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Emil

10 Iun 2011 11:44



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Dupa Starizona

The filters used  in narrowband imaging typically have bandpasses in the range of 3-5nm.  The most popular filters are made by Astrodon and Custom Scientific.  Older Custom Scientific narrowband filters had a bandpass of 3nm.  Current filters typically have a bandpass of 4.5nm, while the popular Astrodon H-alpha filter has a 6nm bandpass.  The bandpass was expanded to allow the use of the popular faster-focal-ratio scopes such as the Takahashi and TeleVue refractors, etc.  At fast focal ratios, narrowband filters shift off band, meaning they shift away from the wavelength they are designed to capture.  The effect is a significant decrease in sensitivity.  A wider bandpass allows the required emission line to remain within the filter's highest transmission zone even if it has shifted slightly.  For very fast systems, an even wider bandpass is required.  For telescopes faster than f/4, such as the Takahashi Epsilon astrographs (f/3 to f/3.8) and Celestron HyperStar-equipped SCTs (f/1.9), a 10nm bandpass filter is required.

Totusi cred ca ideal ar fi daca ai putea imprumuta pentru test un filtru de 6-8 nm inainte de a te decide.
In cazul meu trecerea de la 35 nm pe 6 nm a insemanat
1. expuneri mai lungi
2. fundal mult mai intunecat
Expunerile mai lungi implica o punere in pol mai exacta si dupa cate stiu eu tu esti mai mobil deci nu cred ca esti dispus sa pierzi mai mult timp pentru obtinerea unei puneri in pol mai exacte, eu fiind stationar incerc sa ma mentin intr-o plaja de eroare de ordinul secundelor de arc.