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OneCosmos
21-07-2013, 06:26 AM
Anyone know what this measurement is?
bojan
21-07-2013, 06:50 AM
You mean this?

http://improvephotography.com/4552/back-button-focusing/
OneCosmos
21-07-2013, 07:10 AM
Maybe related but I'm talking about matching the camera with the field flattener. The field flattener has a back focus of between 71.4 and 81mm according to the specs (seems a lot of latitude) so obviously need to subtract whatever the 50D is from that to figure out the length of spacers required.

Chris
bojan
21-07-2013, 07:21 AM
Aha.. then you will find the answer here:
http://en.wikipedia.org/wiki/Flange_focal_distance
adman
21-07-2013, 07:26 AM
Canons EF mounts are all the same - 44mm
OneCosmos
21-07-2013, 07:59 AM
Perfect - thank you gentlemen.