Here is a link on photog glossery terms:
http://www.floccinaucinihilipilifica...raphy:Glossary
I think that there may be some confusion regarding f-stop verses focal length or maybe focal plane?
Depth of Field
Depth of Field refers to range of distances such that elements are in focus. An image with a narrow depth of field has a very small amount in focus. An image with a large depth of field has a lot in focus.
f-stop
The f-stop is the unit of measure for the aperture. The f-stop is the the size of the aperture expressed as a fraction of the focal length of the lens. This is why some zoom lenses have different minimum f-stops based on the amount zoom. An f-stop of f/16 (f being the focal length), means that a 200mm lens has an aperture openning of 200/16 = 12.5mm. A 18mm lens has an aperture openning of 18/16 = 1.125mm. For a given f-stop any lens, regardless of focal length, transits the same amount of light to the sensor or film.
Focal Length
The focal length is the distance from the front element of a lens to the sensor (or negative). The focal length can be used to describe the effect that the lens has on the produced image. A long focal length (say, 50mm and up) make objects look closer (like a telescope). Short focal lengths (24mm and smaller) capture a wider view, making object smaller. Lenses with short focal lengths are sometimes refered to as wide angle.
As you can see the focal length does have an effect on magnifying the object , however a macro lens will still allow the lens to be positioned closer to the object.
I still stand my ground on that DOF is greatly controlled by the f-stop or aperature setting. Try shooting with your DSLR on Aperature Priority and set it to f/2.8. Focus on a subject 4 ft away from you with some background objects. Take a the shot. Next, set your aperature to f/22 and focus again on the same subject. Take a shot. Compare the 2 shots and I can gaurantee you that your DOF difference will be huge, not just cm but in ft. At f/2.8 your focus will only be for the first few feet. At f/22 the focus should be from the subject to infinity. Therefore DOF is largely controlled on by the f-stop.
Jason, I'm trying to understand your point. Is there another way of explaining what you are talking about?
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