I don’t understand how to calculate the zoom factor of this lens. its the Canon EF 70-200mm f/4L USM Lens. This article (http://www.the-digital-picture.com/Reviews/Canon-EF-70-200mm-f-4.0-L-IS-USM-Lens-Review.aspx) says the zoom varies from .21x to .45x depending on the extensions used along with the lens. If someone could explain all these things it would be appreciated. Thanks.
The focal length of 70 to 200mm on most Canon DSLRs means a medium tele (70) to a quite powerful tele (200), good for portraits at 70mm or medium range sports photos or wildlife (except very shy wildlife) at 200mm .
I think the .21x and .45x are refering to the macro magnification, not actually the zoom range. In round terms would mean that you could photograph fairly small objects close-up to fill the frame.
The maximum aperture is f4, good for such a lens (lets in a good amount of light). USM is an Ultra Silent focus Motor. IS is Image Stabilisation – helps get a steady shot in poor light.
August 14th, 2010 at 4:23 pm
The focal length of 70 to 200mm on most Canon DSLRs means a medium tele (70) to a quite powerful tele (200), good for portraits at 70mm or medium range sports photos or wildlife (except very shy wildlife) at 200mm .
I think the .21x and .45x are refering to the macro magnification, not actually the zoom range. In round terms would mean that you could photograph fairly small objects close-up to fill the frame.
The maximum aperture is f4, good for such a lens (lets in a good amount of light). USM is an Ultra Silent focus Motor. IS is Image Stabilisation – helps get a steady shot in poor light.
References :
August 14th, 2010 at 4:51 pm
Zoom factor is the magnification at which the subject gets captured on the sensor/film. It’s application is in ”macro” photography. A true macro lens has 1x factor, which gives the actual size of the subject on the sensor/film. (keep the size of the sensor/film in mind, any object bigger than that would get cropped at 1x) . at .45x you would get the subject at about half its actual size (0 .45 times) and so on.
What you are looking at is an extension tube , which gets attached to the lens to magnify the subject.
Now a days , since dedicated ”macro” lens are available the use of extension tube is on the decline.
References :
August 14th, 2010 at 5:34 pm
200/70 = a 2.9 zoom ratio (rounded from 2.8571428).
http://www.the-digital-picture.com/Reviews/Canon-EF-70-200mm-f-4.0-L-IS-USM-Lens-Review.aspx
The review plainly states: "With a minimum focusing distance of 1.97′ the 70-200mmm … lens yields a maximum magnification of .21X…". Then it talks about adding an extension tube to increase the magnification for close-ups of flowers, insects, etc. So if you photograph a 10mm long ant at 1.97′ it will show as 2.1mm on your sensor. With the extension tube it will be 4.5mm long. A true macro lens will have a 1:1 magnification so your 10mm ant would photograph as 10mm.
References :