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f/0.75 lens?
Old 10-04-2004, 11:55 PM   #1 (permalink)
Kurt_Gearheart
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50 mm f/0.75 Rodenstock TV-Heligon

Here, about 1/4 down the page: http://www.naturfotograf.com/lens_spec.html

Isn't "opener" than f/1.0 kinda like faster than light?

Like, impossible, by definition?

Looking forward to this one explained...
 
 
Common misconception
Old 10-05-2004, 12:22 AM   #2 (permalink)
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People think that a theoretical f/1.0 will let in "all" the light, so you can't have a f-stop less than 1.0 Thats wrong.

The f-number is merely the ratio of the focal length of the lens divided by diameter of the front element. The diameter of the front element is the light gathering element, so the bigger it is, the more light is gathered.

So a 200mm lens, with a 100mm front element will be an f/2.0 lens.

A 50mm lens with a 100mm front element would be an f/0.5 lens, or 2 stops faster than an f/1.0 lens.

So your 50mm f/0.75 lens will have a 68mm front element.

Unfortunately, you start getting a type of paralax distortion when the front element is larger than the focal length, and it gets worse fast. An f/0.75 lens would likely be heavy, as it would need several additional elements to attempt to correct for this msssive distortion.
 
 
Re: f/0.75 lens?
Old 10-05-2004, 12:26 AM   #3 (permalink)
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Here's some info that includes images...

http://www.naturfotograf.com/need_speed00.html


Later,
Israel
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Re: f/0.75 lens?
Old 10-05-2004, 12:51 AM   #4 (permalink)
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Man, there's a lense that I won't be getting. Forget about the price, it's just something that I don't even need or would be conciveably need. But I will say this Man, that's cool!

Isaiah Brink
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