Difference between revisions of "Talk:Lens"
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A caption about astigmatism: "Astigmatism is when a point sending light through a lens cannot be projected as one point behind the lens. It appears as a line on the focal plane. That's the result of faulty lens elements. The best correction of astigmatism is to use faultless lens elements."{{br}} | A caption about astigmatism: "Astigmatism is when a point sending light through a lens cannot be projected as one point behind the lens. It appears as a line on the focal plane. That's the result of faulty lens elements. The best correction of astigmatism is to use faultless lens elements."{{br}} | ||
'''It's a complete nonsense!''' Astigmatism appears - no matter of the lens quality - when beam of light passes through the lens at an angle to the optical axis. In this case vertical and horizontal curves of the lens element, in the place where the beam is transmitted, are different and the beam is focused as two perpendicular lines in TWO different places behind the lens - one by vertical and one by horizontal curve. These lines DO NOT appear at the focal plane but at two different curved surfaces (often close to spherical), as the astigmatism is closely connected with field curvative. | '''It's a complete nonsense!''' Astigmatism appears - no matter of the lens quality - when beam of light passes through the lens at an angle to the optical axis. In this case vertical and horizontal curves of the lens element, in the place where the beam is transmitted, are different and the beam is focused as two perpendicular lines in TWO different places behind the lens - one by vertical and one by horizontal curve. These lines DO NOT appear at the focal plane but at two different curved surfaces (often close to spherical), as the astigmatism is closely connected with field curvative. | ||
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| + | == "Long-focus" vs. Telephoto == | ||
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| + | While some have attempted to enforce this distinction, it is my sad duty to report that your cause is lost. At least in American English, the term telephoto is universal, and it has been for decades. I have beside me a 1958 photo magazine which blithely uses "telephoto" in describing 8mm movie camera lenses, which are almost certainly not of telephoto optical construction. The distinction has also broken down because increasingly photographers use long-focus zooms whose optical design is unknown. | ||
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| + | I have edited the Long-focus section to acknowledge the distinction, but foreground the more familiar word. This is a subject that I've [http://silverbased.org/telephoto-or-not/ blogged about], and I give a fuller defense of accepting "telephoto" there. --[[User:Voxphoto|Vox]] 07:21, 1 March 2011 (PST) | ||
Revision as of 15:21, 1 March 2011
Should the list of lens mounts go to the main page? --rebollo_fr
I would leave it where it is.
Ref: All very fast lenses are interchangeable lenses, so if this will be important to you, you will need an interchangeable lens camera.
I understand what you were trying to say here but this is not entirely true. Many digicams have fast lenses especially for zooms. My Sony f717 has the 35mm equivellent of a 38-190mm zoom at f2-2.4 In the 35mm world that would be a very fast zoom.
Contents
Lens coating has nothing to do with color correction
I've corrected this myth both here and in the glossary. For a very good explanation of how antireflection coatings work, check Rick Oleson's discussion of the matter here. (He's a camera and optical guru.)
From his page:
- One last, unrelated question: Does coating make a lens "color-corrected"?
- No. Color correction is a function of the optical design of the lens, and is not affected in any way by coating. Color correction is the property of a lens that causes all colors to focus at the same [...]
Links
Astigmatism
A caption about astigmatism: "Astigmatism is when a point sending light through a lens cannot be projected as one point behind the lens. It appears as a line on the focal plane. That's the result of faulty lens elements. The best correction of astigmatism is to use faultless lens elements."
It's a complete nonsense! Astigmatism appears - no matter of the lens quality - when beam of light passes through the lens at an angle to the optical axis. In this case vertical and horizontal curves of the lens element, in the place where the beam is transmitted, are different and the beam is focused as two perpendicular lines in TWO different places behind the lens - one by vertical and one by horizontal curve. These lines DO NOT appear at the focal plane but at two different curved surfaces (often close to spherical), as the astigmatism is closely connected with field curvative.
"Long-focus" vs. Telephoto
While some have attempted to enforce this distinction, it is my sad duty to report that your cause is lost. At least in American English, the term telephoto is universal, and it has been for decades. I have beside me a 1958 photo magazine which blithely uses "telephoto" in describing 8mm movie camera lenses, which are almost certainly not of telephoto optical construction. The distinction has also broken down because increasingly photographers use long-focus zooms whose optical design is unknown.
I have edited the Long-focus section to acknowledge the distinction, but foreground the more familiar word. This is a subject that I've blogged about, and I give a fuller defense of accepting "telephoto" there. --Vox 07:21, 1 March 2011 (PST)
