450-480mm lens for 12x20

[David Lindquist]

A bit of an update on triple convertible Protar VIIa coverage: In his mostly technical book "Examples", Ansel Adams mentions that he used a 145mm / 5.5" Protar as a wide-angle lens on 5x7 when making one of his famous Canyon de Chelly photographs. That approximates a 73 coverage angle on 5x7 film.

My circa 1933-34 Zeiss catalog for the U.S. market states for the 14.5 cm "Double Protar": "Diameter of circle covered at small stops... 8 3/4 inches" . The catalogue alternatively gives the focal length of this lens as 5 3/4 inches; 14.5 cm = 5.71 inches. In some of his earlier books, e.g. Yosemite and the Sierra Nevada (1948) Adams described this Protar as having a focal length of 5 3/4 inches. Not sure if he really meant to say 5 1/2 inches in Examples, and not to nitpick but here he alternatively says its focal length is 145 mm. We know from his biographies/autobiography he got his Protar in the 1930's by which time Zeiss described focal lengths in centimeters rather than millimeters.
In Yosemite and the Sierra Nevada there are several 5 x 7 negatives described as being done with the 5 3/4 inch Protar.

David

 

[138S]

14.5 cm "Double Protar": "Diameter of circle covered at small stops... 8 3/4 inches"

This is 222mm circle, so covering 5x7... what a coverage for the focal !

Still it would be interesting to know know what corner performance it has, compared to today's standards.

 

[Dan Fromm]

This is 222mm circle, so covering 5x7... what a coverage for the focal !

Not to be excessively unimpressed or anything, but if I calculated the angle correctly that's 75 degrees. There were much wider lenses in the mid-30s, and I'm thinking of many more than the semi-mythical Goerz Hypergon. Consider, for example, the relatively common and unexpensive 90/14 Perigraphe Ser. VIa.

 

[5x7shooter]

I went back and double-checked the Ansel Adams book and also my own Double Protar VIIa in that "145mm" focal length. Adams definitely said "5.5" inch. I also checked my own Double Protar VIIa in this same focal length. My copy is an original Zeiss in a smaller Compound shutter.

The design and marking of Protar VIIa and other triple convertible lenses may be the cause of some confusion. The combined Double Protar VIIa lens is not labelled 145mm or 14.5CM or 5.5" or whatever. Rather, two Protar VII cells of either the same or different focal lengths are combined in a shutter or barrel to form a complete Double Protar VIIa. Those cells are marked only with their single cell focal lengths. The 145mm / 5.5" version has a 29cm cell in front and a 22cm cell in the rear.

Only when those two cells are combined does the effective focal length of the complete Double Protar unit become roughly about 145mm / 14.5cm. Nowhere is the combined triple convertible lens marked with 145mm or 5 1/2 inches or whatever. The aperture scale will be either a double or triple scale depending upon the combined cells or just in millimeters of opening, letting the user do the f/stop math in their head for the two or three focal lengths.

The basic way to determine the shorter focal length of the two cells when combined is to add the focal lengths of the two individual cells and then divide by a factor unique to that lens design. For combined cell Protars VIIa lenses, I use a rounded factor of 3.5 as the divisor. 29cm + 22cm = 51cm /3.5 = about 14.5cm / 145mm or roughly 5.5 to 5.75 inches.

Even a slight change in the divisor will shift the calculated focal length up or down a few millimeters and that, along with rounding error, can account for why some would term the lens 5.5" and others 5.75" No one is actually wrong, they're just using a slightly different divisor for the sum of the separate focal lengths of the two cells. Besides, Zeiss only labelled the focal length of the cells to two significant places, i.e., 29cm, not 290mm. That can contribute to rounding error.

I have one other Zeiss Protar VIIa lens and three similar license-made Bausch and Lomb Protars. All are similarly marked.

Other "convertible" lenses. such as the older Schneider Symmars and Dagors act similarly when only one cell is used. Each of the single cells in those lenses has a longer focal length than the combined lens. The divisors may be different, though.

 

[138S]

I have one other Zeiss Protar VIIa lens and three similar license-made Bausch and Lomb Protars. All are similarly marked.

Other "convertible" lenses. such as the older Schneider Symmars and Dagors act similarly when only one cell is used. Each of the single cells in those lenses has a longer focal length than the combined lens. The divisors may be different, though.

Let me ask, how would you judge the VIIa optic performance (sharpness, contrast) compared to (say) a symmar convertible ? How are the corners depending on aperture ?

I can imagine perhaps the contrast, but I'm curious about what a Protar VIIa yields in practice.

Not to be excessively unimpressed or anything, but if I calculated the angle correctly that's 75 degrees. There were much wider lenses in the mid-30s, and I'm thinking of many more than the semi-mythical Goerz Hypergon. Consider, for example, the relatively common and unexpensive 90/14 Perigraphe Ser. VIa.

Dan, I was well aware about the Hypergon unicorn (the spinner is the horn !) but I was surprised by the nominal coverage of the Protar anastigmat (the first modern lens), as a general usage lens, was matching the coverage of many modern plasmats, while the plasmat is an enhacement over the dagor.

