Thanks again whostolemymonkey, I have found the article and it is a big help.

I had not thought about the multiple flash you can get on digital cameras but it is possible to turn mine off and use just the single main flash. So I can adapt the EPE design and leave out all the counting stuff and just use the simple bits. I wasn't sure if a Thyristor would be good for the flash trigger but this has answered that point and also the use of a bridge rectifier to ensure correct polarity is a brilliant idea. I will go ahead now with added confidence.

 

Ed