I'm thinking about saving for a decent AF prime again. Anyone have the 21mm DA Ltd, and what do they think? How does it perform?

I've picked that focal length as I find 28mm pretty handy, as Pentax no longer make a 28mm and in any case something slightly wider would be good the 21mm fits the bill.

You can often buy the dioptre adjuster lenses via ebay, although you may have fun finding the precise type you need as obviously they come in different strengths.

It's worth checking for any dirt on the mirror or the eyepiece, although this does sound more like a dioptre thing. Whatever you do, don't attempt to clean the focusing screen. Any form of solvent (even mild stuff like lens cleaning fluid) will wreck it. You can use a puffer bulb to blow dust away or a soft brush if you need to, but be very gentle.

The mirror and eyepiece can safely be cleaned with a cotton bud and computer monitor cleaning spray - just spray the bud and then use it to wipe the components, then use a fresh bud to polish it dry.

Fair enough - there just seemed to be two people enthusiastically saying that Pentax has the best record of backwards compatibility and no previous posts saying the opposite, hence my confusion!

I think a post has been deleted somewhere?

A major reason for my choosing Pentax was the fact that I knew all of their lenses would work, rather than having to spend ages carefully reading the lettering on the front to decide whether it was compatible.

Judging by the sample images it isn't a bad performer, but is a bit soft and seems to struggle with backlit subjects.

The only worry I would have is with attempting to focus manually with the limited depth of field shown by this lens.

The MX split prism screen is ok down to f4.5 or so, although eye position becomes more important.

Nah, it's more like a very undernourished spider on one edge!

Can't get the finishing ring out at all, did try going in from the back but couldn't remove enough to get at the problem area. I've now put it in a separate case with a silica gel bag which should stop it getting any worse. It doesn't appear to have any effect on my test shots, it just annoys me when I end up with stuff that isn't quite perfect any more.

I had a go, but the website appears to be completely borked. I tried feeding it to Google as Japanese, Chinese and finally Korean and I just kept getting "403 image" errors everywhere!

They also do a faster, cheaper 500mm mirror lens: http://www.amazon.co.uk/Opteka-Telephoto-Mirror-Digital-Cameras/dp/B00281OE1K/re...=sr_1_5?ie=UTF8&s=electronics&qid=1276953554&sr=1-5

I'm slightly tempted at that price, f6.3 isn't much slower than my 300mm zoom (f5.6). Presumably mirror lenses have a fixed aperture?

I must try that - I gave it a brief go on my K-m and then rapidly put it aside!

Mixed day. Finished and successfully developed another roll of black and white (my KM is therefore in perfect working order) but also found that my ancient, rare and rather lovely SMC Pentax 85-210mm has a speck of something nasty growing on one of the internal elements. The lens was perfect when I bought it, this has evidently turned up in the past few months. I've put it in the airing cupboard for now on the grounds that fungus doesn't like dry heat, so it shouldn't spread. I really don't know what to do about it, I suspect professional cleaning of a fairly complicated zoom would cost a lot more than I paid for the lens.

I also found that my newly-acquired 2nd version M 28mm f2.8 has something spidery on one element, but as that's a simple prime I should be able to pop the front element group out and clean it. Just need to persuade the finishing ring to unscrew so I can get in with the lens opening tool!