Still, while circle criterions from manufacturers never have been clear, for sure modern glass have a tighter requirements... still those 75º were a surprise to me. Something learned...

 

[5x7shooter]

Let me ask, how would you judge the VIIa optic performance (sharpness, contrast) compared to (say) a symmar convertible ? How are the corners depending on aperture ?

I can imagine perhaps the contrast, but I'm curious about what a Protar VIIa yields in practice.

I cannot make the requested comparison because I've never used a convertible Symmar nor only a single cell of a Dagor. Hence, I have no basis for comparison.

My prior comments referenced ONLY how the focal lengths of individual cells of a convertible lenses are longer than their combined focal lengths and triple convertible lens nomenclature, nothing else. Sorry if I was inadvertently unclear.

Circling back to the starting point of this specific discussion, it was an attempt to get some sense by analogy of the angle of useful coverage for the Wollensak Velostigmat 1a, a well-regarded triple convertible lens similar to the Protar VIIa.

Unequivocal data about the Velostigmat 1a seems largely lost to the mists of time except for one general reference by Wollensak to "85 degrees" found in an old catalogue. We ended up discussing Protar VIIa lenses, which would also seem to meet the OP's initial inquiry about suitable 12x20 lenses.

It seems that there is some reasonable anecdotal evidence that the combined Double Protar VIIa has a useful angle of view similar to modern Plasmat designs, in the 70-75 degree range depending upon one's criteria,

In my more-than-single-copy experience, older Dagor and Protar VIIa lenses of the same vintage seemed roughly similar in optical performance. Recomputed late-model Dagors and MC Plasmats are generally crisper and sharper, if that's one's criteria for choosing a lens - those are mine, but tastes vary, reasonably and thankfully.

BTW, as to the basis for modern Plasmats, one could argue that Plasmats might also be loosely analogized to a Protar VIIa with the third element in each group replaced by an air space.

 

[138S]

BTW, as to the basis for modern Plasmats, one could argue that Plasmats might also be loosely analogized to a Protar VIIa with the third element in each group replaced by an air space.

I guess having an additional element instead an air space may allow a better design. It introduces an aditional variable for the optimization: the refractive index of that element, while air has a fixed value.

 

[5x7shooter]

The Protar VIIa design dates to about 1895 while the original Plasmat dates to about 1920, many years after the Protar VIIa design. So, the time line alone suggests that the fourth element in the Protar VII had nothing to do with the later Plasmat design's air space.

The fully cemented 8/2 design of the Protar VIIa is likely done largely for the same reason as the 6/2 design of the 1892 Dagor, to reduce internal flare in the era prior to lens coating.

Although I have no factual basis for believing that Zeiss did the 4-cemented element Protar VII design to avoid the Dagor's patent, that seems like a reasonable additional basis for the design along with better correction of the individual triple convertible cells. When the Protar VII was introduced, Zeiss dropped its earlier 6/2 Amatar design, which was basically a Dagor clone.

While the combined two-cell Protar VIIa doesn't seem to be any better optically than contemporaneous Dagors, there seems to be general agreement that the individual Protar VII cells are better convertible units than the equivalent three-element Dagor groups.

 

[138S]

The Protar VIIa design dates to about 1895 while the original Plasmat dates to about 1920, many years after the Protar VIIa design. So, the time line alone suggests that the fourth element in the Protar VII had nothing to do with the later Plasmat design's air space.

Yes... 1918, by Paul Rudolph. My understanding is that the Plasmat refines the Dagor design, introducing 2 additional variables for the optimization in each cell (a curvature and a distance) by uncementing the inner meniscus. At the expense of adding two glass-air surfaces in each cell, which had to be painful until coatings were perfected enough.

Although I have no factual basis for believing that Zeiss did the 4-cemented element Protar VII design to avoid the Dagor's patent

This was funny because Emil Von Höegh tried to "sell" his "Dagor" (name used since 1904) design to Zeiss, but they refused, then the chief designer at Goerz died and Von Höegh was hired (1892) in that position, making the Doppel Anastigmat Series III (later renamed Dagor) for Goerz !!!

While the combined two-cell Protar VIIa doesn't seem to be any better optically than contemporaneous Dagors, there seems to be general agreement that the individual Protar VII cells are better convertible units than the equivalent three-element Dagor groups.

Not extrange at all... a (converted) lens made of a single group may improve from sporting 4 elements instead 3, three variables for the optimization are added: one distance, one curvature and one refractive index.

 

[removed account4]

jarin

do you need a shutter??
you might contact Reinhold (http://www.re-inventedphotoequip.com/Home.html)
he makes very large and inexpensive and beautiful Wollaston meniscus lenses that with a Waterhouse stop
at your desired aperture can be pretty sharp. he has samples on his website of what his lenses do. he also makes and sells
guillotine shutters if you need more than a top hat...
have fun !
John
ps. I would suggest a wollensak 1a triple but I don't know the outer reaches of its coverage, both cells on it easily covers 11x14 with a ton of movement room
and with the 1 cell configurations it has a ton of extra coverage but I'm not sure how much...

