Understanding lenses

[JOJO]

Just a question to help with my understanding of lenses.

Reading an article in camera magazine about how to set up camera for a creative shot, it's based on using a standard 18-55mm lens.

It says to set to 18mm 'the widest setting'.

Why is the lower number the wider setting? Is it in relation to F numbers(if I've understood correctly), the lower the number, the wider the aperture?
Many thanks

[mikeaspinall]

Hi

I assume that what they are saying is that the 18mm is the widest setting (wide angle) and nothing to do with
the apertures.

18mm is wide angle
35mm would be medium setting and
55mm the longest setting

This applies to any zoom where the lowest number is the widest setting and the highest number the longest. e.g.
70mm (widest) to 300mm (longest) and so on. Becomes apparent when you rotate the lens.

Apertures mainly apply to depth of field. e.g. Lowest f stop for shallow depth of field (say portraits) to highest f stop
for say landscapes.

Hope that this helps but if not Big John is your man.

[John]

Mike's answered the question, and it can get quite complicated to take in all at once.

The 18-55mm lens is a standard zoom on a "crop sensor" camera, or "APS-C format" camera. We'll not go into larger formats yet, but suffice it to say that film used the larger format that we now know as "full frame". For these larger formats, there will be a different standard zoom.

So, for APS-C cameras, Mike has summed it up.

As far as aperture goes, the way it is worked out is simple. It's a ratio, so f/2.8 for example will be the same exposure value for all lenses. If you have a lens of 50mm focal length and it has an opening (aperture) measuring 25mm, then 50 divided by 25 is 2 and it's an f/2 lens. If the focal length was 500mm the glass would have to be an aperture of 250mm to be an f/2 lens, which would be absolutely horrendous in size. So long (telephoto) lenses tend to have quite restricted apertures to make them small enough to use.

It's a mass of figures and terms I know, but eventually it will all make sense!

[JOJO]

Ah, right. I get the idea now.
My brain goes to mush when numbers are involved

Thanks gentlemen