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01/05/2009 09:20:51 PM · #1 |
| Soooo.. I have a couple of prime lenses, but I don't really know what constitutes prime? Probably a totally dumb question im sure. |
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01/05/2009 09:22:46 PM · #2 |
prime is a lens that has no zoom, say you have a 50mm and a 18mm - 200mm the 50mm is a prime. The other is not.
Just looked at your profile, you have two of the most popular prime lenses.
Message edited by author 2009-01-05 21:24:25. |
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01/06/2009 01:56:22 AM · #3 |
| Thanks. I knew they were primes.. just wasnt quite sure what "prime" meant? :) Thanks for clearing it up! |
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01/06/2009 03:53:22 AM · #4 |
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01/06/2009 09:31:43 AM · #5 |
Prime lenses are usually better lenses. Since they're less complicated, they're easier to make. They also have wider apertures and can take in more light (fast glass).
It's only when you start to change the focal length (zooms) that it get's more complicated. That's why some of the cheaper zooms have a variable aperature (Canon EF 75-300mm f/4.0-5.6 II). The f/4.0-5.6 means at 75mm, it has a max aperture of f/4.0, but at 300mm it's f/5.6.
In the more expensive zooms, the aperture is constant (more complication).
Stick with primes if you want good cheap glass and let your feet do the zooming. |
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01/06/2009 11:23:06 AM · #6 |
| Wikipedia says "This use of the term "prime lens" is an example of a retronym. Early in photography only primary camera lenses were available, and were merely called "lenses" or "objectives". Later, "auxiliary" lenses were available, which usually fit in front of the front element of the primary, or "prime" lens." |
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01/06/2009 12:05:57 PM · #7 |
Originally posted by Nullix:
...some of the cheaper zooms have a variable aperature (Canon EF 75-300mm f/4.0-5.6 II). The f/4.0-5.6 means at 75mm, it has a max aperture of f/4.0, but at 300mm it's f/5.6.
In the more expensive zooms, the aperture is constant (more complication). |
Although this is a common usage, it's slightly misleading. Aperture is the hole itself, and f/stop is the ratio of the diameter of the aperture to the focal length of the lens. On a 50mm lens, a 25mm aperture is f/2, but on a 200mm lens that same aperture is f/8. So if the aperture remained constant on a hypothetical 50-200mm zoom, its maximum f/stop would range from f/2 at the wide end to f/8 at the long end, theoretically. Of course, this is complicated by the fact that the zoom may not actually get physically that long, attaining some (or all) of its zoom by means of internal optical adjustments, but the principle obtains.
On the better zooms, like my 70-200mm f/4L (to name one), the maximum aperture is physically increased throughout the zoom range so the f/stop remains at f/4 regardless of the focal length being used.
R.
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01/06/2009 02:24:12 PM · #8 |
and that fact is one reason why fixed aperture zooms are more expensive than variable aperture zooms,
Originally posted by Bear_Music:
On the better zooms, like my 70-200mm f/4L (to name one), the maximum aperture is physically increased throughout the zoom range so the f/stop remains at f/4 regardless of the focal length being used.
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one other is that in order to increase the aperture size as the focal length gets longer - while still keeping the relative f-stop the same is the size of the glass elements required to compensate for larger ( wider ) openings for the aperture at longer focal lengths. ie: more precision milled glass ( diameter ) required to allow for larger aperture openings = more material and expense to manufacture.
Message edited by author 2009-01-06 14:28:02.
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