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Re: [OM] E-M5 iii + lens

Subject: Re: [OM] E-M5 iii + lens
From: Moose <olymoose@xxxxxxxxx>
Date: Fri, 26 Jun 2020 14:13:57 -0700
On 6/26/2020 9:32 AM, Wayne Shumaker wrote:
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 12-60.

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.

My pleasure. You are now headed down a path I've trodden, more than once. 
Theory is fine, except for:

1. The things we don't know, that otherwise would make calculation possible, 
and perhaps useful.

2. The unknowns we could never know.

Sooo . . . I've been largely an empiricist.

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 situations.

The last point is one of my sticking points:

1. Lens changing in the field. No better than extension tubes.

2. IQ deterioration. It's been many years since I toiled in this garden. My conclusion back then was that matched teleconverters on prime lenses weren't bad, generic ones weren't good. They weren't good for zooms. There are no dedicated ones for the lenses I use.

Your mention that matching C-U lens is not simple.

This is true.

The NiSi is designed for 70-300, and gives +5 diopters.

That is waaaay to strong for 300 mm, let alone 400. Here's a little thing to add to your knowledge. A C-U lens is like a magnifying glass, just a sophisticated one. Just as it can focus the parallel rays from the sun onto a spot, it can take the rays from a spot and make them parallel. Get any further away that FL, and the rays diverge.

Put it in front of a photographic lens and the furthest it can focus is the C-U's FL. That means the MAXIMUM focal distance for a 5 diopter lens is its FL, 200 mm, ~8 in, from the front of the C-U lens. This is so whether it's in from of a 50 mm or 500 mm primary lens.

And 5 diopters on 300 mm is useless. The rule of thumb is that longer lenses 
require lower diopter C-U lenses.

May not work at 400mm. I have a hard time finding "achromatic" C-U lenses. You 
also mention that, and rare Pentax...

They aren't hard to find for moderate FL primary lenses. Oly's MCON-P02, for example, is a really excellent ~= 3.6 diopter C-U lens for shorter FL µ4/3 lenses with 37 or 46 mm filter threads. The older Oly iS/L Lens A-Macro H.Q. Converter f=40cm. and iS/L Lens B-Macro H.Q. Converter f=40cm achromatic C-U lenses for 49 and 55 mm threads, respectively, are good 2.5 diopter C-U lenses. I've used one to excellent effect on the Panny 14-150 zoom, for example.

The problem is with long lenses. Large diameter, low diopter achromatic C-U lenses are thin on the ground. The only one I know of in current production is the Sigma Achromatic Macro Lens AML 72-01. At 1.7 diopter, it's a little high for 400 mm. Might be good for 300 mm?? The 0.76 of the old Pentax67 T132 is about perfect. The 0.44 of the T226 is too weak.

I ran across a B&W 67E NL 0,5, half diopter single element lens. I hoped that perhaps the very moderate power and some B&W magic might make it useful. It's terrible. Gotta have at least two elements.

The Canon 500D, 2.0 diopter, 72 mm thread is available. It's too strong for optimal working distance. It's not bad, but in one to one testing, gives significantly poorer results than the T132. I sent it back.

The Nikon "T" C-U lenses are discontinued, but not hard to find. The 5T, 1.5 diopter, 62 mm filter thread, works very well on the PLeica 12-60.

Here we run into the intangibles. I just tested the 12-60 @ closest focus with the Nikon 5T and an old Minolta #0. (BTW, the Minolta is 55 mm threads. Don't be afraid to use reduction adapters for C-U lenses. No vignetting.)

In theory, the Minolta might be a better match, with 1.1 m furthest focus, vs. 0.67 for the Nikon. At max. mag, both are equal resolution in the center, but the Minolta quite a bit softer in the corners. May not matter. If I want flat field, I use a true macro. The vast majority of my C-U/almost macro shots have nothing in the focal plane in the corners, anyway.

And here a rub. I can theorize why, but testing simply shows it to be true; some C-U lenses work better or more poorly with particular primary lenses. A couple of possible reasons: Contemporary zooms are very complicated. Different achromatic C-U lenses use different glasses and lens shapes. All that matters for power is the difference between curvature of front and rear surfaces. In this example, the Nikon uses much flatter curves than the Minolta. (Yes, I have a curvature measuring gauge.)

There are some calculators on this page
https://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm
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

This is, unfortunately, useless. The problem is that all internal focusing lenses, including all the µ4/3 zooms, focus closer by shortening FL. And you can't know, sans lab equipment, what the actual FL at close focus is.

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.

Theory vs. reality. Extension tubes work quite well on long FLs. 
<http://zone-10.com/tope2/main.php?g2_itemId=4534>

I don't use them for a couple of reasons:

1. Back to juggling gear in only two hands in the field. Often enough with wind 
and dust.

2. Sloooow. I don't know about other folks. I am way too often changing subjects radically over seconds, not minutes. Working in a botanic garden, I've been known to palm the C-U lens and pop it on and off as I work.

3. Lens to camera electrical contacts involve one contact. A telextender involves two brass ends, connected by springs. One TE then involves 4 contacts, Two TEs, stacked, is 7 contacts. The inexpensive TE's I have are just brass contacts, not gold plated. Get two TEs stacked, multiplied by 11 contacts on the camera, and chances of a bad contact out of 77 gets pretty high. Humidity makes it worse. Gotta carry a microfiber cloth, and lose time, here and there.

summary:
C-U lenses gives the most magnification at the expense of working distance. IF 
you can find a good one.

It's the combination of working distance and mag. For example, the new Sigma on 100-400 has a max. working distance that scares off insects. The T132 does so quite a bit less. A shot of a damselfly that doesn't fly away at lower mag is more useful than one at higher mag with no subject. :-) This is a real example, BTW.

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.

Not true, but it doesn't matter, as other factors rule them out for me.

All said and done, I found the perfect telephoto lens to use for a portable 
macro lens:
https://www.studiobinder.com/blog/what-is-a-telephoto-lens-definition/
It is portable, note the handle on the top. And can be used to help with a yoga 
backbend and other exercises.

When I find my 600/6.5 getting loo light, I'll consider it.

C. U. Moose

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