Meeting Photo Challenges
Creative Image Processing
Nature & Outdoor
Creating Better Photographics
Night & Low Light Photography
Light & Exposure
Close-Up & Macro
Digital Black & White
Color & Design
Choosing & Using Lenses
Digital Photography Equipment
Buying A Lens; Tips On Making The Right Choices:
With zoom lenses, you will often see a range of f/stops such as f/4.5-f/6.3. What this tells you is that at the widest focal length the maximum aperture is f/4.5, and when the lens is zoomed out to the longest focal length, the maximum aperture will be f/6.3. A 70-300mm lens, for example, would most likely be used at 300mm with animals and birds, and this is where the maximum aperture is the smallest—f/6.3 in this example.
Unfortunately, large f/stops (fast lenses with wide maximum apertures) increase the price of a lens significantly. Super telephoto lenses in the 400mm to 600mm range can cost literally thousands of dollars more when you opt for a maximum aperture of f/4 versus f/5.6. A single f/stop, though, can make a huge difference in sharpness when shooting in low light conditions.
5. Magnification Factors: Camera manufacturers make many of their camera bodies with less than full-frame sensors because this makes them more affordable. A smaller sensor means that when you make a large print, the quality of the image won’t be as good as what a full-frame sensor (which has a larger physical area and therefore more pixels) would give you. With the advancement in technology, though, smaller sensors will still give you strikingly beautiful results in very large prints.
The point I want to make is that because the sensors are smaller, they crop some of the picture area, (figure #1). A full frame sensor includes the entire area of a typical 35mm piece of film, but as you can see in the diagram the less than full-frame sensor crops into the photo. Canon’s crop is slightly more than Nikon’s. The way you can determine what your actual focal length is for each lens is to multiply by 1.5x for Nikon lenses and 1.6x for Canon. (Note: Some camera bodies, such as the 4⁄3rd System cameras, have a 2x factor. Check the camera companies websites for the multiplication factor of your camera sensor.) A 70-300mm Nikon zoom, for example, becomes a 105-450mm lens. A similar Canon lens would be 112-480mm. This works to your advantage when shooting sports or wildlife because it’s like having a longer lens with no additional cost. Of course, if you took a picture with a full frame and used Photoshop to magnify it 1.5 or 1.6 times, you’d get the same result.
On the wide angle end of the spectrum, the magnification factor works against you. A Canon 16-35mm wide angle zoom becomes a 25-56mm lens, and if you like extreme wide angle perspectives you’ll be disappointed. A 25mm focal length is a decent wide angle, but it’s not as dramatic as a 16mm.
7. Sharpness: The one aspect that photographers always talk about with respect to a lens is its sharpness. Obviously, this is a big deal in photography. If you are a snapshooter and your primary interest is getting some nice shots of the grandkids, then whether or not a lens is tack sharp from the center to the corners isn’t a major concern and, to be honest, it won’t affect your enjoyment of taking pictures. If, however, you are exacting in your work and you will examine your images with a critical eye, then the quality of your lenses is very important.
8. Chromatic Aberration: If you enlarge a photograph on your monitor to at least 100 percent, many times you will be able to see color fringing at the edges of the various elements in the composition. The fringing is usually magenta, cyan, and/or red, but other colors can sometimes be seen as well. An enlargement of (#9) shows this clearly. In (#10), look along the branches and twigs to see the colors that unfortunately occur. This is chromatic aberration. It happens more with wide angle lenses than with telephotos, and it appears more in the corner and edges of an image as opposed to
Chromatic Aberration is the unwanted dispersion of light caused by the fact that colors of the white light spectrum (including the red, green, and blue that make up the channels or components of a digital image) are focused on slightly different places on the sensor. This is a function of how glass bends light. Lenses that have been corrected for this problem are said to be achromatic. Even with modern technology, however, this problem is never corrected completely. Lenses that are very expensive still capture images with color fringing in the corners.
Recommended Lenses For Beginners
The telephoto side of the spectrum is best covered with two different lenses. I feel that a medium telephoto is important, such as a 70-200mm. This is what I have. I bought the 70-200mm f/2.8 and my wife has the 70-200mm f/4. While I have that coveted large maximum lens aperture, my wife’s telephoto lens is much lighter than mine and significantly smaller. This is important to her because she is petite and can’t carry the weight that I am willing to carry.
For macro photography, there are a number of choices. I carry with me the 50mm macro lens, which is quite inexpensive as lenses go and, at the same time, it’s very small and light. Many photographers like a telephoto macro because of the sense of compression and the fact that the out of focus background is completely undefined. The 100mm macro is a great lens and so is the 180mm macro. I go into macro lenses and accessories later in this issue.
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