Sorry, some errors in my previous post.. The spotmatic UNDERexposes (1/1000s vs 1/320s on the Nikon)..
Here's a corrected version:
Hi
Wanted to chime in, since I only just got my Spotmatic SP and replaced the mercury battery inside (no corrosion, lucky me!).
After reading countless affirmations that the 1.5 V Silver Oxide batteries would work as well, I ordered a pack of Varta V394 batteries to test it myself.
(The mercury battery was in a tiny blue plastic ring that held it snug in place inside the battery compartment, and the V394 (aka SR936SW) fits this plastic ring just as well.)
The V394 is the perfect shape and at roughly 2 USD per cell (Varta, not a chinese knock-off), the price is alright.
So, installed the battery, switched on the meter, and the needle moves. Awesome!
Went outside, pointed the lens (a Super-Multi-Coated Takumar 35mm f/3.5) at something homogeneously lit (e.g. the blue sky away from the sun, the green grass, etc.) and played around with the settings.
The meter seems to work fine: reducing shutter speed by 1 stop, I need to open the aperture by 1 stop to get it centered again. So far, so good.
Now, let's compare it to a digital meter..
Took my Nikon D810 (which has a nice meter that I trust) and used the 50/1.8 (don't have a 35 yet) to take the same readings..
Unfortunately, the Nikon had the exposure time by >1 full stop longer than the Spotmatic. (both lenses metered at f/5.6)
I then used my Fuji X-T10 and compared again. Sure, the Fuji has a slightly different approach to ASA values, but it too chose significantly longer exposure times than the Pentax.
Conclusion:
While the batteries DO in fact work, the camera will underexpose by a little over a full stop!
You can, obviously, set the ASA to 100 when using 200 ASA film (or 200 for 400 ASA film) to increase the exposure time.
Sure, film such as Portra 400 shouldn't suffer from underexposure, but I came to like the film overexposed during exposure and pulled when scanning.. Gives it a more film-ish look.
How do you handle the underexposure?
And don't tell me that my cameras are wrong.. Even my Canon 1Ds III tells me that the Spotmatic is exposing wrongly