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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: Mike Gordon via olympus <olympus@xxxxxxxxxxxxxxxxx>
Date: Mon, 28 Jun 2021 22:18:17 +0000 (UTC)
Cc: usher99@xxxxxxx

I have what is probably a stupid question.  I would use a lens like the DZ
50-200/2.8 or the floater DZ 40-150 to get a respectful working distance,
and I'm satisfied with the IQ (whether I should be or not).

Why should I be investigating the use of a diopter?  Tick the boxes:


<<*  Allows use of a desired lens not otherwise serviceable in the
situation/setting

If you require more mag than the lens provides than an achromatic diopter might 
be a good answer.

<<<*  Improves working distance

Max working distance is solely determined by the FL of the diopter.  If the 
zoom is not very long, ones requires a stronger diopter and working distance at 
+1 diopter   (FL 1000/diopter) or 1000mm is already down to 1 meter.  

<<*  Allows use of a lens of better quality not otherwise useable for the
capture, especially desirable because of the speed of the lens or the
characteristics of the glass

A good marriage of an achromatic CU diopter and a zoom lens is very 
idiosyncratic.  One can get some idea form the FL of the lenses the CU diopter 
was designed for, but the matching of the optics is almost impossible to 
predict.  Even the optimal FL for max resolution in a zoom is hard to predict 
except if the lens has known weak spot like the PL 100-400 is a bit weak  at 
the longest FL.  I think the sweet spot of the PL 100-400 is about 250-300mm to 
get max resolution of scales on flutterby  with  more mag from the lens 
helicoid extension than upping the FL--less working distance again but there is 
always some trade-off.   Moose tells me the Pentax T132 works well on the new 
Oly 100-400 .


<<<*  Allows some marriage of non-native glass to foreign camera body
I don't follow you here.

<<*  Allows a lighter kit
Yes---CU diopter  in its case slips in a pocket  vs a macro lens.


*  Esoteric qualities, approaches unobtanium standards---I was surprised how 
well the achromatic diopters can work.  The Pentax T132 is TRASH on the MFT Z. 
12-100 even if wonderful on the PL 100-400 most of the time. I have a stable of 
these but Moose's stable is larger and I think the horses are now even breaking 
out of the paddocks due to overcrowding. 
*  Other -- please specify

Try it, you'll like it------sometimes. 

If there were a 250 mm ish  macro lens for Sonnie or Oly that went 1:1 I may 
leave the CU diopter home, but alas it doesn't exist.  

Mike


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