 

[5x7shooter]

Let me ask, how would you judge the VIIa optic performance (sharpness, contrast) compared to (say) a symmar convertible ? How are the corners depending on aperture ?

I can imagine perhaps the contrast, but I'm curious about what a Protar VIIa yields in practice.

.

FWIW, as part of an additional series of new comparisons, I also tested and compared my best Protar VIIa, a roughly 165 mm Zeiss-made model that is fully symmetrical. Both front and rear components are matched 29cm cells. I compared this best-of-5 Protar to late model multicoated Fujinon NW 6/6 Plasmats, including 125mm, 150mm, and 180mm models.

Tests were made on 5x7 Ilford Delta 100 film developed in XTOL 1:2 with intermittent agitation. Test target was an ISO resolution target against a planar backdrop at the focus plane of low contrast but highly detailed Eastern White Pine needles and other foliage. All photos were shot at f/22 in rapid sequence on a calm, overcast day. All lenses were free from damage. All exposures were consistent. Each of the full-frame 5x7 negatives was then wet-scanned at 2400dpi as 341MB 16-bit BW TIFF files on an Epson V850, imported into Lightroom and identically processed, then compared in Lightroom side-by-side at 1:1 pixel-peeping images.

Results: All lenses, including the older uncoated 165mm Double Protar VIIa, produced high-quality, contrasty images that were excellently sharp at 1:1 and visually nearly identical in terms of both sharpness and contrast. No flare was discernible. Subjectively, I thought that the uncoated Protar showed nice tonal values. I surmise that the fully symmetrical nature of the 29cm/29cm pairing provides better optical correction than Protar sets that combine different focal lengths cells and thus are not fully symmetrical in terms of cancelling aberrations. My other four Protar VIIa sets that use cells of different focal lengths are noticeably less sharp.

The Protar VIIa was sharp to the corners, indicating an angle of sharp coverage of not less than 65 degrees in this situation.

 

[138S]

Results:

hmmm... this is quite interesting ! Thanks for the details.

It is amazing that some ancient lenses can deliver that great performance. I was reading some reports about that (http://hubicka.blogspot.com/2016/03/resolution-of-historical-photographs-in.html) , but to me it's quite interesting to learn more about it.

 

[5x7shooter]

It is amazing that some ancient lenses can deliver that great performance. .

It's worth recalling that when they were made, a fully symmetrical Zeiss Protar VIIa was among the best lenses available. So, it's very likely to be optically better than most other contemporary lenses.

 

[5x7shooter]

i did another triple convertible lens test, retesting the previously discussed`145mm Zeiss-made Double Protar VIIa, consisting of a 29cm front cell and a 22cm rear cell. Hence, this Protar VIIa was not fully symmetrical, unlike the previously discussed 165mm Protar VIIa with symmetrical 29cm/29cm front and rear cells.

I used the same target and test / development / scan / comparison procedure as previously noted, on 5x7 Ilford Delta 100. Lens had no visible decentering effect, no visible damage, and all camera movements were neutral/centered. Planar folage and ISO target was 40+ feet away outdoors, so effectively about 1:90 I again wet-scanned at 2400dpi and then viewed the image at 100%. (Note on scanning - for some earlier scanning calibration tests, I took a very sharp negative and scanned with an Epson V850 at 2400 dpi, 3200dpi, and 4800 dpi. The 3200dpi and 4800dpi scans did not have noticeably better resolution compared to 2400dpi and so I use 2400 dpi here.).

Angle of sharp coverage results, which may be applicable to other Protar VIIa, Wollensak 1a, and similar design triple convertible lenses:

The 145mm Zeiss Protar VIIa lens covered 5x7 to the corners without objectionable vignetting. Lens appeared adequately centered and was nicely and symmetrically sharp almost to corners and edges along 7-inch axis, but started to somewhat soften symmetrically near the corners and extreme edges. Tonal quality was subjectively very nice but not radically different than a 150mm Fujinon NW. The corner softening may be due to either exceeding the angle of sharp coverage or to the asymmetrical nature of the 29cm/22cm combination failing to fully correct for all aberrations at f/22..

My subjective estimate of angle of sharp coverage for this particular lens is about 68-70 degrees, when viewed at 100%. YMMV. As the lens just exceeded its angle of sharp coverage at the corners, the 68-70 degree estimate seems defensible for the limit of sharp coverage.

The tested lens was uncoated. This was not a problem except for some thin stark leafless branches along the top edge that were backlit by a bright overcast cloud layer. These were visibly affected by flare that partially obscured the thin branchlets.

 

[138S]

So it looks its is a competent 4x5" lens ! Thanks for reporting that.

I would like to ask if the wet scan was made on bed of or a wet mount holder. On bed the Epson has a 25% loss compared to holder scanning, as the lower resolution lens is used...

 

[5x7shooter]

I used an Epson wet mount holder and the central high-resolution lens. Yes, certainly a competent 4x5 lens and probably adequate on 5x7 where the corners are not critical and significant movement not needed.

 

[138S]

Thanks