Light (or exposure) meters

The next development was the electronic light meter.  Initially, these had a cell made from selenium that produced a small electrical voltage on exposure to light.  This voltage was then used to move a needle across a scale.  This needle would then point to an arbitrary number that has to be set on a scale.  The scale then indicates a range of appropriate aperture and shutter speeds.  It is tempting to think of these as EV numbers but they are not – at least are not on the three light meters I own.  These worked very well in reasonable light but were poor performers in poor light.  These fell out of fashion and were replaced by CdS meters.  The advantage of selenium meters is that they do not need a battery to work.  A big disadvantage is that they lose sensitivity with time.  Towards the end of their useful life they give a low reading which will eventually cause over-exposed photographs.  For this reason, some people will not use old selenium meters but my old (fifty years old, plus) meters all agree with my modern light meters.

 I suspect that the rate of deterioration depends on how the meter has been stored over the years.  If the meter is in the dark inside a case apart from when actually taking a reading, the deterioration doesn’t seem to matter over a period of sixty or so years.

This is the meter I most often use as it is nicely made, feels good in the hand and produces satisfactory results.  A scanned copy of the Ikophot manual is available for download as is a scanned copy of Zeiss Ikon’s 1930s exposure guide.

The following is an advert from the British journal of Photograph Almanac of 1957:

Lastly, my Bertram Bewi Automat.

Bertram Bewi Automat

This is a German meter (made in West Germany).  Bertram have been making light meters since 1928 . This meter works differently from the meters above.  For one thing, it has a digital read-out rather than an analogue needle pointing to a scale. 

The meter is rather larger than is usual for analogue meter – it measures 90 x 65 x 25 mm not including the activating button.  It is encased in ivory plastic.

 The only control is a ring to set the film speed.  This is calibrated in ranges. For instance, the DIN setting is a range of three numbers – 11-13, 14-16, 17-19, 20-22, 23-25.  That is one stop difference between each range.  Given the exposure latitude of film that is plenty accurate enough.  There are also ranges for ASA and Weston (ASA is the same as ISO and Weston is a defunct film speed system devised by the makers of the Weston series of exposure meters.

Using the meter is also different to analogue meters.  If you point this meter at the scene you intend to photograph, nothing happens.  You need to point the meter, depress the activating button for about three seconds and release.  Once you have done this, the shutter speed scale lines itself up with the aperture scale and you can read off suitable combinations of aperture and shutter speed.

The read out also has exposure values indicated – under L on the aperture scale.  These are adjusted for film speed and can be set directly on an EV enabled shutter.