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To: John Solder who wrote (9417)	4/26/1999 9:52:00 AM
From: Jeff Sheeran	Respond to of 10072

John, I believe that depth of field is also related to focal length. For example a 28mm lens has a much greater depth of field when focused at 10 ft then a 90mm lens. Depth of field is a function of f stop which is a ratio of iris diameter compared to focal length. This is why an f2.8 lens of a 300mm focal length is much larger then one of a standard 50mm lens. Digital only refers to the "capture" of the image, the optics and principals behind them would be the same. You are not exposing film, you are exposing a ccd. Since the "capture" area on a digital is much smaller than on a standard 35mm camera you do no need as long of a focal length to get corner to corner coverage. I believe that standard focal length on a digital camera is somewhere around 25mm? you would have much more depth of field. This is why the Minox spy camera was so effective, it had incredible depth of field with a very short focal length. Take a pinhole camera for example you get focus from near to far, not very sharp but still a focus. Regards, Jeff

To: John Solder who wrote (9417)	4/26/1999 9:52:00 AM
From: Cameron Dorey	Read Replies (1) \| Respond to of 10072

"In a digital camera you are not "exposing" film to light, therefore there is no correlation between shutter speed and aperture size. If this is the case, how can you vary the focal depth ?" Ah, you're not exposing film, but you are exposing CCD's (charge-coupled diodes) in an array simulating a piece of film. Thus, all you have done is change the mode of detection, not the stuff that is being detected. Check out Nikon's specs for the E3 digital camera, which is their best simulation of a film camera to date. You'll find the specs are exactly the ones important for film photography (except the extra ones): nikonusa.com Cameron "Laugh and the world laughs with you. Cry, and someone yells, 'Shut up!'" - from an anonymous 9-year-old philosopher