Exposure Part 2

Exposure Part 2 - Making it work.

This week we look at more on making exposure work on a modern camera.  While early exposure based on the type of light worked, it wasn't really accurate enough, and the first light meters were the result.  At first the meter was a set of neutral density filters, and you would pick the proper filter, which gave your exposure.  This relied on the human eye, which is different person to person.  Then we saw the first electric meters, these were based on selenium, and operated as a type of photo-voltaic cell, it would when exposed to light produce a small voltage, the higher the voltage, the more light there was.  The result was a match-needle system, the voltage would be displayed and as you set the shutter speed or aperture, it moved another needle, when the two needles were matched, you had the correct exposure.   They were terrible in low light, and needed to be quite large, and ceased to be used in the 1960's when Cadmium Sulfide (CdS) based meters were developed.

These worked in a different way, by passing a voltage through the cell, as the light was higher or lower, the resistance was higher or lower.  These meters required a battery that would provide the same voltage from fresh until it suddenly dropped dead.  Mercury batteries had this characteristic and were cheap, until they were banned in the early 1990's.  Alkaline batteries which are cheaper and less toxic, tend to start at a higher voltage and gradually drop, requiring some form of voltage regulation circuit to provide a constant voltage to the cell.  Some meters still use CdS meters are still used, although other sensors are also used.  CdS cells could be quite small, and mounted inside the camera, giving a very good reflective light meter.

Manual mode, this one is for what you think the computer is likely to get fooled, for example when there is a lot of one tone, which isn't your primary subject, or your trying to do something creative.  A photographer by the name of Ansel Adams developed the zone system, for such circumstances.

Aperture Priority mode, when you want to control the aperture, and are not as concerned about the shutter speed.   For example your trying for a certain depth of field.

Shutter Priority mode, when you want to control the shutter speed, and are not as concerned about the aperture.  For example action shots.  Sometimes you will use it to freeze motion, and other times to emphasize it.  This can be very useful.

Program mode, your not really concerned about aperture or shutter speed, and just want an image.

Many modern DSLR Cameras also have "hint" modes, for example Sports or Portraits, these are similar to P mode, but will shift the values, based on the hint.  For example Sports mode, will attempt a high shutter speed to freeze action, Portraits mode will go for a higher aperture, to ensure a face is fully in focus.

B3400088

On my current regular camera, I use various modes, most commonly Av or Tv (shutter priority), there is the ability to shift the exposure by up to 3 stops,  so there is little need to use M mode anymore.  I also sometimes use the hint modes, I don't like P, but it is there....

This weeks image is from well back in the archive, it's a film image that was scanned, I don't remember from where, but I like the reflective nature of the image.  There are hundreds of these, that were scanned and never catalogued, and I am slowly getting them done. One thing I did do, was include some notes, in the exif data  and this one was originally shot on Agfa Vista 200 ASA Colour film, using the Konica FC-1 Camera.  

I think that's about all there is for this week

W.