Here's the circuit- I'm not claiming this is optimal, by any means- parts chosen had more to do with what i had kicking around than any rigorous circuit analysis. This of course is good as a general purpose flash isolator, there's nothing peculiarly sony/minolta about it.
R1, 390Ω, limits the camera flash contact current to around 4 mA. Flash contact voltage is provided by battery B1, it would have been nice to power from the camera, but there's no flash power pin on the sony.
The opto isolator is a MOC3023 opto-isolated triac- this provides complete isolation between the HV side and the LV side. It turns on the Q401E4 triac via R2, the 4.7 kΩ resistor.
The bridge rectifier makes sure the the polarity from the flash contacts is correct, if you only use this with one flash, and you know the polarity, you can safely leave it out. The DB104 bridge is rated for 400v, I'd suggest using one rated for at least 600. You can omit the bridge rectifier. I was asleep while designing this. Thanks to P^2 for pointing this out.
No guarantees that this will work for you- it was tested with a Sony Alpha 100, and a Minolta Dynax 3000i, and the following flashes:
Vivitar 283 ( an old one with high voltage)
Sunpak Gx8r ringflash
sunpak softlite 2000a
It probably won't work with newer low-voltage flashes.
And if any of this is confusing, you probably shouldn't try building this. It's a particularly tight build if you do it like I did, and a single wiring error or short-circuit will send your shiny camera into its next life. There is no undo. Again, if you have the slightest doubt in your abilities, buy the Sony FA-ST1AM.