Batteries

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.

Hi Tonyb,
Whilst the silver cells are a bit more voltage stable, this shouldn't cause any difference as the meter circuits are bridged. I suspect that the problem is more likely meter calibration. It's worth checking the Batt voltage though to make sure on isn't nearly spent.
Regards
Kim

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.

A slight difference may have crept in because the older cameras have centre weighted metering and the newer one may wel be set to matrix metering. These different metering patterns may not give identical results. Centre weighted metering is especially susceptible to underexposure if there are large bright areas in the picture (such as sky).

The batteries are not very likely to be the source of the trouble, but I would always use silver oxide cells as opposed to alkaline ones.

Hi

I'd go along with this, my MX tends to get anything with water, snow or excessive sky in a little wrong, whereas my MZ-3 or z1-p tend to handle all but the most extreme situations very well. I've enver tried centre-weighting on either of these (using either spot or matrix), but if time allows I'll check it out to see what the differences in the 'average' scene are.

Have you tried testing the exposure of all of your cameras on a grey card to see if they all give the same? Failing that, try framing a patch of grass, as (I believe) grass will give similar results as the grey card.

Matt

Just to add a little more, there are differences in centre weighted metering patterns too - in other words, the degree of emphasis on the central part of the picture can vary from camera to camera.

Also, although meters are traditionally calibrated to 18% reflectance, some are in fact calibrated to 10%, which confuses the issue further.

I think my MX was very good for transparencies, as it did give the correct density in the slide. My MZ3 (and the MZ5) tend to give more generous exposure, which without due care can lead to burnt out highlights.

The ME Super meter I have always found to be excellent, probably more consistent than any of the others!

My immediate thought was with regard to the metering pattern also.
It might be worth ascertaining the 'correct' exposure by using the reflected reading from an 18% grey card and comparing the settings chosen by the three cameras but I'm not sure how positive that would be where the perceived error is only around 1/2 a stop.

Hi, not quite on topic, but I use a Lithium cell for my MX and ME Super. There is a single cell replacing the two Silver cells originally used, it is called a 1/3N or DL 1/3N, 2L76, or CR1/3N. They are very stable throughout there life, and have an extraordinary shelf life, (my spare says best before 2010). I don't think the use of the Lithium, the Silver Oxide or the Alkaline cells have made any discernable difference to the metering I have experienced, and I have at times used all three battery types.

Regards, Taliety.

It is not recommended to use lithium cells in the MX and similar cameras, they are not designed for them. It may well be that the nominal voltage is actually higher, but I think it is because of the heat generation from the lithium cell.

It is better IMHO to stick with the instructions and use silver oxide or alkaline G13 cells.

John, you may be right, I had not come across those recommendations. I have been using the Lithium Cells since they came out, probably more than 15 years ago. I am afraid my ME succumbed to me dropping it, rather than the high voltage of the Lithium cell. I must admit, I've never measured it before, but was a little surprised at the 3.3V from a CR1/3N. 2xSR44s are more like 2.6V. The Lithium Cell is the only relieable cell to work at very low temperatures, though.
I shall have to consider whether to continue to use the Lithium cells after this.

Regards
Taliety

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.

Hi,
On the subject of Lithium cells, I used them for a while in my LX. However, I found they didn't last as long as silver cells and with the price of silver cells, they just don't make economic sense.

Kim