problem with focusing in the dark

[kami]

I know usually it's harder for the camera to focus in the dark but can someone explain this.

My D300s seems to have much more difficulty focusing in the dark with my SB600 on-camera flash set to TTL. And usually I get results like the one below even with some ambient light coming from the garage.

But when I have my flash off-camera using the Radio Poppers 90% of the time I have better focused photos like the one below which had no ambient light whatsoever.

I would think that using the red grid lights from the SB600 would produce a more consistent focusing plane for the camera. But it seems the camera focuses better without the SB600 sitting on top of it. I only notice this problem when it's really dark.

Is there something I'm missing?

 

[kami]

When focusing with the SB600 on-camera, it takes about 1-3 seconds before you hear the focus "beep" sound. But it still comes out blurry. About 50% of my photos taken with on-camera flash look like the 1st photo. On the other hand about 90% of the photos taken with the flash off camera look better. And focusing takes only a mere split second even in complete darkness. This confuses me.

FYI, the 2nd picture was taken at a further distance than the 1st picture and it's even cropped.

 

[Big Mike]

:scratch: I don't know...that's a mystery.

 

[kami]

I know, this one baffles me. Both photos were taken on the same night. Same lens, Same flash, except that the off-camera flash photos turn out better results.

 

[Big Mike]

Shutter speed, aperture?

 

[kami]

Oh, never thought of that. I had it on Aperture priority with on camera flash. While off-camera I use only Manual. I'll try manual with on-camera flash... hmmm... thanks!

 

[memento]

maybe you're in the wrong auto focus mode? i use Canon so not sure if this applies to Nikon.
i know my auto focus wont work when in AI Servo. i have to use one-shot.

 

[Big Mike]

Ah....that's probably it.

When in either priority mode, the camera will try to expose for the ambient light. So you likely had a very long shutter speed, which will cause blur if there is enough ambient light. If there was less ambient light, the long shutter speed doesn't matter and the flash freezes the movement.

I thought that might have been it, right at the start...but your example does sort of look more out of focus and not just motioned blurred...but maybe it's the combination of flash and motion blur that was causing me to think that.

FYI, I almost always shoot in manual when I'm suing on-camera flash (and of course when using off-camera flash). Even with E-TTL, the camera is in manual so that I can have full control of the shutter speed etc.

 

[Big Mike]

i know my auto focus wont work when in AI Servo. i have to use one-shot.

The Af assist light on an accessory flash only works in One Shot, not in AI servo.

 

[2WheelPhoto]

Perhaps a focus assist is working on the SB600 and when its of cam maybe closer to the subject it provides better focus light?

I noticed when i went to a Nikkor 24-70 lens from a kit lens focusing in lower light became MUCH easier.

Also i scrapped TTL and sold my flashes, I was always using them manual lately anyway with remote triggers and went with Vivitar. In total darkness now I light my subjects with a LED flashlight now and that provides awesome focus.

 

[Big Mike]

I noticed when i went to a Nikkor 24-70 lens from a kit lens focusing in lower light became MUCH easier.

Many cameras have focus points that become more sensitive, or points that only become active at all....when used with F2.8 lenses (or larger).

 

[cgipson1]

Like Mike said... shoot in manual (ISO 100 to 400 (depends on distance to subject / how powerful your flash is), F2.8 to F8 (for DOF) and vary your shutter sync speed depending on how you want to balance any ambient light. Make that flash WORK for a living! lol! )but with the flash in TTL. It will put out what ever light is needed to meet the other settings (assuming you are close enough and / or the flash is powerful enough)! This is a great way to shoot for low light event photos... works well even when you can barely see the subject.

Nikon's rock at this! Don't know if your radio popper will handle TTL like my PW's do... but usually dead on, especially if I use single point spot metering and AF.

Example (both totally unedited.. just examples of flash use described above!)

Highest ISO my D7000 will do.. still dark

Flash shot in same room in the dark.... it was literally too dark to see! lol!

 

[2WheelPhoto]

I'm not "anti-TTL" but seems I always set compensation for TTL when bouncing any distance or shooting into umbrellas, I found it easier to use the flashes in their manual.

 

[2WheelPhoto]

I noticed when i went to a Nikkor 24-70 lens from a kit lens focusing in lower light became MUCH easier.

Many cameras have focus points that become more sensitive, or points that only become active at all....when used with F2.8 lenses (or larger).

Thanks i didn't realize that

 

[cgipson1]

I'm not "anti-TTL" but seems I always set compensation for TTL when bouncing any distance or shooting into umbrellas, I found it easier to use the flashes in their manual.

I agree with that for static subjects .. but for fast moving subjects, (kids, flying dragonflies, etc) this rocks!