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12/31/2005 07:41:53 PM · #1 |
| Im trying to learn more about different types of lenses, but when i read specs i dont really fully understand what im looking at (like i know f stop, and i have some idea how the mm translate) but Im not really sure how those 2 translate into what type of lens I would want to be using. Ive never really delt with lenses, in the past on my film slr i just used the lens it came with but sime im looking into a dslr in the near future im actually trying to understand what different lenses do. I know i am going to want a telephoto lens and one that can do good macros definatly. I just need to be pointed into the right direction on this one. Thanks |
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12/31/2005 07:46:53 PM · #2 |
| Telephoto will be something like 70-200mm or 75-300...something like that. Basically, on a 35mm sensor (film) a 35mm lens will be no magnification. 70 will be 2x magnification and so on. Wide angle is anything less than 35 that thus has a demagnification (19-35mm lens for example). A macro lens is a macro lens if it can focus really closely and take a picture up close. So a macro lens will usually be called macro. A telephoto can be converted (or almost any lens for that matter) using close up filters or extension tubes. |
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12/31/2005 08:23:40 PM · #3 |
It all starts with the angle of vision that approximates the human eye. The human eye sees at around 45mm - 50 mm (or something like that). Lens that have angle of vision near this are referred to as normal lens.
As the focal length gets smaller, the angle of vision (how far to the sides you can see) gets larger. When the angle gets large enough, it is referred to as wide-angle -- how wide of an angle is wide enough to be wide? That varies depending on who your talking to, and to a large degree is a matter of taste.
As the focal length gets larger, the angle of vision gets more narrow. When it gets narrow enough (again, how narrow is narrow enough varies) it is called telephoto.
For the sake of having something different to call them, lens with extremely narrow angles are referred to as super telephoto.
A prime is a fixed focal length lens, and is given only one of the above designations. A zoom however, may be given more than one; for instance if the lower focal length is wide and the higher focal length is telephoto, the lens will be called a wide telephoto.
The amount of zoom is determined by dividing the higher focal length by the lower. if the higher is twice the lower, the lens has a 2x magnification from lower to the upper zoom.
All lens have a minimum focusing distance, a macro lens is able to focus on a subject that is really close to the lens. Careful with these, as I understand some macro lens are not capable of focusing at distant subjects, while others are.
A fish-eye lense has a convex outter element (glass) that increases the angle to vision more than just a short focal length does. Some have 180 degree vision, meaning the light coming in from the side of the lens is making a right angle turn to get into the lens.
The main thing to keep in mind is the different focal changes the perspective between near and far objects. Hold a glass up at arms length and look at how much of the objects on the other side of the room it covers, then move your head closer to the glass. Notice it covers more of the objects across the room. Now do the same, but move your head further back (may have to sit the glass on something) -- and notice the glass covers less of the objects behind it. If your current camera has zoom capability you can learn more about this by photographing the same object at different zoom levels, but with the distance from the camera to the object changed so the object is always the same size in the final image.
The fStops numbers in the lens discription is the largest aperture (smallest number) that lens is capable of. Reading the lens discription will give the smallest aperture size possible. When a zoom lense gives an fStop range, such as 2.8-3.6, the lower fStop number is the smallest aperture possible at the shortest focal length and the larger fStop number is the smallest aperture at the longest focal length. A fixed aperture zoom is usually desirable, but also more (much) expensive than a variable one.
Anything else? I'll be happy to share the knowledge I've learned while researching my own purchase. ;) Even happier if someone wants to correct any misinformation I have learned.
David
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12/31/2005 10:48:59 PM · #4 |
Originally posted by Britannica:
It all starts with the angle of vision that approximates the human eye. The human eye sees at around 45mm - 50 mm (or something like that). Lens that have angle of vision near this are referred to as normal lens.
This is assuming full-frame, 35mm-film coverage. In dSLR cameras, few have FF coverage, so you need to multiply the focal length by the "crop factor" to get the "normal" lens. In other words, a 31mm lens on a 20D is the same angular coverage as a 50mm on a full frame camera.
As the focal length gets smaller, the angle of vision (how far to the sides you can see) gets larger. When the angle gets large enough, it is referred to as wide-angle -- how wide of an angle is wide enough to be wide? That varies depending on who your talking to, and to a large degree is a matter of taste.
As the focal length gets larger, the angle of vision gets more narrow. When it gets narrow enough (again, how narrow is narrow enough varies) it is called telephoto.
For the sake of having something different to call them, lens with extremely narrow angles are referred to as super telephoto.
A prime is a fixed focal length lens, and is given only one of the above designations. A zoom however, may be given more than one; for instance if the lower focal length is wide and the higher focal length is telephoto, the lens will be called a wide telephoto.
The amount of zoom is determined by dividing the higher focal length by the lower. if the higher is twice the lower, the lens has a 2x magnification from lower to the upper zoom.
