Canon EOS 1Ds Mark III vs Canon EOS Rebel XSi

This is a full comparison between the cameras Canon EOS 1Ds Mark III and Canon EOS Rebel XSi. We compare them by looking at the categories you see below.

Manufacturing

These cameras are both manufactured by Canon.

Type of camera

Both these cameras are DSLR cameras. No difference there.

Sensors / crop factor

These cameras have different sensors. Canon EOS 1Ds Mark III has a "FF"-sensor while Canon EOS Rebel XSi has a "APSC"-sensor, and their difference in sensors will also affect the crop factor and experience focal length. See the table below.

** Experienced focal length when using a lens such as a common "50mm f/1.8"

Learn more about crop factor and focal length multiplier here:
Camera selection can affect the focal length (Canon)

Resolution

Canon EOS 1Ds Mark III has a 21,1 MP (Megapixels) resolution while Canon EOS Rebel XSi has 12,2 MP. If we break down this in more detail this is the data behind the numbers:

Canon EOS 1Ds Mark III has a 73 % larger resolution than Canon EOS Rebel XSi. This could give you more details in the picture but also a possibility to crop more in the pictures, afterward while editing the pictures, if needed that is.

ISO range

Canon EOS 1Ds Mark III has a larger ISO-range than Canon EOS Rebel XSi. Canon EOS 1Ds Mark III has an ISO range that stretches from 50 to 3200 while Canon EOS Rebel XSi has 100 to 1600.

Autofocus and lens compatibility

Both of these cameras have a built-in autofocus motor. Some lenses, that support autofocus, do not have an autofocus motor of their own but this won't cause any problems with these two cameras.

Here is a complete overview of which lenses work with each camera:
Lens compatibility chart for Canon EOS 1Ds Mark III
Lens compatibility chart for Canon EOS Rebel XSi

Pictures per second

Depending on what you are shooting the FPS, or frames/pictures per second, can definitely be of interest. Canon EOS 1Ds Mark III can shoot up to 5 pictures per seconds and Canon EOS Rebel XSi can shoot up to 3,5 pictures per seconds.

Ability to record movies

It is becoming more and more popular to record movies with digital cameras.

Though, neither Canon EOS 1Ds Mark III or Canon EOS Rebel XSi can shoot movies so if that is a functionality that you are really looking for you should look elsewhere.

Weight

The weight of the camera can be an extremely important factor, especially if the camera is about to be used, or carried around, for several hours at a time.

Canon EOS 1Ds Mark III weighs 1385 gr (equal to 3,05 lb) which is 164% heavier than Canon EOS Rebel XSi and its 524 gr (or 1,16 lb).