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Re: [OM] New 90mm Zuiko macro

Subject: Re: [OM] New 90mm Zuiko macro
From: Mike Gordon via olympus <olympus@xxxxxxxxxxxxxxxxx>
Date: Thu, 9 Feb 2023 21:33:21 +0000 (UTC)
Cc: usher99@xxxxxxx
Frank writes:
<<<Actually, the Sigma 180mm 2.8 macro is also effective 115mm at 1:1

<<<If I may believe the formula I found some time ago ;-).

Wow, more than I would anticipate!

Basically all modern macro lenses indeed do drop focal length when they go to 
1:1 but the working distance still much better with the longer FL at lower mag. 
 The "effective focal length" calculations are very very approximate with a 
complex lens, 
but give some estimate of the degree of FL shortening.   My CV 180/4 in OM 
mount goes to 1:4 and does well on extension with good working distance as the 
FL shortening is much more modest--typical for primes. 

Canon 100 f/2.8L - drops to 75mm
Nikon 105 f/2.8 G VR - drops to 78.5mm (25% drop)
Sony 90 f/2.8 G - drops to 70mm (22% drop)
Leica R 100 f/2.8 APO - drops to 75mm with elpro 1:1 adapter (no drop at 1:2)
Voigtlander 125 f/2.5 APO - drops to 95mm (24% drop)
Voigtlander 110 f/2.5 APO - drops to 87.5 (20% drop)

One advantage of the FL drop is less light is lost as less extension required.  
Also the cam is easier to handhold as movement less magnified.  As Moose points 
out a key thing however is axial stability to stack or get optimal plane of 
focus  and that is not fixed by image stabilization.

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