Vignetting problem

[robindurant]

My Canon 5Dmk11 vignettes badly, even when ep viewing, on my MAK137 and not so bad on my WPO Z71, is it possible to fit a Focal Reducer, if one is made for a DSLR to help this problem ? or am I stuck with it, I dont have a problem with my other DSLR cropped sensor 700D, this is the view

[Louis D]

The image circle of many telescopes is simply not large enough to cover a full frame 35mm DSLR sensor.  If you were to draw the bounding box for your cropped sensor on the above image, it would probably show a bit of vignetting in the corners.

A focal reducer will simply squeeze the image circle down even smaller, so you would likely see vignetting on your 700D.

You might want to try a Barlow since it diverges the light cone, spreading it out over a larger image circle.