How can an astrophoto shot through a refractor have diffraction spikes on bright stars?

In your Gallery department (S&TSeptember 2004, page 144), you had a nice image of the star Pollux showing diffraction spikes. That suggests it was taken with a Newtonian reflector, but the accompanying note says a Takahashi refractor was used. Where did the spikes come from?

Many imaging enthusiasts like the look of spikes on bright stars, and they add them by placing some kind of mask in front of the aperture to mimic the effect of a Newtonian reflector’s spider vanes. Almost anything will work. I’ve used perpendicular wires, thin strips of black paper or tape, string, and so on.

As to whether the spikes are always caused by diffraction, that’s a question for another day!

— Dennis di Cicco