Barrel vs. Shutter: Why big difference in size ?

[Nathan Potter]

Dan since you bring it up in this thread, I've always been confused by what exactly is meant by coverage. There seems to be no conveniently used criteria. For instance something like the amount of radial degradation in the COC at best focus - or some other metric with some universality to it.

Nate Potter, Austin TX.

[Arne Croell]

Here are the promised examples.
3 Tessars 210mm: 1 Carl Zeiss Jena in Barrel, 1 Carl Zeiss Jena in Prestor 3, one Docter Optic in Copal 3

2 Voigtländer Apo-Skopar 450mm (45cm), one in barrel, the other in a Compound IV

2 Voigtländer Heliar 210mm (21cm), one in barrel, one in Compound III

In all cases, the length of the mount is practically identical, give or take a mm.

[Ken Lee]

Wonderful - Your pictures are worth a thousand words !

Now (with mild fear and trepidation) if I may ask, concerning those three 210 Tessars: do they give different "looks" ?

From what I have observed comparing my Tessars to my Heliars, the differences seem most easy to discern, when shooting at or close to wide-open. Like the modern Cooke portrait lens, my Heliars (actually Dynars) exhibit some aberration that mostly disappears once we stop down past f/8. At smaller apertures, the difference between my Heliars and Tessars gets hard to judge: not coverage, but the overall rendering of both in and out of focus regions.

[Dan Fromm]

Dan since you bring it up in this thread, I've always been confused by what exactly is meant by coverage. There seems to be no conveniently used criteria. For instance something like the amount of radial degradation in the COC at best focus - or some other metric with some universality to it.

Nate Potter, Austin TX.

Nate, coverage is in the eye of the beholder. The circle covered is the circle within which the image is sharp enough.

What's sharp enough? Beats me.

The closest I've seen to a sharpness criterion that makes sense is EKCo's much reviled Subjective Quality Index. It is tied closely to print size (enlargement, in a word) and the aperture at which the lens was shot. It is a system -- taking lens, film, film development, enlarging lens, paper, paper development -- measure, not necessarily a direct measurement of what the lens itself can do.

Next closest, and tied more closely to the lens itself, is Schneider's working definition. They seem to think that an MTF of around 10% at 20 lp/mm (or some combination like that) is the least acceptable. Whence the angle off-axis that gives the least acceptable MTF at frequency defines the limit of coverage. Still subjective.

Cheers,

Dan

[seawolf66]

Ken Lee go to the camera eccentric web stie and in their for sale section they have a pair of Protars same type but one in shutter and other with out :

[Sevo]

Now (with mild fear and trepidation) if I may ask, concerning those three 210 Tessars: do they give different "looks" ?

They should not - apart from minor changes in coating and assembly, the GDR Jena Tessars remained the same throughout, and Docter merely continued their production in the nineties.

Sevo

[Arne Croell]

They should not - apart from minor changes in coating and assembly, the GDR Jena Tessars remained the same throughout, and Docter merely continued their production in the nineties.

Sevo

Absolutely correct, they are all the exact same design - in this case from 1929 by W. Merté - so the only differences are the mounts and for the Docter version a slightly different coating.