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/photo/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.

[rdenney]

I could be tempted to trade the 45mm Pentax for a Hasselblad SWC. I know. I'm dreaming.

The lens in the original SWC, which is not constrained by accommodating a reflex mirror, was a Biogon, which was the archetype of the Super Angulon type of lens.

Yes, that 45mm Pentax is sharp. The 47mm Super Angulon is just as sharp, and maybe sharper, but it is also remarkably free of distortion, even the little bit of barrel distortion that most folks don't mind in their SLR wide-angle lenses. For architectural work, for example, that distortion-free design is important.

It's also quite compact compared to the Pentax. My older 47/5.6 is mounted in a #00 shutter and has a 49mm filter thread. The Pentax, as you know, requires an 82mm filter, and not just because of the very large diameter 6x7 lens mount, or the extra stop of speed.

Rick "figuring the SA wouldn't extend past the aperture ring on the Pentax when focused on the same thing" Denney

[Eston3]

Just bought a early 210 Super Angulon. It is both MASSIVE and HEAVY.

[Arne Croell]

Just bought a early 210 Super Angulon. It is both MASSIVE and HEAVY.
Lens dimensions (and coverage) for the same design scale linearly with focal length. So compared to the 47mm Super-Angulon, height, width and length are nearly a factor of 4 each, and weight (at least the glass) will be close to 4 to the power of 3, a factor of 64.
I will also cover more than 8x10. By that token, a 210mm equivalent of the Pentax 45mm for example, covering 8x10, would have a filter size of about 240mm....you'd need both hands to turn the focus ring, too.

[rdenney]

Just bought a early 210 Super Angulon. It is both MASSIVE and HEAVY.

You think that's heavy, what would it weigh if it was enough of a retrofocus design to allow that focal length in front of an 8x10 reflex mirror. Something the size of a gallon paint bucket sounds about right.

Rick "giggling at the thought of an 8x10 reflex mirror" Denney