In the Dark

I posted this question on another site and did not get a useable answer.

I will be shooting a lot of indoor low light situations in the near future. I use a Nikon SB-28 flash mounted on a flash bracket with my Nikon F100. I set the F100 to P = Program mode and depend on the flash's TTL setting and all the electronics to take care of the rest. Sometimes it just won't fire if the light is too low.

The respondent on the other site said that perhaps the flash was not ready (we can rule that out) or that the camera may not fire because it is in "focus priority mode." He goes on to say that the problem may be autofocus because proper focus cannot be achieved in low light situations and then the camera won't fire.

All this is well and good in terms of explaining why the camera may not be firing, but it doesn't do much for explaining my options. If I go to a "manual" setting with the camera and set the aperture to "wide open," what do I do with the shutter speed? How does TTL work under this scenario?

I've got that camera and flash so maybe I can help... The first thing I thought of in low light and "P" mode was why not "M"? If it's something like a wedding reception, I'd probably use f5.6 and 1/40 or 1/50. The shutter speed doesn't have anything to do with flash exposure, but slower speeds will help the background (ambient light) from going too dark. Downside is that you need relatively stationary subjects to do this. One nice thing about the F100 is that you can lock your aperture and/or shutter speed so they don't get bumped.

I'm assuming that you mean that the camera won't fire, not the flash - is that correct? What lens are you using? In really low light nothing beats a fast prime - a 50 f1.4 will focus in low light faster than a variable aperture zoom any day. The viewfinder gets more light because it's a faster lens, so it's less likely to "hunt" for focus. The F100 (any Nikon) won't fire in "S" mode if the lens isn't focused.

Try this and see if it works - are you using an SC-17 cord to connect the flash to the camera?

Answers to your questions:

I am using a f/3.5-4.5 28-105. Saving up for the f/1.4 85mm prime so that I can at last have a fast lens. Won't be anytime soon, however.

I am indeed using the SC-17 flash cord.

Thanks for the information.

I've had problems with that lens too in very low light - like the dance floor of a wedding reception. The 50 or 85 f1.4 will be a world of difference here, even using at f5.6 or so because it's letting that much more light in. Those two lenses are at least 2-1/2 stops faster than the 28-105 (at the 28mm end).