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Re: [OM] C-U Lens follies

Subject: Re: [OM] C-U Lens follies
From: Moose <olymoose@xxxxxxxxx>
Date: Sun, 1 May 2016 13:55:20 -0700
On 5/1/2016 1:11 PM, Mike Gordon via olympus wrote:
Interesting!  Not a folly of any sort.  You certainly confirm the therory that  a +1.5 
diopter should focus at 1/1.5m  or 26.4"---close enough.  The FL of lens behind the 
diopter will not affect the working distance but only mag--all will focus at 26." if 
set at infinity.   I have never read that that was from the front of the CU lens but 
makes sense.

Yes, but I'm happy to have it confirmed.

The diopters were designed for max FL of 200mm and I have never read anywhere 
if sensor  size or Effective FL based on FOV makes any difference.  Have to 
think about that.

I don't think so. At least in this case, where one outperformed another, I assume it's some aspect(s) of the specifics of C-U lens design, glass and curves, and the way those work together with the base lens as a single optical system. Given the complexity of the zoom, it's entirely possible that the 500D could outperform the 5T at some other FLs and/or focal distance settings. But I'm only really interested in infinity focus @ 400 mm.

JS has stated that on a 300mm lens (FF) he would not risk a diopter over 
+1.0---never have seen a high quality one of that strength easily available.

I have a 55 mm Minolta No. 0, +0.94 diopter, on the way. (Why not just call it +1?) I don't know if it will vignette, probably? possibly?, but enough to matter? 400 mm is a pretty narrow AoV.

I am thus not overly surprised that the +1..5 Nikon out performed the  +2.0 
Canyon at 400mm--might be worth a quick check at shorter FL.

If I need it, I'll use it, but no formal testing for me.

The lens already gets to an impressive 0.25mag natively and thus must be over 
0.8 with the diopter at 400mm.

My calcs are 0.8 for +2 and 0.6 for +1.5 (1.6 and 1.2, FF eq.). I guess I could measure a $ bill and get an actual measurement. Not sure I care, as I've already proved that in this case mag. doesn't equal detail resolution.

I also still wonder how the IQ with all the extension would behave but would 
not get anywhere close to that mag at that FL but could try at shorter 
FL--might be better IQ for largish B'flys.

I'm mildly curious, but think that may be a rabbit hole for actual field use. Just as one is ready to shoot, one of the connections chooses that moment to crap out. One tube seems to be pretty reliable, in my limited experience. There are 11 connections, body to lens. Each adapter has a pad, spring and pin for each, so 22 places inside each adapter for a bit of moisture or corrosion to compromise a connection - in each adapter. With three adapters stacked, that's 88 contacts twixt body and lens, vs. 11. And none but body and lens with gold or other high quality contact surfaces.

Even at that I occasionally have had to dismount a lens and wipe body and lens 
contacts, both on Canon and µ4/3.

Another question is how much does the diopter throw off the optimization for 
the IS?

EFL with the 5T is 250 mm.

(not that anything can be done but would be applicable to a MF lenses)

One could test with a short, manual extension tube. Or try the 400/6.3, same FL and aperture. But I've used that lens, and its IQ is up to the PanLeica.

The 500/8 also takes a 72 mm filter. :-)

Paying close attention,  Mike

Hah! ;-)

Hold Me Close Moose

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

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