

It may look small at 93M miles away, but it is 865,000 miles in diameter. In fact, the Sun is a very large extended source. All solid etalons that I have made for space flight have been fused silica. In most cases for solar this is solid material is Mica, and in some cases it is fused silica. What one should keep in mind is that, in any case, an etalon specified by surface reflection at the interface of the internal plates, thickness of gap, and gap medium only, will NOT perform to that optimal specification should there be anything other than collimated light passing thru it.į30 does not apply specifically to airspaced etalons due to the higher index material utilized at the gap of the solid design. That adds up fast.Īnother rule of thumb that I have heard is that the acceptance angle of an airspaced etalon is 0.5 degrees. The basic rule of thumb for an etalon is the price is a function of the area.
#Tilt to live hd stay perfectly still as long as possible full#
Internal etalons are situated internally to the scope, allowing for a full aperture objective to pass the light thru a smaller etalon due it being placed further down the optical path.

Well that gap is getting very narrow.Įxternal etalons are used on the front of an existing scope, and the user typically asks that the etalon be full aperture. The defining difference between an External etalon vs an Internal etalon has typically been Price vs Performance. Typical Solar Etalons have a bandpass of <1.0. For Solar applications it is generally accepted that the lower this number, the better. Typically the peak transmission should be between 80-90%, so the bandpass of the etalon will be measured between the 40-45% points. An etalon's transmission has a broad base and a sharp peak. The main parameters that define an etalon are:īandpass: This is the width of the curve that defines the transmitance of the filter at 50% of the total transmision of the filter. Thru interference at this gap, only light meeting the correct angle of incidence to the surface and is not "interfered with" can pass, all other light is lost. The light resonates in the gap by internal reflection off the highly reflective layers on the surfaces. This gap can be either air or a solid material. These optical surfaces are seperated by a gap.

Due to it both being simple and the need for precision, there are many compromises that can influence the quality of an etalon filter.Īn etalon is comprised of 2 flat and parallel optical surface that have been optically coated with a high reflective dielectric layer with the high reflector layer peaking at the desired bandpass point for best results. (I love that stuff)Īn etalon refers to an interference type filter typically used in Solar Telescopes because of the desire for an ultra narrow bandpass.Īn etalon is probably one of the simplest designs for an optical filter utilizing some of the most precise optical specifications. Unless you are an Optical Physicist of course. For those who have googled "what's an etalon?" the returned results outlining complex looking optical equations, mathmatical relationships, and technical references probably didn't do much to answer the question.
