Solar Telescope

The latest edition to our range of optical equipment is a Televue 102 + Coronado filter designed for observing the Sun SAFELY! This was the first instrument of its kind in amateur hands in the UK!

The Coronado AS1-90 Hydrogen-Alpha filter was donated to WYAS by Barclays Bank PLC as part of a solar telescope package. The filter has a fixed wavelength of 656.28nm with a full filter wavelength of less than 0.7A. The temperature coefficient is less than 1A/2,000 degrees C and the aperture is 90mm.

The filter is thermally stable for observations of the Sun in H-alpha light. It is directly mounted onto the Televue 102 and comprises two units; the narrowband element and the blocking filter which serves to eliminate the infra-red heat from entering the telescope as well as cutting off the UV side of the blocking filters rejection band.

When the filter is adjusted properly and in focus, prominences and other surface detail on the Sun can be seen clearly. To compliment the superb telescope and filter we have a range of first class eyepieces and Barlow lenses.

Introduced in the Summer of 2000, the "102" telescope is a variation derived from the fifth generation TeleVue "101" and "Renaissance" telescopes. The 101 systems are each a four element refractor design succeeding the original 5 inch "MPT" system introduced in 1982, the beautiful brass 4 inch aperture f5.5 "Renaissance" telescope introduced in 1984, the "Genesis" 4 inch f 5 telescope of 1988, and the "SDF" 4 inch f5.4 of 1993. Al Naglers patented four element design is based on the "Petzval" concept where a two element air spaced objective lens at the front of the telescope passes the light through to a second doublet lens positioned at the rear of the telescope and before the focuser. The rear doublet lens group functions include 1) reduce the effective focal length, and 2) reduce or eliminate curvature of field.

The 102 telescope is similar to the 101 series in that it employs the large air gap SD apochromatic doublet (two lens) objective for very good control of chromatic and spherical aberration. However, the 102 does not incorporate the second doublet lens (telecompressor - focal reducer, and field flattener element) as does the 101 series, and so the resulting effective focal length of 880mm is longer in the 102 telescope than it is in 101 (540mm focal length) series.

The objective lens of the 102 is of an SD air spaced doublet design where two lenses (crown and flint) are matched to work as one; the positive element is of a fluorocrown substitute with special dispersion glass. In fact this design allows excellent colour correction without annoying purple fringes (secondary colour) common to less sophisticated achromatic refractors. And it will perform better than a number of older triplet and modern doublet apochromat designs. There will be a barely perceptible false colour in this design, and what there is may be visible only to the more discriminating observers when using the telescope at very high magnifications well in excess 300x on some of the very brightest starts. Spherical correction is very good also with the air gap objective contributing to this correction. Images of the stars and the planets are presented in their natural colours, daytime objects viewed at commonly used magnifications will appear quite three dimensional, sharp and high in contrast.

The objective's four air to glass surfaces multi-layer anti-reflection coatings improve overall light transmission across the visual wavelengths and from 400nm to well beyond 700nm. Overall the complete system provides about 202 times the light gathering power of the unaided human eye. On most nights, the settling down time for the lens is on the order of minutes: from room temperature to sub-freezing conditions it rarely requires more than 30 minutes to acclimate.