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Old Nov 4, 2005, 12:04 AM   #1
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I just got a Sigma 150mm EX DG MACRO lens off a lens trade with someone. This is my first MACRO lens. I looked thru the "user manual" and it doesn't say anything how to use the lens. For example, what the heck are these switches for:

FULL, 0.52m to infinity, 0.38 to 0.52m

Also, I find the lens to be hunting quite a bit in low light. And according to the one of the tables in the manual, minimum focusing distance is about 1.25 ft. I tried 2 ft, and it's unable to focus.

During my testing, I just left my 20D in "One Shot" mode, the dial on "M", f2.8, ISO 400, 1/25 shutter speed, no flash.

I tested it for front and back focusing problems...and no problems at all. Is the auto focus hunting normal on these lenses on low light?
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Old Nov 4, 2005, 3:39 AM   #2
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They are call the limit switches :idea:

-> Unlike a regular lens, a macro focusing is very precise and take more displacement of the focusing ring to focus. To speed up this process the limit switches are designed to narrow the focus to a range for exampe for close-up only 0.38 to 0.52m is required -> you don't need to swing alll the way to infinity... for an insect

The higher the magnification the higher the sensitivity to camera shake - you have to be extra steady or use tripod for the camera to AF, but pretty soon you'll realize that for macro with very shallow DOF you want to be on manual focus to highlight the right part anyway!!! :-) :-) :lol:
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