Lens Nomenclature

Hi,

I'd be grateful if some could point me toward information about lens nomenclature. For example I don't know what 1:3.5-4.5 35-70mm acutally means.

Many thanks, Colin

Colin,
I haven't got any links to information, but I can tell you what that means.
1:3.5-4.5 35-70mm tells you two sets of information.

Firstly, the focal length ranges from 35mm at the wide angle end, to 70mm.

The second piece of information is how bright the lens is. When set to 35mm focal length, the lens will have a maximum aperture of f3.5. When set to 70mm, it will have a maximum aperture of f4.5.

If you need to know in more detail about focal length and aperture, I'm sure we can dig out a link or two

Hope that helps,
Matt

I thought I'd just add that for 35mm cameras, 50mm lenses are considered 'standard' (approx the angle of view of the human eye) and give a natural perspective. Anything shorter is wide-angle and longer is telephoto.
The 35-70mm zoom is therefore slightly wide-angle, through standard to slightly telephoto.
Most zooms of moderate range are capable of good results at all focal lengths and aperture settings but 'superzooms' ie. 28-200mm, whilst being very versatile, make too many optical compromises and tend to deliver really good results only at certain settings and prime (single focal length) lenses and moderate zooms should be used where optimum quality is required.

Zoom lenses with wide ranges also tend to have smaller maximum apertures - making them less useful in low light situations.

Many thanks Matt and Kimbo. I'm happy with 35mm, 70mm, wide, tele and standard.
I now understand the relationship between focal length and the aperture stops in the example, thankyou.
What is the " 1: " bit all about ? It indicates a ratio to me, but of what ?

TGIF Colin

Ah, well this is where my knowledge is a little sketchy but I think I'm right in saying that the 1: refers to the focal length in use, so at 35mm the diameter of the max. aperture (lens wide open) can be divided into the distance between the front and rear elements 3.5 times. At 70mm the effective aperture becomes smaller and can then be divided into the focal length 4.5 times.
So yes it is a ratio or you can think of it as a fraction ie. 1/3.5 or 1/4.5
Just remember 'big number ~ small hole', so f22 (1/22) is a tiny hole that allows only a small amount of light to pass through the lens and onto the film.
Smaller apertures (big numbers) require correspondingly longer shutter speeds but enable greater depth of field.

The ratio could be between the front element and the film plane but either way, I think I've got the gist of it right



BTW, lens construction is not an exact science and the figures quoted are approximate. The number of elements, focussing and zooming mechanisms will determine the actual physical size of the lens but the figures will indicate the size of the image rendered on the film.
Therefore, you can have two lenses of the same focal length that are quite different in terms of their physical dimensions but which both deliver approx. the same angle of view.

Just a couple of links:
http://www.cladonia.co.uk/photography/exposure/e-13.html
http://www.riversidecardiology.com/fstop/f-stop.htm
http://www.photoxels.com/tutorial_aperture.html

Excellent links Matt

Thank you both. I now understand. Good links too.

Bon weekend, Colin