Sb-600 /800, D300s and light sensitivity..

[Foques]

Been shooting in a club for last couple of weeks, and one of the issues I am running into is trouble focusing.
I have to rely on autofocus as my eyes are not in the perfect shape, but when the subject is dark, it is a tad hard to pull off.

I realize that there is a focus assist light that is built into D300s, and sb-600, but I can't seem to get them to engage consistently.. since there are light sources in the club.

Question comes to mind - is there a way to force either flash or camera to run at a lower light sensitivity or somehow get the focus light to engage manually?

Thanks in advance.

[Qarik]

what lens are you shooting with? What AF mode as well? Note that in "S" servo mode the IR assist pattern from the flash doesn not work.

[Foques]

i'm shooting with 17-50 2.8, I was under impression that assist doesn't work in C mode, but in S it does? 0_o

[Qarik]

ahh..yes. I was thinking "S" as in servo mode but it is "C". You are correct. Is this a nikkor lens? (17-55mm?)

Some obvious stuff:

1) I assume you were shooting close to wide open?
2) I assume subject matter wasn't too far away?
3) you can see the IR assist beams from your flash?

[Foques]

no, I shot with 17-50.. it is a tamron glass
1) yes
2) yes, and no
3) sometimes.

[ziggy53]

ahh..yes. I was thinking "S" as in servo mode but it is "C". You are correct. Is this a nikkor lens? (17-55mm?)

Some obvious stuff:

1) I assume you were shooting close to wide open?
2) I assume subject matter wasn't too far away?
3) you can see the IR assist beams from your flash?

The AF assist beam is a visible deep red. An IR beam will not work for AF assist because InfraRed would focus at a different point and visible light images would be out-of-focus if using an IR beam.

Many older lenses actually have a different focus mark for InfraRed focus (the "R" designation in this case):

http://ziggy53.smugmug.com/photos/856238624_QPj6f-O.jpg

[Foques]

yeah, Ziggy is right (as always)..

SB 600 is putting out the red grid for focusing..

[Qarik]

Yup I am being sloppy with my wording. red..not infrared.

So if understand you correctly..stray lights at the club are causing the AF assist beams to deactivate causing focus issues?

I just did some experiments with D700 and SB900. Focus assist light on the body only activates when no flash is detected (or turned off). The AF assist on the flash only seems to activate when there is not enough light/contrast in the focal points through the lens.

I don't see any camera or flash settings to have the assist beams "always on" so you may be out of luck from that POV. You can try 2 things though..shoot with a lens hood on if you not doing so. This may help keep the odd strobe stray light out. Also as a work around..if you stick you hand directly in front of the lens and depress the shutter button 1/2 way..the AF assist beam always turns on because it thinks it is dark. If you then remove your hand, then assist beam stays on (even if you are pointing at a bright light) long enough to achieve focus. Then it shuts off and shutter actuates normally. This is potential workaround.

Note the tamron is not the fastest at focusing and that might effect this workaround I presented. I was using nikkor 24-70mm fyi.

[Bigalsmugmug]

The last time I used the Camera and flash I did Head Shots with off the camera C mode. I reset the SB-600 flash back to TTL flash and put the Nikon D90 back to the original mode. Now I don't have the red grid no matter how dark it is . Did I reset a Flash Default for the red grid not to appear? I will review your post and try to look to see if the d90 menus look the same. Does anyone know the best way to see if I screwed up something or if the Flash focus grid is NG? Thanks Al, this is my first post dpedit@hotmail.com (dpedit@hotmail.com)

[ziggy53]

The last time I used the Camera and flash I did Head Shots with off the camera C mode. I reset the SB-600 flash back to TTL flash and put the Nikon D90 back to the original mode. Now I don't have the red grid no matter how dark it is . Did I reset a Flash Default for the red grid not to appear? I will review your post and try to look to see if the d90 menus look the same. Does anyone know the best way to see if I screwed up something or if the Flash focus grid is NG? Thanks Al, this is my first post dpedit@hotmail.com (dpedit@hotmail.com)

I don't believe that a flash will emit the AF assist light in AF-C (continuous shooting) mode. Switch back to AF-S (single-shot) mode and see if the light works there.

[Foques]

^^
absolutely correct. as always.

[insanefred]

The AF-assist, only works at certain focus points (some deactive at some focal lengths) in AF-S. You'll have to look in your manuals on which ones.
The SB-900, can use a wider range of focus points and focal lengths. Because it was built for the Multi-cam3500FX/DX. The Sb-600 and 800 are a bit less versatile.
I don't know which page on the D300 manual. D700 manual: 382

[Bigalsmugmug]

:barbThanks to all! Your absolutely correct. I had the camera set to AF-C for Continuous focusing (when I was shooting a pro wakeboarding practice session) and never thought about putting it back to AF-A or AF-S. Man what a relief. I was starting to track SB-600 and SB-900 on Ebay... Now I can put that money into glass. Thanks again and a lesson was learned. Hope to help others some day. I am a newbie and see such a value in this site! Feel free to check out any of my work at bigal.smugmug.com Thanks again to all.

[jasonstone]

to be honest i've just done a heap of indoor lower light photos of cars for sale with my D7K and the Tamron 17-50 f2.8 and found that it hunted quite a bit for focus sometimes - never noticed it as badly as I did last week

Bit annoying really but given the price disparity and the still very good quality of the Tamron I can live wtih it....