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View Full Version : Focal length mm VS Optical zoom X


MALI
21st of January 2006 (Sat), 11:48
How do these two compare in terms of zooming capability?

For example, Canon S2 IS has 12X optical zoom.

What does that translate into focal lentgh mm in a zoom lens? Would that be for instance equal to a 200mm zoom, etc?

Thanks.

MALI

ShadowFlyP
21st of January 2006 (Sat), 11:52
How do these two compare in terms of zooming capability?

For example, Canon S2 IS has 12X optical zoom.

What does that translate into focal lentgh mm in a zoom lens? Would that be for instance equal to a 200mm zoom, etc?

Thanks.

MALI

Optical zooms for point and shoot cameras are usually the range of zoom the camera offers, from the wide-angle all the way up to the telephoto. In the case of the Canon S2, dpreview has an article that states the S2 (http://www.dpreview.com/news/0504/05042201canons2is.asp) has a 36 to 432mm (35mm equiv.) lens. Notice that 36 * 12 = 432, hence the 12x zoom.

Jon
21st of January 2006 (Sat), 12:09
12x zoom can mean any old thing - all it says is that the longest focal length is 12x what the shortest one is. A large "x" zoom range is easier to do with the short focal lengths of the digital P&S cameras. Getting a good large zoom range with a lens for a DSLR is much harder. Most 12x zooms for DSLR aren't worth the price - unless you absolutely can't possibly change lenses, you're better off getting several lenses to cover the same range. The theoretical limit for Canon, considering shortest to longest lenses, and without teleconverters, is something like 150x (8 mm fisheye to 1200 mm tele).

foxbat
22nd of January 2006 (Sun), 04:56
I've tried the 12x zoom on the Panasonic FZ5 with its supposedly high class Leica lens. At the long end the quality is very very poor compared to what you will be used to from your 20D + 70-200. Soft at the corners and lots of CA.

SkipD
22nd of January 2006 (Sun), 06:30
How do these two compare in terms of zooming capability?

For example, Canon S2 IS has 12X optical zoom.

What does that translate into focal lentgh mm in a zoom lens? Would that be for instance equal to a 200mm zoom, etc?As has been said, a "12X zoom" specification says nothing about the actual focal length range. If you look at the specifications for any Canon camera, they will probably give you the equivalent (on a 35mm camera) focal length range for that camera.

A good example is my Canon PowerShot G2. It has a zoom lens that has a focal length from 7mm to 21mm. It is advertised as a "3X" which is the 21mm divided by the 7mm. The manual for the G2 says that the field of view is equivalent to a 34-102mm zoom on a 35mm camera.

In order to figure out what lens would provide equivalent fields of view ON YOUR CAMERA, you need to take the 34-102 numbers for the equivalent on a 35mm camera and apply any crop factor to that. For example, if you have a 20D body, you would divide the 34-102 by 1.6 and come up with approximately 21mm to 64mm. Thus, to match the field of view of the G2's lens, you would need a 21-64mm zoom on a 20D (or 350D, etc.).

There's more to matching lenses than merely matching focal lengths, but I won't get into that here.

There is one thing you need to know. There are very significant engineering problems with designing zoom lenses. Without getting into the details, it is much more difficult to make a lens with a very high zoom ratio (10X, 12X, etc.) and retain the optical qualities that can be built into a zoom lens with a shorter zoom ratio such as 3X. You will notice that all of the L-class Canon zoom lenses have quite short zoom ratios - the maximum I can find is 4.3X, and most are 3X or less. There are a very few lenses out there with 10X zoom ratios that are acceptable to picky photographers (though not nearly as good as the better zooms). In my opinion, when picking zoom lenses it would be best to stay with the 4X - or less - class of zoom lenses to have affordable quality.

lakiluno
22nd of January 2006 (Sun), 08:27
Don't forget the only reason companies make superzooms is to give the versatility of an SLR focal range without needing the pain of buying lots of lenses and changing them. The moment your prepared to change lenses in the field etc, then having such a great focal length difference at a loss of overall quality doesn't seem like such a good thing.

Leo