Re: [OM] E-M5 iii + lens

Subject: Re: [OM] E-M5 iii + lens
From: Wayne Shumaker <om3ti@xxxxxxxx>
Date: Fri, 26 Jun 2020 09:32:12 -0700
At 6/23/2020 10:45 PM, Moose wrote:
>With a filter holder on belt or in vest pocket, and XUME filter holders, into 
>and out of C-U mode is a matter of a very few seconds. Standing in a dusty or 
>muddy field, maybe wind blowing, juggling lens and tubes is just awful. Been 
>there, not going back.
>Unfortunately, matching C-U lens and main lens is not simple calculation. For 
>example, the Canon 500D achromat simply doesn't give as good resolution on the 
>PLeica 100-400 as the  Nikon 5T. I mostly use the rare Pentax T132 for that 
>lens; lower mag, but much better working distance. The 5T works well on PL 
>There is a current achromat, the Sigma Achromatic Macro Lens AML 72-01 that 
>works pretty well on the 100-400, but the max working distance is a bit short 
>for me.

Again thanks for the info. After doing research, and since I have the sonie 
100-400, which already has a native close focus of 0.35x at 400mm, adding a 
1.4x would actually be the most practical for me in the long run. It would 
increase the 0.35x magnification to 0.5x and be useful in general, not limit 
focus range, increase or maintain working distance, and be adequate for most 

Your mention that matching C-U lens is not simple. The NiSi is designed for 
70-300, and gives +5 diopters. May not work at 400mm. I have a hard time 
finding "achromatic" C-U lenses. You also mention that, and rare Pentax...

There are some calculators on this page
A C-U lens option does give the most magnification with a telephoto. Assume 
400mm with 0.25x native and adding a C-U with various diopters gives:
+1 -> 0.75x
+2 -> 1.25x
+3 -> 1.75x
+4 -> 2.25x
+5 -> 2.75x

The extension tube works best on a shorter focal length lenses. On the 90mm 
macro, for instance, according to above site, adding 25 mm extension only 
improves the 90mm from 1.0x to 1.28x. If the 90mm macro, at close focus, has a 
shorter effective focal length, for instance, a 90mm becomes 60mm effective at 
1:1, then the 1:1 + 25mm = 1.4x. Some, but not much, advantage.

C-U lenses gives the most magnification at the expense of working distance. IF 
you can find a good one.
1.4x teleconverter preserves working distance, useful at all focal lengths, but 
only 1.4x increase.
Extension tubes only give an advantage with shorter focal length lenses.

All said and done, I found the perfect telephoto lens to use for a portable 
macro lens:
It is portable, note the handle on the top. And can be used to help with a yoga 
backbend and other exercises.

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