Spiders When I made my first telescope back in 1958, there weren't too many choices when it came to the selection of Spiders for amature telescopes.  Today, that has changed in the opposite direction to the change in the available qualities of Flats. Today, I have many types of Spiders to choose from, and can not find a Flat with a wavefront error of less than 1/19 P-V @ 550 nm.
Today's Engineers are not taught to make things to the best of their ability, but to make things just as good as they need to be to do the job. Any Composite Wavefront Error less than 1/4 P-V @550 nm is considered adequate, so four optical elements in a system with P-V Wavefront Errors of 1/19 @ 550nm each will make the grade.  With the increased popularity of Astronomy, more and more Amatures encounter difficulties that could be improved upon by more advanced Spider designs.