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04/09/2007 02:57:40 AM · #1 |
Can someone point me in the right direction, a site or book perhaps, on understanding lenses, how they work etc. I bought a new lens, it was cheap, and I like it. However, I'm finding it hard to understand why one lens is so much more expensive than the other, even after attaching it to the camera to test it.
I want to know how to shop for lenses. |
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04/09/2007 03:00:03 AM · #2 |
| Generally, you get what you pay for. |
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04/09/2007 03:51:31 AM · #3 |
This is overly simplistic, I think. Like most consumer goods, really cheap ones are too bad to bother. Then you have the sweet spot, where for a reasonable cost you get reasonable quality. And then you have the high end, where you get an ever decreasing amount of quality for an ever increasing amount of money.
I hope this makes sense
Harry |
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04/09/2007 06:38:37 AM · #4 |
| I was thinking even simpler. When it says AF it means Auto Focus right? Well, I didn't know this until the other day. A kind of noob to lens article...what all the milimeters stand for etc. |
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04/09/2007 06:43:57 AM · #5 |
| I am also interested in lenses explained in laymans terms. When people tell me what what type of lens they have in mm's I get lost. |
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04/09/2007 07:06:09 AM · #6 |
AF does mean Auto Focus.
The focal length (mm's) is basically a measure of the angle of view of the lens. The lower the focal length the wider it is. On a film camera a 50mm is considered normal, anything lower is wide angle and anything longer is telephoto.
The best thing to do is to grab a zoom lens, set it to a certain focal length and look through the viewfinder. Seeing how the view changes with the focal length will give you a good idea of what the mm's mean.
If you have any specific questions feel free to fire away. |
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04/09/2007 07:12:46 AM · #7 |
Beginner's Guide to Lenses
Looks like the article is based on SLR film cameras. Due to the smaller sensor in a digital SLR (except the Canon 5D and 1DsMkII), a lens acts a bit longer than it would on a film camera. For Nikon multiple the focal length by 1.5 and for Canon 1.6. For example, on my D200 my 50mm f1.8 will have the same angle of view as a 75mm lens on a Nikon film camera. |
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04/09/2007 07:14:24 AM · #8 |
| Thanks for your help. Will remember your offer |
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04/09/2007 07:35:11 AM · #9 |
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04/09/2007 07:38:09 AM · #10 |
Explanations of lenses tend to depend on optical terminology.
Wikipedia has a lot of links in the text, but that may be as confusing as it is helpful.
If you can remember using a magnifying glass to concentrate the rays of the sun in one spot (say to burn a hole in some paper, or something) then you can see for yourself a demonstration of focal length. The distance from the lens to the point at which the rays converge is the focal length of the lens (as near as damn it, anyway). On a camera, the focal length is the distance from the glass at the front of the lens to the film in the back of the camera. On a 35mm (35mm is thirty five millimetres, the approximate lenth of the rectangle of film onto which the image is exposed) camera, 50mm (that's about two inches, in case the SI flew right by you) is reckoned to be the focal length that gives the most 'normal' perspective. The smaller the focal length, the wider the angle. The greater the focal length, the narrower the angle and the greater the magnification.
Then you get to the aperture. That's a dinky little device in the lens that you can open and close to regulate the amount of light coming through. I can think of no reason, except that maybe the people who designed and developed early camera equipment were number geeks, for apertures being represented by such complicated numbers (f/5.6, f/4, f/2.8 etc). Actually yes, the reason for the numbers themselves is that they represent the focal length of the lens divided by the diameter (?) of the aperture. The result of this is that bigger apertures have smaller numbers. It's really not a very user-friendly set-up. Cameras and lenses are user-friendly, however, so the good news is that the main aperture sizes that are given are ordered by doubling the amount of light available to the inside of the camera. This has the same effect in terms of exposure as halving (?!?) the shutter speed, i.e. keeping the shutter open twice as long. For reasons that you'll learn about later, if you haven't given up yet, you may want to work these two against each other. Conveniently, then, 1/250 sec at f/16 exposes the same amount of light to the film or sensor as 1/500 sec at f/11.
1/250sec being half the speed (or twice the time) of 1/500sec is fairly easy to grasp, I think. It's less easy to see how f/11 is twice f/16, but that's because of the way the numbers are derived. The convenient thing is that lenses and camera software are sorted around f stops and double-and-halved shutter speeds, so you can effectively click the aperture ring or whatever you're using and a) the camera will understand and b)you will have stayed within the annoyingly geeky fstop system.
