From the start, the Astronomik OIII filter has been very specifically designed for the visual observation of gaseous and planetary nebulae. The extremely narrow pass band of the two OIII lines brings a substantial contrast gain to these lines even under best observation conditions. On faint super nova remnants and faint planetary nebulae the Astronomik OIII filter will often make the difference as to whether the object can bee seen or not! The optimal aperture ratio for the use of the filter is 1:3.7 to 1:15 with apertures of more than 6" (150mm). Transmission losses and chromatic distortions, which arise with other filters, occur with Astronomik OIII filters only when extremely bright aperture ratios of 1:3 and more come into play. The Astronomik OIII filters thus can expand the view of dispersed objects, generally speaking, to the whole visual field of view of the eyepiece and are not limited to only the center of the eyepiece. Main use Since enough light must be available to make use of the OIII filter it is best to use this filter with apertures of more than 6" (150mm). Smaller instruments do not gather enough light for meaningful and satisfying astronomical work. However, please note: Many experienced Deep Sky observers, with apertures of more than 10" (250mm), prefer using the OIII filter instead of the more versatile UHC filter. Due to the high optical quality of the Astronomik OIII filter substrate you will see the same needle-sharp stars as you would from your regular telescope. more information about the visual Astronomik filters Suitability Visual observation (dark skies): Very good, huge contrast enhancement at O III-emission nebulas Visual observation (urban skies): Very good, huge contrast enhancement at O III-emission nebulas Film photography: It depends, very long exposure time CCD photography: Good, when used with an additional IR-block-filter DSLR photography (original): Very good, huge contrast enhancement at O III-emission nebulas DSLR photography (astro modified): Very good, huge contrast enhancement at O III-emission nebulas DSLR photography (MC modified): Good, when used with an additional IR-block-filter Webcam / Video (Planets): Unsuitable Webcam / Video (Deep Sky): Reasonable, if light pollution is a big problem and OIII Objects are being observed Specifications Technical Data typically. 95% transmission at 496nm (OIII) typically. 95% transmission at 501nm (OIII) Complete blocking of all disturbing wavelength coverages The ideal filter for telescopes 10 " (25cm) and larger Main operational use: Planetary nebulas & super nova remnants No moisture-sensitivity, no aging, and totally scratch-proof Excellent carrier material - substrate is optically polished. The optical performance (resolution & contrast) of your telescope is not reduced in any way by the filter. Par focal with other Astronomik filters Glass thickness: 1mm Completely resistant against high humidity, scratches and aging effects Diffraction limited, the filter will not reduce the optical performance of your telescope! Astronomik filters are delivered in a high-quality, long lasting, filter box
