What doe it all mean

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27 Feb 2004 - 11:50 AM

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mikeo

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27 Feb 2004 - 12:14 PM

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a fast lens is one with a wider maximum aperature than another one!If you had a 300mm lens with max aperature of 2.8 compared to a 300mm lens with a max aperature of 5.6 the 2.8 lens would be 3 stops faster then the 5.6.The wider the maximum aperature,the faster the lens...

alansnap (e2 Member)

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27 Feb 2004 - 12:43 PM

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Mikeo is right, but as you're new to this I'll give you a broader definition. Basically a fast lens is one which allows you to use faster shutter speeds in a given lighting than so called slower lenses. This much the same way as fast film.

To work out how fast a lens is look at the maximum aperture. Confusingly the greater (wider) the maximum aperture is then the lower an f number it will have. For example I have a number of lenses for a Leica and 2 Canons. The fastest lens I have is the old F1.8 50mm for my Canon AE1, closely followed by an F2 Leica 35mm for my M6. My standard zoom for my EOS 33 is the 3.5-4.5 28-105 zoom, and my tele zoom for my AE1 is an F5.6.
So in practical terms what does this mean?

It's best illustrated by a table and I'm not sure how well this will work, but here goes. For a give film speed say the meter says 1/125 s at f5.6 how does this translate to other lenses?

Aperture............2.......2.8.....3.5.....4....... 4.5.....5.6
Shutter Spd..1000..500....320.....250.....200.....125

As you can see, my fast f2 lens lets me use 1/1000 where I'd only be able to use 1/125 on my old zoom. Basically the faster the shutter speed you can use the sharper the picture because there's less chance of camera shake. As a general rule try to use at least a shutter speed od 1/focal length if you're going to hand hold a lens (though IS lenses break this rule). So for a lens at 50mm use at least 1/60s, for 100mm 1/125s and so on. Faster lenses and faster films help with this.

But remember that the wider the aperture you use the shallower the depth of field you get, but that'sanother story.

Hope this helps

Alan

alansnap (e2 Member)

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27 Feb 2004 - 1:55 PM

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Thanks Anne, Alan takes bow and is soundly kicked.
Problem is if you understand it it's easy, if you don't, well just take our word for it. Do you want me to start on the maths and why f-stops remain constant??
Tried this for the club magazine. They actually claimed they understood what I wrote. Shame really, you can fool some of the people all of the time)

Alan

alansnap (e2 Member)

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27 Feb 2004 - 5:04 PM

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Hey Anne so was I. I know this is all very hard to get your head around. I hope your course goes really well.

I learnt my photography with an old manual camera and a hand held meter, and that's how I learned all this. The camera was an old Zeiss Contina from 1952 and it had a neat mechanical method of locking aperture and shutter so that when you changed one the other changed too so the ratios I showed in my first posting were maintained. Certainly helps fix these ideas as did my Weston meter.

Pete,

Is there any way to post a word file? I have a brief explanation of f stops, depth of field and so on that I produced for my club magazine. I can share it if anyone wants it.

Alan