ignorant88 wrote:since cropping came up....any problem with taking a wider view an then crop the pic? will it affect qlty of pic or is it just a matter of perfection that one should not crop their pic?
Cropping a wide-angle image to get close up of a small object will cost you lots of pixels, so you will be left with a low-resolution image!
The Tamron 90mm f/2.8 macro is VERY sharp, recommended by most macro photographers I know. I have the Sigma 105mm f/2.8 myself though, and I am very happy with what it delivers.
Focal distance (?? mm) does not tell you anything about how close you can get, the maximum magnification does that! The focal length tells you something about the field of view you will get with the lens, exactly how i will not bother explaining unless you are good at maths!
- But shorter focal length is wider FOV.
Sigma have all their info publicly available, for example for the 105mm macro max. magnification is 1:1, for the 10-20mm it is 1:6.7 - Info is in the lower right side of the page:
http://sigmaphoto.com/lenses/lenses_all ... avigator=5
http://sigmaphoto.com/lenses/lenses_all ... avigator=6
A magnification of 1:1 means that you can have an object the same size as the sensor fill the whole image at closest focus. A magnification of 1:6.7 means you can have an object 6.7 times larger than your sensor fill the image at closest focus!
A fullframe sensor is 24*36mm (approx 1*1½ inch), so at closest range a 1:1 macro will get you so close that most butterflies will be too big to fit into the image!
On my 350D a bee takes up a good deal of the image at closes focusing distance.
Brian