kevinsproule
newbie
Reged: 18/06/2008
Posts: 8
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Can Someone be so kind to explain the basics of the lense for example what f/2.8 means and the different characters for example i think i know IS means Image stabalizer?
I've made my mind up and am going to buy the canon 450d, it will be mainly for taking pictures of pets, family around the garden, beach...
not really for close up shots of flowers... but also for pictures of things in the distance as i live right beside the mourne mountains...
what combination of lens would best suit my needs?
budget around £500 for the pair...
thanks
Kevin 
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Malcolm_Stewart
Pooh-Bah
Reged: 11/07/2005
Posts: 2249
Loc: Milton Keynes, UK
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Quote:
Can Someone be so kind to explain the basics of the lens for example what f/2.8 means and the different characters for example i think i know IS means Image stabalizer?
I've made my mind up and am going to buy the canon 450d, it will be mainly for taking pictures of pets, family around the garden, beach...
not really for close up shots of flowers... but also for pictures of things in the distance as i live right beside the mourne mountains...
what combination of lens would best suit my needs?
budget around £500 for the pair...
thanks
Kevin
"f/2.8" is an indication of the diameter of the aperture of the lens, and is precisely what it says, where "f" is the focal length, the "/" indicates division and the "2.8" is one of a common series of numbers used for this purpose. Frequently, the "/" is missed out, but the meaning is the same. The common series includes f/2, f/2.8, f/4, f/5.6. For a 100mm focal length lens, the diameter of the aperture is
d=50, 35.71, 24, 17.86mm etc.
More importantly, the (light passing) area is pi. d^2 /4. So we get 1964, 982, 491, 245 sq.mm i.e. every step halves the light passing area. The brightness on the film or sensor is the same whatever the focal length, and this is why aperture, expressed in this fashion is important and the standard way of doing things. Lenses not only have Maximum Apertures which indicate how suitable they are for low light usage, but also have variable aperture mechanisms which allow the light passing are to be reduced. Similarly, the shutter can be adjusted to be open for different lengths of time, and these too are frequently set out in a doubling series 1, 1/2, 1/4 etc. with slight rounding variations along the series.
The IS version of the "kit" lens (Note: only 1 "e") has quite a good reputation, better than the earlier version, and will allow quite a range of work. Few lenses work superbly well at maximum aperture, so photographers often choose to work at smaller apertures such as f8 or f11 where faults (aberrations) will be reduced, but the shutter speed may then have to be longer introducing a risk of camera shake. It's all a matter of compromises, and today's cameras are excellent at offering good quality results with fewer compromises than earlier. (Cf film at an ISO (film speed) of 1600, very grainy, versus a DSLR set to 1600 ISO, now fairly free of noise.)
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Malcolm Stewart
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kevinsproule
newbie
Reged: 18/06/2008
Posts: 8
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thanks malcom, dont think i could have got a better awnser..
but what lens do you think would best suit my needs with a budget of 500 for a long distand and lense for family and pet photos?
thanks
kevin 
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NorthernMonkey
enthusiast
Reged: 01/05/2007
Posts: 270
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If your budget can stretch to it, then the canon 17-55 2.8 IS
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Malcolm_Stewart
Pooh-Bah
Reged: 11/07/2005
Posts: 2249
Loc: Milton Keynes, UK
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Quote:
d=50, 35.71, 24, 17.86mm etc.
Ooops!
Obviously should have been:
d=50, 35.71, 25, 17.86mm etc.
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Malcolm Stewart
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Norman
Reged: 23/09/2004
Posts: 1547
Loc: West London, UK
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Malcolm's done a sterling job there but for a little more detail try here.
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Regards,
Norman
www.photobox.org.uk
A woman has the last word in any argument.
Anything a man says after that is the start of a new argument.
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