|
Phillip I assume you are using a GstarEX.
For any focal reducer there is an optimum distance from the sensor to get the flattest field. For full frame or even c size sensors you are basically limited to a reduction of 0.85 to at best 0.70. The field of any simple optic is curved concave towards the optic and if you go for too much reduction it then curves the other way ie away from the optic.
As the GstarEX is at most 8mm (diagonal) so even a highly curved field for a large sensor will be approximately flat for the centre part of the image plane.
So a reduction of 0.2 is quite feasible as long as the focal length of the FR is many times the size of the imaging sensor diagonal.
Bert
|