zoom help

[andrecb]

I'm new to photography, and there is still something I dont understand.

I have a P'n'S with optical zoom of 3x and there are many other P'n'S with different kind of zoom, 4x 5.5x 12x ...

but DSLR lenses are in mm, 50mm 18-55mm 70-200mm

what I dont understand is what is the proportion from mm to how many times is zoomed like for eg: 18mm its 1.5x zoom or something

[acedrew]

The zoom "x" number is equal to the ratio of the wide end of the zoom focal length to the tele end of the zoom focal length an 18-55mm would be 18:55 (55/18) = a 3.05x 70-200=2.85x zoom now if you have both an 18-55 and a 70-200 lens you have the equivalent of a compact 11x zoom.

The "mm" in the lens is the focal length, literally thus "the distance behind the lens that light entering the lens from infinite distance focuses" The focal length plus the frame size of the camera gives you all kinds of good info like field of view and other fun stuff.

Check this guide out to learn the basics of optical principles that control photography: Photography (Basic) - Introduction to photography and other graphic techniques

Andrew Rodgers
Perfected Perspectives -- Photography by Andrew Rodgers | Andrew Rodgers (acedrew) on Twitter | Login | Facebook

[wulf]

Zoom multipliers have become part of marketing speak, especially when they fudge the line between optical zoom and digital zoom (the latter will be much lower quality - it is better to crop the picture later than perform the operation in camera).

The DSLR system is more informative as it also gives some idea of the effect that different zoom levels will have - ie. 18mm (wide angle) will disort things up close or 300mm (telephoto) will tend to flatten perspective in a scene.

Note also the high regard which fixed focal length lenses are held in. These tend to be good quality and fast (allowing decent pictures in low light conditions and also playing with narrow depth of field). They don't have a zoom factor at all!

Wulf

[andrecb]

well thank you for the good explanation

I have a P'n'S Sony 10Mp with 3x zoom
I intention to buy Eos 1000D with kit lens 18-55mm IS

I will have 3x zoom like? but with way better quality isn't it?

P.S. Thanks for the links I will study it more

[wilswong]

Originally Posted by andrecb

well thank you for the good explanation

I have a P'n'S Sony 10Mp with 3x zoom
I intention to buy Eos 1000D with kit lens 18-55mm IS

I will have 3x zoom like? but with way better quality isn't it?

P.S. Thanks for the links I will study it more

Quality wise, the kit zoom lens will definitely be better than the point and shoot lens. A very practical way to see this is the amount of light the lens allow the light to hit the sensor just by looking at the front of the lens.

This is not scientific but is a good gauge. A large lens out front usually means more light will hit the sensor at any given time.

About zooms, we usually talk about the speed of the lens and we equate the speed with the aperture setting of the lens. So if the lens can accommodate F2.8 for all zoom ranges, it is better than a zoom lens that has variable aperture settings at different zoom range. For e.g. F3.5 at 18mm and F5.6 at 50 mm. It just means the minimum aperture settings at the two extreme zoom range of the lens.

Why is this important? If I have set a camera for a particular scene and yet the settings has changed just because I have zoomed into a scene, it will compromise the shutter speed.

As with the lens, the sensor size also plays a part. Imagine having 100 squares in a basketball court as opposed to 100 squares in a football field.
Which individual square will be larger in terms of area? Apply that to a camera sensor and one would quickly see that a larger sensor with the same pixel count as a smaller sensor will tend to exhibit better light capture capability and hence lower sensor noise because of the physical pixel size.

It is a very simplistic way of putting it across about the ability to catch light efficiently.