I have a question about using a flash unit with my 35mm camera. It's a Nikormat EL, with a synch speed of 125 seconds. The flash unit is a Vivitar 285.

The Vivitar has a dial wherein I can input up to ASA 400 speed film.

I want to take some black and white photos of a person cooking a meal inside their kitchen. There won't be any really quick motions from the subject just normal moving around with normal ambient light.

Questions.

1. With 400 speed film at 125 will the flash freeze the movement of my subject?
2. If I used faster film e.g. 1600 should I turn my flash intensity down to or power?
3. There is a removable insert over the bulb that softens the flash effect, would that be good to use with the 1600 speed film or with all or any other speed film.

I want the subject to appear to be lighted naturally rather than harshly as some flash pictures appear to be.

Any help you can give would be helpful. The shoot is going to take place before I can do any experimenting before hand.