A quick question about Large Format Optics...

[numnutz]

Hi - just a quick question about Large Format Optics...

If lens manufacturers can make a telephoto lens - i.e. a lens with a focal length greater than the amount of bellows draw. Why can't they make a wide angle lens that requires more bellows draw than its focal length. This would prevent large format users having to use bag bellows or recessed lens boards. I know that it is done with lenses for 35mm and digital SLR cameras, so why not with the larger formats. (unless of course, someone knows better!)

nn

[Songyun]

Hi - just a quick question about Large Format Optics...

If lens manufacturers can make a telephoto lens - i.e. a lens with a focal length greater than the amount of bellows draw. Why can't they make a wide angle lens that requires more bellows draw than its focal length. This would prevent large format users having to use bag bellows or recessed lens boards. I know that it is done with lenses for 35mm and digital SLR cameras, so why not with the larger formats. (unless of course, someone knows better!)

nn

Schneider digitar WA 28mm

[wfwhitaker]

Because you wouldn't (or couldn't) pay for it if they did.

[Oren Grad]

I know that it is done with lenses for 35mm and digital SLR cameras.

And you pay a substantial price for it in optical performance, size and weight.

[Dan Fromm]

numnutz, learn to look before you ask.

If you look here http://www.rodenstock-photo.com/ you'll see that Apo Grandagons' flange-to-film distances are longer than their focal lengths. Similarly for Super Angulon XLs and jes' plain Super Angulons. Look here http://www.schneideroptics.com/pdfs/...LensCharts.pdf for SA XLs and here http://www.schneiderkreuznach.com/archiv/archiv.htm for jes' plain SAs.

[Eric Leppanen]

Why can't they make a wide-angle lens that requires more bellows draw than its focal length.

They can. It is called a retrofocal wide-angle lens, and such lenses are typically used with SLR cameras (where the mirror box precludes a conventional wide angle lens design), or with view camera digital sensors which cannot handle off-axis light as well as film. By positioning the lens further from the sensor, the retrofocal design allows light to hit the sensor at a "straighter" angle, improving image capture quality.

Film, on the other hand, handles on-axis and off-axis light equally well, so with LF cameras there is little motivation to incur the downsides of retrofocal design (greater bulk and cost, increased distortion, reduced image circle and edge sharpness). In probably most cases a retrofocal design would not increase focal length enough to eliminate the need for a WA bellows. So why incur the downsides?

Indeed, one of major strengths of wide-angle LF film shooting is the ability to use conventional wide-angle lens designs, as such lenses provide the highest optical performance.

[Wimpler]

Also, it would require a larger setup. Smaller and lighter setups are generally preferred

[Peter K]

All WA-lenses from the Biogon type like the Super-Angulon, the Grandagon etc. are compound retrofocal lenses with a negative element in the front and in the rear to increase the illumination at the outer parts of the image. So the backdraw of conventional WA lenses, much less illumination in the outer part as in the center, could be surmounted.

As mentioned before a longer flange-to-film distance is only neccessary with very short focal lengths like the WA digilenses. But with longer flange-to-film distance the image-circle shrinks also.

[rdenney]

Lenses for single-lens reflex cameras use one or more negative elements in front of a more typical normal lens to de-magnify the scene before it gets into that normal lens (which decreases the effective focal length). This is indeed the opposite of the telephoto design that uses negative elements behind the objective to increase the magnification (which increases the effective focal length). Most people use the term "retrofocus" to describe the reversed telephoto design (after Angenieux, who first marketed the design).

But those negative elements have to be big enough to cover the embedded normal lens's field of view, and the resulting lens is often quite large. The further in front of the film the lens is put, the bigger that glass has to be.

Compare, for example, the 15mm Voigtlaender ultra-wide for the Bessa rangefinder to a 14mm prime intended for an SLR. I have a 14mm Sigma lens for my Canon that is quite large and very heavy. Those negative lenses are thick at the edges and weigh a lot. The lens for the rangefinder is much less retrofocus and therefore much smaller and lighter. (It's a better performer, too, but there are excellent retrofocus lenses out there if you are prepared to pay for them.)

Another example: I have a 47mm f/5.6 Super Angulon, which is designed to cover the 6x9 format. I also have a 45mm SMC Pentax lens for the 6x7, which has less coverage by a bit. The Pentax lens has to go in front of that acre or so of reflex mirror on the Pentax 6x7, so it is a retrofocus design. It's much bigger and heavier than the Super Angulon, despite that it has less coverage.

As was mentioned, the Super Angulon and other very short lenses for large-format cameras are a variation on the later Biogon design, which is really a pair of opposing retrofocus lenses. Thus, they can be big and heavy, too, especially in their wider coverage designs. But they provide image quality and, particularly, lack of distortion difficult to match with regular retrofocus designs.

Rick "who found it cheaper to find a camera that could manage a two-inch lens" Denney

[venchka]

I've never even seen a 47mm S.A. much less used one. I wouldn't trade my 45mm SMC Pentax lens for the S.A. It's big across, but nearly "square" and much lighter than it has any right to be. It's also sharp enough to cut you wide open and focused at 14". I could be tempted to trade the 45mm Pentax for a Hasselblad SWC. I know. I'm dreaming.