Unit Focusing Tessar...

[jb7]

I've just separated a 13cm f/6.3 Zeiss Tessar from an old Kodak folder-
It's going to fill a niche in my 4x5 lens set...
Not a bad old lens, not perfect, but I'm looking forward to seeing what it does-
it's in quite an accurate sounding dial set shutter too-

This is a front element focusing lens, and I have a question...

If I focus the lens as a unit, what position should I set the front element to?
Infinity, closest focus, ⅓ in, ⅓ out?
Yes, I know, I should test- and I'll probably run a comparison at each end, and see if I can tell the difference, but perhaps someone here can point me in the right direction?

[GPS]

By moving the front element of this Tessar lens ahead you focus it at the closer range - with a small degradation of the image quality compared to the focusing of the lens as a unit for the same distance. So it seems to me that it would be advantageous for you to focus the lens at infinity before you do your unit focusing with it at a closer distance.

[jb7]

Thanks GPS- your hypothesis makes sense-
especially as the focal length of the lens should be calibrated for infinity, by definition...

Assuming optimum performance is delivered with the correct air space for the focal length, how might the quality of the image be altered by moving the front element for focus?
I presume that what is actually happening is that the focal length is being altered?

Should I be looking for less resolution overall, or at the edges, some field curvature, or something else?

I look forward to having a little test, though I'm quite certain that I'm not going to find any differences that couldn't be blamed on my usual errors...

[Dan Fromm]

I'd expect that the lens is best set for midway between infinity and the near focusing limit. This because that will give better performance than having it right at one end of the range and very wrong at the other.

FWIW, I have a 1912 vintage 130/6.3 CZJ Tessar extracted from a Folding Pocket Kodak. It is unit focusing, shoots very well on 2x3. I expect that yours will please you.

Which Kodak camera did yours come from? I ask because the f/6.3 Tessar, both Zeiss and B&L, was a premium lens in its day and was fitted to EKCo's top-of-the-line cameras. All of the cameras in catalogs at http://mgroleau.com/catalogues_kodak/ that had f/6.3 Tessars had unit focusing lenses. Also, if yours is echt Zeiss, not B&L, EKCo last used Zeiss lenses, at least in North America, in 1915. I've seen mid-20s Kodak UK folders with Zeiss lenses, all unit focusing.

1915 and earlier Tessars in EKCo (North America) cameras were all in Compounds. What shutter is yours in?

[EdWorkman]

In my experiences with kodak Monitors, the lenses are "adaequate" at f 11 and smaller holes- noticeably not very sharp at and near wide open, but way back then I had only VP. TX or HP5 should allow small holes with reasonable shutter speeds. The other question is what is the camera to subject distance and why not use that to set the lens- it does focus, to an extent, after all.

[jb7]

Thanks Dan, Ed-

Correcting the focal length for the middle of the range would seem to be a sensible approach too-

The lens came out of a 1A Junior Series 2- the camera is not in great condition,
and although I could cobble together a system for exposing 120 film in it (it takes A116 film)
I think I'd get better use out of it on 4x5. It's going to be much easier to focus using the camera than the lens...

I looked up the serial number on the lens- 1929. It's in a Compur Dial Set shutter-

I'm not necessarily looking for maximum resolution all the way to the edges,
though I seldom shoot at infinity anyway- but I'm looking forward to seeing how it looks-

Thanks for the responses-

[IanG]

I'd expect that the lens is best set for midway between infinity and the near focusing limit. This because that will give better performance than having it right at one end of the range and very wrong at the other.

FWIW, I have a 1912 vintage 130/6.3 CZJ Tessar extracted from a Folding Pocket Kodak. It is unit focusing, shoots very well on 2x3. I expect that yours will please you.

Which Kodak camera did yours come from? I ask because the f/6.3 Tessar, both Zeiss and B&L, was a premium lens in its day and was fitted to EKCo's top-of-the-line cameras. All of the cameras in catalogs at http://mgroleau.com/catalogues_kodak/ that had f/6.3 Tessars had unit focusing lenses. Also, if yours is echt Zeiss, not B&L, EKCo last used Zeiss lenses, at least in North America, in 1915. I've seen mid-20s Kodak UK folders with Zeiss lenses, all unit focusing.

1915 and earlier Tessars in EKCo (North America) cameras were all in Compounds. What shutter is yours in?

Are you sure EKCo last used Zeiss lenses in 1915 or do you mean Zeiss badged Zeiss lenses

I'm fairly sure Zeiss lenses with first their own name then later Kodak's were on EKCo's Recomars, OK the cameras were made in Germany at Kodak's Nagel factory but for the US market and finally assembled in the US (range finder & lens).

Kodak's other pre-WWII European plants came under Kodak Limited (UK) a separate company. Kodak did shift their headquarters for a short time to the UK after taking over Wratten & Wainright, who's research department under Mees provided the backbone for both EKCo (Rochester) and Kodak Ltd (harrow) research.

I must mount my pre-WWI (1913) 165mm f6.3 Tessar on a lens board again, it's the sharpest Tessar I've used on a 5"x4" camera. Just got a load of cheap LF film from someone going fully digital so will do the Tessar/Xenar/G Claron/Sironar tsets next week

Ian

[Dan Fromm]

Ian, EKCo was and is a multinational firm. The North American branches (US, Canada) last used Zeiss-made lenses in 1915, at least on Vest Pocket and Folding Pocket Kodaks. After 1915 B&L-made "Zeiss" lenses were not engraved "Zeiss." B&L continued making Tessars and Protars until some time after WW-II.

After WW-I Kodak North America used B&L and then their own lenses. If you wade through the catalogs on Mario Groleau's site -- tedious -- you'll see that during the '20s EKCo phased out B&L and other makers' lenses, phased in their own.

As I reported, Kodak UK used lenses by Zeiss (and other makers, which I didn't mention) after WW-I. Kodak France used French-made lenses, presumably for tariff reasons.

I have several f/6.3 CZJ Tessars, also some B&Ls. The B&Ls aren't all the same and not all of them all shoot really well. Some of this may be due to the cells being (my opinion) in the wrong barrels but my two 85/6.3s, both extracted from Premo #12s, really are different and one is much better than the other.

[GPS]

Thanks GPS- your hypothesis makes sense-
especially as the focal length of the lens should be calibrated for infinity, by definition...

Assuming optimum performance is delivered with the correct air space for the focal length, how might the quality of the image be altered by moving the front element for focus?
I presume that what is actually happening is that the focal length is being altered?

Should I be looking for less resolution overall, or at the edges, some field curvature, or something else?

I look forward to having a little test, though I'm quite certain that I'm not going to find any differences that couldn't be blamed on my usual errors...

Lenses, Tessar being no exception, are made to be unit focused. Only some of them, Tessar being among them, can be focused by moving the front lens element. But in such a case, their optical performance is slightly impaired, if still to an acceptable degree. On a higher end of these small cameras, Tessar lenses were unit focused!
There is no doubt that using the front element focusing the lens has less good optical performance than that of unit focusing. It was a poor man's focusing, to exaggerate a little bit, accepted in some cameras for its mechanical advantage.
I cannot tell you exactly what optical corrections are hit most when you use the front element focusing but the general knowledge speaks about the overall optical performance.
Optically, you have nothing to loose, only to gain, when you focus your lens as a unit - lenses like it more that way...

[GPS]

Focusing a Tessar as a unit to infinity doesn't make it worse for focusing - as a unit - at a closer range. It is simply the most correct way of focusing. Tessars are not "half way prefocused" with their front element before they are put to the photographer's hands to be unit focused, that would be simply a silly idea.