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  A Photographer's Review of the Canon EOS 10D Digital SLR
Subject:   Focal Length -- Well...
Date:   2003-05-06 07:40:19
From:   anonymous2
Response to: Focal Length -- Well...

hi Matt,

I am no optics expert but I think i can explain the scenarios you are confused about.

Essentially canon have crammed their CMOS censors into a smaller area than the 35mm back of a standard SLR (1.6 x smaller?). So, only the light rays travelling very close to parallel with each other, directly into the camera, will be represented on the final image.

A zoom lense does exactly the same thing, except it uses a lense to take a small area of light and expand it onto a 35mm back. This is why they need more light (bigger f-stop) to be used at the same shutter speed. If you pretended that the 35mm back was 70mm and the magnification was 2x then you would have the same pictures....

You are never bringing a subject closer, only by optics selecting which light rays you want to see. The rest are either out of focus or off the frame...

Does that make sense?


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  • Focal Length -- it's like higher resolution
    2003-10-30 20:43:16  anonymous2 [View]

    if you crop an image, you rae losing image quality, but reducing the number of pixels in the image (assuming you stretch it to its pre-crop size,) if you took a 4MP image and cropped it to a center portion, you would not have as good of quality asif you cropped the same frame in a 6MP image. this is the effect that the magnification factor gives. That is it crops the image a certian ammount while not sacrificing image quality. So you dont get the same light loss or depth of feild changes as you would with a longer lens, but the practical effect is the same