"Back in 1932 a group of great American photographers, including Ansel Adams, founded Group f/64. The name was derived from the small aperture opening the group members deemed necessary for achieving acceptable depth of field with use of large-format view cameras.
Now, most writers say F/64 gives you a huge depth of field. Let us have a closer look. A full-format view camera has a frame of (approximately) 8x10 inches. This means, that for a given image angle, it needs a focal length 7 times larger than that for a 35-mm camera, and 28(!) times that for the [Olympus digital camera] E-10/E-20.
A quick application of the André's Rule brings us the bare truth: from the viewpoint of DOF, F/64 on an 8x10 camera is equivalent to F/9 on your 35 mm SLR, and to F/2.3 on the E-10/E-20 (or F/1.9 or so on most non-SLR digital models). In other words, the depth of field attained by closing a view camera lens all the way (with the resulting multi-second exposure times) is provided or exceeded by your digital camera's lens fully open!"
The implication of that is that it's not really necessary to focus a digital camera - pictures can be sharp from 2m to infinity at F/4 - and it's not particularly necessary to use F numbers larger than 4. Another implication is that you can't take a picture with a sharp foreground and a blurred background (a portrait for example) using a digital camera.
Does that make sense? Why, then, do all but the cheapest digital cameras have fancy auto-focus systems? Are they necessary?
This page seems to confirm the above. It has a 'depth-of-field' calculator; notice that you get a huge depth of field even at small F numbers for digital cameras.
The main factor seems to be simply that the standard focal length for digital cameras is so tiny - 5mm or so, compared to 50mm / 35mm for (old fashioned film) SLR / point-and-shoot cameras.
Auto-focus (or manual focus adjustment) is necessary for digital cameras because most have an (optical) zoom, which takes the focal length into high double digits.
Still, a basic digital camera stopped down to F/8 (maybe good for daylight on a cloudy day) could, in theory, have everything in focus from about one foot to infinity.
Seems to me, nnn, that the natural market for compact digital cameras is among people progressing from compact 35mm cameras. In their film cameras they considered that one without auto-focus was very down-market, so not to have the feature in a digital camera would adversely affect sales. Maybe the manufacturers put in a rudimentary system (because that's all that is needed) and trumpet it loud because the buyer wants to find that feature. Make sense?
Posts: 744 | Location: Surrey, England | Registered: 06-03-02
My experiences more or less confirm newnickname's theories. My digital camera focuses a wide range of distances simultaneously, but while I think Ewood is onto sometihng, I can notice some differences at mid-range distances, and close objects still need a fair degree of focusing.
PMFJI since I'm new here, but I don't think a large depth of field is always desirable. With my 35 mm SLR I like to shoot portraits using a long lens and wide aperture, so that when the subject's face is in sharp focus the background is blurred.
How do I do that with a digital camera?
Posts: 1917 | Location: U.S. | Registered: 06-03-02
You'd need to use the fastest possible shutter speed, the longest possible zoom, and stand far away. I guess the idea with digital is, however, that you can easily process the image later to get any kind of background you like. It's a different world.
I've been using a Pentax K1000 for years. It, of course, has nothing automatic. I read a review that actually said that if you use a K1000, you'll hate digital cameras.
So, following the questions above, I bought a Samsung 301. ($150 Canadian; 5.1mm fixed focus lens; no zoom; max aperture F/8; all my Korean students tell me that Samsung sucks...) I like it. I suppose you just have to get your head around the idea that it's a different kind of photography. It's difficult even to adjust to the idea that you can take, check and delete as many shots of something as battery-life allows, until you get one you like. Spooky.
What you're talking about is true of the lower-end consumer cameras on the market. Same idea as the old Kodak Instamatic. Use a very wide angle lens and there isn't much need to focus. But once you get into multi-step optical zoom and head toward the pro-level equipment, you'll see that they operate pretty much as a film camera does. Canon's top line models even match focal lengths of the lenses exactly to 35mm film cameras.
Hmmm, yes, but the point is that digital cameras are different. For an angle of view equivalent to a point-and-shoot film-camera's 30 or 35mm lens, a digital camera typically has a 5 or 6mm focal length. It's not so much that cheap digital cameras are 'very wide angle' but that their 'film' (the light sensitive part) is relatively small, and therefore so is the focal length.
Right NNN. As I said, the trend at the upper end is to match focal lengths to those found on 35mm SLR film cameras. With those cameras you have all the DOF control you could ever want. I have used the high end Nikon and it is really sweet.
Teeceeum's point is interesting, too. I hadn't known about the high-end cameras copying the 'traditional' patterns. I guess, following the usual course of events, what is state-of-the-art now will be entry-level in a couple of years.
Actually, I'm a little disappointed. If digital cameras are designed to end up doing exactly what older ones can, then it all begins to look like a complicated conspiracy just to make us buy more batteries.
It'll be sad to see film go the way of vinyl lp's. I know, for one thing, that there's nothing to stop a K1000 working perfectly for another couple of decades, where digital cameras (certainly the little Samsung) are most likely engineered to fall apart after as many years.