All lens have a minimum focusing distance, a macro lens is able to focus on a subject that is really close to the lens. Careful with these, as I understand some macro lens are not capable of focusing at distant subjects, while others are.
A fish-eye lense has a convex outter element (glass) that increases the angle to vision more than just a short focal length does. Some have 180 degree vision, meaning the light coming in from the side of the lens is making a right angle turn to get into the lens.
The main thing to keep in mind is the different focal changes the perspective between near and far objects. Hold a glass up at arms length and look at how much of the objects on the other side of the room it covers, then move your head closer to the glass. Notice it covers more of the objects across the room. Now do the same, but move your head further back (may have to sit the glass on something) -- and notice the glass covers less of the objects behind it. If your current camera has zoom capability you can learn more about this by photographing the same object at different zoom levels, but with the distance from the camera to the object changed so the object is always the same size in the final image.
The fStops numbers in the lens discription is the largest aperture (smallest number) that lens is capable of. Reading the lens discription will give the smallest aperture size possible. When a zoom lense gives an fStop range, such as 2.8-3.6, the lower fStop number is the smallest aperture possible at the shortest focal length and the larger fStop number is the smallest aperture at the longest focal length. A fixed aperture zoom is usually desirable, but also more (much) expensive than a variable one.
No, the smallest f/stop number is the LARGEST aperture available. F/stop is the ratio between aperture diameter and focal length. It helps to hink of f/22 as 1/22 of the focallength in size, and f/4 as 1/4 the focal length in size..
Anything else? I'll be happy to share the knowledge I've learned while researching my own purchase. ;) Even happier if someone wants to correct any misinformation I have learned.
David |
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01/01/2006 01:55:04 AM · #5 |
Originally posted by Bear_Music:
Originally posted by David.C:
It all starts with the angle of vision that approximates the human eye. The human eye sees at around 45mm - 50 mm (or something like that). Lens that have angle of vision near this are referred to as normal lens. |
This is assuming full-frame, 35mm-film coverage. In dSLR cameras, few have FF coverage, so you need to multiply the focal length by the "crop factor" to get the "normal" lens. In other words, a 31mm lens on a 20D is the same angular coverage as a 50mm on a full frame camera. |
yes, I realized I hadn't made that clear once I left the house after posting -- I come back to clarify and find you already have. :D
Originally posted by Bear_Music:
Originally posted by David.C:
The fStops numbers in the lens discription is the largest aperture (smallest number) that lens is capable of. Reading the lens discription will give the smallest aperture size possible. When a zoom lense gives an fStop range, such as 2.8-3.6, the lower fStop number is the smallest aperture possible at the shortest focal length and the larger fStop number is the smallest aperture at the longest focal length. A fixed aperture zoom is usually desirable, but also more (much) expensive than a variable one. |
No, the smallest f/stop number is the LARGEST aperture available. F/stop is the ratio between aperture diameter and focal length. It helps to hink of f/22 as 1/22 of the focallength in size, and f/4 as 1/4 the focal length in size.. |
Damn -- got my big and little mixed up while rewriting the middle of the paragraph. One of these days I'm going to learn to reread fully everything I rewrite for 'clarity'. :(
Thanks for catching my flubs.
David
Message edited by author 2006-01-01 01:58:08.
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01/01/2006 02:24:05 AM · #6 |
When choosing which lens to use in a given situation you may also want to consider how each type of lens affects perspective in order to best obtain the effect you want. For instance, a wide angle lens is going to make your subject appear much smaller in the frame and look like it's much father away than what you remember when shooting it at the scene. It will also give you a greater sense of depth to the scene...a deeper depth of field. Parallel lines will appear to converge, such as when shooting a skyscraper you will see the sides of the building get closer together as the sides approach the top of the building. Foreground objects will look rather large and background objects rather small. Not a good lens to use for portraiture unless you want to make an amusing image of someone with a rather large nose and distorted features.
A telephoto lens, on the other hand, has the opposite effect. It tends to flatten out the scene so that objects in the scene will appear right on top of one another. Objects will appear larger, as the lens is magnifying. Tele lenses have a much narrower depth of field so that only those objects at, or near to, the focus point will appear to be in focus and those outside of that region will appear a lot softer. These are good lenses to use if you want to blur the background to make your subject stand out.
Hope this was helpful. |
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01/01/2006 03:16:23 AM · #7 |
There is an old saying that says that most lenses are better than most photographers.
This is so true.
Sadly, the only way to really appreciate good glass has nothing to do with reviews and ratings, but everything to do with experience and personal results. Besides, until you have used some really bad glass, you simply can't fully appreciate the good stuff.
The moral is not to lose any sleep over lenses until it becomes an issue worth worrying about. You'll know it when the time has come. Until then, frame, shoot, and be merry! |
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