I have to admit, I've had enough of the weird diffraction spikes coming from the WO Star71. I think part of it is that I'm undersampled and it seems to cause really weird looking small stars, part of it is that it must be having some sort of affect on the overall quality of the data, and part of it is I want my stars to look nice and round. Lots of good ideas were thrown around and I agreed with the idea of the step down mask. I think initially some were trying to put something right up against the element, but I didn't like that idea as I didn't want my grubby hands or my plastic piece resting on the glass, so I made a mask to go over the dew shield. It slides on very easily, it is cheap, it is light, and I designed a bahtinov mask plug for it so it doesn't need to be removed for focusing if you are manually focusing. The mask and bahtinov mask has been made with a 3d printer and can be easily replicated if others are interested.
Here's my results with an inside diameter mask of 64mm. I wasn't happy with the stars until I got down to 64mm as the effect was still visible. These are two stacks of 5x3' of the star Per near the California Nebula taken in the same hour. I'm pleased with the results, but a little aggravated that it needs to be stepped down to f/5.45 to get diffraction free stars. The affect does seem to be a little temperature dependent and is more dramatic when it is colder from what I've seen. If anyone has any other ideas on how to beat this problem without slowing the scope down, I'm all ears!