Is this sigma 17-70 ok?


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lizzy

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Dec 26, 2004
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#1
is below the correct way to check for FF and BF issue? is the below sigma 17-70 ok?
if this is ok, does it means the focussing will also be ok for taking group photo using wide angle?

17mm, 100% crop, focus on the dot


70mm, 100% crop, focus on the dot
 

#2
Ideally, FF/BF should be checked on a testing chart with metering ...

This lens is a good buy and I doubt FF/BF is less of an issue given its focal length range being quite "normal".

Otherwise it is quite an performer (a bit large in size personally).
 

lizzy

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Dec 26, 2004
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#3
Ideally, FF/BF should be checked on a testing chart with metering ...

This lens is a good buy and I doubt FF/BF is less of an issue given its focal length range being quite "normal".

Otherwise it is quite an performer (a bit large in size personally).
thanks for the tip... i tested using the below and it looks fine :)
http://focustestchart.com/chart.html
 

fengwei

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Aug 25, 2004
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#4
is below the correct way to check for FF and BF issue? is the below sigma 17-70 ok?
if this is ok, does it means the focussing will also be ok for taking group photo using wide angle?
Although it might not be the best way to test FF or BF with a chart like what you used, I still think the lens seems more than okay :)

Now go out and take some photos. If you are satisfied w/ what you get in the real world, then the lens is a good one :D
 

lizzy

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Dec 26, 2004
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#5
Although it might not be the best way to test FF or BF with a chart like what you used, I still think the lens seems more than okay :)

Now go out and take some photos. If you are satisfied w/ what you get in the real world, then the lens is a good one :D
you are right! but testing is faster to determine if the lens is ok before the 1 to 1 exchange period is over.. :bsmilie:
 

chegr

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Jan 31, 2007
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#6
I'd say it's off by about 0.5mm.. Time for exchange.. LOL
 

Vulpix0r

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Oct 2, 2002
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#7
The only way is to keep shooting photos, because when you start nitpicking on your photos you will know whether there is any FF/BF issues.
 

airconvent

Senior Member
Apr 12, 2005
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#8
Hi
This may not be related but I also did a test using a 50f1.4 with the following results some time back. Any comments on it?
Cheers :)






 

lizzy

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Dec 26, 2004
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#9
looks ok to me, the focussing point is in focus...

Hi
This may not be related but I also did a test using a 50f1.4 with the following results some time back. Any comments on it?
Cheers :)






 

airconvent

Senior Member
Apr 12, 2005
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#10
Thanks lizzy
that's what I can see also but there is a variation between forward and backward focus.
I am wondering if both sides of the focus should be symmetrical...:think:
 

Vulpix0r

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Oct 2, 2002
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#11
Aiyah don't worry man, to be honest if there is any really big FF/BF issues you will only see it when you take proper actual photos.
 

creampuff

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Jul 11, 2006
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#12
Thanks lizzy
that's what I can see also but there is a variation between forward and backward focus.
I am wondering if both sides of the focus should be symmetrical...:think:
How can it be symmetrical? If you understand depth of field you will know that it always extends beyond more than forward of the point of focus.
 

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