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[OM] Re: A couple of E-500 observations

Subject: [OM] Re: A couple of E-500 observations
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Mon, 09 Jan 2006 07:50:26 -0500
No, you're not doing something wrong, I am.  Your numbers are correct. 
I went the long way and computed the glass area and verified your 
numbers.  I had been using what I thought was a shortcut to the 
calculations. Applying ratios to the focal ratios.  Well, it's a 
shortcut all right but it's wrong.  I'll have to rethink what I was doing.

What's interesting out of all this is that, as you report, 1/3 stop down 
from 2.8 (2.828427) is 3.1.  My camera, however, reports it as 3.2.  3.2 
is also a value you're somewhat likely to see printed on a lens as its 
maximum aperture.  I think 3.1 there is an unlikely value.  How come 3.2 
seems to be the commonly used value?

Chuck Norcutt

Moose wrote:

> Chuck Norcutt wrote:
> 
> 
>>Not that it's terribly significant but 3.5 is actually 2/3 stop slower 
>>than 2.8.  
>>
> 
> You beat me to it! :-)
> 
> 
>>1/3 stop is 3.2, 1/2 stop is 3.4.
>> 
>>
> 
> Here, my numbers start to disagree with yours., 1/3 stop down from f2.8 
> as f3.10 and 1/2 stop down as f3.27.
> 
> 
>>I'm showing off. :-)  Now that I've got a digital read-out for shutter 
>>speeds, aperture and ISO all in 1/3 stop increments I'm beginning to 
>>memorize all the intermediate settings.  But I did have to calculate the 
>>1/2 stop increment.  Actually, the precise value is 3.43.
>> 
>>
> 
> Again, I get the precise value of 3.27. Am I doing something wrong? 


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