Thursday, March 6, 2008

Wide angle - telephoto

In my last blog the illustration I used was taken at mximum wide angle. Todays picture is taken with the lens set at near full zoom. The camera I am using for these shots is a Minolta Dimage 7i. This camera has a 5 megapixel ccd and is more than adequate for this demonstration although a Canon 350d or 400 would be slightly different on the depth of field examples - you have to try this for yourself. The the longer the focal length of a lens the narrower the band of sharp focus you also get a change in perspective. In the not too distant past text books on portraiture would advocate being at least 2metres (6ft approx) from your subject so it would be useful to have a lens that fills the field of view with the subject. In my illustration you will see the depth of field quite clearly when shot zoomed in on the subject. The effect of stopping down is also very noticeable. You will perhaps notice (with your own camera) that your wide angle images and zoomed images behave differently. This is because the focal length to ccd size varies considerably from camera to camera. With the Dimage 7i the true focal length of the lens is 7.3mm which is the equivalent of 28mm on a camera with a full(35mm) size ccd. (the ccd is the part of the camera that is in the 'film' plane and receives and converts the image to digital data).

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