From: "Ellen Mackenzie" 
To: 
Reply-To: "Ellen Mackenzie" 


Yes the 100 mm lens has four time the light collection, BUT, the image area
is four times larger making the light intensity per square unit the same

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of Emery
Greg
Sent: July 17, 2003 9:54 PM
To: John Sherman
Cc: atm{at}shore.net
Subject: Re: ATM First Question (More)







> Now imagine two f/2.8 lenses, one has a 50mm focal length and the
> other has
> a 100mm focal length. Now, you want to make an image of a person
> on a piece
> of film, say. If you use the 100mm lens the person will be twice
> as tall as
> if you used the 50mm lens. Of course the aperture is the same, and

If both lenses are f/2.8, won't the 100 mm lens have twice the aperture of the 50 mm?

The 100 mm lens has a larger image and 4 times the light collection.

ttfn
greg

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