Yes, CH, you are absolutely right. I am confusing f/11.8 in guide
number calculations with the nomenclature on the Sekonic meters. In the
guide number calculations f/11.8 is some small fraction away from f/12
and not 0.8 stop up from f/11 or 80% of the way to f/16.
Sheesh. It's time to go to bed. I think I'll do that.
Dr. (sheepish) Flash :-)
C.H.Ling wrote:
> Hi Dr. Flash, F11.8 is equal to F11 +0.8 stop? So F12 is equal to F11 +1
> stop? then F12=F16??? The formula should be more complex than you think :-)
>
> C.H.Ling
>
> ----- Original Message -----
> From: "Chuck Norcutt"
>
>> I was working from my head and could well be wrong but let's just take
>> the 35mm GN118 example. At 10 feet GN118 should yield f/11.8. The
>> measured result was f/8 + 0.7 stops. Therefore the measured result is
>> 0.3 stops short of reaching f/11. Yet the requirement is for 0.8 stops
>> above f/11. Adding the 0.3 stops short of f/11 + the 0.8 stops yet to
>> go sure sounds like 1.1 stops to me.
>>
>> Me thinks your math is wrong if you equate f/11 + 0.8 stops (meaning
>> 8/10 of the way between f/11 and f/16) to f/11.2. It's actually
>> somewhere between f/14 and f/16.
>>
>> Chuck Norcutt
>>
>>
>> Ian Nichols wrote:
>>> 2009/8/21 Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>:
>>>
>>>> for zoom setting 35mm you got
>>>>
>>>> GN30 - F2.8 0.1
>>>> GN42 - F4
>>>> GN59 - F5.6 0.1
>>>> GN84 - F8 0.1
>>>> GN118 - F8 0.7 (full power)
>>>>
>>>> At 35mm all of these up to full power are less than 1/3 stop error. But
>>>> at full power you should have gotten f/11 + 0.8. Instead, you got f/8 +
>>>> 0.7 or *more than a full stop off*.
>>> My gut feeling was that you were wrong there, Chuck, so I threw
>>> together a quick spreadsheet, getting the f numbers for the fractional
>>> stops by n*(2^0.05) - a half (i.e. square root) time a tenth- where n
>>> is the next lower full stop number.
>>>
>>> The resulting table says that f/8 +0.7 stops is f/10.2 and that f/11.8
>>> is f/11 +0.2 stops - only half a stop out.
>>>
>>>> for zoom setting 85mm you got
>>>>
>>>> GN29 - F2 0.9
>>>> GN41 - F2.8 0.8
>>>> GN58 - F4 0.8
>>>> GN82 - F5.6 0.8
>>>> GN116 - F8 0.8
>>>> GN164 - F11 0.5 (full power)
>>>>
>>>> At 85mm GN29 is correct, GN41 is 1/3 stop low, GN58 and GN82 are 0.4
>>>> stops low, GN116 is 0.8 stops low and GN164 is 0.9 stops low.
>>> Similarly I make f/11.6 = F/11 + somewhere between 0.1 and 0.2 so
>>> 0.3-0.4 stops low, and f/16.4 = f/16 + less than 0.1, so only about
>>> half a stop low
>>>
>>> Didn't check the others because it was only those that looked wrong at
>>> first glance. So one of us is working this out wrong. If it's me,
>>> I'd like to get my head around what I'm doing wrong.
>>>
>>>
>> --
>> _________________________________________________________________
>> Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
>> Archives: http://lists.thomasclausen.net/mailman/private/olympus/
>> Themed Olympus Photo Exhibition: http://www.tope.nl/
>>
>>
>
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|