New or improved for commercial telescope optics?

Published 20.3.2015

Astronomical telescopes for commercial use have their own points to consider, and variations for each purpose are too many to count.

Commercial astronomical telescope optics development has followed a straight tangent for decades now. Focal lengths have shortened while image sizes have grown. Refractive telescopes houses five or even six lenses, making them more and more like over-sized camera optics, driving up manufacturing costs fast. Producing more and more expensive and generic products for smaller and smaller range of enthusiasts does not pay back development.

Optical problems with short focal length are not limited to following. The increased field of view is honey to astrographers as is the stability and shorter optical tube that comes with shorter focal length, but manufacturing difficulties and the resulting price are not. The trend of shortening the focal length and by that, increasing the field of view, has already surpassed the actual needs for it, as most deep-sky objects simply aren't that big. When increasing the FOV, one also increases the amount of air glow the aperture admits, further reducing contrast. Ideally a short tube, long focal length telescope with a large image field would satisfy deep-sky astrographers best. Such a setup could be a large aperture telescope with a Bravais lens as an add-on. Reflective and catadioptric systems have a shorter tube length than refractive telescopes, but suffer from field effects. A Bravais lens add-on would magnify the high-contrast field areas to fit sensor size.

For the more casual observer, such as the family guy taking his family out for a weekend camping, the usual offerings are disappointments, mostly. Cheap (main requirement) is not particularly usable in the long term. The learning curve for use and setup of telescopes is steep, and poor plastic lenses are hideous. Purely astronomical telescopes are not easy to use for anything else, ending up as ornaments mostly. For the first-timer, a selection of simple Galilean and Gregorian telescopes might be the best recommendation, not because they would be particularly cheap to produce, but because they can be used in terrestrial observation as well, as the image does not flip over, making it usable for i.e. bird-watching or scenery viewing.

Another source of disappointment for astrophotographers is the use of JPG image format for astrophotography. Designed for compression via loss of data, it is not suitable at all for photography with high contrast differences such as astronomy. With modern memory cards with double-digit gigabyte storage space, the one and only benefit of JPG, small image size, is no longer necessary. JPG actually increases aberrations not visible with visual inspection or RAW format.

There are casual observers who wish to buy an inexpensive setup, requiring ease of use up to at least a mediocre result, and instructions on what and how to observe. For them, requirements for an enjoyable viewing are not optics related (other than the easy Galilean/Gregorian type telescope), but could be filled with a proper guide book on magnifications, magnitudes and other observation techniques. For the rich enthusiast, the fastest and cheapest way is through market study to find out what they actually want (instead of telling them that) and do only that. The market share of enthusiasts are usually very low anyway, and targeted products don't need big investments and long commitments. Even a hard-core enthusiast is happy with an add-on that could transform his existing setup to something else.