I've seen a few scopes based on this design no-one has reported it being too bright, but I'll be doing more homework before anyone goes near the eyepiece. One can never be too careful when it comes to the Sun.
From the design sheet:
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The solution was still to use the Newtonian configuration but to have all the optical surfaces uncoated. For safe viewing, the image of the Sun needs to be reduced by 100,000 to 1 in brightness across the full spectrum. This is an Optical Density of 5 ( LOG(100000) = 5). Bare glass reflects about 5% of the light striking it. This translates into an OD of about 2. The two reflections in a Newtonian would results in an OD of 3.5. Still too bright for comfortable viewing so a third reflection is needed. I used a homemade Herschel wedge to achieve this. I also took advantage of the fact that when light is reflected off of bare glass at an angle it becomes polarized. The closer the angle of reflections gets to the Brewster angle of 57 degrees, the more complete the polarization. With both the diagonal mirror and Herschel Wedge placed at 45 degrees the light becomes crossed polarised and the image brightness can be farther reduced.
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