A few things are in order first:

- The FOV Crop on the 300D, like the EOS 10D, is 1.6. This is because the CMOS sensor is smaller than a 35mm frame.
- The focal length of a lens is the distance from the rear glass element to the focal plane at infinity focus.
- We're used to relating the 35mm focal-length to what we see in a picture as "zoom"

Since the 300D/10D/other digicams have smaller sensors, they're only seeing a portion of the image that a 35mm full-frame sensor or film would see. This is where the FOV crop comes into play.

That said, taking a picture with Canon's excellent 50mm f/1.8 lens is still a normal lens. Distortion of the image will be the same in full-frame as in the smaller sensor. However, you won't see as much of the image -- you'll see the same amount of the image as if you had an 80mm lens on there (50mm * FOV Crop). This is why a 50mm prime lens is still good for the 300D/10D sized sensors as a "normal" lens.
marius@marius.org

I thought I'd try and explain this minefield for the newcomers who don't understand and think that they're getting a free 1.6X teleconverter with their 300D ..

The 300D and 10D like the D30 and D60 before them use a smaller than 35mm sensor, about APS-C sized in fact, the result is that the sensor only records part of the image circle presented by the lens.. The easiest way to explain this is to take an image from a 35mm camera and see the relationship between the different field of view crops (below - this is NOT accurate, just an illustration to give an idea)

IF the cameras were all the same Pixel density IE- the full frame camera being 11Mp, the 1.3X being something like 8.5Mp and the 1.6X camera being 5.3Mp then the effect would be just like as you see there , simply like cropping a larger photo BUT the confusion arrises when sensors are of different densities and a 6.3Mp 1.6X sensor will look like it's had a teleconverter added compared to a 6.3Mp full frame - that isn't the case as all that is happening is that there are more pixels in the cropped area - think of it as a sort of Hardware Digital Zoom where they've done it by adding pixels (with no quality loss) instead of upsampling the image like Consumer Digicams do (resulting in severe image degradation) -- think of the 10D as a 13 Megapixel full frame DSLR with some of the sensor masked out in effect. Yes the effect IS of telephoto effect BUT the perspective is the same for the lens if it had been on a full frame camera ..

Similar effect is Fisheye lenses compared to Rectilinear lenses - take a 15mm Fisheye and a 14mm rectilinear and take a shot of a scene with a church in the middle - straight out of the camera, the church would be CLOSER to you with the Fish than with the 14mm BUT you can see MORE of the scene at the sides due to the 180 degree field of view - SO when De-fished you end up with what looks like a wider angle photo OR a larger one depending on how the software works..

I hope that this has been of some help - everytime someone mentions the 1.6X "multiplier", someone is always there to correct them and the Correcting person is RIGHT - BUT if you ignore the fact that 1.3X and full frame sensors exist you CAN actually think of your 1.6X crop as a 1.6X TC BUT you'll always have the characteristics of a lens of it's native focal length ..

To see perspective - take your standard zoom (28-135IS would be ideal) and shoot a scene with a focal point (a Person is totally ideal) at 28mm then wind out to 50mm, walk back to get that person filling the same area in the viewfinder and shoot again , do the same at 135mm and see how the perspective changes with the scene around the person shot..

Just to clarify a common misunderstanding: perspective is effected ONLY by the relative distances between the subject/background and camera. Perspective is not altered by changing the focal length of the lens. All that changing the focal lengh of the lens does is crop the image.

marius@marius.org