Zoom?

[abruzzi]

Before anyone jumps down my throat, I'm not actually interested in using a LF zoom, just intellectual curiosity.

Anyway, the other day I was wondering about the various lens types common on smaller formats--telephoto, retrofocal, zoom (i.e. varifocal and parfocal). I was curious about their application in large format. Telephoto is easy--there are a number of well know lenses in the telephoto type. Retrofocal, I don't know, I could see their use with people using recessed board so they can focus or perform movements with wide lenses, but I've not seen any lenses that are explicily retrofocal.

Zooms, I also didn't see anything. I assumed that no such lenses existed for large format. Then I stumbled across this brochure:

https://www.pacificrimcamera.com/rl/00718/00718.pdf

And the page for their telephoto lens thows this:



As best as I can tell shrinking or lengthing the tube changes the zoom ratio. Am I misreading anything here? Or is this telephoto, really a telephoto zoom lens? Are there other zooms in the LF world?

(BTW, searching for 'large format zoom" brings tons of hits for large format cine camera lenses, not really anything about large format still cameras.)

[Bernice Loui]

Lenses for small film formats aka 35mm, 620, 120 roll film descended from view camera lens designs. Examples of this are found in the folder roll film cameras that were once very common. These roll film folders are essentially a view camera without camera movements and a view finder device added to them. The bellows and method of focusing was determined by the focal length of the lens which had no back-focus length correction, just pure lens design.

~This lens design fundamental remains true and correct for the Vast Majority of all view camera lenses designed and produced over over a Century.
~This Fundamental design element persist due to the fact and given a view camera that is flexi in the center (bellows) and adjustable ends for the lens and film
or image recording device can be made to accommodate any given lens need. This is why deciding on Print Goals first, then Lens(es) required to achieve the
Print Goals then camera and remainder applies to a view camera as a view camera is not a lot more than just a light tight box that is flexi in the center (with
some specific requirements).

Enter the 35mm roll film Leica, originally designed and made to evaluate exposure for film, then evolved into a camera. This roll film camera is essentially a fixed dimension light tight box that is NOT flexi in the center with the ends also fixed. This demands the lens be made with back-focus compensation and some other means of focusing the lens (helical focus or similar). To achieve the design requirement of a lens to meet the fixed back-focus distance the lens can be designed to the fixed distance of the light tight box, but that results in a single fixed focal length lens. To achieve a shorter focal length lens aka "wide angle"
the reverse telescope aka "Retrofocus" lens design (and yes Dan, Taylor, Taylor & Hobson 35mm f/2 (1931, UK) then Angénieux Retrofocus 28mm f/3.5 Type R11 of 1953) was done to accommodate the fixed light tight box dimensions... driven by the cinema or film making industry as cinema cameras have the same fixed-non movable light tight box as the Leica 35mm range finder and similar range finder cameras and later Single Lens Reflex cameras.

The cinema industry needed both large aperture lenses to make films indoors with artificial lighting that were powered by electrical rather than chemical light making process. These optics designed found their way into other roll film cameras. With more passage of time, development of optical technology variable focal length lenses happened. Again the first innovative variable focal length lens (zoom) happened with Cooke in the UK (Bell & Howell Cooke Varo 40-120mm Lens (British patent 398,307, Arthur Warmisham) for 35mm format. The lens was manufactured and sold by Bell & Howell.):
https://www.cookeoptics.com/t/history.html

Angénieux took "zoom" lens design as one of their primary optics offerings to the cinema industry.

But, there is more:
https://www.zoomlenshistory.org.uk/

~What is not often appreciated, both the Brits and French made very great innovations to the world of optics design, yet too many worship German as THE optical center of the lens universe, not true or correct, yet remains a persistent photographic myth. Each nation involved with optics design made specific contributions to this technology based on the markets they served and are forced to conform to the way Nature is (laws of Physics as we know them today) with no exceptions.


As for why there are few if any zoom lenses for sheet film cameras, consider how a typical view camera is used and the types of images they produce. Add to this the innate complexity, size, weight and more of a high performance zoom lens to produce an image circle large enough for a roll film or solid state imager?

Then consider how these cameras are used?

The absolute advantage of a view camera is the ability to be flexi in the center allowing the plane of focus to be "moved". This allows recording of images that no fixed light tight box camera can achieve. This recent post sums up why view camera:
https://www.largeformatphotography.i...ong-amp-Linhof

As for that odd looking lens in the Rodenstock catalog, it is one of their TelePhoto design lenses allowing longer effective focal length with reduced back focus length much like the Tele Xenar, Tele Nikkor, Tele Fujinon and etc... The extending-contracting lens barrel was to allow this lens to be used on cameras with limited bellows and camera extension.. same limitations many field folder cameras have to this day when the need for a long focal length lens is needed.


Bernice

Before anyone jumps down my throat, I'm not actually interested in using a LF zoom, just intellectual curiosity.

Anyway, the other day I was wondering about the various lens types common on smaller formats--telephoto, retrofocal, zoom (i.e. varifocal and parfocal). I was curious about their application in large format. Telephoto is easy--there are a number of well know lenses in the telephoto type. Retrofocal, I don't know, I could see their use with people using recessed board so they can focus or perform movements with wide lenses, but I've not seen any lenses that are explicily retrofocal.