There is a useful (and user-friendly and commonly used) term, EV, or exposure value, which is what I called the amount of light that is available to the inside of the camera. When you double the shutter speed/halve the exposure time and at the same time open the aperture 1 stop, you keep the same ev.
Message edited by author 2007-04-09 07:40:38. |
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04/09/2007 08:03:03 AM · #11 |
Cheap lenses do the same job as expensive lenses, but to a less perfect degree. More expense lenses might have...
Better quality glass. Cheap lenses sometimes even use plastic, but there are better qualities of glass that will give less distortion, better colours and contrast.
Aspherical grinding - provides a more precise optical result, but aspherical griding is more expensive.
Lens coating - helps to reduce flare/ghosting.
Mechanical considerations. Cheap lenses are generally plastic. Expensive lenses for professional use are metal construction.
USM/HSM/AF-S - faster focus motors
Better optics - wider apertures - expensive lenses will have a wider aperture, which gives better results in lower light, shallower DOF options, and better motion-stopping with faster shutter speeds.
So, that's a few things I can think of. But yes, every lens is a compromise, for different needs. Some consumer lenses go for a bigger zoom range at the expense of optical quality. Professional photographers are happy to sacrifice the convenience of a long zoom in favour of optical quality, and are willing to pay more for a more rugged lens at the expense of weight of each lens.
If you have a lens already that you are happy with, use it, learn, and figure out what you need different for your next lens. Then direct your next lens research to what you need the next lens for.
I've rambled long enough. It's late. :)
(edit - wow, when you leave the computer for several hours in the middle of a reply, lots of people get in with many answers! Cool.)
Message edited by author 2007-04-09 08:05:49. |
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04/09/2007 09:08:04 AM · #12 |
I'm guessing your new lens is the 50mm you show listed in your profile. You have good reason to like it, even though it is a less expensive lens. Many, many people swear by this little lens for its sharpness and low-light capabilities, and best bang for the buck capabilities. It is what you call a "prime" lens, having just the one focal length. It's a very simple lens, with 6 small(er) glass elements, so material cost is kept at a minimum at the production line. Your 18-70mm lens has 16 larger elements so the material cost is more.
Primes usually give better image quality than a zoom lens of equal quality glass and construction since they are designed specifically for that focal length, with no need to compensate for other focal lengths. There is no "sweet spot" in a prime's focal length of course, but lens aperture can vary the quality and sharpness of an image, usually wide open (f/1.8 on your lens) won't be as nice as f/5.6 due to sharpness and C/A (Chromatic Aberration).
Anything with a range of focal lengths is called a "zoom" lens, like your 18-70mm lens. Image quality usually suffers a bit due to more glass elements used in the lens to provide the range, and the extra bending of light that happens as light passes through those elements. Zooms usually have a "sweet spot" where the lens performs better, usually somewhere in the middle of the range in both focal length and aperture. The more expensive lenses usually have better components and better engineering to provide a much broader range of the sweet spot, and some even are superb throughout the range.
This is very generalized, and there are exceptions depending on different lenses, but I hope this helps a bit. Enjoy your new toy! |
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04/09/2007 09:41:58 AM · #13 |
The 18/70 that you have is my choice for a great everyday lens to use, as it is sharp, contrasty, and light to haul around. You will notice the difference in available (faster) shutter speed with the 1.8/ 50mm for shooting in low light if you use aperture priority, and set it to 1.8 . A good second choice for lenses would be the 70/300 D-ED if you want to keep similar image quality to the 18/70 and have a good telephoto zoom capability without paying a huge price. I have both the 70/300 G, the cheap model, and the D-ED, and I can tell the difference in contrast and sharpness in my images with the two of them. For macro, you may want to get a good macro lens. Another option for macro is to get a reversing ring, which allows you to put the 50 on your camera backward. An extension ring is a second option for macro without much expense. The 18/70 will not work with either of them because it has no manual aperture control on the lens.
There are several websites offering good reviews of Nikon lenses, old and new. My fav when shopping eBay is naturfotograph.com by Bjorn Rorslett for the older Nikon lenses.
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04/09/2007 10:55:55 AM · #14 |
| Thanks for all the answers. I'm going to have to read the links and maybe post some more 'in-depth' questions. |
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