Dangermouse wrote:
For ease of use the A is better, set the aperture to "A" and it works like the current DA lenses but with manual focus only. However, the M is usually a lot cheaper.

Optically they're identical, the SMC coating may have changed but that's all.

Dangermouse wrote:
If you want a 50mm it's also worth keeping an eye on auctions for the following cameras:

MV
ME
ME Super

The M 50mm f1.7 was a kit lens for these bodies and you can sometimes find a cheap lens if you're willing to give a camera body shelf room (or sell it on). You may also find the f2 version which isn't quite as good but still a solid performer.

Other bodies were also supplied with this lens but they tend to be more desirable, like the MX and late sales of the original K bodies (KM/KX/K2).

The same goes for the A 50mm f1.7 - a kit lens on Super/Program A, P30 series, P50, A3/A3000 and also some late ME Supers.

Pentaxophile wrote:
To check the focal length of the lenses, zoom in to 28mm and 50mm on your zoom!

For me the 50mm is probably the natural first lens. Although of course it depends on what you like to shoot, but I think the very fast aperture of f1.7 will make owning the lens more worthwhile than the 28mm f3.5, which has the same maximum aperture as the kit lens at it's wide end. The 50mm f1.7 is over 3 stops faster than the kit lens at full zoom!

The fast f1.7 aperture of the 50mm will allow you to shoot images which look markedly different than the kit lens. Shooting at f1.7-f2 will allow you to blur the backgrounds of portraits very pleasingly.

If portraits and little details aren't really your thing and you just want a lens which is a bit smaller and has a nicer manual focus feel than the kit lens, the 28mm is a good choice.

Of the two versions Matt is talking about above, the original SMC Pentax version is slightly better than the M version. It's more expensive though.

Dangermouse wrote:
It really depends what you want to shoot.

The 28mm lens is great as a replacement for a standard zoom and gives you a pleasing field of view.

The 50mm is longer, but popular as a portrait lens. I find it falls into a bit of a dead zone for me - too long for walkabout use but too short for long distance stuff.

If you don't mind stop-down metering then look for the Pentax 28mm f3.5, it's sharper than the f2.8 version. Pentax made two generations of the lens, the original SMC Pentax and a physically smaller SMC Pentax-M replacement.

grahamwalton wrote:
The M lenses are usually cheaper to buy than the A lenses, but they are of good optical quality. To use a M lens on your camera you will have to enable the use of an aperture ring in the Function Settings and use the camera in Manual Mode. You will need to set your chosen lens aperture on the lens ring.

Pentaxophile wrote:
To begin with, the A lenses are nice and easy. The A50 f1.7 is a very good starting point. A lenses will work just like your kit lens, with the exception of manual focus, and you need to input the focal length to help the shake reduction work.

M and K lenses are well worth trying too, as they are cheaper and sometimes more interesting, but the exposure is also manual and its slightly more complicated.