Re: f number adjustment to increase light level

[Lew <lew1716@xxxxxxxxx>]

 Yes, but a quick look at any lens or light meter tells you just as much without any calculations at all. Each stop signifies a factor of 2, so to get 4x the amount of light, click over 2 stops & you're done. Teaching a student all this math (if this is what the thread is about, I wasn't in on the beginning) is very academic. It's not anything a photographer with a camera in hand would ever do.

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From: Kim Mosley <mrkimmosley@xxxxxxxxx>

Sender: owner-photoforum@xxxxxxxxxxxxxxxxxx

Date: Fri, 21 Jan 2011 08:08:01 -0600

To: List for Photo/Imaging Educators - Professionals - Students<photoforum@xxxxxxxxxxxxxxxxxx>

ReplyTo: photoforum@xxxxxxxxxxxxxxxxxx

Subject: Re: f number adjustment to increase light level

f number-new =  f number-old / sqrt(light increase factor)

So if you want 4 times the light, you take the square root of 4 or 2.

16/2=8   f/8 gives 4 times the light as f/16

On Fri, Jan 21, 2011 at 7:53 AM, Lew Schwartz <lew1716@xxxxxxxxx> wrote:

Your mensa-like friend might do well to reflect that "f" numbers are
stated as reciprocals, so f/16 is actually much smaller than f/2,
smaller numbers = less light (f/16 being smaller than f/2). Other
ponderings about the area of the aperture opening are, however that
area is relative to the focal length of the lens in question (the "f"
part of the f number).

--
Kim Mosley
mrkimmosley@xxxxxxxxx
Website: http://kimmosley.com
Blog: http://kimmosley.com/blog