Hardware - - Zoom

yuppicide · #1 04-24-2005, 09:18 PM

I'm looking at lenses and they say for example 18-55mm. How do I find out how much zoom this would be in x terms?! Like for example the Olympus C765 Ultra Zoom says 10x optical zoom?!

I'm trying to compare the two so when I guy a Digital SLR and have to get a lense I'll know how much zoom I can expect.

CJ Swartz · #2 04-25-2005, 04:12 AM

Quote:

Originally Posted by yuppicide

I'm looking at lenses and they say for example 18-55mm. How do I find out how much zoom this would be in x terms?! Like for example the Olympus C765 Ultra Zoom says 10x optical zoom?!

I'm trying to compare the two so when I guy a Digital SLR and have to get a lense I'll know how much zoom I can expect.

To figure the zoom factor, divide the larger number (55mm) by the smaller (18mm), and your answer is 3. This lens has a zoom factor of 3x. The Olympus C765 Ultra Zoom has a lens that offers a range of 38-380mm (380/38=10x zoom factor). BUT there is MORE to know before choosing a lens for a SLR or DSLR or camera with a fixed zoom lens. There is a difference between a 3x zoom of 18-55mm and another 3x zoom of 100-300mm. You need to think about what type of photography you are interested in doing to know whether you need a wide angle view, a more "normal" photographic view, or a telephoto view, although some of the 10x-12x zoom lenses are covering ranges from "slightly" wide-angle through the normal range and well into the telephoto range. An over-simplification might say that wide-angle views are especially useful for landscape photography, normal view for portraits of family/friends, and telephoto for wildlife. Do some reading about lens focal lengths, and thinking about what subjects you are likely to be photographing before you decide what to buy.

I've been looking for some websites with good basic explanations to help you -- these might help you get started.

http://www.betterphoto.com/buyers/lensesChoosing.asp

http://photography.about.com/od/basics/a/bplens.htm

http://www.bobatkins.com/photography.../choosing.html

http://photoinf.com/General/Wim_van_...hotography.htm

http://www.halley.cc/photo/cropfactor.html

Doug Nelson · #3 04-25-2005, 05:15 AM

It also helps to know the diagonal distance of the image area (the negative/slide or CCD). For 35mm film that's a little over 43mm, so a 1:1 magnification lens would be a 43mm. The industry has standardized on a 50mm lens as "normal", but it actually offers about a 10% magnification (but it's much handier for the math). So if a 50mm lens is 1x, then a 100mm lens would offer 2x magnification (or "zoom").

Different digital cameras have CCDs of differing measurements, but most make a focal length multiplier available (usually in the vicinity of 1.5, so a 50mm lens would actually magnify by 1.5x using a CCD).

So there's (at least) two ways of calculating this. Marketers usually choose the one that sounds best

yuppicide · #4 04-25-2005, 04:26 PM

Thanks for the help. That was easy enough. Helps a real lot! I've settled on the Canon Rebel XT camera finally. It's almost as good as the EOS 20D, but not as good autofocus and the EOS has a faster burst. Most of the "kits" come with the body and an 18-55mm lense.

I know what you mean about some are wide angle. I'm just looking to get something 10x or 20x in power and later on down the road I'll get a wide angle. You've helped me make my decision that I need something more zoomy.

yuppicide · #5 05-06-2005, 11:28 AM

Did I tell my friend something wrong?! The other day we went to take some pictures at an abandoned rock quarry. He has a Minolta 35mm SLR and I had a crap 2mp Olympus digital. The Olympus had 3x zoom. I looked on his lense and going by the numbers it looked like his was about 3x zoom, but his zooms in a lot farther than the Olympus.