# What Does the 'mm' Mean?



## PhilGarber (Dec 21, 2008)

Hey all,

What does 'mm' mean in the sense of camera lenses (ie; 18-55mm kit lens)? It can't stand for millimeter.. can it?:blushing:

Thanks,

Phil,


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## SanctuS (Dec 21, 2008)

It does stand for millimeter...


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## rufus5150 (Dec 21, 2008)

It's the distance (in millimeters) from the front element of the lens to the camera's sensor.


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## ANDS! (Dec 21, 2008)

PhilGarber said:


> Hey all,
> 
> What does 'mm' mean in the sense of camera lenses (ie; 18-55mm kit lens)? It can't stand for millimeter.. can it?:blushing:
> 
> ...



Yes it can.  However it's not referring to what you think its referring to.  The MM is the ". . .distance between the front of the image sensor (or film in a film camera) and the optical center of the lens when the lens is focused at infinity," - or focal length to be brief.  

And I'm sure a majority of people new to photography assumed it meant how far can the lens see (as in yards) - which I suppose is true in an indirect sense.


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## jrizo1 (Dec 21, 2008)

if that is tha case how can you know hoe far the lent can see?


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## ANDS! (Dec 21, 2008)

jrizo1 said:


> if that is tha case how can you know hoe far the lent can see?



If I understand how this works, the MM is the measurement of how much magnification the lens can "see" at infinity (which should be the end of a lens focal length).  Thus a higher MM lens will have a higher magnification and will enable you to get in closer.  

Now how all this works with focus distance, I don't know.


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## Dao (Dec 22, 2008)

Focal length - Wikipedia, the free encyclopedia


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## PhilGarber (Dec 22, 2008)

edit


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## ksmattfish (Dec 22, 2008)

jrizo1 said:


> if that is tha case how can you know hoe far the lent can see?



As long as the light is not being blocked or distorted all lenses can see forever.  Point a lens at a star; it's many light years away, yet you can still see it.

Usually the longer the focal length the greater the magnification though.  Sometimes magnification is described like 1:4 or 1:1.  1:4 would mean that at the lens' max magnification the subject will be 1/4th real life size on the film or sensor.  1:1 would mean that the subject would be life size at the film or sensor.  Imagine laying a dime on your sensor (just imagine, don't really do that   ); with some cameras the dime would actually be larger than the sensor.  If the dime covers most of the sensor then when you make enlargements the dime will cover most of the print (with a lens capable of 1:1).


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