Shutter speed in Aperture mode with DS 125

Hi,

I received my DS 125 yesterday, and I made some tests at home with my canon G2 (Ikelite housing).

1st test : strobe switched on TTL mode / Aperture priority mode f2.0 , f5.6, f8 : the camera selected a 1/60 shutter speed for all of them. Why? I thought that the shutter speed would have been higher with a wider aperture...

2d test : strobe switched on full -> did not work (the strobe cannot display 2 full power flashes in manual mode)

3d test: strobe switched on 1/2-> did not work (the strobe cannot display 2 1/2 power flashes in manual mode)

4th test : strobe switched on 1/4 -> overexposed photo, shutter speed 1/60 !!

4th test : strobe switched on 1/8 -> overexposed photo, shutter speed 1/60 as well !!

Why does my camera choose a 1/60 shutter speed all the time in aperture priority mode, whatever the set up of the strobe?

Thanks.

Just to be clear Ben,

You don't have an external flash or ANYTHING hooked to the hotshoe on your G2, right?

You are using Ike's Digital TTL Slave sensor?

Cheers

James

As for the question of why 1/60th. When the camera meter is trying to expose for the background and it is too dark for a reasonable shutter speed it defaults to 1/60th so that you don't get obvious camera movement. If you have enough ambient light the shutter speed will change as the aperture changes.

Some cameras (not the G2) let you override this default so that the meter will expose for the background properly even if it is a 1 sec exposure. This has typically been called rear curtain sync in the slr world but in the digital prosumer world I think they are calling it slow sync.

If you are going to see a difference in shutter speed when there isn't enough ambient light it will be when you zoom in. In that case the shutter speed will probably go to 125th since that will prevent camera shake at that lens position.

Shutter speed makes very little difference in the exposure of the flash. This is because the flash duration is much less than the duration that the shutter is open. A typical flash duration is around 1/10,000th. To see a difference in flash exposure (with manual flash settings) change the aperture.

Thanks a lot, that's very clear!

In TLL mode, flash exposure is automatically adjusted... the foreground exposure should be approximately the same for different aperture, right? Only the background exposure will change for different aperture (and the DOF...). Am I right?

You are correct.

TTL Flash = foreground exposure adjusted automatically, background exposure adjusted via aperture and/or shutter speed.

Manual Flash = foreground exposure adjusted via power setting and/or distance to subject and/ or aperature, background exposure adjusted via aperture and/or shutter speed.

James,

--------------------------------------------------------------------

Just to be clear Ben,

You don't have an external flash or ANYTHING hooked to the hotshoe on your G2, right?

You are using Ike's Digital TTL Slave sensor?

----------------------------------------------------------------------

No, I don't have any external flash... the camera is in the housing (with the diffuser masking the internal flash)

Yes, I am using Ike's TTL Salve sensor

1st test : strobe switched on TTL mode / Aperture priority mode f2.0 , f5.6, f8 : the camera selected a 1/60 shutter speed for all of them. Why? I thought that the shutter speed would have been higher with a wider aperture...

I think this has been answered sufficiently but here's another tidbit more. On most cameras, this only happens in "P" mode and in aperture priority mode. In "M" mode, you select anything you want (naturally). I've recently used manual mode for all my underwater shots. After you're familiar with it, it just seems simpler than having a camera try to outsmart you.

2d test : strobe switched on full -> did not work (the strobe cannot display 2 full power flashes in manual mode)

This is correct.

3d test: strobe switched on 1/2-> did not work (the strobe cannot display 2 1/2 power flashes in manual mode)

Not correct. I use 1/2 power all the time with this strobe and a camera that requires two flashes. Don't know what happened here.

4th test : strobe switched on 1/4 -> overexposed photo, shutter speed 1/60 !!

This will depend on your aperture and strobe-to-subject distance. Shutter speed has nothing to do with strobe lighting.

4th test : strobe switched on 1/8 -> overexposed photo, shutter speed 1/60 as well !!

See above.

Why does my camera choose a 1/60 shutter speed all the time in aperture priority mode, whatever the set up of the strobe?

As others have said, once the ambiant light gets so low, the camera assumes a minumum shutter speed to prevent blurr from movement. With low ambiant light, the only light will be fro the strobe and that will be the same regardless of shutter speed.

I am almost positive that the G2 has a slow sync option? I am not at home to verify this, but I will later and report back.

Anyone else have a g2?