Originally Posted by bdht
Gotcha thx. Do you happen to know if there are any picture or diagram examples of first surface mirror draw lines? I havent been able to find anything and wonder how noticeable theyll be.
I'm not sure about pictures or diagrams being available...
Draw lines are a function of how flat the surface is, i.e., a tolerance measurement. They can be or are orientated both horizontal and vertical.
Most of the rear projection rigs from companies like Da-Lite, Draper, etc., use first surface mirrors of 1λ flatness or what's often called typical grade, having surface quality and flatness characteristic typical of standard commercial grade soda lime float glass.
Moving up to λ/4 flatness, considered precision grade, is quite expensive as it requires extensive polishing to achieve that tolerance. Cost increase is usually a factor of 10. And as you may imagine, stepping up to λ/8 and higher is going to cost considerably more.
The naked eye cannot see the difference between a 1λ and λ/4 surface by just looking at it, instruments are required to measure the difference.
Other attributes to consider with a first surface mirror are percent wavelength reflectance at various spectrum nm values and defects like pinholes, scratches, circular defects, etc.
I wouldn't obsess over it too much as you will always have draw lines regardless of what grade you pay for as the reflected light will always react to any surface anomaly. A temperature difference on any part of the glass' surface causing expansion of that area can cause draw line type distortion.
Long story short, a glass first surface mirror of 1λ flatness from a company like FSM should do what you want to do.