A quick test of a simple-to-make focussing mask for astrophotography, as designed by: http://www.iceinspace.com.au/forum/showthread.php?t=90080

Presented here is a collage of pictures while going from 'in front of' to 'behind' focus with the bowtie mask in front of the lens, pointing towards Arcturus (which was in the center of the frame but placed decentered in these crops to also show the small star in the bottom right as a measure of focus).

In liveview at 10x magnification, I could not make out the diffraction spikes, rendering the usability of the focus mask (with my 150mm lens) very low. When taking a picture and using full magnification in the image review on my camera's lcd screen, I could discern somewhat the diffraction spikes. However, the small shift in spike geometry from before to behind focus (with critical focus being achieved here in the third image from the left) and inability to see this in liveview makes this focus mask method useless in my opinion without tethered shooting. (note that the view on the lcd screen is somewhat similar to looking at the 'large' image size of this image here on pbase, so one does not see all the details) For my purposes, focusing based on the liveview image appears to stay the best compromise at these short focal lengths.