Field Flatteners, Back Focus
My new HOTECH field flattener came with an instruction sheet that indicates that the sensor should be 55 mm back from the flattener. My Nikon SLR claims to have a flange distance of 46.5 mm, which leaves me 8.5 mm to fill.
I haven't even tried hanging the camera on the back of this, yet, but I already know, I don't have an 8.5mm extension tube; and it isn't clear that I can get one. Do I have to head to a machine shop?
Generally the field flattener attaches to the camera with a T-Ring, this ring can increase the backfocus by up to 10mm. In addition, they sell T-Thread spacers that go between the field flattener and the T-Ring in increments of 10mm, 20mm and 30mm (separately or in a kit with all three sizes). These are available from many places including from Orion.
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