I found an Asahi Pentax Spotmatic, and I was anxious to test it out to see how it worked. It’s a completely manual camera, and was one of the first to have TTL metering. It meters in stopped down mode, so you focus first (with the lens wide open) then press a button which turns on the meter, goes into stopped down mode, where you can check the depth of field, and set the exposure. Then you can take the shot, and the meter turns off automatically. So, let’s go into the field to see how it works.
I actually think it’s a good idea to let students use a camera like this, so they understand how cameras have evolved, how metering has changed over the years, and to learn a little about how a light meter actually works.
My camera is an original Spotmatic SP circa 1966 with a Super-Takumar 50mm f/1.4 lens. I also have a Super-Multi-Coated 28mm f/3.5 lens, but I’m not sure how much I will use it now. I’m going to concentrate on the 50mm prime lens for my first tests.
When I was in high school, I used a GAF L-CM camera, which was made by Chinon back in the 70’s. It metered the same way (stopped down mode) – which was replaced by fully auto lenses, which allowed the lens to stay open to it’s maximum aperture during metering, and the lens communicated the aperture setting (mechanically back then, and electronically today) as the photographer adjusted the f-stop.
Here’s something else about these older cameras. From the 1940’s through the 1970’s, some lenses were made with radioactive materials. Interestingly enough, the Pentax Super-Takumar 50mm f/1.4 lens is one of the lenses that may have been constructed with radioactive thorium in the glass. Thorium emits both alpha and beta radiation, and, I suppose, may not be healthy to spend too much time around. If the eyepiece were made with thorium, that would actually be much worse, since the radiation may harm your eye, but may not penetrate skin to harm other parts of your body. From my research, it looks like no camera eyepieces were made with thorium. Here’s a blog post listing lenses made with thorium, as well as other information about these “radioactive” lenses. Apparently, the thorium used in these lenses isn’t strong enough to harm photographers using them… but it still feels weird having lenses that emit radiation.
One other side-effect, I guess you could call it, of lenses made with thorium, is that the glass frequently yellows or turns brownish over time (like decades). So, the thorium lenses that I have (my new Super-Takumar 50mm f/1.4 as well as a Zuiko 50mm f/1.4) have both turned yellow – some more than others. This means that color photos taken with these lenses will generally have a yellow/brown tint. Black and white photos probably won’t look unusual. Even if this property (changing color over time) was known, most of these lenses were used for black and white photos – so a color shift probably wouldn’t have been considered a negative back in the 1940’s or 50’s.
To see an example of how the color might shift, take a look at my blog post comparing digital and analog – where I showed analog photos taken with my Zuiko 50mm f/1.4 lens, which has thorium and is quite discolored.
So, here are some photos taken around town with my Asahi-Pentax Spotmatic. Some were taken with the 50mm f/1.4 (with thorium) and a few with the 28mm f/3.5 (no thorium).
I’m not completely happy with the exposure. There were a few photos (not shown) that were way off because I had the battery in backwards. Now I’m having trouble with the meter working at all. I’m going to try some other batteries to see if I can get it to work. The Spotmatic, like the Canon EF, has a voltage regulator built in so you can use a 1.55 volt battery instead of the original 1.35 volt mercury batteries (which are no longer available). I hope I can get it working again.