I've just recieved the M2 DIY guide and they mention a DCX lens to be placed in front of the ground glass.
What exactly is a DCX lens and where to buy it?
DCX stands for double convex lens, meaning it is convex on both sides. This is probably in the designs to help reduce vignetting of the GG image. I'm not familiar with the RR DIY guides but you can buy all kinds of lenses from places like Anchor Optics, ThorLabs and especially OptoSigma. Do google searches on these. Then the only other thing to know is what focal length and diameter to buy it in.
