Photo from Canon A75 page

Sensor type: 1/2.7" CCD Pixels: 3.2 Mp, 4:3 Pixel pitch: 2.58 μm/pixel	1536 pixels 3.96 mm = 388 px/mm
2048 pixels 5.27 mm = 389 px/mm

Remote capture: Yes
Remote focus control: No
Lens compatible with eyepieces: Yes
Raw mode: No (yes with CHDK)
Filter mount: Yes, 52 mm, with LA-DC52C adapter

Computer control ('remote capture')

The A75 supports control of the camera from a computer via USB. There is 'live view', but the image is only 320 pixels wide, making it somewhat difficult to use, eg., for focusing. Focus can be locked (at whatever focus setting the camera happens to then be in), or set to auto-focus (the camera decides when a photo is taken), but otherwise cannot be controlled directly. Most other camera functions can be controlled.

Canon provides a software package "Remote Capture" at no cost, and Breeze Systems offers "PsRemote". The two packages are functionally similar, having the same camera controls, but PsRemote has a better user interface and its 'magnfied' live view makes it slightly easier to tell if an image is in focus.

One hassle is the absense of focus control when using the camera via USB. Auto-focus can be used, but then the magnification of the image will vary slightly with focus distance. This can be overcome by locking the focus, making each photo of a set the same. However, to lock the focus at a known point, eg., infinity, one has to get the camera to focus at infinity and then lock it. I haven't figured out a way to do that without taking the camera off the phototube momentarily.

Focal lengths

The camera has seven focal lengths: 5.41, 6.59, 7.84, 9.41, 11.3125, 13.4375, and 16.2188 mm, as reported in image metadata.

Photographing what human eyes can see through optical instruments

The entrance pupil of this camera is similar to the human eye, so it's suitable for taking photos through optical instruments such as a microscope or binoculars. Here's a page with ideas for afocal adapters to use this camera with various optics.

JPEG compression: Fine vs Superfine

Based on MTF analysis and test photos, I'd say 'superfine' compression is slightly better than 'fine' on the A75 and therefore worthwhile, especially since by today's storage standards, either file size is modest.

Spatial frequency response: MTF

The A75 would be diffraction-limited at ƒ/8.2, which is just outside its smallest aperture of ƒ/8. Below is a MTF at ƒ/4.8 at full zoom (16.2 mm), using a slanted edge with contrast low enough to not trigger the camera's in-built image sharpening mechanisms (at least that's the presumption; at higher contrasts, there is an obvious overshoot in the edge profile created by sharpening). The target was a test pattern on an LCD display, photographed with the camera tilted 5 degrees. The JPEG compression was set at 'superfine'.

Canon A75, ƒ/4.8 at full zoom (16.2 mm), 'superfine' JPEG compression

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