Thanks for the info guys.
One more question:
If I want to image with "normal" colours plus Ha, like what one would get with an 810a or 60Da, would I just put an "L" filter in the train?
Like this one:
http://www.bintel.com.au/Astrophotog...oductview.aspx
In fact can I just use that "L" filter instead of that LifePixel or Kolari hot mirror filter? It seems that they basically do the same thing except I assume the "L" filter will pass more light at Ha wavelengths...?
FYI just got off the phone with Whilton Camera Service in Sydney and they won't do the mod. Strange as I thought I'd seen someone on here mention that they'd had theirs done buy them... perhaps not a Sony A7s though...