Paul C. Buff, Inc. Technical Forum

I used the 22" high output beauty dish yesterday with a diffusion cover and had problems with the light output. Despite powering down my alienbee 800 to the lowest setting the beauty dish still produced overexposed images. My camera was set on manual with the highest shutter speed (250), ISO 200 and tried it on ISO 100, plus set my camera to -3.0 compensation. This was an indoor shoot. Is this beauty dish so high output that it may generally require adequate diffusion for under normal shooting situations? :roll:

No, it's not that powerful . . . must have something set wrong, 22HOBD with diffusion sock should produce around f11 max at 10' ISO 100 with B800 on full 320WS. that's f11 @5' at 1/4 power and f5.6 @ 1/16 power and f4 @1/32 power. Without the sock the output is way higher . . . 2-3 f stops. If you're talking about the light blocker rather than the sock the output at close range will be way high . . . the light blocker doesn't drop output much.

Kyra,

If you are using -3 on the exposure compensation then that means you are using one of the automatic modes. (Program, Aperture Priority or Shutter Priority) When using these modes you are using the camera's meter to measure the light needed for proper exposure. The camera has no way of knowing you are using an external flash/strobe. The camera is measuring the light from the room or your modeling light coming through the lens which does not include the light produced by your strobe unit. As soon as your strobe fires it is adding many stops more light to the room than was there while you were metering. That is probably why all your pictures are coming out over exposed.

Set your light to its lowest power. Make sure your camera is set to manual mode. Choose 1/125th for your shutter speed, 100 ISO and f/5.6 for your Aperture. Keep in mind that the shutter speed only affects ambient light coming through the lens. You use aperture to control flash/strobe light. Check your shot. If it is too bright change the aperture to a higher number like f/8. If it is too dark change to a lower number like f/4. Most cameras can adjust Aperture in 1/3 increments but I am using whole f stops to keep it simple. Keep adjusting your aperture until you get an exposure you are happy with. Keep in mind your depth of field though. If doing a portrait of someone you might not want to go below f/4 or 5.6. If your image is too dark at these f stops then raise the power on your light instead of opening your Aperture wider. Each marked section on the light is one stop. ie 1/32 to 1/16 raises it one stop. Going up to 1/8 from 1/32 is 2 stops more. You will need to experiment to get the results you want.

I highly recommend buying a light meter for use with a strobe unit. It will save you time and a lot of trial and error. I hope this helps.

Good Luck!

Thomas L

I agree with Thomas and Paul. However, you can still be in manual mode, but some Nikons have an auto ISO, which you may have been set to. I know you specified ISO 200, but on some models you can dial in an ISO, but sometimes that is just setting a minimum or maximum limit. The auto ISO will have the same effect as what Thomas described.

Incidentally, on many cameras, in full manual everything, you can set -3 exposure compensation, it just will not do anything (or may adjust only your speedlite if you are using one).

thank you all for your help. I'll experiment today.