Is this a sign of "back focus" lens?


kenny888

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Oct 24, 2003
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#1
hi all,

i've noticed something which is bothering me, i'm not sure if my lens has "back focus". i've posted some pics. could u guys help me to check pls?

in theory, DOF covers a zone of 1/3 in front of the focus point and 2/3 behind the focus point. so with this in mind, i began to shoot some figurines that i have at home.

here are pics that i shot with the first lens at different focus point.

focus on center


focus on the right


here are pics that i shot with another lens. it seems that this lens has back focus is it? or am i wrong? i'm very puzzled.

focus on the right


focus on center



pls advise. is my second lens having some problems? tks!
 

daredevil123

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Staff member
Oct 25, 2005
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lil red dot
#3
use a focus chart for more accurate test
Download the focus test chart here: http://focustestchart.com/focus21.pdf

Follow the instructions.

Do note:

1. Use a tripod. No handholding.
2, Be mindful of the MFD (minimum focusing distance) of each lens and make sure the chart is beyond MFD.

BTW... I have Del Piero.. And he is often my subject for lens tests too. ;)
 

Last edited:

kenny888

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#4
ooo i have that chart too. but to put it at 45 degrees exactly might be difficult. i'll try it out tmr. tks. coz as u can see in the pics, it seems that it has back focus, thats worrying me.

haha oo u got that figurine too? LOL! i havent touch them for a loooong time, been in my drawer for many years. finally took it out to test my focusing lolx.

wow this is the first time only one reply after one full day LOL!
 

daredevil123

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Oct 25, 2005
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lil red dot
#5
ooo i have that chart too. but to put it at 45 degrees exactly might be difficult. i'll try it out tmr. tks. coz as u can see in the pics, it seems that it has back focus, thats worrying me.

haha oo u got that figurine too? LOL! i havent touch them for a loooong time, been in my drawer for many years. finally took it out to test my focusing lolx.

wow this is the first time only one reply after one full day LOL!
Don't have to be exactly 45deg la. Agar Agar.
 

Reportage

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Nov 24, 2008
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#6
if in doubt and have time, send the lens to the service center for testing.
 

zk-diq

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Jan 1, 2009
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#7
You may use a lens test chart to do your own testing and know your equipment better.
ie resolution/coma/colour fridge
 

kenny888

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#9
okiee i'll update u all when i'm done with my testing on the focus chart.
 

kenny888

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Oct 24, 2003
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#11
the last second pic is actually FOCUS ON THE MIDDLE. but end up the left object is pretty clear too. i type wrongly.

past two days wasnt really at home. outside with some events. finally have some free time lolx. okie i'll update all tmr.
 

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