Camera to flattener distance

[andyboy1970]

I have a Williams optics flattener I & Flattener III and both quote 56mm spacing, does this mean from the thread or actual lens?

I will be using them with my ATIK16hr with 18mm back focus and Canon 550d with 44mm back focus.

I was going to get spacers, 38mm for the ATIK and 12mm for the Canon would that be correct?

[rpineau]

It's usually from the thread. For the Canon you just need the regular T-Ring adapter and it'll put you exactly at 56mm ( something like this one : http://www.firstlightoptics.com/adapters/skywatcher-dslr-m48-ring-adapter.html ).

And yes for the ATIK you'll need the 56-18 = 38mm spacer.

Rodolphe

 

[andyboy1970]

I suspected that, they just don't make it very clear.

Thanks.