Make Me a 100" Lens

[Hermes07]

Well... technically my goal is a 95.5" lens but that doesn't sound as catchy.

After a lot of research and some very helpful answers on the forum I've concluded that's it's basically impossible to get hold of a lens longer than 70" / 1800mm, other than stumbling over one by chance in the wreckage of a crashed spyplane prototype or an abandoned nuclear testing bunker. My goal is a 2400mm lens with at least 24 degrees of coverage, I would appreciate a wide-ish aperture (f/16-22) but I'll settle for something narrower if need be.

My question then is this - if you needed a 2400mm lens, what would you do to go about building/finding/adapting one? Would you get the best results by finding an existing lens and adding a negative/tele group to the back of it? Would you crack open lenses already in your possession and swap elements over? would you try building something entirely from scratch?

I'm planning on trying all of the above, starting when my shipment of elements from SS finally turns up, but I'd be grateful of any pointers. I don't have an unlimited budget but I'm willing to spend time and money on this - I also have a range of wide-aperture lenses all the way up to 1200mm and I wouldn't hesitate to "borrow" bits of any of them to make this a reality if that's what it takes.

[Math]

4 cheap M42 2x tele converters added to a small but long lens?

[Nathan Potter]

Essentially you could use/modify a reflecting telescope. Field of view might be a problem though, but there are wide field designs. Check into it. There are some astronomical types here who might help.

Nate Potter, Austin TX.

[Dan Fromm]

Look around on this http://alag3.mfa.kfki.hu/astro/giantlenses/index.htm site, which has some links to manufacturers. Ask about long focal length refractors on astronomy sites.

If you've got the money, honey, the manufacturers have the time.

[Jim Galli]

OK, I'll bite. Why do you need a 95.5" lens?

We use 117 inch lenses on tracking telescopes, f8, but they only cover half frame 35mm movie film, and a crane is required to lift them. BTW, you can only focus on the ground for about 5 minutes in the morning in perfect conditions and perhaps 8 to 10 minutes on a perfect afternoon just about 15 minutes before sunset. Prime time.

[ic-racer]

You need a 48X telescope. However the clincher is that the magnification specs for the telescopes are calculated with various eyepiece magnifications. If you take away the eyepiece to put on your camera adapter, you magnification is much less. For example a typical consumer scope that with specs of "100mm 50X power" with its eyepiece, may only be a 600mm focal length lens when you take off the eyepiece and attach a camera.

Another option is to use a 0.5 diopter lens (2000mm focal length) or 0.25 diopter (4000mm focal length) B&W makes both of those.

[sanchi heuser]

There was a thread from the italian cube project:
http://www.largeformatphotography.in...ad.php?t=71684
and a manufacturer of lenses was mentioned:
http://www.adrianololli.com/
$$$$

[Hermes07]

Ok... so I guess I'm in a 'telescopes only' region now

Dan, I have browsed that Giant lenses database often - I own a couple on the second page, as well as 1 or 2 more that would have a place on there if I submitted them. The trouble is that the lenses on there are mostly achromats and I have been reliably informed (ahem) that I'd be wasting my time trying to get any sort of sharp, wide field out of those.

I don't think I'd really need any sort of record-setting lens in terms of weight or diameter though. I have a 300mm lens, a 600mm lens and a 1200mm lens, all with 6"-ish diameters. All are roughly the same size & weight and are usable with a strong front standard and long bellows - a 2400mm lens with the same sort of dimensions doesn't seem so far-fetched. I'm sure from an optical design point of view it wouldn't have been any harder to design a 2400mm f/22 than a 1200mm f/11 if the demand had been there. This is what has got me hoping that there is a relatively simply change I can make to one of the lenses I already have to extend the focal length.

Jim, I need it to cover a 2 metre-high negative... of course I'm trying to achieve 2400mm specifically just because I'm fairly obsessive. As I mentioned, I already use lenses which are roughly 150mm f/1.2, 300mm f/2.5, 600mm f/5, 1200mm, f/10, e.t.c. so 2400mm f/20 would be the next logical step. From a practical point of view having my lenses spaced like this in terms of focal length and aperture does help as my field of view options and depth of field calcs stay pretty consistent between formats.

The telescope suggestions are appreciated. It looks like this is something I'll have to get to know in more depth.

[Steve Barber]

Maybe a ZEISS Apo Sonnar T* 4/1700 and a 2x Mutar? It weighs 564 pounds, but it would cover a 6x6 frame.

[Dan Fromm]

But Zeiss, some of the Russians, and some of the Chinese makers offer what they call apochromats. Asking is cheap ...

FWIW, the 2500/12.5 ApoSaphir covers a little over 1.3 m at infinity and is quite hard to find. Boyer is out of business but the Apo Saphir prescription is on www.dioptrique.info. All you need is a pot of money and a merchant lens maker.