# Distance scale window - how to use it?

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#### cks2k2

##### New Member
Noob here, I just acquired a better lens for my 450D which comes with the distance scale window. How is it used? I googled up some threads where old timers from the manual focus era will state that it's pretty useless on modern AF systems while others will keep mentioning about hyperfocal distances etc.

Can someone explain the function of the distance scale in simple enough terms? Much thanks in advance.

#### zac08

##### Senior Member
Noob here, I just acquired a better lens for my 450D which comes with the distance scale window. How is it used? I googled up some threads where old timers from the manual focus era will state that it's pretty useless on modern AF systems while others will keep mentioning about hyperfocal distances etc.

Can someone explain the function of the distance scale in simple enough terms? Much thanks in advance.
Basically, it shows you the distance between the subject and your image plane. If you're using AF, then it gives you a guage of how far the subject is to you.

If you MF, then setting to the apertures on the scale will show you in between which distances would give you correct DOF sharpness...

I.e. If your scale shows you 16 marks on both sides, and the markings of infinity corresponds to the left 16 mark and the marking of 2 feet corresponds on the right 16 mark, then the distance of 2 feet to infinity would be sharp at this aperture and distance

#### cks2k2

##### New Member
My distance scale doesn't have any aperture markings, only ft and m and the infinity symbol (0.24, 0.4, 1, infinity in meters).
Let's say the '|' marking is between 0.24 and 0.4 m, does that mean anything btw 0.24 and 0.4 m away from my focal point is in focus? And if it's between 1 m and infinity that means anything btw 1 m to infinity is in focus?

#### zac08

##### Senior Member

Hyperfocal Focusing

#### cks2k2

##### New Member
Thanks for the link - I think I'm getting the idea.

#### denniskee

##### Senior Member
most modern AF lenses dont have DOF markings on the lens (but only meant for FF cameras), only focus distant and the offset u need to manually adjust when doing IR photography.

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#### calebk

##### Senior Member
If the distance 0.4m falls exactly at | marking, then whatever is at 0.4m is in focus. Depending on depth of field, things nearer and farther than 0.4m may also be in focus.

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