Thursday, March 20, 2008

Depth of Field and Telephoto -Zoom

The depth of field in a picture is the two points, in front and behind, of a subject that appear in sharpest focus. These distances are governed by four things in the main
Firstly - the actual focal length of the lens. Second - the distance the subject is from the camera thirdly - the aperture that is set on the lens and finally the size at which the image is to be viewed. These are not in order of importance they all effect the result. The two images I am going to use for this do two things they show the difference between wide angle close up and long focus.

The left image is taken with the lens on maximum zoom and the right image is shot at maximum wide angle. They both had the same aperture (fully open for the zoomed shot and stopped down a tad for the wide angle shot).
As you can see the longer the focal length the less the depth of field is - there is more apparently sharp in the wide angle. Shot - but if you click on it to make it larger - there is less apparent sharpness. This is the result seeing the image small it looks sharper than if you enlarge it. If I had used a smaller aperture ie stopped down to the cameras smallest aperture of F8.0 then the sharpness would be increased quite a large amount in both cases.
The only thing remaining is the 'apparent' focal length. My camera says that the wide angle setting is eqquivalent to 28mm on a standard 35mm camera but, it is in fact only 7.4mm. This shorter focal length will produce substantially sharper looking images than an actual 28 mm lens at the same aperture. The reason is the same as for the difference in the above two pictures. Let me know if you still have a problem with that.

No comments: