Zoom is the ratio of the longest and shortest focal length.So 18-55 mm is 55/18=3.05x while 70-300 mm is 300/70=4.29x.You say you have Sony H1. The lens is 36-432 mm or 12x..

The dSLR with crop factor 1.5 will give you for 18-55 mm an equivalent range of 27-82 mm while 70-300 will give you 105-450 mm.VictorBucuresti, Romaniahttp://s106.photobucket.com/albums/m268/victor_petcu/..

**Comment**#1

Numbers such as 10X, 12X, etc., are zoom ratios, and are no indication at all of the type of zoom lens you have. you have to compare the actual focal length of the lens in question as that determines how much image magnification you will see. A 12-24mm zoom lens is considered a 2x in terms of zoom ratio....this is an extreme wide angle lens, giving you a very wide field of view..

An 18-55mm zoom is a 3x lens, which goes from a wide angle view to a normal perspective on a typical DSLR. A 100-300mm zoom is also a 3x lens but it gives a much different perspective, from short telephoto to a long telephoto....so looking at the zoom ratios tell you nothing about the lens other than the ratio of the focal lengths. You have to lok at the actual focal length to comapre the lenses..

As a general rule of thumb in terms of the field of view in a standard 35mm camera, focal lengths from 10-35mm are considered wide angle, 35-55mm is considered a normal field of view, 55-300mm is considered telephoto and anything over about 300mm is considered a long or extreme telephoto..

The previous poster pretty much answered your specific question on the lenses in question but hopefully this will also give you a general idea in terms of what type of field of view to expect from other lenses. Just always keep in mind that zoom ratios where manufacturers stress we have a *12x* zoom! mean nothing unless you look at the focal lengths......the gimmick of a zoom ratio is really just that, an advertising gimmick to sell folks cameras by making them think that a huge zoom ratio is important and necessary. Actually, the shorter zoom ratios lend themselves to much better designed and optically corrected lenses than large ration lenses. A pair of high quality 3x zooms, such as an 18-50mm/2.8 and a 70-210mm/2.8 will yield much better images than one 18-200mm zoom lens.JohnPentax *ist-D, K100D, Fuji F20/31fd, Oly Stylushttp://www.pbase.com/jglover..

**Comment**#2

As stated, a lens of about 50mm gives the perspective (view) that is about equivalent to what you see with the unaided eye..

So to assist you in visualizing what any given focal length will give, if you divide the focal length by 50 you can get a close approximation of what to expect from that lens:.

100mm will give you a view that is twice(2x) as close as the 50mm150mm ... 3x200mm ... 4xetc..

Works in reverse too...25mm ... ~0.5x12mm ... ~0.25xetc..

Remember these are only rough approximations..

Long zoom ratios will also yield lenses that are slower than shorter zoom ratios. Most zoom lenses today are of a variable aperature design - which means that the wide open aperature changes with focal length (ie: 28 - 200mm f3.5-5.6)..

You can get fixed aperature zooms, but thay are (usually) considerably more expensive than their variable aperature counterpart..

The greatest of mankind's criminals are those who delude themselves into thinking they have done 'the right thing.'- Rayna Butler..

**Comment**#3

Jimwh wrote:.

I'm trying to figure out what a 10x optical zoom equates to inmillimeter size..

Answer: 18-180mm or 28-280mm.

For example, what would the Nikon 70-300mm f/4-5.6G.

Autofocus Zoom Lens equate to in terms of X times.

4.28X.

While I'm at it, what would Nikon 18-55mm AF-S DX Autofocus Zoom Lensequate to in terms of X times zoom?.

3.05x.

Perhaps you see a opricess here: divide the telephoto end (in MM) by the wide angle end (in mm) for the Zoom Ratio.

Van..

**Comment**#4

John p vansteenberg wrote:.

Jimwh wrote:.

I'm trying to figure out what a 10x optical zoom equates to inmillimeter size..

Answer: 18-180mm or 28-280mm.

Or a Sigma 50-500mm.........if you got about a thousand dollars! .

JohnPentax *ist-D, K100D, Fuji F20/31fd, Oly Stylushttp://www.pbase.com/jglover..

**Comment**#5

Thank you all...I'm fully straightened out now and know what to look for..

Many thanks again for your input...

**Comment**#6

A useful way to compare optical zoom range is by magnification. This is often stated in terms of 50mm being a normal lens (magnification =1.).

Non-DSLR cameras often state their focal length range in 50mm equivalent. A Fuji f20 compact camera's equivalent range (printed on the lens barrel) is 35-105mm for example (3x)..

For this lens:.

Minimum magnification 35/50=.7xmaximum magnification 105/50=2.1x.

Magnification ratio 2.1x/.7x=3x.

A Panasonic FZ30 has an optical magnification range of .7x-8.4x for example..

I think this is a more reasonable way to state the range than 35-420mm, or 12x, or 8-96mm..

Dave.

For a DSLR the appropriate crop factor must be taken into account; the "normal" or unit magnification focal length being 50mm/(crop factor)..

**Comment**#7

Baloo_buc wrote:.

You say you have Sony H1. The lens is 36-432 mm or 12x..

Note that this is the "35mm-equivalent" range for field of view..

The actual focal lengths for that lens are quite a bit shorter than 36-432mm. But the small sensor of the superzoom P&S produces an even bigger "crop factor", so to speak, than the crop factor of the DSLR...

**Comment**#8