Help Explaining...

Joined
Jul 22, 2008
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I am trying to explain lens to my friend who is getting a D60. He is taking Photography up as a hobby. but having only done photos for 1.5 years and a freshman in college... I can't really explain the whole bit about lenses to him. Liki tody i told him to get a basic 18-55mm lens. and told him to get a UV filter. so he asked if he should get a 55mm filter. I told him to get a 52mm because its the same lens i have.

But i guess my question is that the 18-55mm is the focal length right? and then the size of the filter has to do with the diameter of the lens right?

I guess I need a crash course on lens real fast. got an explanation? or a website?

Thanks,
 
Joined
Jul 30, 2006
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Yes, the 18-55 is the focal length. To know what filter size it needs, just look on the inside the the lens cap, it will be written right on it.
 
Joined
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ya, thats what i thought. thank you. can you explain the focal length a little more? obviously the distance is Millimeters but is the 18-55 just the movement within the lens itself? or does it have something to do with the sensor?
 
Joined
Jan 26, 2005
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San Jose, CA
ya, thats what i thought. thank you. can you explain the focal length a little more? obviously the distance is Millimeters but is the 18-55 just the movement within the lens itself? or does it have something to do with the sensor?

You're getting filter size and focal length confused. There is no relationship. Focal length is the distance from the front element of the lens to the sensor. Filter size is related to the diameter of the front element, which also determines the maximum aperture size.

This little tutorial might be of help.

http://www.paragon-press.com/lens/lenchart.htm
 
Joined
Apr 17, 2006
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Focal length is the distance from the front element of the lens to the sensor.

In real life it is not. Optics in lenses make it shorter than focal length for teles and longer for wide angles.
 

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