Used Astronomik 31mm Narrowband Filter Set - Sold
The Astronomik 6nm H-alpha filter is an extremely narrow emission-line filter for CCD photography. The filter lets the H-alpha light of emission nebulae pass and blocks nearly the whole remainder of the spectrum where the CCD is sensitive. The full width at half-maximum (FWHM) of 6nm is optimized for a maximum contrast between the (H-alpha emitting) object and the background. The contrast gain is much higher than with our 12nm emission line filters but you won't see as much stars in the resulting images. The design of the transmission curve makes it possible to use the filters with instruments from 1:3.75 to 1:15.
The Astronomik H-alpha-CCD (6nm version) increases the contrast between objects, in this case between the H-alpha emission line and the skyglow background in the same way as the 12nm version. The gain in contrast is much higher due to the smaller FWHM. The 6nm H-Alpha filter is the right choice for extremely dim objects, even in the milky way, and for observations from heavily light-polluted places. The Astronomik 6nm H-alpha-CCD completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow. Transmission losses and chromatic distortions, which arise with other filters, only occur with Astronomik filters when extremely bright aperture ratios come into play.
Using the Astronomik 6nm H-Alpha together with the 12nm H-Alpha gives you the ability to have a maximum contrast in the HII objects and to keep the stars in the final image. The Astronomik 6nm H-Alpha filter may NOT be used for solar observation. If you plan to do (false-)color imaging with other emission line filters, you should get the matching filters with 12nm FWHM. Images taken with filters with differing FWHM are very difficult to combine into the final image.
ASTRONOMIK 6 NM OIII MFR NARROWBAND EMISSIONLINE FILTER
Astronomik OIII Narrowband Filters are suitable for false color imaging of emission nebulae emanating doubly ionized oxygen (OIII). The contrast between an object glowing at 501nm and the background is increased significantly due to the high transmission and effective out-of-band blocking!
The OIII line (501 nm) is in the blue-green portion of the spectrum. Planetary nebulae & supernova remnants are considered emission nebulae, since they produce their own light, and so objects like the Ring, Dumbbell, Veil & Crab nebulae are common targets using OIII filters since doubly ionized oxygen is the main emission for these interesting objects.
This Astronomik OIII MFR Narrowband filter has a 6 nm FWHM. The extra narrow bandpass of 6 nm filters are most appreciated with cameras that offer extremely low dark current and good cooling, or when imaging in areas with severe light pollution. The higher level of out-of-band blocking allows you to take longer exposures and choose objects imbedded in normally over-bright, crowded areas of the Milky Way. Extra blocking causes faint stars to disappear from the background, and brighter stars will be pin-pricks of light.
ASTRONOMIK 6 NM S-II MFR NARROWBAND EMISSIONLINE FILTER
31mm ROUND MOUNTED
Astronomik SII Narrowband Filters are suitable for false color imaging of emission nebulae emanating singly ionized sulfur. The contrast between an object glowing at 672nm and the background is increased significantly due to the high transmission and effective out-of-band blocking!
The SII line (672 nm) is in the deep red portion of the spectrum, beyond H-alpha.
This Astronomik SII MFR Narrowband filter has a 6 nm FWHM. The extra narrow bandpass of 6 nm filters are most appreciated with cameras that offer extremely low dark current and good cooling, or when imaging in areas with severe light pollution. The higher level of out-of-band blocking allows you to take longer exposures and choose objects imbedded in normally over-bright, crowded areas of the Milky Way. Extra blocking causes faint stars to disappear from the background, and brighter stars will be pin-pricks of light.
- Special Coatings Allow Filter Use Across Most Focal Ratios: Astronomik Narrowband Emissionline filters have been designed to be used with a wide range of focal ratios. The special MFR (multi-focal ratio) coatings applied to the 12 nm FWHM filters make them compatible with optics as fast as f/3, and the 6 nm models perform well with focal ratios as fast as f/4. This means you won't need to buy different filters for your fast refractor and your SCT, and you won't have to pay premium prices for high speed filters.
- Amazingly High Out of Band Blocking: Astronomik Narrowband Emission-line Filters offer superb blocking of unwanted wavelengths, from UV up to IR. Transmission of 90% is guaranteed by Astronomik, but the typical transmission can be as high as 96% on both 6 nm and 12 nm Narrowband filters. This feature translates to extremely high contrast and pleasingly dark background skies, even under heavily light-polluted conditions, allowing you to take longer exposures if you so desire without creating an overly bright (or saturated) background. Another benefit of good out-of-band blocking is the reduction of stray light and haloes. Stars display as sharp points of light on a velvety black background, providing the perfect backdrop for the deep-sky object you are imaging.
- Image During Full Moon or Under Light Polluted Skies: Because Astronomik Narrowband Emission Line Filters have a high transmission rate for the chosen wavelength but blocks pretty much everything else, you can image from your own backyard, even if your neighborhood suffers from light-pollution (which is pretty much everybody). If it's a beautiful night with great seeing but the Moon phase doesn't support visual deep-sky astronomy, you can pull out your telescope, camera, and Astronomik filters and still get great results.
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