They seam to have a flatness of λ/2 - λ/4 and are quite cheap, 10 bucks for a 25mm diameter one (that 1/5 the price of a normal 25mm secondary elliptical mirror)
They seam to have a flatness of λ/2 - λ/4 and are quite cheap, 10 bucks for a 25mm diameter one (that 1/5 the price of a normal 25mm secondary elliptical mirror)
Silver should have good reflection over most of the spectrum, guess its the coatings making things strange then :/
I know enough about these kinds of optics to be firmly in the valley of despair on the dunning kruger graph. It’s super complicated and well beyond my understanding.