Exposure issues with older manual lenses

So which camera bodies did you use? The implication of what you are saying suggests that you might have been using manual focus bodies?

Broadly speaking, I think the mount "crippling" as it's referred to came with the AF bodies.

If this question is addressed to me, then the answer is Pentax ME Super and Ricoh KR 10 Super for a long time. I still have a Ricoh XR-X and KR 10 Super, and a Pentax P30N (2 more film SLRs than I need, but this was a result of a process of rationalisation via eBay a few years back, which ended up wholly irrational!).

Irrational rationalisation, love it! It has to be the best kind.

That's why it's not been a problem yet then. The "crippled" mount came with the first AF bodies I think, when the "A" lenses had been around for some time. It may well have been related to cost, or perhaps to technical issues that were too expensive to solve.

If you can, using A lenses might not cost too much as the prices for your M lenses could be quite good on eBay. Otherwise, it's a problem that just needs working around. In some ways it's easier to use screw thread lenses, which is a bit ironic I suppose.

The first Crippled mount body was the MZ-50 (or possibly the 10? not sure about that one), all the A, SF and Z series bodies have a fully functional mount as do all the single diget MZs

I think the 10 was the full mount as well. Thanks for the reminder re the various bodies.

I'm sure it'll be quite familiar to many people on here. You have a bunch of cameras and you think "I don't need all these, I'll sell these two on eBay and buy this one", or whatever. It doesn't quite go according to plan, and once the eBay frenzy has died down, you realise you actually have more cameras than you started with.

The 300mm one is likely to be the most expensive one to replace, I imagine. I could swear I had an A 50mm lens, but having looked through all my lenses, I find I have 3 M ones instead (including the XR Rikenon f2 lens of legendary sharpness).

I meter manually more often then not.
the only time I ever had an exposure problem, was over exposure caused by an old lens that had the aperture blades leak lubricant and get sticky.
so my advice is use a handheld meter; or get a newer lens and take a meter reading, then swap back to the older lens and meter again...
is the readings similar?
if so snap the photos and compare.
is the manual lens overexposing the shot at the same settings as the new lens? if so get your old lens cleaned and lubed and it should work better.

remember using flash with a manual lens mean FULL power only for the built in flash! that will also overexpose.

The easiest procedure would be to meter at maximum aperture first.
Then set the aperture to its desired value, i.e. stop down (e.g. 3 stops).
Use the first measurement and apply the necessary compensation (here: 3 stops).

Are you sure it's 3 stops to compensate - that's a heck of a lot.

I think froeschle is suggesting the user take over the role normally played by camera electronics in open aperture metering systems.

ie, meter wide open, stop the aperture down a known number of stops, reduce shutter speed by the same number of stops, shoot.

That would wok well if someone routinely shot at f/8 or f/11 or whatever aperture as the error would be consistent.

IIRC the instruction manuals state that the evaluative metering doesn't work with pre-A lenses and centre-weighted is used instead (spot still works). This goes back to the Z-1 (the first Pentax to have evaluative metering). This could be one reason why metering with pre-A lenses is different. I haven't noticed it as a problem but then I rarely use evaluative metering.

Lenses with sticky apertures might also be the cause of metering issues depending how you stop them down. One of my lenses has a sticky aperture, using the green button didn't stop the lens down fully before metering BUT using the K-5s 'stopdown' position of the shutter release collar (where you can hold it stopped down for as long as you wish) solves the problem. The actual exposure isn't affected as much because the lens would usually stop down enough before the exposure.

Evaluative metering requires data which is only available from the A series lenses, I used to know exactly what but I can't remember, it might be something like the absolute value of wide open apperture.

As a brief follow-up, I've been taking some photos with my 28mm A f2.8 lens, and the exposure seems pretty spot-on to me. (Having said that, a bunch of the photos are incorrectly exposed in some way, but that's no fault of the lens. Every tried photographing a black kitten? Very difficult, especially when she's alongside her ginger brother).