front and back focusing


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rodel

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Sep 22, 2006
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#1
what do front and back foucusing problem means?
 

zac08

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Feb 21, 2005
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#2
what do front and back foucusing problem means?
Front focusing, the camera and lens focuses in front of the spot where you wish to focus on.

Back focusing, the camera and lens focuses at the back of the spot where you wish to focus on.

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1

let's use this scale as an example... if you focused on number 5 with a large aperture (to ensure a small DOF) and when you take the picture, the number 6 onwards is sharp instead of 5, this is called back-focusing.

If you take the photo with 5 as focal point, and the sharp area is 4 or smaller, then it's called front-focusing...
 

Denosha

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Dec 25, 2003
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#3
Just to add on, you'd only really call it a front or back focusing problem if it consistently happens to somewhat the same degree when using the same body + lens combo. Ie. It will front focus most of the times.

Also, both the lens and body can be calibrated so it's also important to find out if it's the body that is causing the problem (most of your lenses will have the same focusing problem when used on this body) or the lens (other lenses focus fine when used on the same body).
 

lastboltnut

Senior Member
Mar 23, 2006
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Where the wind blows...
#4
Note that #9 is farther to you than #1.

Front focusing, the camera and lens focuses in front of the spot where you wish to focus on.

Back focusing, the camera and lens focuses at the back of the spot where you wish to focus on.

9
8
7
6
5
4
3
2
1

let's use this scale as an example... if you focused on number 5 with a large aperture (to ensure a small DOF) and when you take the picture, the number 6 onwards is sharp instead of 5, this is called back-focusing.

If you take the photo with 5 as focal point, and the sharp area is 4 or smaller, then it's called front-focusing...
 

cantaresg

New Member
Feb 23, 2007
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#6
If 1 and 9 are the same distance from you, then all the numbers will be more or less focused. Unless the lens is soft at the edges. Only when the different numbers are at different distances, with 1 nearest to you, and 9 furthest, will the FF or BF be of any issue.
 

rodel

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Sep 22, 2006
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#7
thank you to all responses.
 

zac08

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Feb 21, 2005
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#8
If 1 and 9 are the same distance from you, then all the numbers will be more or less focused. Unless the lens is soft at the edges. Only when the different numbers are at different distances, with 1 nearest to you, and 9 furthest, will the FF or BF be of any issue.
Eh... I mentioned large aperture... this reduces the DOF to a small amount... if you have a f2.8 lens, set it to f2.8
 

lastboltnut

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Mar 23, 2006
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#9
O, I have to be clearer...I meant if you arrange #1-#9, the #1 is nearer to the cam and #9 is away from the cam....because the way you present #1-#9 is in vertical (as view on monitor)manner, so all on the same focus plane on the monitor.....just worried that TS may be confused....nothing much actually. Sorry if I caused confusion instead of clarification.:embrass:


the point being?? :dunno:
 

lastboltnut

Senior Member
Mar 23, 2006
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#10
Thanks cantaresg for helping me to explain my intention.:)

If 1 and 9 are the same distance from you, then all the numbers will be more or less focused. Unless the lens is soft at the edges. Only when the different numbers are at different distances, with 1 nearest to you, and 9 furthest, will the FF or BF be of any issue.
 

Denosha

Senior Member
Dec 25, 2003
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#11
[URL="http://www.focustestchart.com/focus21.pdf]http://www.focustestchart.com/focus21.pdf[/URL]

To avoid confusion, just follow the above link. Has all the documentation on how to do the test properly as well as a printable focusing test chart. And no, it doesn't just work on D70s or Nikon cameras although some of the more camera-specific info like the focusing pts might be slightly different.

Happy testing.
 

zac08

Senior Member
Feb 21, 2005
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#12
O, I have to be clearer...I meant if you arrange #1-#9, the #1 is nearer to the cam and #9 is away from the cam....because the way you present #1-#9 is in vertical (as view on monitor)manner, so all on the same focus plane on the monitor.....just worried that TS may be confused....nothing much actually. Sorry if I caused confusion instead of clarification.:embrass:
I see... thanks for the clarification...
 

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