I don't understand sensor crop

[Jim Lundberg]

When a camera with a sensor smaller than 35mm, such as my 40D, "crops" the image, does excess focussed light fall outside the sensor, or is the smaller sensor closer to the lens. Is part of all that expensive glass on my 300 2.8 wasted? If I used a full sized sensor camera with my lens, and cropped to the same size as the small sensor, would the resulting cropped image have the same quality as my 40D (ignoring other camera factors)?

[hollis_f]

When a camera with a sensor smaller than 35mm, such as my 40D, "crops" the image, does excess focussed light fall outside the sensor, or is the smaller sensor closer to the lens. Is part of all that expensive glass on my 300 2.8 wasted? If I used a full sized sensor camera with my lens, and cropped to the same size as the small sensor, would the resulting cropped image have the same quality as my 40D (ignoring other camera factors)?
The excess light does fall outside the sensor, so I suppose some of that glass is being wasted. Canon do make EF-S lenses, where the sensor is closer to the lens.

Yes, the image quality of a cropped Full Frame image would be the same if one ignores other factors (which, of course, one can't do in the real world).

[Jim Lundberg]

The excess light does fall outside the sensor, so I suppose some of that glass is being wasted. Canon do make EF-S lenses, where the sensor is closer to the lens.

Yes, the image quality of a cropped Full Frame image would be the same if one ignores other factors (which, of course, one can't do in the real world).

Frank,

Thank you for the information. I had, only briefly, considered getting a full frame sensor camera mostly for landscapes. I will give it more consideration now.

Take care, Jim

[QuantumTiger]

There is a diagram on wikipedia (http://en.wikipedia.org/wiki/File:Full-frame_vs_APS-C.svg) which shows it quite well.

As to will the cropped image be of the same quality it's not entirel straight forward. If the pixel densities and noise characteristics of the two cameras were the same then the answer would probably be yes. Larger sensor cameras typically have much lower pixel densities than smaller sensor cameras - so you will get less pixels in the crop. But on the plus side larger photosites tend to be inherently less noisy.