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Old Nov 23, 2008, 10:41 PM   #1
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I have been trying to research the best camera for my wife who loves to watch nature.... particularly birds. We presently have an old Minolta with a 12x zoom (stated as 420mm). The new Casio is a 20x with a translation of 520mm.

Is there a way to determine the actual gain in distance? $600 is a rather large amount to find there is an insignificant gain in ability to see the subject.

Thanks for the feedback..............and help.
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Old Nov 23, 2008, 11:54 PM   #2
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You provided just barley enough information to figure this one out. So here goes....

Your actually asking for a comparison of the field of view (fov) between the two cameras at some distance.

Your old camera I am guessing is a DiMage z3 with the 420mm lens which has a 1/2.5" sensor with a crop factor of 5.99 (you need the crop factor to determine the fov).

Your new camera I am guessing is an EX-FH20 with the 520mm lens which has a 1/2.3" sensor with an (estimated) crop factor of about 5.7.

Using the fov calculator at http://www.tawbaware.com/maxlyons/calc.htm
and assuming a target distance of 100 feet (a wild guess) we get...

420mm at cf of 5.99 at 100 feet results in
horiz fov 1' 5.1"
vert fov 11.4"
diag fov 1' 8.6"

520mm at cf of 5.7 at 100 feet results in
horiz fov 1' 2.6" increase of 2.4" or 16%
vert fov 9.7" increase of 1.7" or 17%
diag fov 1' 5.5" increase of 3.1" or 17%

So you can go cut a piece of paper 1' 5" by 11" and draw a rectangle in it measuring 1' 3" by 9.7", measure out 100' on the front lawn and prop up the piece of paper and see the difference.

Hope it helps....

all of this is roughly porportional to the 100mm increase from 420 to 520 or 100/520=19%)

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Old Nov 23, 2008, 11:58 PM   #3
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Figures such as "12X" and "20X" don't exactly relate to focal length. They are for zoom lenses, and state the ratio of the shortest focal length to the longest focal length. A zoom lens is a lens with an adjustable focal length and therefore an adjustable angle of view. shorter focal lengths provide wide angles of view, while longerfocal lengths provide a narrower angle of view. The ratio of a zoom lens that has a focal length of from 5mm to 25mm is a 5X zoom lens, but so is a zoom lens that has a focal length of from 10mm to 50mm. P&S digicams all have very similar angles of view at their shortest focla length, so the "12X" and "20X" figures are a way to determine which camera has the longest lens, but it's by no means exact.

To further confuse things, different cameras have differnet size image sensors. Cameras with larger image sensors have wider angles of view than cameras with smaller image sensors. In order for a camera with a smaller image sensor to have the same angle of view as a camera with a larger image sensor, it must have a lens with a shorter focal length. In order to make some sense out of all this, manufacturers use a '35mm equivalent focal length', which is the focal length of a lens that would give an equivalent angle of view on a 35mm film camera. This makes it easier to compare 'apples to apples', even if you aren't familiar with 35mm film cameras.

For birding, you would certainly need a longer focal length lens, so a longer '35mm equivalent focal length' would be desireable. But there are other factors to consider as well, such as high ISO performance and image stabilization. And you might want to take a look at the Wildlife Photosto see what other people use to take the kinds of photos you want to take. And, of course, it's a good idea to try a camera out to see if you can comfortably use it.
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Old Nov 24, 2008, 12:03 AM   #4
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You could also have a look at the focal length comparison page at http://www.tamroneurope.com/flc.htm

Now it only goes up to 500mm, but it should give you some idea of the difference.

Select the 35mm film icon ( so it turns yellow ) and drag the blue slider to 420mm and then to 500mm
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