Naslov
Correctors for Wide-Field CCD Imaging: How to Design, Manufacture and Use Them

Autori
Andreić, Željko

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), stručni

Izvornik
MACE 2002 CD / - Višnjan : Zvjezdarnica Višnjan, 2002, 55-67

Skup
MACE 2002, Meeting on Asteroids and Comets in Europe

Mjesto i datum
Višnjan, Hrvatska, 16.05.2002. - 19.05.2002

Vrsta sudjelovanja
Pozvano predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
wide field telescope correctors

Sažetak
In recent time, many advanced amateurs and small astronomical facilities, have access to 1 m-class telescopes. Most of these telescopes are Newtonians or classical Cassegrains, both types having parabolic primary mirrors. These instruments are either self-made, or are old instruments that are not primary research instruments anymore. To adapt them for CCD photography, one usually needs a field corrector which corrects the of-axis coma of the primary mirror and, at the same time, flattens the image plane so that the whole CCD sees a sharp image. If this lens system also shortens the focal length, it is usually called a telecompressor. It is supposed that such telescopes will be equipped with 1” CCDs, with a possible upgrade up to 2” in the years to come, as the prices of such cameras fall with time. Also, a point source (star!) image of about 30 mm is taken as the upper limit of the acceptable image blur. Larger instruments (focal length of abut 3 m upwards, will have larger seeing blurs, so 50 mm blur can be tolerated in such a case. A review of suitable corrector designs is presented, starting from a single lens field-flattener, up to a 5-lens multiple-glass focal corrector. It is found that single-lens correctors have no sense in such an arrangement, as the image improvement is marginal or non-existent. At telescopes around 0.5 m in diameter, field-flatteners do improve the image sharpness a little, but this effect is completely hidden by the of-axis coma. The first usable corrector design is a two lens Ross corrector, which is usable at focal ratios of about F/4 or larger. For faster mirrors, it fails to produce small enough point images, although coma is still greatly reduced. The great advantage of a Ross corrector is that it is one-glass design with relaxed tolerances, so it can be produced by a skilled amateur optician. Many amateur telescope builder are skilled enough to attempt such a work. The first really good corrector is the three lens Wyne corrector, which is often used on larger telescopes. It is still one-glass design, but the tolerances of individual lens surfaces are very tight. A skilled optician is needed to produce such a corrector successfully. Last, but not least, an example of modern multiple-glass, 5 lens focal reducer for an F/3 parabolic mirror is presented. Its tolerances are not so tight as the ones of the Wyne corrector, but it requires 3 different glasses, at least one of which is difficult to grind and polish. Again, a skilled optician is the best choice for manufacturing of such a corrector.

Izvorni jezik
Engleski

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