Lens information help

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Permalink Reply by Dimitris on May 21, 2008 at 11:56pm

Also, keep in mind that a fixed focal length tele photo lens is quite expensive.
And, never forget that the bird foto you see on a magazine is shot with a profesional camera with a profesional lens on it.

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Permalink Reply by Ragai Karas on May 22, 2008 at 7:09am

Thanx

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Permalink Reply by Tom Wilson on May 20, 2008 at 5:25pm

I understand what you are looking for but let's first start with the basics. The two numbers you see on the end of your lens refer to focal length (mm) and aperture (f). Focal length represents the distance from the center point of your lens (usually the aperture blades) to the point at which the subject, when focussed at infinity, appears sharp. This is your camera's sensor. In bird photography it is important that your subject represent as large a percentage of the sensor size as possible. As you double the focal length of your lens, the subject size will also double. The sensor size, will of course, remain the same. For example, if the Yellow Bellied Sap Sucker you captured fills 15% of your frame with a 200 mm lens, it will fill 30% of your frame when shot with a 400 mm lens.
The next number (f) represents the maximum aperture of your lens. These are universal numbers that represent the amount of light that the lens will transmit to your sensor. These numbers are constant. Expressed in "Stops," as follows: f/1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 and so on. Each f stop will transmit twice as much or half as much light as the next or previous number. The larger the f stop number the smaller the aperture. Smaller apertures mean less light will hit your sensor.
Making your subjects (birds) pop out of the picture is obviously your objective. This is where it can get very expensive. The biggest advantage of using long lenses with very large apertures (small f stop numbers) in bird photography is the ability to fill your frame with the bird and narrow your depth of field, leaving just the bird in focus. The larger your aperture (small f stop number) the shallower your depth of field. If your bird is perched on a low branch halfway between you and a wooded area, you may well lose the detail of the bird in the background which will be in focus as well with small apertures (larger f stop numbers).
I mentioned the proportionality between focal length and subject size. I wish the proportion between maximum aperture, focal length, and price were as forgiving. As you double the focal length of your lens the maximum aperture will typically be cut in half, at best. When you double the focal length of your lens and the maximum aperture is unchanged, the price will have increased from a few hundred dollars to a few thousand. Long lenses with large maximum apertures, 300 mm f 2.8 for example are very expensive. Tele-converters (TC) are an option but have there limitations. A good rule of thumb is you will lose 1/2 the light (go from f 4 to f 5.6) when doubling the focal length of a lens with a TC.
Ragai, you mentioned you are using a Nikon D40. You are fortunate because you can mount many different older Nikon lenses on this body to great effect. Feel free to shoot me an e-mail and I will be glad to help you decipher any listings for used Nikon lenses you may find. Good luck!

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Permalink Reply by ian neilson on May 20, 2008 at 8:20pm

Hi, go to www.photo.net there you can read all about lenses and what they do for you photos...Ian

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Permalink Reply by Ragai Karas on May 21, 2008 at 12:12pm

Thanx

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