The Spotmatics were unique in that they used a bridge circuit. This measures
the DIFFERENCE between a fixed resistor and the photocell. Therefore
it is relatively independent of battery voltage.

Most cameras measure thevoltage drop across the photocell, or in other
words how much electricity it conducts, which is greater with more
light. In order to work properly they need an exact voltage source.
Mercury and silver oxide batteries hold their voltage across their
entire life, alkeline batteries drop off relatively quickly.

In those devices you can replace the mercury battery with a  silver oxide
one if you can recalibrate it for the higher voltage. Many people have had
success using a diode to drop the voltage. Often they have not had to
recalibrate the device. With the diode alkeline batteries would work too,
but they drop out of calibraition relatively quickly with use.

To be totaly off topic, one well known repairman will modify Olympus
cameras cheaply by installing the diode internaly for a small additional
fee while doing a CLA on the camera.

It's a good deal because he is only charging you for the diode a few
minutes of his time, as he already has to take the covers off and realign
the light meter anyway.

Forget the zinc air batteries, they are a necessary comprimise and have
their faults. Use the alkeline or silver-oxide batteries instead.

Note that the cameras in question are almost 40 years old, photocells
age and resistor elements wear out. It simply may not be possible to
get the cameras working up to original specs again. That would be a
shame as the Pentax lenses were top notch.

Geoff.

Hey, I appreciate all the information. Now, I must confess that I should
probably retract the issue with the needle moving in the opposite direction
when exaggerating the exposure. It may have been operator error since I'm
not used to turning the aperture ring in the direction the Spotmatic
requires. I say this because yesterday's shoot presented no such problem.

What I did learn by consulting a manual about the lens/camera combination
is that I should really keep the stop-down switch in the AUTO position and
use the DOF button to activate the meter when using the Super-Takumar
lenses. I should leave the switch in the AUTO position when using the the
full-aperture metering (SMC) lenses anyway. This leaves less room for error
on my part as I adjust to the camera.

I am enlightened by Colin's post about the initial needle fluctuation. This
makes sense to me now - THANKS!

I'm going to shoot another roll today sometime and see if I have it right
about my mistake.

Later,
Peter

For older cameras, following a visit to the camera doctor, a
prescription of Vexposa taken 1 hour before metering will set it right
in 70% or more of cameras.

Cheers,
Alan.

Full-aperture metering with the SP-F (as well as ES and ES II cameras)
only works with lenses labeled "Super Multi Coated Takumar" or "SMC
Takumar".

Sometimes referred to as ES mount lenses, they have an additional
coupling that transmits the set aperture to the camera body.

When using earlier Takumar lenses (including Super Takumars) on the
SP-F,
you must perform stopdown metering, just like earlier Spotmatic bodies.

Excelsior, you fatheads!
-Chris-

Read a good website for Pentax:
http://www.aohc.it/indexe.htm
To replace batteries:
http://www.aohc.it/batte.htm
The screw mount evolution:
http://www.aohc.it/tak00e.htm

Michel
http://perso.wanadoo.fr/krg

I think Chris explained it quite well after your post. In my case I have
both types of lenses ranging from 17mm to 200mm with duplication at 28mm,
50mm and 55mm - the duplicates are the full aperture types. (I went a
little crazy on eBay over the last 2 weeks once I saw the vast supply of
these screw-mounts).

Well, with the Super-Takumars when the switch is set to AUTO the meter will
only be engaged when the DOF button is pressed. And I'm quite used to this
from a Fujica ST701 I used until 1994 (I recently replaced it with the SPF).

over exposure, and up means underexposure?

Um, I probably wasn't clear. No, down means underexposure and up means
overexposure. I was exagerrating the setting to try and get a response from
the meter. Which actually did work. It was my misinterpretaion of which
direction it should have moved. My problem was that I imagined a left to
right turn on the aperture ring should have opened the iris wider and visa
versa. But this is not the case: left to right closes down the iris, right
to left opens it up. Too many years away from a manual camera, I guess.

Nope, the meters in box cameras are fine. The needle needs a second or two
to settle in some situations, that's all. I have obtained good results with
the last 3 rolls (Fujicolor Super HQ, ISO 200), shooting landscapes
primarily.

Now I'm experimenting with my 50mm f/1.4 Super-Takumar mounted on my Kodak
DCS Pro using an adapter. This is a challenge since the internal meter is
totally disabled and I'm too lazy to hunt down my hand-held. What fun would
that be, anyway?

Thanks for all your collective input!

Peter