A simple way to trigger studio flash from any camera is with a non-dedicated hot shoe flash, that has only the main center contact on its shoe. This will avoid using any of the camera's preflash, or other activities, and just flash when the shutter is open. Or use the bult-in D70 flash on manual - see below.
Then use an optical slave trigger on the studio flashes, if they don't already have an optical slave built into them.
The easiest choice with a D70 is to use its built in flash. Below is a copy of the text on this area, from my PDF tutorial on the built-in flash.
Ron Hirsch
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MANUAL - In the CSM19 camera menu (pg 150 of the samera manual), select “Manual”. You can adjust the light output over the range of “Full” to 1/16th. Choose the desired amount, and exit the menu. Now, whenever the D70 flash is used, that light amount will be produced. There are no preflashes, and no calculations. If the camera exposure is set to “M” mode, the required f stop can be calculated by using the applicable guide number for that flash level setting. If in P, S, or A mode, some experimentation may be needed for optimum results.
At full power, the built-in D70 flash has a guide number of 56 (ft) at ISO 200. At 1/4 power, the guide number would be 28.
In Manual mode, no pre-flash in emitted. So, if you were using the D70 with external 3rd party flash units attached to optical slave triggers, they would fire correctly, and not be confused by any preflashes. To minimize the light contribution of the D70 flash, if desired, just set it to the lowest power level which will reliably trigger the optical slave sensors on the remotes.
