I don't know why, but when using my Sigma EF 500 Super and Sigma 500 DG flashes on my N80 and N70 film cameras on program, I'm getting substantial flash underexposure. When the flashes are turned off for existing light photos, the meters in the cameras produce accurate exposures. I have checked the flash's outputs with a separate flashmeter, and when the camera aperture readout in the finder says f2.8, the actual flash exposure will be about f1.8. I've tried setting +1 flash exposure on the camera bodies, but the separate flashmeter still reads f1.8.
This happens with both my N80 bodies, and my N70, and with all 5 of my Sigma flashes. When putting a Sunpak 383 shoe mount flash into the hot shoe (with safe sync connector) and shooting on manual power output with guide numbers, I get great exposures.

Also, when using the Sigma flashes with my digital D70s bodies, the exposures are acceptable, but when shooting many different frames of the exact same scene, the flash exposures vary a lot from frame to frame. I can see the brightness of the images change from exposure to exposure as I review them on the screen on on my computer.

Help! Any suggestions? Is this just the nature of the beast, or do I need to spend $300.00+ for a SB800?
- Rob in Oregon