Originally posted by ziploc
Hi ckiang,
I've got a question: so how to determine what is the correct sync speed for the camera?
What I was trying to do was to use my SB25 in auto mode with my G2. I set the SB25 to auto mode and ISO50 f/4 as on the G2, and tried shutter speed 1/60, 1/125 and 1/250. All were overexposed except 1/250 which was acceptable, but the exposure seems better if I set ISO100 on the flash (with G2 still at ISO50 1/250).
And then another problem is zooming. I am not too sure what to set on my flash when zooming in on the G2. The exposure looks different then in wide angle. If I zoom on the flash, the pic is severely overexposed. If I don't zoom, the result is better but still look overexposed.
Any idea? Thanks.
The G1/G2 has very weird flash implementation, especially if you use Av. Other cameras seem to work fine.
Flash sync speed on focal-plane shutter cameras like SLRs and interchangeable lens rangefinders are between 1/60 to 1/250. On in-lens shutters and electronic shutters like DCs, it can actually be anything. Shutter speed does not affect flash exposure. The manual should state the recommended flash sync speed.
That said, bear in mind that if your ambient light reading requires a shutter speed of say, 1/125 and you are trying to use 1/60, you will get overexposure, flash or not. In that case, lower your aperture.
For the zoom head, either leave it at the widest or match it with your G2's zoom (troublesome). If you are using bounce, then it's an non-issue. If you zoom-in the flash head, the beam of light will be concentrated on your subject, which might cause overexposure.
One more thing, the G2's ISO 50 might not really be ISO 50, but maybe 80. This might cause some discrepancies as well. Which might well explain why you get better results at ISO 100 on the flash.
Rule of thumb for flash exposure:
1. Only aperture controls how much flash exposure is given.
2. Shutter speed has no effect on the flash exposure.
3. Aperture also controls the ambient exposure.
4. Shutter controls ONLY the ambient exposure.
Regards
CK