At the end of August 2007, Canon announced the new EOS 40D which will replace the popular 30D. As it has done with previous updates, Canon has made incremental improvements over the 30D.

The most obvious difference is the larger LCD screen on the back of the camera. The photos below show the difference - Canon has increased the screen size from 2.5" to 3". The extra screen space makes it easier to quickly scan the playback of an image to make sure it is in focus.

The 40D gets a resolution bump over the 30D (10.1MP vs. 8.2), a new Digic III processor, the sensor cleaning system that the Rebel XTi uses and Live View.

Live View allows you to use the LCD screen as a viewfinder, although it is mainly designed for use in manual focus mode. If you wish to use Live View with autofocus, it is a bit convoluted and can only work with static subjects. You must hold the camera still, press and hold a button until the camera beeps, release the button and the press the shutter to take the photo. There may be uses for Live View outside the office, but we don't see it being used very often for clinical photography.

The 40D also gets interchangeable focusing screens and a grid screen is available. This was a very popular upgrade back in the days of the Yashica Dental Eye and should be very useful for image alignment.
The dimensions and weight are almost identical - the 40D is 2mm taller and .1 ounce heavier than the 30D.

Canon designed the 40D to be compatible with most of their EOS 35mm camera accessories, including the Canon MR-14EX macro ring flash, Canon MT-24EX dual point flash and the Sigma EM-140DG macro flash. This allows E-TTL (evaluative through-the-lens) flash metering for automatic exposure. Just as you would with a 35mm clinical camera, you simply set the magnification and f-stop and then move towards your subject until the image is in focus - the 40D takes care of the rest. Or switch the lens to AF (auto focus) and let the camera do the focusing. You have the choice.