Saturday, 27 August 2011

Part 4 Light–Project:The Intensity of Light

Exercise: Higher and lower sensitivity
The objective for this exercise is to take a number of shots in a marginal  light situation i.e. a difficult shooting situation where, movement, depth of field or image quality could be compromised. The first shots with a low sensitivity setting  and then with a higher one to see if  there was an improvement.
This exercise sounded easier to achieve than it actually was. I got a nice dull day so drove into town to find a busy shopping street but the place was very quiet. I wandered around for about 75 minutes and got a few shots, I’ll write a few up but I think I’ll have to try again. (All of the photos were taken with 18-200mm Vibration Reduction lens which allows me to hand hold at lower shutter speeds and the matrix meter setting was used throughout)
7333: 1/45s f11 ISO 100                                                 7335: 1/45s f38 ISO 800 
DSC_7333_edit01_web DSC_7335_edit01_web
My idea here was to make a direct comparison with  the depth of field available using different sensitivities. I kept the shutter speed the same but the higher sensitivity allowed me to decrease the aperture to f38. The difference in the depth of field is very clear.

7342: 1/60s f19 ISO 800 150mm
7343: 1/60s f8 ISO100 120mm
Here, I was demonstrating the difference sensitivity would make to the aperture setting. I would have expected to have needed f22 with the ISO800 setting but perhaps the slight difference in focal length accounts for the ½ stop difference. There is very little impact on the depth of field at this focal length. At ISO100 there is slight blurring of movement at 1/60s but this may be more to do with the speed of movement. (comparing the feet of the pedestrians, see below).
DSC_7342_crop_web DSC_7343_crop_web

7348: 1/15s f5.6 ISO 100 170mm
7349: 1/180s f5.3 ISO 800 95mm
These shots demonstrate the effect of attempting to shoot moving creatures at low sensitivity levels. These Mallards were very lively and difficult to pin down using an ISO of 100. Increasing the setting to 800 has a dramatic effect on the ability to freeze movement in the image.

7353: 1/20s f5.6 ISO 100 170mm
Although the blurring of this image suggests movement, because the shutter speed is so low, very little of it is focus, even with the VR lens, I was not able to prevent camera shake.
7354: 1/125s f9.5 ISO 800 75mm
The sense of movement is now suggested only by the diagonals whereas the image is sharper with the ISO increased to 800.

Noise at high sensitivity:
Looking at the two areas indicated in the course materials i.e light and dark areas at both ISO100 and ISO800, the grainy effect of higher sensitivity on the darker areas of the image is well marked but there appears to be very little difference in the paler areas, as indicated from the enlarged sections of the images below:
ISO100                                                          ISO800
DSC_7343_close_pale_100       DSC_7342_close_pale_800
ISO100                                                        ISO800
DSC_7343_close_dark_100      DSC_7342_close_dark_800
Conclusions from this exercise:
Although I was unable to make the required number of images, I think I have demonstrated that higher sensitivity settings on a digital camera can be used to improve performance, both in terms of the usable aperture to control depth of field and to give a faster shutter speed to enable sharper definition of moving objects within the frame.
When  the opportunity presents itself, I will attempt to make some more images.

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