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Re: [OM] 50mm/55mm/500mm Lens questions -Reply

Subject: Re: [OM] 50mm/55mm/500mm Lens questions -Reply
From: David Irisarri Vila <valicors@xxxxxxxxxx>
Date: Thu, 17 Aug 2000 23:31:36 +0200
It´s very easy to understand f numbers, just only
pick up your calculator and begin to play!
Pick a standard f number like f2. Now 
2 x 1.414 = 2.8
2.8 x 1.414= 4
4 x 1.414= 5.6 etc...
So 2 / 1.414 = 1.41 
Why "1.414", because it´s a geometric progresion. 
Now we can convert this magic number into something
easier!!! We konw that if we stop down we have 1/2
less light than the last f number. For example
My 50mm Zuiko lens at f1.4 has a surface of ¶r².
3,14 x (50/1,1414)²= 3925.80
Now f2 should have exactly the half!!!
3,14 x (50/2)²= 1963.49  OK!!!!!!!!
This is an aritmetic progresion.
So f1.2 is 1/3 more.
3,14 x (50/1,2)²= 5454.15

5454.15/3925.80 = 1.38 times more light!!!!

Best regards,

Dave
Frank Berryman wrote:
> 
> f1.2 is then 1/2 stop faster that 1.4?
> 
> -----Original Message-----
> From: Scott Nelson [mailto:SNelson@xxxxxxxx]
> Sent: Thursday, August 17, 2000 12:38 PM
> To: olympus@xxxxxxxxxxxxxxx
> Subject: RE: [OM] 50mm/55mm/500mm Lens questions -Reply
> 
> No, F:1 is a full stop faster than f:1.4.
> 
> >>> Frank Berryman <FAB@xxxxxxxxxxxxx> 08/17/00 10:03am >>>
> I am a little slow on the uptake this morning.  Is a f1.2 lens one stop
> faster that a f1.4 lens?
> 
> -----Original Message-----
> From: Dirk Wright [mailto:wright@xxxxxxxxxxxx]
> Sent: Thursday, August 17, 2000 4:15 AM
> To: olympus@xxxxxxxxxxxxxxx
> Subject: Re: [OM] 50mm/55mm/500mm Lens questions
> 
> > Now I found
> >an 1.2/55 lens, faster but heavier - that should not the point for me.
> >After reading Gary's marvelous lens test once again
> >I think they are comparable in picture quality. Am I right
> >or does daily work suggests some difference ?
> 
> No. The 55/1.2 is much softer in the corners at all apertures than the 50/
> 1.4.
> 
> --
> Be Seeing You.
> Dirk Wright
> "Let me assure you that to us here at First National, you're not just a
> number.  You're two numbers, a dash, three more numbers, another dash
> and another number."
>                 -- James Estes
> 
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