Zooms, I also didn't see anything. I assumed that no such lenses existed for large format. Then I stumbled across this brochure:

https://www.pacificrimcamera.com/rl/00718/00718.pdf

And the page for their telephoto lens thows this:



As best as I can tell shrinking or lengthing the tube changes the zoom ratio. Am I misreading anything here? Or is this telephoto, really a telephoto zoom lens? Are there other zooms in the LF world?

(BTW, searching for 'large format zoom" brings tons of hits for large format cine camera lenses, not really anything about large format still cameras.)

[abruzzi]

The extending-contracting lens barrel was to allow this lens to be used on cameras with limited bellows and camera extension.. same limitations many field folder cameras have to this day when the need for a long focal length lens is needed.

Is that the case, though? On the inner barrel, it looks like markings for 4x, 5x, 6x. Its a little hard to make out though. The text also mentions:

"the combined focus being considerably longer than that of the collective element, and is greater or less according to the separation of the two elements. This variability of focus enables one to obtain from a fixed standpoint pictures of varing size of one and the same object."

I read that to mean that the telephoto group is in the rear, and the "collective element" is in the front and varying the distance varies the enlargment of the image, i.e. the zoom.

[erian]

The catalog states: "The telephotographic lens consists of a collective element of long focus and a dispersive element of short focus, the combined focus being considerably lo nger than that of t he collective element, and is great er or less according to the separation of the two elements. This variability of focus enables one to obtain from a fixed standpoint pictures of varying size of one and the same object."

This sounds like a zoom lens to me.

[abruzzi]

I googled a bit, but I can't find any real world photos of that barrel. Like I mentioned, I don't need a zoom lens, and I doubt I would even want one, but it is interesting to think about.

[reddesert]

Anyway, the other day I was wondering about the various lens types common on smaller formats--telephoto, retrofocal, zoom (i.e. varifocal and parfocal). I was curious about their application in large format. Telephoto is easy--there are a number of well know lenses in the telephoto type. Retrofocal, I don't know, I could see their use with people using recessed board so they can focus or perform movements with wide lenses, but I've not seen any lenses that are explicily retrofocal.

Zooms, I also didn't see anything. I assumed that no such lenses existed for large format. Then I stumbled across this brochure:

https://www.pacificrimcamera.com/rl/00718/00718.pdf

And the page for their telephoto lens thows this:



As best as I can tell shrinking or lengthing the tube changes the zoom ratio. Am I misreading anything here? Or is this telephoto, really a telephoto zoom lens? Are there other zooms in the LF world?

People have said that the Komura wide angle lenses for large format - Super-W-Komura - are slightly retrofocus and have a larger flange to focal distance than expected for their focal length. I've never had one so I can't attest to this myself.

Most telephoto lenses operate on the principle of a convex front group and a dispersing (concave) rear group, as stated for the pictured lens. The dispersing rear group increases the focal length to be greater than of the front group alone. It makes the cone of rays appear as if it came from a larger distance. There is a diagram in the Wiki article on telephoto lenses:

(click to enlarge) from https://en.wikipedia.org/wiki/Teleph...elephoto_1.svg

The focal length of the combination does depend somewhat on the separation between the two groups, so if you change that distance it's theoretically a "zoom" lens. However, I don't think it's effective - it's not going to cover a large range in focal lengths, and there's some separation where the corrections for off axis aberrations are optimal, while performance will suffer at other separations. It's a curiosity.

[J. Patric Dahlen]

I googled a bit, but I can't find any real world photos of that barrel.

Google Rietzschel Telinear, it's a lens of the same type.

[Bill Rolph]

Schneider produced a 240-255 f/5.6 zoom, designed for reproduction with the shorter end optimized for 1:1 and the longer for 1:0.61.

[LabRat]

The application of LF zoom on a large scale is in use for copiers... But due to the longer FL's we normally use, there would be little change in magnification, more like moving camera a little forward/backward...

Don't expect a LF lens would give the massive zoom range of lenses made for MP or our digital cousins...

A long FL zoom on a MP camera is heavy and huge!!!

Steve K

[Jody_S]

Most telephoto lenses operate on the principle of a convex front group and a dispersing (concave) rear group, as stated for the pictured lens. The dispersing rear group increases the focal length to be greater than of the front group alone. It makes the cone of rays appear as if it came from a larger distance. There is a diagram in the Wiki article on telephoto lenses:

(click to enlarge) from https://en.wikipedia.org/wiki/Teleph...elephoto_1.svg

The focal length of the combination does depend somewhat on the separation between the two groups, so if you change that distance it's theoretically a "zoom" lens. However, I don't think it's effective - it's not going to cover a large range in focal lengths, and there's some separation where the corrections for off axis aberrations are optimal, while performance will suffer at other separations. It's a curiosity.

This is the basic idea behind the G. Guilbert Polyopse varifocal projection lens I'm currently restoring. Standard Petzval with a bi-concave twin lens group in the rear, in a sleeve that slides over the main lens barrel. You slide the rear group in or out to adjust the projection angle, then focus as normal.