also, when i turn the camera on with this 28mm A lense (Sigma) it asks me what lense size it is, so i choose 28mm. an expert in a shop told me it shouldn't ask me - instead it should detect automatically - if i have a correctly working 'A' lense...

any other advice at all??

Wow thanks for the rapid and very informative response Matt! Yes I have much to learn about technicalities. The 28mm lense comes out at 45mm once on the km. I have a 50mm, sadly without the a setting, which comes out at 80mm, which seems too close. Ideally I just want 50! But I'm certain you know all this. I'll try again with the advice u gave...

hi, i've just signed up to what appears to be a complete fountain of knowledge on here, hope you can help... apols if this question has already been answered - is similar to a recent topic

i have a pentax k-m dslr. i'm trying to get going with an old lense for portraits but am struggling to make the camera work as it should...

i've just bought this lense - hope the link works: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=17...

its a 28mm with the all important 'A' on the aperture ring. i've locked it to the 'A' setting on the lense ring, then put my k-m on manual focus, permitted aperture ring in the settings (and tried prohibtited as well), but on 'Av' (aperture priority mode) the F stop value seems to be stuck on F4. the screen just displays 'F---' and the light meter doesn't work.

any advice anyone???

i'd really really appreciate it as i got the lense especially for a shoot this friday - i really need shallow depth of field to do portraits for a small charity's staff and blur out their terrible office in the background!

thanks in advance