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A repairshop frequently recommended in the German LF community is http://www.fotomechanik-reinhardt.de/index.html
Mr. Reinhard has an excellent repution for bringing even very old and badly damaged...

There is an overview of the various original Zeiss Protar series, together with tiny pics showing their lens design, and in which mountings they were offered: ...

For making sure that your shutter has the proper aperture scales for your Protars, you could measure the actual iris diameters at some F-stops, and compare them with the diameters provided by Zeiss...

Schneider's first original design was certainly not the Angulon (which btw was patented two years earlier, in 1930, and was based on the Dasykar, also an original Schneider WA design (1920).
...

My Anthony Illustrated Catalogue, January 1891, lists such a cone barrel lens under "Anthony's Single Combination Lenses" and says:

(full quote)
For ordinary landscape work these lenses give...

The formula is here (equation 1.16 or 1.17):
http://www.mellesgriot.com/pdf/001.8-1.10.pdf

"at f9, the Kollinear is likely an "apo-kollinear"

The Apo-Collinear is the only "Collinear" or "Kollinear" made by Voigtländer with an f9.

According to Affalter the 9/30cm covers 30x36cm at...

Isn't there somebody here who owns such a tack-sharp Artar of same age or similiar serial number, and who is kind enough to measure the lenght between the apex of the front lens surface to the...

The Bistelar was not only the "first fixed focal length telelens", as Ernest wrote, but also the first complete tele lens. All tele lenses before were only supplementary lenses: a "tele negative" -...

Thiele has two series of Rietzschel Baryt lenses listed: a type 6.8/ fl 120 - 210mm (60°) introduced in 1908, and a 7.5-8/ 90 - 120mm (65°) introduced in 1900; according to him it was a 4-4 design...

According to Zeiss brochures your Protar lenses were to be used with barrel size "VIII".

There is a nice "aperture table" that will relieve you from computing the stops....

Thiele's book can also be bought in USA at
http://www.camerabooks.com/

The lowest numbers given by Hartmut Thiele for Voigtländer lenses are 24.450 - 39.465 for the period 1884 - 1890. So your # 21506 should have been made before 1884. This rules out any Euryskop...

Thanks,Jim,
I posted it too hastily. But if you compare those two early Voigtländer 6-2 lenses, you'll see that they are closely related by patent numbers. The later one is a supplement.
Just a...

Here is the patent for this lens design:http://www.google.com/patents?id=1GpfAAAAEBAJ&dq=562614

The Collinear Series III (which is quite similar to Steinheil's Orthostigmat) should cover an angle of at least 60° (according to Hartmut Thiele) . Patent numbers are D.R.P. 90482 and 91883. If you...

What I would do first, provided the original springs are not broken and still cosmetically okay: I'd call a metal workshop that's specialized in hardening steel, or a seasoned gunsmith. They should...

Hollis,

I guess, by knowing 50 German terms ( Brennweite = focal length ...) you'll unfold at least 80 percent of Thiele's lens data collection. Add another 10 percent that can be inferred from...

Gene,
I get the feeling you are some kind of occupational therapist disguised as student.

Uli

Arne,
Flügge's book is great. But I am probably not in a position to say this because it includes so many pages full of equations that make me dizzy and sleepy (my Mr. Sandman).
Since you know...

Indispensible, but only covering German lenses (a wide field):

Where I look first:
Hartmut Thiele: DEUTSCHE PHOTOOPTIK VON A - Z, Munich 3rd ed. 2007
(mainly lists, incl. pat.numbers, designer...

Dan,
I overlooked your post. I sold an uncoated Meyer WA-Aristostigmat 6.8/165 to a friend who uses it on a 8x10. His verdict: quite sharp, ample coverage, but prone to flare ( using a lens shade...

Those Meyer Weitwinkel-Aristostigmats are of the double-gauss type: 4 menisci in 4 groups, the outer lenses positive. In principle the same design as WA Ektars or Plaubel's Rapid-Weitwinkel-Orthar. ...

There is no Serie VI 419mm ( = 16 1/2" ) Anastigmat-Satzlinse in the Zeiss list; but this focal lenght is halfway between size 4 ( 385mm) whose largest lens diameter was 31mm, and size 5 (450mm) with...

Here is in an illustration and a detailed description of the "Serie VI" Zeiss Anastigmatlinse (1893). Three lenses cemented together....

For further research I recommend to consult the Zeiss Archive. A starting point may be this:
http://www.archive.zeiss.de/hzeig.FAU?sid=5095055041&DM=2&THES=1&DESK=%2300000C88%23

Like Ole, I'd rule out a Zeiss Dagor-type lens; the patent for the Doppel-Amatar was granted in 1908, and this lens looks older.
I'd also rule out that the lens was made after 1900, because in this...

Thanks, Ole!
I forgot that. Especially a Petzval lens with its large air-spaces must be prone to show this effect, when not used carefully within its designated angular field.
Uli

Ole wrote:
The swirl is not so much a result of optical design as of physical design - it's caused by physical vignetting at large apertures.[/I

Why this?- Mechanical vignetting is used for...

Gorgeous! - the photo and the lady. A very convincing example IMO that these lenses- when in the right hands and used with discretion- can add impact, whereas other types of lenses, when used for...

Was the intent of this device to quantify bokeh, or did it merely provide a way to demonstrate in a controlled manner a lens's ability to render OOF objects

Eric, this is a tricky question. But I...

Ok, let's start with defining the measure of performance.

For this, one needs a device to record 'spatial" performance on a sound basis; the purpose of Rudolph's 'device'. IMO first comes a...

Neither a statement on Apo-Tessars in general nor about this particular lens. Just a quote from a Zeiss price list of the late twenties or early thirties:

Tessar 3.5/21cm............... 380,-...

Thanks, Steve.
I have a copy of this article. But the two illustrations would need quite a bit of 'photoshopping' before being of much use if thumbnailed here. If you want to use your skills with...

Whatever the concept of "bokeh", and by whichever factors(s) it's produced, these disputes IMO will perpetuate without tangible results as long as there are no generally accepted test methods to...

All aplanats suffered from curvature of field and astigmatism. But the designer had options to balance these aberrations against other ones according to the purpose for which the lens was to be used....

Jim,
your method can also be used to measure the amount of light that is lost in a lens by the glass itself (absorption) and by internal reflections. For this one only needs to fix between light...

Neill,
I fully back what Ole said in his last post. Even better than compromizing center sharpness for more sharpness at the periphery is it to turn this aberration into an advantage.
...

Whatever led to the Tessar's development (its origin can as well be traced back to the "Portrait-Antiplanet" (Steinheil), or to Taylor's triplet, or to the "Protar-Unar" line,as preferred by Zeiss...

Ole,
this is not a question about "clarity" ( broad brush strokes, simplication ..) versus "precision" (number of digits after the decimal point ...).
What I am saying, is, your Tessar...