(also known as 'EOS 350D Digital' and 'EOS Kiss Digital N')

Photo from Canon Rebel XT page

Sensor type: APS-C CMOS Pixels: 8.0 Mp, 3:2 Pixel pitch: 6.42 μm/pixel	2304 pixels 14.8 mm = 156 px/mm
3456 pixels 22.2 mm = 156 px/mm

Remote capture:  Limited (no live view)
Remote focus control: No
Lens compatible with eyepieces:  Generally, no
Raw mode: Yes
Filter mount: Generally, yes

Note that the lens used here, the EF-s 17-85 f/4-5.6 IS USM zoom, is not the one that comes in the kit, as pictured in the top-right figure.

Computer control ('remote capture')

The Rebel XT can be controlled from a computer via USB, but because it doesn't support 'live view', there is no view at the computer of what the camera sees. This is quite inconvenient for using the camera with optical instruments, eg., a microscope. The camera needs to be focused using its optical viewfinder, which can be difficult.

Canon's EOS Utility program can set most camera functions, trigger the shutter, and transfer files.

Photographing what human eyes can see through optical instruments

With most lenses typically used with this camera, the entrance pupil of this camera is much larger than a human eye, so it cannot take full-frame photos through optical instruments such as a microscope or binoculars. However, with no lens attached, real images produced by optical instruments and eyepieces can be projected directly onto the Rebel's large sensor, often eliminating the need for several pieces of glass and thus producing sharp images.

Other

Colour artifacts, Rebel XT

The sensor of the Rebel XT appears to exhibit (self-generate) colour artifacts (colour moiré) due to aliasing with spatial frequencies comparable to its pixel pitch. The photo to the right ought to have no colour. Later Rebel models apparently have filters to reduce such artifacts.

To protect the sensor from dust, etc, a simple method is to get a body cap ($5), cut a hole in it, and glue in an optical-quality plano glass (or glass from a filter, eg., a skylight filter).

Spatial frequency response: MTF

The EF-s 17-85 f/4-5.6 IS USM zoom lens with this camera is diffraction-limited at ƒ/20.6, which is inside its smallest aperture of ƒ/32. This means that photos taken with apertures smaller than ƒ/32 with this camera will have sharpness limited by diffraction (a 'pinhole' effect), even if the optics were perfect. Below is an MTF analyses at ƒ/5.6 at full zoom (85 mm), using a slanted edge with low contrast. The target was a test pattern on an LCD display, photographed with the camera tilted 5 degrees. The image was captured 'raw' and converted to TIFF without any processing (specifically, no sharpening).

Canon Rebel XT with EF-s 17-85 f/4-5.6 IS USM zoom lens, ƒ/5.6 at full zoom (85 mm)

The pale, dashed brown line marks the limit set by diffraction by the lens aperture and the pixel spacing. At ƒ/5.6, above, the MTF curve is well below the diffraction limit, and is therefore limited by the lens optics. There are many reviews of this lens on the internet, eg, at dpReviews.

For more information about MTF and resolution, see Measuring resolution.