I would have avoided large, flat surfaces near the face of the D-ERF or large objective lens. A more conical form would have avoided local solar heating. With plumes of convection currents in the light path possibly spoiling high res images. Perhaps the thermal differential is too small to matter? Here I am thinking of the use of fans to cool mirrors in reflecting telescopes.
Even in white, one can't ever be sure of reflectivity at all solar wavelengths. A remote sensing thermometer or [much better] an IR camera would confirm or rule out local heating. It may be that there is really nothing to worry about but I do concern myself with these details. Particularly when subjecting larger telescopes to many hours of deliberate sunbathing.
A bare, black anodized, objective cell will certainly warm where an internal D-ERF is used/abused. IR scanning a complete solar instrument, while in use, might be rewarding. A truss based OTA might have unknown hot spots close to or actually in the light path.
Above all avoid stainless steel in solar telescopes. In my experience SS sheet will become very hot in sunshine. While polished aluminium does not.
Just as a final plot twist I'd avoid tightly holding optics with plastic. Large, thermal contraction and expansion coefficients may distort the precision optics one has paid so much to enjoy.
Enter the physicists [stage left] to deny any of my points holds true.
