Swapping lenses in a Petzval

[goamules]

From the few diagrams I've seen, the Dallmeyer "patent" has thicker glass in one rear lens, can't recall which, than the original Petzval formula. It stands to reason that an expert lens grinder, who invented many designs around 1866 (Landscape Rectilinear, Triple Achromat, Rapid Rectilinear) would have optimized his rear lenses for the reverse ordering.

If charley's lens appears to shoot worse in one or the other config, it's probably because it's glass is optimized for one or the other config. I don't believe Dallmeyer simply reversed the rear and said "give me a patent."

Also, "traditional swirl" is the opposite of what Dallmeyer was looking for. They wanted to reduce aberrations and have as wide a field as possible before falloff. Still, it is strange that your first set shows such falloff in the Original Config, such a lens would hardly be useful in the day.

[BarryS]

Garrett, I also think Charley's lens originally had the Dallmeyer design based on his experiements. I mentioned the swirl because it's usually the natural byproduct of many Petzval designs--so it points in the direction of that configuration as the original. I wonder about Dallmeyer's patent, though. Sure--they probably optimized the design for the reversed rear cell, but I'm not convinced it was any better than traditional Petzval design. Based on my 3A and similarly designed Vitaxes, I'm pretty sure the "soft focus" control is mostly hokum. I have all the respect in the world for Dallmeyer, but the reversed cell and soft focus control were probably more for marketing purposes--a way to distinguish the lens line from other Petzval makers.

[goamules]

...I mentioned the swirl because it's usually the natural byproduct of many Petzval designs--so it points in the direction of that configuration as the original...

Actually, what I was trying to say is the more a configuration shows "swirl" which is spherical aberration, the less likely it is the correct config. You can misconfigure a petzval in several ways and get a ton of aberrations, which point to it being assembled wrong.


But I agree with you, the rest of his righthand picture of the birdhouse looks great and is typically petzval. His experiments are very interesting.

[eddie]

... I'm pretty sure the "soft focus" control is mostly hokum. ......

SSSSHHHHHH! you are going to ruin the SF market with such blasphemy.....

[CCHarrison]

[QUOTE=BarryS;629081]. Based on my 3A and similarly designed Vitaxes, I'm pretty sure the "soft focus" control is mostly hokum. QUOTE]



Keep in mind that Dallmeyer originally touted unscrewing the rear most element and creating a "diffusion of focus" was a way to increase depth of focus (field), not really to create a Soft Focus lens as we know it today.

Below is an excerpt from my page on Petzval lenses found here: http://www.antiquecameras.net/petzvallens.html


"In 1866, Dallmeyer patented his most significant variation on Petzval's design, with his " "Diffusion of Focus Portrait Lens."

This lens was also called Dallmeyer's "Patent Portrait" Lens. Dallmeyer basically took the rear element group in Petzval's original design, flipped it and re-worked the lens a bit. He marketed the lens as having numerous benefits over Petzval's original design. It claimed better sharpness, reduced flare, and less distortion and vignetting. Additionally, Dallmeyer touted the feature of being able to unscrew the rear element group to introduce spherical aberration to the lens, resulting in image having varying degrees of a soft, dreamy quality. These images would also appear to have more of depth of focus ("diffusing" the focus). This feature was to endear the lens to photographers who were creating more soft focus and "artistic" work in the 1860's. In fact, this lens gave birth to intentionally made "soft focus" lenses that would become very popular in the 1880's and beyond.

Dallmeyer's "Diffusion of Focus" claim led to a firestorm within the optical and photographic communities, especially in England. The Photographic News and British Journal of Photography contained numerous accounts and bitter exchanges between Dallmeyer and challengers to, what they felt, was an erroneous claim that defied the laws of optics [ that is, the ability to increase DOF by increasing SA ].

Here is one account from London's, The Photographic News from May 2, 1884:

"In the year 1866, the late Mr. J. H. Dallmeyer patented a variation of the Petzval lens. This variation consisted in reversing the elements of the back combination with such a modification of the curves as this change involves. The particular advantage claimed at the time for this form of lens has since been abandoned. The putting of the negative lens at the back allowed its distance from the positive element to be varied, and thus the perfection of its correction for spherical aberration to be modified. It was stated that by altering the distance of the back lens, so as to re-introduce spherical aberration, and sacrifice definition at the focus, improved definition was obtained upon the planes not in focus. This claim—" diffusion of focus" it was called—was shown to be mistaken, and is no longer made. The lens, however, when employed with the element in the position of best definition, is a useful one, other well-known opticians have for some time past issued a series of lenses of this form. In this case, however, the back lenses are burnished together into their cell, and no shifting or alteration of their position is possible. While on the subject of "diffusion" or "depth "of focus it may be remarked that a delusion on this point is cherished by a vast number of photographers. For this the manufacturing opticians are somewhat to blame. They have been in the habit of advertising lenses as having great "depth of focus," whereas that is a quality that, except as attained by the use of a small aperture or diaphragm involving slowness of action, does not exist at all. Still many photographers -careful, practical men, too, some of them—will tell you that they have, or have had, some particular portrait lens that will give the various parts of a sitter's head, through the background behind him, and generally objects on different planes, with sharper definition than other lenses of similar aperture and focus, that have as fine, or finer definition on any one plane. This is a curious case of mistaken observation; but in photography, unfortunately, mistaken observations may pass current as scientific facts."

CONTINUED BELOW

[CCHarrison]

In the book, Photographic Optics: A Text Book for the Professional and Amateur By William Kinninmond Burton 1891 (NY), also discusses the issue:

"An arrangement whereby spherical aberration could be produced at will in a lens was, I believe, first suggested by my esteemed friend, J. Traill Taylor, and the idea was first put into practice by the famous optician Dallmeyer. It is said of a which it is possible to produce spherical aberration at will that it possesses a diffusion of focus arrangement. Such an arrangement is of lens in use only in the cases where it is not possible to get of focus by the introduction of a small stop, as in the case of portrait lenses, where the small stop would, in certain circumstances, depth prolong the exposure to too great an extent. The dispute diffusion of focus is as to whether it does or does not actually increase depth of focus. It does not actually make any part of an about image sharper; on the contrary, it makes every part less therefore, say some, produces no increase in the depth of focus. The opponents of these, on the other hand, argue that as there is sharp; it no actual depth of focus, as the whole question is one of definition as judged by the eye, an arrangement which makes the definition of objects at different distances apparently more equal does actually increase the depth of focus. The question is in reality purely one of terms, and where the terms cannot be strictly defined it is idle to argue one way or the other. I leave the reader free to take what view of the question he likes, a thing which he would probably do whether he were left free or not."

In the 1884 advertisement below, the final paragraph claims that by unscrewing the rear cell, the lens produces "...the impression of a general distribution or depth of focus; and this is in proportion to the amount of unscrewing."

Dan

[goamules]

Interesting stuff on the soft focus aspect of the Dallmeyer reverse order. I concur that I've never found the "soft focus" on these lenses to do anything other than un-focus the image. If you focus a Dallmeyer Patent or Vitax, then move the diffusion device, yes you will get a soft look. But if you then adjust your focus slightly, you will bring the image back into total sharpness. In other words, making the image slightly out of focus does the same thing as the "soft focus" mechanism.

I also have some of the original Voigtlander's who of course first produced Professor Petzval's design, and the original is just as sharp and nice as the later Dallmeyers. I prefer the Voigtlanders, actually.