How does digital camera magnification (eg 2X optical and 3X digital) relate to otical focal length (eg 200 mm)? Also, what are the tradeoffs as magnification increases? Also, what is the difference in optical versus digital magnification?

-- Tennent Houston (tennent@merryland.com), October 07, 1999

Answers

The digicam marketing guys decided that if you have a 35mm wide angle setting, and a 105mm telephoto, that's 3x (these are 35mm photgraphy equivalents). At least they all do the same thing so it's not so confusing. I think in normal photography this would be a 2x lens. (105 is about a normal 50 times 2).

Digital zoom essentially just crops the image, so image resolution goes down the tubes quickly as you use more digital zoom. Bad. Optical zoom brings the whole CCD to bear at all settings. Very good. Optical zooms cost more, but if you want quality shots at telephoto settings its worth it. Digital zoom is handy in a pinch.

Most of the cams have 3x optical zoom, or just digital zoom. Some of the newer smaller cams like canon s10 and nikon 800 have 2x. The Sony 505 has 5x, and a good lens. The mavicas have really long zoom, but comparing image quality with other cameras, they're the absolute worst, unless you just want to post fuzzy pics to ebay. For ebay, having bad image quality is a plus, to hide defects in your product. :)

-- benoit (foo@bar.com), October 07, 1999.

Magnification ratio is expressed in digital cameras exactly the way it is done with film cameras. Or video camearas, for that matter. Divide the longest focal length by the shortest focal length. That gives a figure such as 2X, 3X etc. It is simply the focal length range of the lens.

The digital magnification figure represents the magnification power that is accomplished electronically above and beyond any optical magnification. If you started with a 115mm focal length lens, applying a digital 2X magnification to it achieves an equavilant focal length of 230mm.

Optical magnification gives a much higher quality image than the same magnification done digitally. However, optical magnification is more costly to do. It requires more complicated design, bigger and heavier glass elements, and you have to trade off the speed of the lens (f- stop). Optical engineers are now able to get zoom ratios as high as 10 or 11X. However, you are not likely to find digital cameras with more than about 5X at this time.

-- Steve (tuna-boat-captain@attglobal.net), October 07, 1999.

optical mag good. digital mag no-good. Digital mag ties up camera resources for features in all of the digital programs. You can do digital magnification easier and better on the computer. It is simply a marketing gimmick.

Optical magnification provides a better immage at the camera. You can not do this with any program after you have taken the picture. Go for optical magnifiation!

-- Dave Clark (Daveclark@prodigy.net), October 09, 1999.

Don't knock digital zoom quiet yet. There are a couple of things that they do offer over cropping later, but not over optical zoom. When you digitally zoom in on an object your movement and subject movement will be more obvious. The will help you realize you need to hold the camera more steady. Also the digital zoom limit the camera to using less area to determine the auto focus and exposure there by putting more emphasise on the subject. I have used this to my advantage. I had 3 deer back in the shadow of a timber but the bright foreground was making them too dark and out of focus. When I turned on the 2X digital zoom it acted like spot metering and spot focus by cropping the picture and gave me a better shot of the deer. There are many cases where this won't be the case and cropping at the computer would be easier. Just don't mothball the digital zoom completely.

-- Bob G. (rgreg88721@hotmail.com), October 09, 1999.

Bob,

I had never thought of those two features of using digital magnification. I not sure that I agree about a smaller image makes one hold the camera more steady, but the point about better meter reading would be valid. My camera has spot metering, but I usely have it set at average. Those little buggers won't stop and wait until I change settings. Perhaps another feature is focusing. Since my camera adjust the focus based on what is in the image, the smaller image would be more likely to be in focus vs an average of the total large image. Black deer did you say? Shame I can't see your note only the original.

-- Dave Clark (daveclark@mail.com), October 10, 1999.