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Re: [OM] Heliar (Was: 50mm 1.8 (Re: Hoarding & Varimagni))

Subject: Re: [OM] Heliar (Was: 50mm 1.8 (Re: Hoarding & Varimagni))
From: "Carlos J. Santisteban" <zuiko21@xxxxxxxxx>
Date: Fri, 21 Jan 2011 18:49:05 +0100
Hi Mike, Andrew and all,

From: usher99@xxxxxxx
>(previously took 8 to 10 elelments to achive that reduction in
>aberrations)

In fact, the Planar / double Gauss formula is somewhat earlier, from the
late 1800s... but without anti-reflection coatings, so many air-to-glass
surfaces made it unfeasible because of flare. This was the reason behind the
Tessar and Heliars -- a development of the classic triplet instead of a high
performance design from the scratch, in order to keep the three-group
configuration for good flare resistance.

It goes without saying, a Tessar (and surely a Heliar too) with modern
coatings is *extremely* flare resistant...

>I believe these
>types of lenses are aberration, not diffraction limited for the most
>part.

Stop down enough, and any design will be diffraction-limited :-) I can see
some edge degradation on Tessars wide open, but not _that_ terrible... Not
everything about a lens is MTFs and lp/mm, I do like the Tessar's rendering
a lot.

>lens design of the CV 75, but it didn't register.  It seems to have
>rendering qualities similiar to the original Heliar

Really have little experience with it (and none with the original) so I
can't tell for sure...
<http://www.flickr.com/photos/zuiko21/3559972756/sizes/o/> (quick and dirty
scan)

>but I don't
>understand the naming  of it at all.  Perhaps it is marketing decision.

I think only Zeiss uses the optical design as the key for naming: Distagon,
Biogon, Tessar, Planar, Sonnar... Nowadays, Leica names just mean the
maximum aperture:

Elmar: F3.5 - 4
Elmarit: F2.8
Summarit: F2.4 - 2.5
Summicron: F2
Summilux: F1.4
Noctilux: F1.2 or faster (currently 0.95!!!)

As for CV naming... it seems plain marketing to me, too -- the Heliars are
the 12/5.6, 15/4.5 and 75/2.5, plus the new, classic design, limited edition
50/2 and 50/3.5.

Update! There's the new "Heliar Classic" 75/1.8... I've found a schematic of
it, and it seems yet another formulation of the classic Heliar (as
suggested) with a doublet replacing the negative central element:
<http://www.cosina.co.jp/seihin/voigt/v-lens/v-l-m/75-1.8/75-1.8.jpg>

But the non-classic designs are just double-Gauss (75/2.5) or mild
retrofocus (12 & 15mm):
<http://cameraquest.com/jpg4/vm-12.gif.gif>
<http://cameraquest.com/jpg4/vm-15.gif>

And *very* good, extremely compact lenses they are...

On the other hand, there seems to be a pattern with some of the rest: Nokton
is for high-speed lenses (F0.95 - 1.5) while Ultron is for lenses around F2.
Most lenses F2.5 of slower are called Skopar.

Speaking of Nokton... I'm impressed with the performance of the 50/1.1. Most
super-speed lenses are mediocre performers and/or complex designs (the very
nice Canon FDn 50/1.2*L* has 8 elements, with some aspherical surfaces) but
the Nokton is a run-of-the-mill 7 element-6 group formula with no aspherical
surfaces, no LD elements... like most 50/1.4s on this planet -- usually much
poorer performers!

>APO dosen't seem to mean as much anymore either.

Even without being corrected for *three* colours of the spectrum, that
usually means better colour correction. IME, modern Tessars (and the Russian
Tessar-like Industar-61 L/D) are very good at this. And back to CV, the
APO-Lanthar 90/3.5 (another double Gauss) is very, very, very, very good --
not that it's a difficult lens to design, but this one performs just great.
Did I say it's very good? :-)

So far, the only lens with the honour of being CA-free, at least within my
measurement / observation range, also comes from CV: the tiny Skopar 28/3.5.

From: Andrew Fildes <afildes@xxxxxxxxxxxxx>
>I just bought a modern Cooke Triplet - the Perar Super-Triplet - a hand
built run of
>200 by MS Optical -
>
http://www.japanexposures.com/shop/product_info.php?cPath=33&products_id=423

Yes, I know them! They make interesting mount adaptions of classic lenses...

>This one was an attempt to demonstrate that a Cooke Triplet, properly
designed and
>with modern coatings, can exceed the performance of a Tessar design.

This is getting *very* interesting... as I mentioned above, a "classic"
design may perform much better than expected thanks to modern technology,
but I'd love to see your results with it...

Cheers,
-- 
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
-- 
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