Tuesday, 6 September 2011

Light: Project - The intensity of light

Exercise: Measuring Exposure

Aim:  This exercise is in two parts.  Part one is a series of shots that are deliberately lighter or darker than average with a description why.  Part two is series of 5 shots but for each shot there are 5 exposures based around the average to see whether lighter or darker exposures are more accurate or provide a better image.

Approach and results:

Part 1:  The first thing to note here is that the shots that are deliberately dark have small but bright points of interest that do not look good shrunk for the blog.  The following three images are all darker than usual because I wanted the particular bright areas to be the interest in the picture.  In the first picture it was the shaft of light round the end of the arch and the sunlit leaves that caught my eye.  I took a series of pictures to get to this result.  The first picture gave an even exposure bringing all the detail out in the foreground and walls but blowing out the sunlit areas.  At this point I set the camera to manual, set the aperture I wanted for the depth of field and then altered the shutter speed until I got the result I wanted.
For the shot of the church window I took a spot reading from the window as the average exposure lost all detail in the stained glass (which was the reason for the picture).  I then set the exposure in the same way as I did for the first picture.  I approached the shot of the stairs in the same way.

F7.1 1/125sec ISO200

F7.1 1/100sec ISO200

F5.6 1/200sec ISO200
The next two images are lighter than average.  This first image had dark shadows and a lack of detail in the window, lemon and chillies.  I took a different approach to getting the exposure I wanted by using the cameras exposure compensation and pushing the exposure by 0.7 stops.  I did this in aperture priority so the camera did not alter the depth of field.  This brought back the detail I wanted whilst only lightening the brickwork by a small amount.  I have no idea why a lemon and some chillies were nailed to a wall in a Manchester back street!!
For the second shot of the vine I took a spot reading off the grapes as the first exposure made them too dark with very little detail.  The background is now bright but surprisingly acceptable as it is not the focus of the picture.

F8 1/30sec ISO200

F4.5 1/160sec ISO200
Part 2: For this part of the exercise I took 5 seperate pictures but bracketed the exposures one stop either side in half stop increments.  The aim is to see what acceptable tolerances there are around the average exposure.  Bracketing is something that I used to do a lot with film as you were never sure of the result.  Using digital this is not something I do as much anymore.  I used the evaluative metering for all the images.  The results depend on two things; how the camera metered the scene and what I wanted in the image in the first place.

Using the first shot of the stained glass window, half a stop over brings out more green in the image, the white remains bright, the writing in the middle is clear and the blacks are still black.  One stop over makes the writing blown out by the white background.  Under exposing makes the white start to look grey and more of the green turns almost black.

The second shot of the bins is tolerable half a stop either side but not any further.  One stop over washes out the colour in the bins and one stop under loses the red bins in the background.

The third shot of the backstreet is interesting as I think all the results are ok depending on what you are looking for.  The overexposed shots bring out the detail in the dark backstreet without overexposing any particular area giving it an almost filmset appearance.  The underexposed shots create a darker,more realistic but more mysterious image reminiscant of the large areas of black in a Bill Brandt type image and would probably look good in black and white.   

The most obvious use for bracketing is in the 4th image where the sky and ground are 50/50 making the average less predictable.  In this case the under exposed shots are preferable as the detail in the tree and sky is not lost.

The fifth image suffers as a result of the sun going in and out so the average shot is brighter than the others.  As you under expose the detail in the sky comes out more but this is not the main focus of the picture and therefore does not work.

Learning points:

There are a number of ways to get the exposure you want including using the right metering method, bracketing, using the cameras exposure compensation or using manual mode.
I was surprised to see how many of the over/under exposed images were actually ok in my eye.
If the subject is correctly exposed there is more tollerance for areas of the picture that are too dark or too light.
Images with less extremes of light and dark are more tollerant to over or underexposer.

Technology has moved on.  I can expand the dynamic range in camera which also has built in HDR but these functions should be used with caution.  Extremes of light and dark can be an important part of the image the photographer wants to create and evening things out can be detrimental as it changes the focus of the picture and can reduce the dramatic impact.

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