Letter of the Week Special: The full frame decision continues

To: RE: Full frame DLSR Mr. Richards presented the pro/con on sensor size quite well, however I must take exception with him on the perpetuation of the myth that a small sensor magically multiplies the focal length of a given lens. It does not. It only changes the field of view. I have proven this by shooting pictures of the same object from the same spot using an APS size camera (Canon Digital Rebel) and a full frame camera (Canon 5D) using a 300mm lens.

To:     POP Editor
Subject:  RE: Full frame DLSR

Mr. Richards presented the pro/con on sensor size quite well, however I must take exception with him on the perpetuation of the myth that a small sensor magically multiplies the focal length of a given lens. It does not. It only changes the field of view. I have proven this by shooting pictures of the same object from the same spot using an APS size camera (Canon Digital Rebel) and a full frame camera (Canon 5D) using a 300mm lens. The image from the APS sized sensor was cropped, but the image of the object in question was identical in size. Try it and see for yourself.

Lynn Sellers
Mary Esther, FL

We never said that the focal length was multiplied—a 300mm lens is 300mm, regardless of the format of film or sensor. We simply stated that, for purposes of comparison, you can use an arithmetical factor to determine an equivalent focal length in the well-known 35mm film format. People were doing this long before digital cameras were invented—pick up a Pop Photo from 50 years ago and you might well find a table stating that a 50mm lens on a 35mm camera was equivalent to an 80mm lens on a 120 rollfillm camera.

In your comparison, the size of an object relative to the background (perspective) remains the same in the two formats because the two photographs were taken at the same distance. (You have to change distance to change perspective.) The image from the EOS Digital Rebel, however, will show the object taking up a greater proportion of its frame, because its frame is smaller. If this were mere "cropping," you would expect that the resolution of the Rebel image would roughly equal the cropped center portion of the image from the EOS 5D—and this would indeed be the case if this were done on film. But in fact, because of the greater pixel density of the D-Rebel, its resolution of the object's image will be greater than that of the 5D—6.3MP versus about 4.87MP for the 5D. The difference would be even starker with a 12.2MP EOS Rebel XSi, which would produce more than 50 percent greater resolution than the 5D in the same scenario. That ain't just cropping.
--Dan Richards
Senior Editor