At 12:08 AM -0500 3/1/06, Bill Gillooly wrote:
I wish Canon (or somebody) would make the equivalent of a 1000D, a well corrected, double-element if necessary, close-up lens that would allow a zoom lens to extend the close-focusing capabilities without any gap. I've used the 500D with a EF 80-200m f/2.8L and there is a huge jump between minimum focusing distance of the lens and the maximum focusing distance of the lens plus 500D.
True, there is a gap, but there really isn't a gap in the reproduction ratios, which is what is important to me.
Using either the 70-200 2.8 or 100-400 with a 500D lets me go pretty well continuously from 0 reproduction ration to the maximum, which is at the close focussing limit of the lens at longest focal length with the 500D attached.
I can get a lower reproduction ration by reducing the focal length, or by focussing at longer distances, or both. When I've set the lens at infinity and the focal length at the shortest, I have a lower reproduction ratio than by using the lens without the 500D focussed at the closest distance and using the longest focal length.
True, a real macro lens lets you choose your reproduction ratio in a single throw without stopping to take the closeup lens on or off, but the zoom and 500D gives you other options.
As the name implies, the 500D has a focal length of 500mm, so when it is used on a lens set to infinity, it will be focussed on an object 500mm in front of the lens, no matter what lens it's on. That can give very decent working distances on a 400mm lens, and used in that way the optical quality is quite decent, and the effective focal length is 222mm, which gives a lot more working distance than the 180 macro, which probably has an effective focal length of 160mm at a similar reproduction ratio.
Quality won't be quite as good, but effective focal length is often more important.
Modern IF lenses, whether zoom or fixed focus, generally work better with closeup lenses than with extension tubes, because the designers didn't have to be concerned with lens corrections when the whole assemble is moved further from the film/sensor plane, as the IF would be used for focussing and correction. So even an excellent lens like the 100 USM macro performs better with a close up lens, if you want a bit more magnification, than with extension tubes.
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