film has different tonal curve than the d100's but a variation from f8 to f22 is quite unusual, to say the least. it would be interesting to know your settings and maybe see the pics. my D100 is pretty much dead on with my Minolta IV flashmeeter. you should not judge the exposure by the camera LCD and your computer monitor should be calibrated.
>My settings are as follows. > >I used the built in speed light to trigger 2 slaved units ( >the guide number of the speedlight is so low compared to our >ProPhoto units that it doesn't show up in the shot) >
This is where your problem lies. The pop-up flash in TTL mode (like the other Speedlights), emits a pre-flash before the actual exposure is made. Based on the reading from the light reflected from the subject from this pre-flash, the actual flash exposure is calculated. THEN only does the main flash burst occur when the mirror is up and the shutter is open.
So what is happening is that your studio slaves are tripping on the preflash, and not on the main flash.
You can see the preflash when you set your camera to rear-sync curtain, and use a slow shutter speed like 1 sec. You will see two flash bursts .. the first one will be softer .. that is the preflash. Test your studio set-up like this .. with the rear-curtain sync, and you will see that the studio lights are tripping on the initial flash burst.
The way to go around this would be to use a larger Speedlight and set the flashgun to give around 1/16th manual flash output. There is no preflash with manual flash. This is not possible on the SB50-DX hoever, since this flashgun only has full manual power.
Saxofonix could be right the pre-flash is automatic with the internal flash and would trigger the strobes twice, hence the variation in light. try disabling the D-TTL feature in the camera menu. that should take care of the pre-flash.
It seems that this is the problem. I set the flash mode to manual in the custom settings and eveything works fine now.
I was sure that setting the exposure mode to manual would override any of the auto functions.
I taped a small mirror in front of the speedlight so as not to affect the shot at all.
I have read that some cheaper flash units (not Nikon) can send current back to the camera so I am scared to death to hook the ProPhoto units up to the AS-15. Infr-red and radio units are $ 500 so I think the mirror will be fine for now.
>I have read that some cheaper flash units (not Nikon) can >send current back to the camera so I am scared to death to >hook the ProPhoto units up to the AS-15.
old strobes can fry a camera and the AS15 doesn't offer any protection. you can get Wein Safe-Sync HS Hot Shoe Mount Voltage Regulated PC Adapter. it sells at BHphoto for $39.95. I have one and it works great.
You've found the solution to your exposure problem. I experienced the same until I figured out the pre-flash thing. Since going to straight manual and using PocketWizards to trip the strobes I find the exposure to be very consistent with my Sekonic L-358 meter. The PocketWizards also eliminate any voltage concerns, while freeing my up from unfuriating cords getting in the way.
PocketWizards are just wireless slave units. (http://www.pocketwizard.com/) One sits on the hotshoe of my D100, and one hangs by a strap off of one of my studio light stand knobs with a cord running from it to the light. The Transmitter unit on the camera is triggered at exposure time and wirelessly sets off the strobe light. My other lights trigger of photos laves from the first light.
It's a great solution for under $300 US. Quantum makes a similar unit that many pros use. I went PW because they are owned by Mamiya who also owns Sekonic, so they have a transmitter module option that is integrated into some of their Sekonic meters allowing me to trip the lights from the meter, another great little feature.
Thanks for the info. I just thought than the product "PccketWizard" implied a small low cost unit. I have looked at both the radio and Infra-red products here in Canada and they are in the same price range.