Even the 180 Canon macro ends up being 120mm.
This focal length drop is due to internal focussing I think? At least most
of the lenses without have extending helicoids.
Is that also where 'focus breathing' comes from?
The 180mm Sigma is 3.5 btw. The newer 2.8 (with IS) is 118mm.
Op do 9 feb. 2023 om 22:33 schreef Mike Gordon via olympus <
olympus@xxxxxxxxxxxxxxxxx>:
> 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.
>
> Mike
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