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Author Topic: New Wide Angles Lenses in 2013 [CR2]  (Read 78982 times)

AUGS

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #180 on: March 14, 2014, 06:03:20 AM »
The f stop value of a lens is defined by the focal length of the lens divided by the diameter of the objective lens (front element). so a 300mm lens with a 100mm front element has an f stop value of f2.8. That's how it works.
I'm not sure you are correct.  By this formula, the new 24-70LII has an f stop of about 24/64 = 0.375.  But its a 2.8 lens.  While the approximation approaches this as the focal length gets longer and the angle of view becomes narrower (telephotos and telescopes), it is not true for all focal lengths, and especially the wide angles.
My understanding is the f stop is calculated from the focal length divided by the apparent iris aperture via the optical formula of the lens (which includes all the magnifications of the optics).
I may be wrong, so I'd be happy to be corrected.

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #180 on: March 14, 2014, 06:03:20 AM »

privatebydesign

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #181 on: March 15, 2014, 12:32:39 AM »
AUGS you are 100% correct.
Too often we lose sight of the fact that photography is about capturing light, if we have the ability to take control of that light then we grow exponentially as photographers. More often than not the image is not about lens speed, sensor size, DR, MP's or AF, it is about the light.

9VIII

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #182 on: March 15, 2014, 10:20:54 AM »
The trick here is you have to realize that optical designers can do very funny things with focal length, like making an 800mm lens that's only 461mm long, or "retrofocusing" design with an effective focal length that exists entirely outside the lens.
The "focal length divided by aperture" rule is true, but the definition of focal length is more than meets the eye.

I'm sure the video guys here would point out we would all be better off using T-stop anyway.

GMCPhotographics

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #183 on: March 18, 2014, 07:08:36 AM »
The trick here is you have to realize that optical designers can do very funny things with focal length, like making an 800mm lens that's only 461mm long, or "retrofocusing" design with an effective focal length that exists entirely outside the lens.
The "focal length divided by aperture" rule is true, but the definition of focal length is more than meets the eye.

I'm sure the video guys here would point out we would all be better off using T-stop anyway.

The word "telephoto" indicates that a lens' focal length is longer than it's physical length. So a 135L is a telephoto lens, but a 85L isn't. Many photographer's assume that a "tele" indicates a longer focal length, but it doesn't. It is possible to have a fairly wide telephoto lens.   

StudentOfLight

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #184 on: April 13, 2014, 01:28:47 AM »
The trick here is you have to realize that optical designers can do very funny things with focal length, like making an 800mm lens that's only 461mm long, or "retrofocusing" design with an effective focal length that exists entirely outside the lens.
The "focal length divided by aperture" rule is true, but the definition of focal length is more than meets the eye.

I'm sure the video guys here would point out we would all be better off using T-stop anyway.

The word "telephoto" indicates that a lens' focal length is longer than it's physical length. So a 135L is a telephoto lens, but a 85L isn't. Many photographer's assume that a "tele" indicates a longer focal length, but it doesn't. It is possible to have a fairly wide telephoto lens.

I learnt something today. So the 40mm pancake is in fact a telephoto lens. Who knew?
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GMCPhotographics

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #185 on: April 17, 2014, 06:18:17 AM »
The trick here is you have to realize that optical designers can do very funny things with focal length, like making an 800mm lens that's only 461mm long, or "retrofocusing" design with an effective focal length that exists entirely outside the lens.
The "focal length divided by aperture" rule is true, but the definition of focal length is more than meets the eye.

I'm sure the video guys here would point out we would all be better off using T-stop anyway.

The word "telephoto" indicates that a lens' focal length is longer than it's physical length. So a 135L is a telephoto lens, but a 85L isn't. Many photographer's assume that a "tele" indicates a longer focal length, but it doesn't. It is possible to have a fairly wide telephoto lens.

I learnt something today. So the 40mm pancake is in fact a telephoto lens. Who knew?

Yup! While the 50mm f1.4 USM isn't a telephoto either!

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Re: New Wide Angles Lenses in 2013 [CR2]
« Reply #185 on: April 17, 2014, 06:18:17 AM »