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Flash/Focus Question
  
 
jimlp
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p.1 #1 · Flash/Focus Question


Hi guys and gals. When shooting with a flash will the focus assist light on the flash make the camera focus better/more accurately? As an example say you were shooting an object during the day and had inconsistent focus issues, if you had to back and shoot the same object at night with flash would the focus assist light make the focus more consistent or would the focus issue remain the same? My friend just got a new lens and he is having a front focus issue, he wanted to do some more shots this evening with flash but we were not sure if it would give us false returns due to the focus assist on the flash possibly being another variable. I guess what I want to know is if the way the camera focuses differently with a flash on it or if the system works the same way. Thanks for any replies I may receive.


Aug 12, 2013 at 03:27 AM
BrianO
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p.1 #2 · Flash/Focus Question


If the light level is so low that the AF system has trouble locking on, then the AF Assist can help; but if the lens is out of calibration, causing out-of-focus images in good light, then the AF Assist won't help.

What camera does your friend have? If it has AF Micro Adjust then doing a calibration of the new lens would be in order.



Aug 12, 2013 at 05:23 AM
jimlp
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p.1 #3 · Flash/Focus Question


BrianO wrote:
If the light level is so low that the AF system has trouble locking on, then the AF Assist can help; but if the lens is out of calibration, causing out-of-focus images in good light, then the AF Assist won't help.

What camera does your friend have? If it has AF Micro Adjust then doing a calibration of the new lens would be in order.


Thanks for the response. We figured there would have to be some MA applied, with a zoom do you just pick a focal length in the middle and use that? Do you do MA while the lens is wide open?



Aug 12, 2013 at 11:01 AM
BrianO
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p.1 #4 · Flash/Focus Question


jimlp wrote:
...[When doing AFMA] with a zoom do you just pick a focal length in the middle and use that? Do you do MA while the lens is wide open?


I don't know what the experts do, but on my 70-200L I did several tests, each at a different zoom setting, and then averaged the numbers. It worked reasonably well.

Yes, the lens should be wide open so there is the least depth of field. That will show when it is or isn't in focus more easily than if the lens is stopped down.



Aug 12, 2013 at 04:37 PM





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