Posted on Jun 27, 2012, 11:57 amAuthor: Jen Winter
Refractor Telescope Configuration
DayStar filters work great on refractor telescopes. A majority of our customers are refractor owners. Any refractor from a little cheap 60mm doublet all the way up to a high end APO refractor can be used with a DayStar filter. While good glass with a good optical figure and good prescription matters, it is not necessary to have the color correction effects of an APO telescope in order to enjoy a good view with the DayStar Filter. Remember that an APO telescope is designed to color correct different wavelengths or colors of light. Because the DayStar is only viewing in one single wavelength, this correction is not necessary.
FRONT MOUNTED COLORED GLASS ENERGY REJECTION
Refractor owners with expensive or complex optical telescopes would likely appreciate the extra security of the front mounted ERF filter. As shown here, the Front mounted ERF filter is colored glass and rejects (by absorption) all light below 600nm or 500nm before it enters the telescope.
REAR MOUNTED UV/IR CUT ENERGY REJECTION
Refractor owners with inexpensive telescopes with simple optical design may want to consider the rear mounted ERF choice of the Dielectric UV/IR filter. The Dielectric UV/IR cut filter, acting like a mirror, will reject by reflection instead of absorption. This means that when mounted in the rear of the telescope as shown below, the UV/IR cut filter will reflect energy from the UV and IR part of the spectrum like a mirror, while passing the visual spectrum. It should be noted that the UV/IR cut filter must be introduced prior to any optical element which might encounter a concentrated beam. That means if a diagonal is used, the UV/IR cut filter must be inserted (threaded) before the diagonal. If no diagonal is to be used, then the UV/IR cut filter can be threaded directly onto the Powermate barlow.
The UV/IR cut filter is available from many different manufacturers in 1.25" and 2" apertures, with standard eyepiece threads. The UV/IR cut filter is typically used in imaging and can be acquired from telescope dealers who sell CCD imaging supplies.
DayStar Filters does not recommend use of UV/IR cut filters on SCT or reflector telescopes, whereas the UV/IR cut filter cannot be applied prior to the secondary. The secondary mirror of a reflector would encounter a concentrated beam and gain heat, possibly damaging the adhesive and causing it to fail; or causing expansion of the optical element and causing it to crack. RED or YELLLOW colored glass filters cannot be used in rear mounted applications, as they reject by absorption and will gain heat, expand and crack.