Q:  Dear TRA,
I was looking for a Medium Format Film Camera and chanced upon your  website after some research.  From the comprehensive info from your  website, it convinced me that Pentacon Six is the camera for  me. I Thank you for the excellent efforts to put together a wealth of info for the Pentacon Six camera.
 I have just bought a Pentacon six TL with the metering prism.  The  camera works perfectly and I just receved the metering prism and I am still waiting for the  PX625 battery to test the metering prism, but suspected the metering prism may have a problem. The  description of the problem as below,
I am trying to use the stop down metering mode as per your website  suggestions. I suspected the middle dial maybe"misaligned" and would like to seek clarification from your vast experience using the  camera.
1. There is no click switching from one shutter speed to another. Is  that normal?
2. If I set my Film speed to ASA9 , the maximum I can move the  middle dial clockwise is at 500 (white stripe position) while the maximum counterclock-wise position is over the scale of the slowest  shutterspeed (1).
3. If I set the Film speed to ASA1000, the maximum clockwise position is over the max shutterspeed (1000) scale while the maximum counter-clockwise position is 30. 
I saw there were 3 retaining screw holding the middle dial in place,  not sure if some dial position adjustment needed to fix this  "problem" .  Would be glad if you can assist me in this matter.   Thanks

Regards
CM

A: Hello CM

Thank you for writing to me.  I am glad that my website has helped you, and that you have been able to buy a Pentacon Six TL and a metering prism.  Last week I received back from processing three films that I took recently with my Pentacon Six TL, using the metering prism.  All frames were perfectly exposed.

Your metering prism is probably NOT faulty.

1.  There is no click switching from one shutter speed to another on the back dial on the metering prism.  That is correct and normal.

2.  Every light meter, from any manufacturer, covers a range of exposures that changes depending on the sensitivity of the film.
So, with extremely high-speed sensitivity film, some of the longer exposure settings will not be available,
and with extremely low-speed sensitivity film, some of the shorter exposure settings will not be available.

This normal, and in fact corresponds to the photographer’s needs:
with an extremely high-speed (highly-sensitive) film, very long exposures (for instance, several seconds at a large lens aperture, for instance, f/2.8) will not be needed for most types of photography, as this would over-expose the film;
and with an extremely low-speed film (low light sensitivity), very short exposures (for instance, 1/1000 sec at a small aperture, for instance, f/22) will not be needed as the film would be under-exposed with most normal light sources.

The way that the Pentacon Six metering prism is designed reflects these natural limitations on the range of exposures that it needs to offer.  I have tested with one of my Pentacon Six TTL meters, and it seems to have the same limits as you observed with your meter.  In fact, I have the bright Rollei focussing screen installed, and when this is used, the film speed has to be set against the white dot instead of the white triangle index point, so the range of speeds is slightly different.

However, I mostly use films of within the range from 100 ASA/21 DIN (= ISO 100/21°) to 400 ASA/237 DIN (= ISO400/27°), and have never been hindered by the range of the meter.  In other words, it always gives a suitable exposure in any light from extremely bright sunlight down to very low light, at which point a flash gun would be needed.

It is these days difficult to find a film with a lower sensitivity setting than ISO 100/21°, although of course at the other end of the range there are films that are more sensitive than ISO 400/27°.  However, these mostly have a lot more grain, and for most photographic purposes that is not desirable.

Nevertheless, I have also shot 1000 ASA (31 DIN) black and white film, which resulted in a very grainy image when processed in Rodinal (now called Adonal) developer.  This can be good if you want a special effect.

Once you get the battery, I suggest that you test the meter with the setting at the actual film speed sensitivity that you intend to use, possibly comparing the suggested shutter and aperture combinations with those suggested by another meter or another camera.  However, to do this, you need to know how to set the same ISO setting on the other meter or camera, and a difference of about half a “stop” (aperture setting) is normal.  (Remember that it could be the other camera or meter that needs calibrating!)  It is also difficult to meter exactly the same area with two different meters or cameras, so you should not be concerned if there appear to be minor differences.

Then shoot a film, preferably negative film, following my loading instructions carefully (here).  After the film is processed and printed, you will be able to evaluate the accuracy of the meter (and the camera shutter).  If frames in different levels of light are consistently over-exposed or consistently under-exposed, you have two choices:
1)  Get the camera shutter speeds checked on a shutter speed tester, and have the shutter serviced if necessary;
2)  With a white marker make a new index mark on the outer black meter ring, and with a black marker cover over the original index marks (the triangle and the dot).  Choose the position of the new index mark to give you slightly more exposure if your frames are under-exposed, and slightly less exposure if they are over-exposed.

Of course, it is easy for a camera technician who knows the camera and the meter to adjust the meter sensitivity, but I would not say that this is a job for a non-technician.

In all probability, your meter will give perfectly-exposed pictures.

I wish you enjoyment and success with your new camera, and many beautiful photographs.

Mr Pentacon Six