The equation accounts for it perfectly... it's just that you have to
compute the effective focal ratio. Not hard actually if you refer to
your macro lens's exposure table. If it says to increase the exposure
by a factor of two at a given extension then the effective f-stop is one
stop smaller than indicated. If it's reading f/8 then it's actually f/11.
Chuck Norcutt
On 6/24/2012 12:16 AM, Jim Nichols wrote:
> Thanks, Chuck. You expressed it in a nutshell, which I appreciate.
>
> Probably the best image I ever made with this camera/lens combination, at
> least the one that gathered the most compliments ( and contained no
> senoritas) was a shot of a red Canadian Beech Staggerwing cranking up. It
> was shot at f/10, so I suspect that f/8-f/9 is about right for the upper
> limit. The link to that image is given below:
>
> http://gallery.leica-users.org/v/OldNick/Staggerwing+Cranking+NI.jpg.html
>
> Just to ponder a bit, a macro lens extends quite a bit on closeups,
> effectively increasing the f-number. How does your equation account for
> that?
--
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