An Evaluation of Automatic Exposure Characteristics & Scene Modes
 

By Alan Fleming
 
 
 
 

Introduction :-

Modern cameras often have a number of "automatic exposure modes" intended to help the photographer get the best pictures without worrying too much about some of the technicalities and effects of shutter speeds and aperture values. The Olympus C5050 Zoom is no exception and has a "Program Mode" (labelled P) and a number of Scene Modes (including Portrait, Sports, Landscape, Landscape + Portrait, Night). Whilst it is often convenient to let the camera select the "best combination" of aperture and shutter speed for a given user selected "Mode" it is also an advantage to have some idea of the way the camera is "programmed" to select the "best combination".

This document gives the details of a simple evaluation of the various daylight "Modes" of the Olympus C5050Z and the findings of the measurements. These results must only be treated as a simple comparison of the exposure characteristics of the relevant "Modes" - there are clearly many other complex "in camera" scene evaluations and processing per mode which are not taken into account with this crude method of comparison measurements.
 

The Camera Settings :-

The following camera settings were used throughout all of the measurements :-

1) The Light Source :-
A standard 35mm slide projector with the AC supply via a "light dimmer". Light, through an empty slide carrier, projected onto a " "bright white" screen at approx. 1 metre from the projector. The light intensity was varied from off to full intensity using the AC "light dimmer".

2) Camera :-
The Olympus C5050 Zoom camera was mounted on a tripod approx. 1 metre from projector screen. The Camera LCD screen was used throughout. The LCD focus / exposure mark was positioned to be in the middle of the projected bright area. Camera settings were as stated above. NOTE - Camera "White Balance" was left on "Auto" setting even though the light characteristics were from a tungsten lamp. A quick evaluation of changing the white balance setting did not seem to make any difference !

3) Measurements :-
The light intensity was increased slowly with the camera set to "Program - P" Mode. The camera LCD exposure value reading was noted and the light value increase stopped at every stable reading. The "P" exposure values were noted. The camera mode dial was then switched to each other Mode and the exposure readings noted. After switch back to "P" the light was then increased to next stable reading.
Repeated until maximum light available. All readings repeated to confirm measurement repeatability.
 

The Results :-

The readings of Shutter Speed and Aperture were obtained for varying light intensity for the "Modes" of "Program = P", "Portrait", "Sports", "Landscape + Portrait", & "Landscape". The "Night" mode was not measured. The results are presented in a graphical form. The detailed numerical results table is at the end of this document.
 
 

Observations and Conclusions :-

For the camera settings as stated above -

• All of the modes indicated the same "exposure value characteristics" in low light conditions - i.e. up to approx. 1/50^th at f1.8
• "Program - P" Mode, "Landscape + Portrait" Mode, & "Landscape" Mode all display the same (or very similar) exposure evaluation characteristics - i.e. Maximum f1.8 aperture below 1/60^th; at 1/60^th go from f1.8 to f4 as quickly as possible; then hold at f4 for shutter speeds above 1/60^th up to 1/800^th. 
  As expected these settings are biased to smaller aperture for greater depth of field. The camera no doubt does other subtle things internally - which will probably vary from one mode to another.
• "Portrait" Mode & "Sports" Mode both display the same (or very similar) exposure evaluation characteristics - i.e. Maximum aperture of f1.8 until 1/800th; then hold at 1/800th and stop down the aperture. As expected these settings are biased to a larger aperture + faster shutter speed for less depth of field (Portrait) and to stop action / movement (Sports). Again the camera no doubt does other subtle things internally - which will probably vary from one mode to another.
• No allowance has been made in these measurements for changes in the "colour temperature" of the variable light source. Exposure readings noted are therefore only a comparison between the different modes selected and are NOT an absolute measurement of any exposure values for a given lighting condition.

A graphical representation of the results :-

Detailed Results Table :-

Measurements taken using variable light source and noting camera exposure readings in each mod. Increments determined by watching for stable exposure value readings on camera LCD in "P" Mode.
 

Disclaimer :-

This document and these results were compiled by Alan Fleming, Glossop, Derbyshire, UK.

All the results given and any opinions expressed or implied are solely those of the author.
 
 
 
 

Issue 2.1 7^th April 2003