Canon Extension Tube EF 25 II + Canon EF 70-300mm f/4-5.6?

How much additional magnification will I get?

With the 1.4x Extender?

With the 2x Extender?

Canon Extension Tube EF 25 II + Canon EF 70-300mm f/4-5.6?secure browser

A general rule is to divide the length of the extension tube by the focal length of the lens. At the 70mm side there would be a magnification of about .36x and at the 300mm side a .08x. However, the reason for using an extension tube is to be able to get closer to the subject at the minimum focusing distance. You will loose the infinity focus. Then it is simply a matter of adding the extender. However, this is NOT the proper way to go for figuring out magnification. You need to determine how big the actual subject is in real life and then how much larger you want to photograph it. If for example you use the 70mm side of your zoom lens and want to photograph a penny actual size -- you will need 70mm of extension. Keep in mind two very import things. A lens is the stated focal length only with the lens at infinity. The instant you focus closer then infinity, the lens is NO LONGER the stated focal length. In order to get a 1/1 reproduction of a one inch object using a full frame SLR you need equal amount of extension tube (or bellows) as the lens focal length AND and the same lens to subject distance of 50mm. Therefore, a 50mm lens with 50mm extension at 50mm away from a one inch subject will yield a 1/1 reproduction ratio. However, there is NOT much room to light the subject, and that is why longer lenses are used, and, of course longs tubes, or bellows, to get a better lens to subject working distance. Last, the greatest magnification is obtained by using wide angle lenses in reverse position.

Canon Extension Tube EF 25 II + Canon EF 70-300mm f/4-5.6?

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