The sad part for buyers is that others will see it and price accordingly, so this becomes the standard price. I saw this everywhere when looking for an M 40mm f2.8, all the sellers were setting prices around the £100-£120 mark, because that had become the going rate despite it not being especially rare or expensive when available new. I made a cheeky £70 offer to someone asking £99 or best offer and was amazed to have it accepted, considering auction final bids I've seen since that wasn't bad at all for an excellent lens with original front cap.

Much, much better than the real world camera shop which said they had one for £150 and seemed a bit bemused by my wincing. I'm happy with the lens but wouldn't have paid over £70 for one!

Ebay prices vary. Which version do you have, as Pentax changed the design of this lens during its lifetime? The earlier version was identical to the even earlier K series version, just with "-M" added to the lettering. It has a chrome ring around the barrel between the lettering and the grip. The later version doesn't have this chrome. You can see both of them at the Dimitrov Pentax K-mount site, with photos that should help you identify yours.

I haven't tried the later version but the earlier one is very nice indeed, I picked up an optically superb example for £20 or so last year on impulse. It looks as though it has been well used but carefully as while the paint is worn there are only a couple of scratches and no dents. I mostly bought it as I rather like the original K series lenses, so finding something that is a K in all but name for sensible money was a pleasant surprise.

I've since seen them priced at around the £50 mark for a good example, mind you all lens prices seem to have gone really silly of late. Have a quick look on ebay first before deciding whether you want to have it fixed, or replace it and then maybe have a go at sorting the old one yourself.

I think Kris means this Alan?

He's a well respected independent repairer, I sent a 200mm prime to him a while ago to have fungus removed and he did an excellent job.

I think that's why I've only bought a couple of them, aside from the fact that they never give Pentax any space. I pick up a magazine and see heavily post-produced images which I know I haven't a hope of emulating and don't really see the attraction in.

If you're looking to assemble the classic film-era three primes kit then you'll also want the Pentax-M 28mm f3.5 and the 50mm f1.7 (or f1.4 if you can find one). Great lenses all and capable of showing up new gear costing several times as much.

I just wish they'd made an A version of that 28mm, the f2.8 isn't as good IMO.

There was a K 17mm f4 fisheye too. Currently one is up for grabs on ebay, although it won't go cheap and has a reserve on it.

Are they making a new Dental Macro or was that the old M series one?

I have one, I like it, and although it doesn't see much use I won't sell it!

Seriously, the M 135mm f3.5 is a fairly common lens and will come up for sale pretty often. People may have bought mixed lots of gear in order to get hold of a specific lens or body, then sell off the duplicates in order to recover some of their outlay. 135mm was the standard telephoto lens before zooms became cheaper, so there will be plenty out there and most lots of "camera with lenses, filters, etc" will probably contain one.

Just wondering whether it's safe to leave it a bit or whether I should dip into the overdraft until Wednesday. It's interest-free but I like to stay in the black!

I agree with at least two of those points. Small, fast lenses are very handy. That's why I like the 100/120/135mm lenses, most of which are f3.5 or faster and all of which are fairly compact. Mind you, I also have a soft spot for the big K 85-210mm f4.5 zoom, which is about 18" long and weighs in at just under a kilo. You need something to rest your elbows on while using that lens, Snowdon is about right...

I'm struggling to talk myself out of an M 100mm macro, there's one on ebay for £100 at the moment which looks pretty much mint. Is this sane money and should I be pouncing on it?

I quite fancy a go at macro, and that lens has a very good reputation both for macro and normal use.