, in M mode it just stops down the les as far as the aperture ring allows. If you use an M lens in Av mode then the camera cannot alter the aperture so it treats the lens as if it has one aperture - wide open (even if you set the aperture ring, in Av mode the camera does not stop down). This is not a great issue because in M mode you can use the green button/AE-L or the DOF preview to meter (the camera will stop down the lens to the aperture setting), it is just one more step and no great issue.

I have M and M42 lenses (as well as some A and DA) and I prefer M42 to M lenses. To be honest A is not a great issue to me, I can meter with the camera, so the extra cost of an A lens over an M lens is not worth it - I would much prefer to spend the money on glass: a better M or Tak lens. Note that some M42 lenses need some EV adjustment if used in Av mode, I find that my CZJ Flektogon 35/2.4 meters perfectly on my K100D, but my CZJ Sonnar 135/3.5 needs +1.5EV.

Richard

K mount = Bayonet
M42 = screw
Ricoh=screwed kmount...