Nikon D70 – how to tigger a slave with the built-in flash?
The Nikon D70 uses an i-TTL system. Unfortunately, this system uses a pre-flash, so you need to forget about i-TTL. Instead, you need to go into the D70 menu system (item 19) and switch the popup flash to manual. Set it to the lowest power possible. This will eliminate the preflash, but it will still be strong enough to trigger the studio strobes. If you are really concerned about even this amount of light from the flash in manual, then tape a piece of unexposed film over the popup flash, so that only IR gets through to set off the strobes (no visible flash to affect the exposure). Alternatively, use an IR sender unit (link below) which fits in your hotshoe and triggers the strobes via an IR “flash”.