optics question

[xkaes]

The closest example I have is with my Yashica Samurai Z. The built-in lens is a 25-75mm zoom. SUPER sharp which is good because it is a half frame camera. I have two front end converters for it. A really neat 0.43x Vivitar wide-angle converter which turns it into an 11-32mm wide-angle zoom, and a Tokina 2X tele-converter which creates a 50-150mm telephoto zoom. Converting that into 4x5 format is basically lenses from 60mm to 600mm. Others here will trash it, of course, but it works great for me. No, I do not use these converters on my 4x5 gear -- but I could.

A similar set of converters might work for your situation, but as others have pointed out, why not just buy the entire lenses? If you have one lens/shutter and six "converters", why not use seven lenses instead? Size and weight will be about the same, and perhaps cost.

With a 150mm LF lens, a x0.43 converter would be 65mm, and a 2x would be 300mm. Not a bad spread. I might just give it a try!

Why not just try a set of diopter lenses for the front. That would be lighter than extra lenses. A 150mm lens can be turned into a 60mm lens with a #10 diopter lens on the front. OOPS. Once again, I'm sure I've crossed the line of LF purity. I'll be in the basement awaiting the mortar fire!

http://www.subclub.org/fujinon/close-up.htm

[Jim Andrada]

Just a comment re the Nikkor with interchangeable rear cells. I have the 360/500/720 and the lens(es) are surprisingly sharp in all configurations.

[Pere Casals]

Could a lens be designed such that the rear element always produces an image circle of 200mm, but the front elements could be swapped such that the angle of coverage goes from wide to tele? Or could a spacer tube for the front element or rear element change the focal point such that it would render a similar image circle?
I.e. a kit with effectively 65mm, 90mm, 135, 180, 250mm front elements with decreasing angle of views with same max aperature.

This would require one back element and one shutter.

Some of the Nikon telephotos were built something along these lines - the front cell remained constant and the rears were changed. There were two families, 360/500/720 for 4x5/5x7 and 600/800/1200 for 8x10. While Nikon's literature claimed a constant image circle for each family, I believe the IC actually increased as the focal length got longer.

What you propose is probably possible, but you might not want to pay for it... I hope Jason (Nodda Duma ) chimes in.

A reversed Nikon T... It would be interesting to know what criterion Nikon used to rely in interchangeable rears instead of fronts, a lens designer perhaps would say it...

Yes, it could be done. However, it wouldn't be any cheaper than a set of fixed focal length lenses on separate lens boards to swap out as needed. Especially in today's market.

A large format continuous zoom would be fun to design. It wouldn't be as big as one would think.

I would like to introduce a question in that discusion... what happens when giving up the symetric design for LF lenses?

LF lenses have to work with very large circles, and for sure the symetric (or close) design is sound for the corrections do work in the outer as in the center.

The Nikon T design is non symetric and with interchangeable rears, but image circle is not large for the focal, here in page 11: http://www.kennethleegallery.com/pdf...rmatLenses.pdf

...it says angle of coverage is from 11º to 22º (very f/ dependant !). So the Nikon T design it may be appropriate for extra long focals as with a narrow angle the format can be covered.

Still, for sure it can be done, but if we sacrifice the symetric design and want to obtain a well corrected and large circle (65º...) with interchangeable front cells, then perhaps we will need a lot additional elements to make front and rear parts independently well corrected, better than the Symmar convertible, in order it works.

IMHO that design saves shutters, lens boards, and weight, but the challenge would be correcting well aberrations, flatness and distorsion of the full system without going too much expensive. This is IMHO, perhaps an optician can say it for sure.

