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500mm lens on Baby Speed?

 
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jdman



Joined: 13 May 2001
Posts: 302
Location: Midwest

PostPosted: Sun Oct 27, 2002 4:52 am    Post subject: Reply with quote

Anyone notice the 500mm Kalimar lens mounted on a Baby Speed on EBAY? Wonder how that works, notice it has a support and sticks out about a foot in front of the camera. Russ
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Les



Joined: 09 May 2001
Posts: 2682
Location: Detroit, MI

PostPosted: Sun Oct 27, 2002 1:29 pm    Post subject: Reply with quote

First off, let's talk about telephoto lense vs normal lenses. A normal 20" lens, say a process lens will need 20" from the rear nodal point to the film in order to focus at infinity. That's not a problem with an 8x10 Deardorf or a 24z36 galley camera.

But when we want the focal lenght without the bellows draw, we have to cheat. If you take an 11 3/4" norma lens and add a 1.7 negative element to the back, the image will get spread out over a large area. If you keep the same format, taking only the center section the image will appear to have been magnafied--magnified to the same image size as a 20" lens, but with the bellows draw of an 11 3/4" lens. However doing this imparts distortion on the image and the outer area of the image circle suffers. This isn't a problem because you are only using the 'sweet spot' of the image circle.

This is how the 8",10, and 15" teleoptars work. The 15" tele will easily cover 8x10. but I wouldn't call the image sharp.

The stronger the negative element, the worse the image is.

with 35mm equipment the bellows draw to focal lenght is even worse. We have the audacity to demand a 8" lens to focus with a 1 to 1.5" bellows draw (the thickness of the body). In truth what most lens makers do is add a large tube to the back of the lens, so that in effect the body is deeper. That's why that 500 and 1000mm Hassy lens is so light. Others may add another element to the back to help correct the pin-cushin distortion. Which is what I think the Kalimar has.

In short. I think it will do what he says it will do, but I wouldn't expect to make tack sharp 20x24s from the neg. You'll be doing well to make good 11x14s.
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Dan Fromm



Joined: 14 May 2001
Posts: 1883
Location: New Jersey

PostPosted: Mon Oct 28, 2002 1:59 pm    Post subject: Reply with quote

Quote:

On 2002-10-26 21:52, jdman wrote:
Anyone notice the 500mm Kalimar lens mounted on a Baby Speed on EBAY? Wonder how that works, notice it has a support and sticks out about a foot in front of the camera. Russ
Take a look at http://medfmt.8k.com/bron400mm.html . I think the ideas carry over cleanly to 2x3 Speeds.

On the other hand, I have a 500/5.6 Century in T-mount and a 700/8 Questar, also in T-mount. Neither will cover much more than 24x36 because of mount vignetting, and I'm not about to take a hacksaw to either. Some things, especially Questars, are sacred and anyway a test published in MP suggests that the Q700 won't cover much more than 24x36 no matter what.
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