Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon Lenses

Thread Tools Search this Thread
Old Nov 3, 2005, 11:04 PM   #1
Senior Member
AlpineMan's Avatar
Join Date: Mar 2005
Posts: 357

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?
AlpineMan is offline   Reply With Quote
Sponsored Links
Old Nov 4, 2005, 2:39 AM   #2
Senior Member
NHL's Avatar
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,331

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:
NHL is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -5. The time now is 2:47 PM.