In part the Cooke Triple convertible and Symmar convertible are nice solutions in that direction. Some discredited those lenses in the converted configurations because not being aware of the focus shift when stopping (at least with the symmar), but we have to remember that "according to an article by Gordon Hutchings in View Camera magazine, July/August 2004. Ansel used the 19" (480 mm) component for "Aspens, Northern New Mexico," 1958; both components to get 12" (300 mm) for "Clearing Winter Storm, Yosemite National Park," 1940; and the 23" (580 mm) component for "Moonrise, Hernandez, New Mexico," 1941. Enough said?"

http://www.kenrockwell.com/schneider/150.htm

[Pere Casals]

A large format continuous zoom would be fun to design. It wouldn't be as big as one would think.

Yes but... any succesful zoom in the LF history ? why ?

I'd ask what will it happen with focus flatness in the film plane if we have 60º coverage, and with distorsion, and Sph and Chr aberrations...

Sure it could be done with a lot of elements and with the help of Asph, perhaps it would be difficult to beat MF performance if not going too much big and too much expensive. Still a simple system it would be nice for creative usage, but competing (cost-performance) with a plasmat derivative in the +60º coverage realm it is not easy.

[Len Middleton]

The last casket sets offered were Berthiot's Ser. IVc, which contained 3 or 4 individual lenses. Last offered around 1951. These are somewhat an exception to the different apertures for each combination rule, single cells were typically f/12, combinations f/6.7 - f/8. There was only one Ser IVc set for 4x5 (cataloged for 9x12), #1, with six focal lengths, 88, 100, 135, 142, 230 and 305 mm. Not exactly what Eric wants.

Dan,

Was the Wisner convertible plasmat sets (made by Schneider) considered casket sets?

Seen them offered on rare occasions, so not certain how successful they were in the market, or how practical they were in actual use...

Just looking for clarity.

Thanks,

Len

[Dan Fromm]

Len, of course you're right. I'd forgotten them completely. Thanks for the correction.

[Jody_S]

Yes but... any succesful zoom in the LF history ? why ?

I'd ask what will it happen with focus flatness in the film plane if we have 60º coverage, and with distorsion, and Sph and Chr aberrations...

Sure it could be done with a lot of elements and with the help of Asph, perhaps it would be difficult to beat MF performance if not going too much big and too much expensive. Still a simple system it would be nice for creative usage, but competing (cost-performance) with a plasmat derivative in the +60º coverage realm it is not easy.

I had a Reitzschel Telinear for a few years, an early (1920s?) LF zoom lens (though mine was the smallest, designed for 9x12cm). Did it actually zoom and produce an image? Yes. Would I use it? No.

1) calculating aperture was a PITA, and 2) the aperture was located just in front of the rear element, which means that at the wider configuration it would cause extreme vignetting, so practically, the lens had to be used wide open.

[Pere Casals]

I had a Reitzschel Telinear for a few years, an early (1920s?) LF zoom lens (though mine was the smallest, designed for 9x12cm). Did it actually zoom and produce an image? Yes. Would I use it? No.

1) calculating aperture was a PITA, and 2) the aperture was located just in front of the rear element, which means that at the wider configuration it would cause extreme vignetting, so practically, the lens had to be used wide open.

Interesting... thanks for pointing it, I did not know Rietzschel Telinear. I searched information on it and it's a very interesting lens. I was knowing the Adon but not the Telinear...

[Jody_S]

Interesting... thanks for pointing it, I did not know Rietzschel Telinear. I searched information on it and it's a very interesting lens. I was knowing the Adon but not the Telinear...

Most people think the Adon was the first 'zoom' lens, but in fact the Reitzschel version pre-dates it. I never opened it, but it seems to have been quite simple with a front and a rear element. I didn't use it enough to learn if it was better at the shorter or longer focal length.

[Bob Salomon]

Most people think the Adon was the first 'zoom' lens, but in fact the Reitzschel version pre-dates it. I never opened it, but it seems to have been quite simple with a front and a rear element. I didn't use it enough to learn if it was better at the shorter or longer focal length.

Zoom lens or varifocal lens? While what they do is similar in the end, change focal length, what happens when they do it are very different,