Why is the zoom lens in a dSLR-like camera (eg Sony DSC-H5 with 12x zoom) is so much smaller than a zoom lens of equivalent power (eg. up to 400mm) for a normal SLR camera? There are few factors that determines the size of a lens. The CCD is much smaller than a 35 mm film, so effectively everything becomes smaller. Meaning the CCD is about 1/4 the size (I'm estimating) the size of 35 mm film (linear measurement). So the lens can be made smaller.
The other factor is that 12x zoom on Sony is relatively poor quality 12x zoom. They most probably used lots of plastic lens. By itself plastic lens are not all that bad, but most SLR owners want glass lens.
Sony is trusting that people who buy their camera are impressed with big numbers like 12x (and not worry too much about quality).
Finally it is easier to create a zoom lens for smaller CCD area then it is for the larger 35mm lens system. Many of the digital camera is of "video lens" quality.
One last thing is that: I said "relative poor quality". I didn't mean that Sony was bad. In fact many people are loving it. You can read the full review here:
http://www.dpreview.com/reviews/specs/So...
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Don't forget to vote for the BEST ANSWER - please - whoever it may be.
FACT: You also get +3 points when you vote for BEST ANSWER It's bigger because it has to cover a larger image area. Great question!
Take a look at the sensor sizes of the H5 (1/2.5-in. type about 5.4 x 4 mm) vs. the size of 35mm film (36 x 24 mm) and you'll get an idea of what the other posters are saying. | 