[Alt-photo] f stop and log values

Christina Z. Anderson christinazanderson at gmail.com
Fri May 26 19:48:43 UTC 2017


Even easier. 

Numerical factors for fractional stop exposure time sequences
Increment	Description	Value	Inverse		 
Half stops	square root of 2	1.414	0.707	Multiplying 2x gives	2.0000
One third stops	cube root of 2	1.260	0.794	Multiplying 3x gives	2.0000
One fourth stops	fourth root of 2	1.189	0.841	Multiplying 4x gives	2.0000
One-sixth stops	sixth root of 2	1.122	0.891	Multiplying 6x gives	2.0000
One-eighth stops	eighth root of 2	1.091	0.917	Multiplying 8x gives	2.0000
One-tenth stops	tenth root of 2	1.072	0.933	Multiplying 10x gives	2.0000
> On May 26, 2017, at 1:12 PM, Loris Medici via Alt-photo-process-list <alt-photo-process-list at lists.altphotolist.org> wrote:
> 
> Let me do it for you Keith;
> 
> 1) Increasing the exposure means multiplication with the factor,
> 2) Decreasing the exposure means division by the factor,
> 3) For 1 stop the factor is 2^1 (^ being the exponentiation operator)
> 4) For 1/2 stop the factor is 2^(1/2)
> 5) For 1/3 stop the factor is 2^(1/3)
> 6) For n stop the factor is 2^n
> 
> Regards,
> Loris.
> 
> 
> On May 26, 2017 9:44 PM, "Keith Schreiber via Alt-photo-process-list" <
> alt-photo-process-list at lists.altphotolist.org> wrote:
> 
> Bob -
> 
> To reduce exposure by 1/3 stop, multiply by 0.79.
> 
> If you are interested in how this this figure is derived I'll explain it
> late. Gotta run now.
> 
> Cheers,
> Keith
> 
> Keith Schreiber
> jkschreiber.com
> 
> 
> 
> 
>> On May 26, 2017, at 12:05 PM, Bob Cornelis via Alt-photo-process-list <
> alt-photo-process-list at lists.altphotolist.org> wrote:
>> 
>> I have a 31 step stouffer step wedge and need to know what fraction to
>> increase/decrease exposure time when steps need to merge or separate.
>> 
>> I know each step is 1/3 of a stop but wasn't able to find the
> corresponding
>> fraction to adjust exposure. The Stouffer website has this info in the FAQ
>> section for the 21 step wedge only.
>> 
>> My math is not good enough to wade through all the equations on Wikipedia
>> to get the answer!
>> 
>> Thanks
>> Bob
>> 
>> --
>> 
>> http://www.bobcornelis.com
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>> Alt-photo-process-list | altphotolist.org
> 
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