Have you seen the postage they are charging - £12 to post a lens!! May be there is a surcharge for the radio-activity!

That's quite a difference - I'll make a note of Camera Direct. I have bought quite a bit of stuff from Morco over the last couple of years and they are reliable - but a price difference like that could easily tempt me .

Morco do them - 01623 422828

I've just bought a new Pentax 28mm AF lens from the Jessops website. It said it would take between 4 and 6 weeks - ordered Friday - arrived Monday. And they've reduced the price to £199.99. I wasn't expecting that kind of deal on a new Pentax prime lens these days.

Thanks for all the advice. I've done a test of the 3 cameras along with a Sekonic L308 exposure meter against an identical scene - a plain emulsion wall - which has given an interesting result. The cameras were all set to 400 ASA and had the same lens. The Sekonic, MX and ME-Super all read F2.8 for 1/30. The MZ-6 read F2.8 for 1/20. So it looks like the MZ-6 is over-exposing rather than the others under-exposing, and as the meters are different that probably explains the discrepancy.

Thanks Kim. The batteries in both the MX and ME Super are near new (and the previous batteries acted the same) so I think you are probably right about calibration. The MX is a recent purchase and has always underexposed. The ME Super I have had since new (1980ish) and originally did not underexpose. The original batteries lasted for years and I don't know which of the two types they were. I have only noticed the underexposure for the last couple of years, and its easy to accommodate. But that's why I thought it may be the batteries as I may have unknowingly switched types at that stage.
I did have it serviced about a year ago and that didn't make a difference, but I did not specifically ask for the exposure meter to be recalibrated.

I have three Pentax cameras - an ME Super, MX and MZ-6. The former two take button cell batteries (LR44 or SR44) and the MZ-6 takes a larger cell battery. I find that the ME Super and MX slightly underexpose compared with the MZ-6. I would estimate the difference to be around half a stop.
As there is a choice between LR44 and SR44 could this account for the underexposure - is one acceptable and the other not.