Flash guns

[ericmark]

I am completely baffled as to why the second flash reduces the light? I have tried leading and trailing and I is not set for red eye reduction. But using built in flash the use of a second flash fired by the light from built in flash reduces exposure. Even using the -2 to +1 option for TTL built in flash it still fails.

Using the Vivitar 3500 on hot shoe and Prinz Jupiter 177 hung below the camera I have been able to take close-up without the huge shadows cast using single flash gun. However the settings are a bit hit and miss. Set to minimum focus and camera positioned so in focus and set manual ISO 100 and 1/180 second taking two sets of flowers one needed f22 the other f11.

I realise why it's all to do with the flash measuring the light reflected back so items well away from focus range are shutting down the flash at different points. Need to retest using motor drive setting (flash was from film days) I think this may produce more consistent results. On manual it is consistent but far too bright.

[thoughton]

Hard to tell what's going on from that description, eg what mode are you shooting in and what mode are the flashes set to? Im still inclined to think the PTTL pre flash is to blame. Can you post some examples with full exif data?

[ericmark]

OK more experiments. If I use a lens without any electric contacts internal flash fires slave A1 so there must be a pre-flash to set the focus. Tried turning off auto focus with electric lens on camera but still must activate pre-flash.

Fill in flash seems to be a problem in fully auto mode (green) it will not fire flash gun unless there is low light. I am told by others that with non dedicated flash guns it will not fire flash at all. Mine is part dedicated it has two contacts not the four used on modern ones but seems to work OK. It stops the spark sign flashing when charged and fires when required.

The camera speed does seem odd. The F stop will vary from f3.5 to f5.6 according to focal lenght. As one goes to wide angle which is f3.5 then the speed goes to 1/30 second. But as one zooms in the speed changes to 1/60 second. I will guess it's not to do with F stop but more to stop camera shake?

In the semi-auto mode (A) the speed is also odd it will let you reduce speed but not increase so your forced to use 1/30 second. Once in the Sv, Tv, Av or TAv modes it limits one to 1/180 second which is what I would expect as that's fastest speed where the shutter is fully open.

Because one needs to set the flash gun to the same aperture as camera for the sensor to work Av mode is of course the best option. although I have been using the manual and motor drive settings on the flash when using out doors as the sensor seems to give some odd results when there is no ceiling to reflect the light back onto the sensor.

Below is one of the results using out doors. Likely could have been improved by altering ISO but was in a hurry to catch bus.