Tuesday, 16 February 2010

Exercise 3

What: The brief for this exercise was to examine the different depths of field produced at different apertures. The brief states that at least three photographs must be taken at different apertures, i.e. Widest middle smallest f/stops.
Where: In the back garden
When: After 1 O'clock in the afternoon
How: The camera was set on a low tripod and locked off so that it could not move. I then focused at the main object for the photographs which was a small piece of stone and dirt half way up the garden. Then three photographs were taken at the differing apertures. The camera was set to ISO400, I was using a 55-200mm lens set at 55mm.

Once I had set the camera on Aperture Priority I noticed straight away that the every time I stepped down on a 1 f/stop the camera adjusted the speed 1 stop down.
After I had taken the photographs, I then examined each photograph and highlighted a rough area where the image was at it's sharpest. The circles show the depth of field, however I have added the arrows to show that the depth of field should be considered as a column rather than a 2 dimensional circle.
f/4 1/250 ISO 400

f/10 1/40 ISO400

f/22 i/8 ISO400

One of the first things I have learned from this exercise is, location, location, location.
The first group of photos I took for this exercise turned out to be very disappointing in that I had covered such a wide area of ground that it was almost impossible to differentiate the area of focus. I had obviously chosen to far away a midpoint.
I have noticed one thing with the two kit lenses that I used; in both the the failed attempt and the photographs that I uploaded, that it is that the lenses did not create the sharpest of images at f/22. The middle photo at f/10 or f/11 produced the sharpest images of all. This may be down to the manufacture of the lenses and them not being of the highest optics.
My main learning point of this exercise is that the depth of field is really a sort elliptical cylander shape. For some reason I was under the impression that the depth of field for a photograph was like a flat oblong.

This exercise has left me with a couple of questions.
1. Why at f/10 did the camera set the speed to 1/40th of a second but at f/22 the camera set the speed at 1/80th? I would have though that the camera should have stepped the speed down, not up? The amount of light did not change between photographs.
Answer; I did not read the Exif information nor my log book correctly. I shoudl have noted 1/8th of a second instead I read of 1/80th. My mistake, next time I'll double check. Dyslexia sucks. Error Corrected.
2. Why is f/22 not as sharp as f/11? I would have thought that at f/22 the total depth of field should be the sharpest and the clearest.

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