Minolta Hi-Matic 7s auto-exposure

I was wondering if anyone has considered how this camera actually works?

Page 34 of the instruction manual includes a graph of the automatic exposure aperture and shutter speed selection profile. Assuming this is accurate, it suggests intermediate apertures and shutter speed values are invoked: there are only four EVs at which the profile intersects standard stop combinations:

• f/2 @ 1/30th for EV 8,

• f/5.6 @ 1/60th for EV 11,

•f/11 @ 1/125th for EV 14, and

• f/22 @ 1/250 for EV 17.

I'm not sure what to make of this - it seems an unlikely profile for a wholly mechanical camera? I think if the Hi-Matic was capable of setting intermediate values, this would have surely been something worth mentioning in the literature.

Any thoughts?

I am intrigued by the operation of this camera as well. This chart appears to me to be the automatic settings that the camera will assume given different EV Values. I don't think its a chart of what aperture and speeds to set in manual mode. Most cameras of this vintage are either aperture priority or shutter priority, set one and then set the other according to the light meter. It looks like this one takes a meter reading and sets the aperture and then links that to the appropriate shutter speed. Its most likely a trap needle meter and then a link to the shutter speed. I'll have to take the front off to have another look.

The CLC part is a mystery to me. Contrast Light Compensating is the name but I cannot work out how it is done. There is one Cds cell and one set of leads coming from it.

How that translates to CLC I don't know.

I have used this camera in its manual and automatic mode. The automatic mode works very well.

Hi Greg: Yes that is a chart of the automatic settings.

I can throw some light on the CLC part, but the explanation probably begs more questions in the case of the Hi-Matic ... as you have suggested.

In the SRT 101 SLR, the metering employs two separate cells, situated at the top and bottom view screen edges. These cells measure the light falling on different parts of the view, such that readings may better take into account the contrast in a scene, thereby reducing underexposure of shadows, or other dark areas, and minimising the influence of particularly bright regions (as in backlighting situations). The CLC appears to be a metering circuit designed to give a little bit of bias towards extra exposure when the readings in different parts of the frame varied widely. In effect, CLC metering seems to be bottom weighted average metering to typically prevent a bright sky from causing underexposure in the foreground.

Given that the Hi-Matic has one cell, I guess the CLC effect is a global under-exposure?

This camera is more mysterious than I had first realised.

Hello, sorry about commenting on an old thread, but I can explain how the automatic mode on this camera works if anyone's still interested. It does set intermediate shutter and aperture values.

The reason is the way the automatic mode works: as your finger presses the shutter release button down, the aperture slowly closes, and the shutter speed is reduced, by two cams. The moving mechanism that performs these actions is a lever beside the metering needle in the viewfinder. As it descends, the far end of the EV needle stops the motion of the mechanism (the needle is firmly held in place by friction at the first moment of pressing the button - maybe what @greg_nixon2 referred to as a "trap needle meter"?). At the moment when the mechanism touches the end of the needle, the motion stops, and the shutter speed and aperture value are frozen in that position until the shutter button reaches the bottom of its travel, and the shutter release triggers. So the two exposure settings are both continuously variable. It's a very ingenious mechanism and is a testament to the talent of Minolta's engineers.

For the CLC - I think it may be a special CdS cell with two halves on the front, upper and lower. In the Himatic 7 when they weren't claiming "CLC" on the front, they had a totally different type of cell inside a glass tube of some sort.

3 hours ago, smonson said:

The moving mechanism that performs these actions is a lever beside the metering needle in the viewfinder. As it descends, the far end of the EV needle stops the motion of the mechanism (the needle is firmly held in place by friction at the first moment of pressing the button - maybe what @greg_nixon2 referred to as a "trap needle meter"?)

Yes it's a "Trap needle" or "Grab the needle" meter, very ingenious indeed. One thing to remember is that the camera, if worn through lots of use, an Auto exposure image may vary from a manual exposure image on the same EV. I did a test shot on Auto with my well used 7S and noted the EV number, them took a shot of the same scene, using the same EV number, and there was about 1 1/2 stop difference. I went on ebay and bought three 7S's, hoping one would be good, and one was, so I use that one now.

It wasn't the meter itself, it was good. Apparently it was the worn mechanical workings that came out of sync with the aperture and shutter. I suspect lack of lubrication may be the cause of the problem.

Actually the 7s has some kind of CLC. The CdS cell is divided in two halfs, and light comes in through a small window. So a bit similar to a camera obscura, the upper half of the scene is projected on the bottom half of the CdS cell and vice versa. Since the higher resistance part of the CdS - the less illuminated one - dominates the exposure, it will compensate somewhat for a "darker half" of the scene.