What is a normal lens?

Knowing this is important when you buy your camera and lenses and when you decide what to take along on your trip.  What you know about a normal lens for a 35-mm film camera might not apply for a modern digital camera.

A "normal" lens is technically defined as a lens that has a focal length (in mm) that is the same as the camera's capturing area's diagonal dimension.  This lens approximates what a human eye sees, in terms of image size and field of view.

For example, for a "35-mm" (a misnomer) film camera, the capturing area (film frame) is 24mm in height and 36mm in width, so the diagonal is 43mm in length.  Therefore, a "normal lens" for a 35-mm camera has 43mm in focal length.

Now, for digital SLR cameras, only a few professional digital cameras have the capturing sensor that is the same size as the "35-mm" film frame ("full-frame" sensor).  These include:

* Canon EOS-1Ds Mark III

* Canon EOS 5D Mark II

* Nikon D3x

* Nikon D3

* Nikon D700

For these cameras, the normal lens is 43mm.  Therefore, the "focal length multiplier" is 1.0.

The rest of the digital SLR cameras have smaller-size sensors, therefore the normal lens for each is different:

Cameras with normal lens of 34mm (focal length multiplier of 1.3):

* Canon EOS-1D Mark IV

* Canon EOS-1D Mark III

Cameras with normal lens of 27mm (focal length multiplier of 1.6):

* Canon EOS 7D

* Canon EOS 50D

* Canon EOS Rebel T1i

* Canon EOS Rebel Xsi

* Canon EOS Rebel Xs

All Nikon digital SLR cameras (except the ones listed above) have a normal lens of 28mm (focal length multiplier of 1.5).

Why knowing all this is important?

* When you buy:  Retailers often package the cameras with all kinds of lenses, some of which are not useful for the consumers.  For example, one offer may be a kit of a digital SLR and a zoom lens of 28-135mm.  Sounds good.  However, when you look at the camera, it's a Canon T1i (for example) which has a focal length multiplier of 1.6, therefore that zoom lens is the equivalence of a 35-mm zoom of 45-216mm, not too bad but it's not for day-to-day shooting because it lacks the wide-angle component.

* When you decide what to take along on your photographic journey:  When I travel, I carry light.  I want one zoom lens that can go from wide-angle to tele-photo.  So if I have to pick one kit, I have to know what camera it is, what the range it needs, and bring with me the proper lens.