Reply To: Let's Talk Lenses!

[cameraclicker]

Since the whole magnification factor story is a pet peeve of mine, I would like to jump in here and point out that the crop is just like taking a pair of scissors to a print from a full frame image, if the pixel density of both sensors is the same, so you get an equivalent angle of view with a crop sensor by multiplying the focal length by 1.6, but the lens does not magically gain focal length.  Since the lens does not gain focal length, depth of field does not change, unless you move the camera to adjust for the reduced angle of view.

Pixel density determines apparent magnification, so if you have two crop sensor bodies, an older 8 mpx body and a newer 18 mpx body for instance, you will see apparent magnification from the 18 mpx body, if an image is taken with both, at the same place, of the same subject, with the same focal length.  Angle of view, however, will be the same.

If your reference is a full frame Canon 1Dx (18 mpx) and your crop body is one of the several with an 18 mpx sensor, then you will see the 1.6X change in angle of view, and also in apparent magnification.  Even in this case, the lens itself does not change focal length and if taken from the same position, same subject, same focal length, etc., depth of field does not change.

If you think you will move to a full frame body at some point, you want fast prime (one focal length) lenses, or you want constant aperture zoom lenses, you should consider getting full frame lenses.  But, full frame lenses weigh more.  My 24-70 is hardly ever used because it weighs so much.  There are many good zoom lenses, made by several manufacturers, for APS-C bodies.

A good place to start is to look at your photos for the last year or two.  Decide what you like, and what you don’t.  Then decide if some feature of a different lens would help correct what you don’t like or would emphasize what you do like…  For instance, I like very, very close-up photos of things so I have extension tubes and macro lenses.

Actually the difference between an EF and EF-S lens is the diameter of the image circle.  EF-S lenses only need an image circle with a diameter of the diagonal of the APS-C sensor, so they can be made of smaller lenses, which makes them lighter and (usually) less expensive.  Canon lenses have a protrusion that fits inside the camera body and that keeps them from being used with a full frame body and some accessories like teleconverters.  Other manufacturers like Sigma and Nikon make lenses for crop sensor bodies without the protrusion, so they will fit on full frame bodies.  With most Nikons, the crop lens will cause the body to take the photo in a cropped mode giving the usual rectangular shape.  Canon bodies still take the full sensor sized image so the image has black brackets on either side.  It is one way to get a very large, heavy, vignette.  You can manually crop the image to APS-C dimensions, but if you are going to spend the money on a full frame body, you might as well get a full frame lens to go with it.