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-   -   A/F Assist Beam (https://forums.steves-digicams.com/canon/180972-f-assist-beam.html)

ogrob Dec 5, 2010 7:46 AM

A/F Assist Beam
 
What exactly is the A/F assist? Does it matter if I have it covered when shooting outdoors in the daylight, not using the flash?:)

frank-in-toronto Dec 5, 2010 9:12 AM

It "assists" the auto-focus mechanism in the camera in obtaining focus. In low light, it provides the light. i turn mine off all the time (however it uses the built in flash for af assist. sony a550) as it is very annoying to a nearby subject. The sx20is you mention in another post uses a green led. this is probably less intrusive and your af system may need more help than a dslr.

you could try a test to see if your camera is benefiting or not. take a few shots indoors at varying distances and light levels. then take the same shots with af assist off. if your camera focuses just as quickly and correctly, then you have the choice of off or on. some more detailed info is available at
http://www.cambridgeincolour.com/tut...-autofocus.htm

this reminds me, i need to check if my external flash can turn off the af assist or if i need it in low-light situations.

ogrob Dec 5, 2010 1:15 PM

Thanks Frank......
 
Thanks Frank.....

This is all about me finding a way to keep my camera out of the extreme cold.:rolleyes: I should have given more details in my post (sx20is). Thanks for digging that point out.

Quote:

Originally Posted by frank-in-toronto (Post 1174753)
........your af system may need more help than a dslr.

By this you mean my sx20is may not react the same as your Sony?

Quote:

Originally Posted by frank-in-toronto (Post 1174753)
....you could try a test to see if your camera is benefiting or not. take a few shots indoors at varying distances and light levels. then take the same shots with af assist off.

I did this (outdoors) the same shot three times (a number of shots, three times actually). Not sure if you'll be able to see the difference in these pictures.

#1...with A/F blocked (inside a fleece bag).
http://lh3.ggpht.com/_PudDMl_3h9I/TP...0/IMG_0003.JPG

#2....with the A/F turned off

http://lh4.ggpht.com/_PudDMl_3h9I/TP...0/IMG_0008.JPG

#3....A/F turned on

http://lh5.ggpht.com/_PudDMl_3h9I/TP...0/IMG_0013.JPG

Quote:

Originally Posted by frank-in-toronto (Post 1174753)
.....some more detailed info is available at
http://www.cambridgeincolour.com/tut...-autofocus.htm

I'll check this out.

Thanks for your time,
Rob

frank-in-toronto Dec 6, 2010 6:43 AM

Quote:

Originally Posted by ogrob (Post 1174826)
...By this you mean my sx20is may not react the same as your Sony?...

yes. mostly it's just the p&s vs dslr difference. not specific to your camera choice.

your samples look fine. as expected. the af assist really is there for when the light levels are too low for the in-camera af system to see sufficient contrast to focus. in outdoor light, it won't matter.

i do leave af assist turned on for my p&s. a red or green led isn't going to be bothersome. so, my advice, forget it. if you accidently cover the af light and you find indoor focus isn't quick enough, uncover it. otherwise, let it go.


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