canon 18-55mm EF-S lens.

[phiduypdn]

please!could anyone tell me how many times the lens above ( accompanied with canon 500D) can zoom..?

is it only 3 times zoom?

[Colin Southern]

please!could anyone tell me how many times the lens above ( accompanied with canon 500D) can zoom..?

is it only 3 times zoom?

Hi Phiduypdn,

That's an easy one

55 / 18 = 3.06x

On a Canon crop-factor camera such as the EOS 500D this lens will give you equivalent focal lengths of 29mm to 88mm

[phiduypdn]

thanks Colin. I wanted to confirm if my assumption is right.
But howcome such a " big" lens like that has only 3 times zoom..i mean.. less than even that of a lens on my compact carmera ?

[Colin Southern]

thanks Colin. I wanted to confirm if my assumption is right.
But howcome such a " big" lens like that has only 3 times zoom..i mean.. less than even that of a lens on my compact carmera ?

The higher the zoom range (especially when going from a wide-angle at one end) the more difficult & expensive it is to design a lens that gives good performance - which is probably why the EF-S 18-55mm costs a lot less than the EF 18-300mm! It's true that many compact cameras have zoom lenses with a greater zoom range, but it's a lot cheaper to design a lens for a camera with a 1/4" sensor than it is to design one for the size of the sensors used on DSLR cameras.

[phiduypdn]

i'm a very new comer. So if i have problems pertaining to camera and lens i hope you're eager to help ( in case i did read something on Google but useless)

things come out clearer to me now. Thanks again Colin

[rpcrowe]

Welcome phiduypdn,

I have always found that I can get answers and solutions (and occasionally supply answers or solutions) to questions and problems regarding digital photography.

As opposed to some other sites, members here never belittle newcomers. Instead, there are friendly and helpful responses.

One thing that I would like to add to the above: The zoom-ratio (or X-factor) is most often used in marketing point and shoot cameras. Although ALL zoom lenses have a zoom ratio, it is seldom considered in lenses for DSLR cameras.

Two exceptions are:

1.
When describing a lens such as the 18-200mm as a "wide range zoom". Wide range zoom lenses are very convenient to use because they reduce the amount of lens switching in the field. However they have some shortcomings such as smaller f/stops, slower autofocus and lower image quality.
2.
When explaining why present zoom lenses are constrained regarding their aperture: Present technology limits zoom lenses of a constant f/2.8 aperture to a 3x zoom ratio. Or stated in reverse, lenses of a greater than 3x zoom ratio cannot have a constant f/2.8 aperture. An example of this is the Canon 28-135mm f/3.5-5.6 IS lens. This lens has a zoom ratio of almost 5x and thus has a variable aperture which decreases in size from f/3.5 at its widest focal length (28mm) down to (f/5.6) at its longest focal length.

Strangely, the descriptions of "constant" and "variable" apertures can sometimes be confusing. The actual size of a 'variable" aperture remains constant as the lens is zoomed. Since f/stops are a relationship between the focal length and the size of the aperture; the f/stop is decreased as the lens is zoomed out.

On the other hand the aperture of a lens with a "constant" f/stop is actually variable since the aperture size increases and decreases as the lens is zoomed out and in. The mathematical relationship between the aperture size and the focal length remains the same. Thus we have a constant f/stop.

[phiduypdn]

Hi rpcrowe,

I already read your post and I think I really got the picture. I also read something about the relation b/w the aperture and focal length on wikipedia. And then, reading your post, I find it really goes with my assumption.
Thanks you for helping me confirm that.

[phiduypdn]

by the way rpcrowe, wish your family joy and happiness