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Re: [OM] "4th of July" B'fly count at Appleton Farm

Subject: Re: [OM] "4th of July" B'fly count at Appleton Farm
From: Moose <olymoose@xxxxxxxxx>
Date: Sun, 27 Jun 2021 21:21:50 -0700
On 6/27/2021 6:38 PM, Mike Gordon via olympus wrote:
<<Curious what the
<<working distance was with the 100-400 + diopter?

As you know the  max working distance is solely a function of the diopter.  The 
Fl of the diopter is in its name--works out to 0.76 diopter.  So max working 
distance
is 1/0.76 m or about 4 1/3  ft.   Good enough for many nervous little critters. 
 The FL of the lens attached determines the mag.

In this case, with this lens (and the Oly 100-400), that is the crossover point, as close focus without diopter lens is 4.25 ft.

With the C-U lens on a Xume magnetic filter ring, just pop it on and off for 
under and over 4' focal distance.

This is why the almost mythical Pentax T226 achromat, giving a longer working distance, isn't particularly useful with these lenses; less magnification and no working distance advantage.

A. Chromatic Moose

--
What if the Hokey Pokey *IS* what it's all about?
--
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