Astronomik H-Alpha 6nm CCD Filter - 31mm Round - Unmounted
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. Selected filters for faster system are available upon special request. The Astronomik 6nm H-Alpha filter is offered in three qualities: B, A and A+. Filters with a maximum transmission of 80%-85% are class B, 85%-90% are class A, and filters with a transmission of more than 90% are class A+.
All transmission curves of the 6nm filter are measured individually. Because of this procedure you can get the optimum filter for your telescope: If you place a direct order please specify the focal ratio of your instrument and we will select the best filter for your setup. So you may get the best filter without paying for an A+ filter.
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. Selected filters for faster systems are available upon special request.
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 must 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 H-Alpha 6nm CCD Filter - 31mm Round Unmounted Features...
- Parfocal 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
Relative transmission curve of an Astronomik CCD Ha filter (filter number 1). From left to right the dashed lines indicates the position of Hb (bleue), [OIII] doublet (green), Ha at 6563 A (red) and [SII] line at 6730 A (cyan).
Detail of an Astronomik CCD Ha filter transmission near Halpha line (red dashed line). Filter #1
Relative transmission curve of an Astronomik CCD Ha filter (filter number 2). From left to right the dashed lines indicates the position of Hb (bleue), [OIII] doublet (green), Ha at 6563 A (red) and [SII] doublet at 6730 A (cyan).
The central wavelength of the filter #2 is significantly shifted toward the bleue. Efficiency at the Halpha level is reduced by a factor 0.9 comparatively to an hypothetical correct filter. The proof...
Up image, part of the sun spectrum taken with the LISA spectrograph (intermediate resolution mode - 600 grooves/mm grating). Middle image, same observation condition, only the Astronomik Ha filter #2 is added in the optical beam. The red shift of the transmission curve relative to the Halpha line position is very evident. Down image, an Edmund Optics Halpha is now used (ref. 43-086). The central wavelength position is now correctly adjusted (but in the same time the peak transmission of the Edmund filter is near 50% only, and near 90% for the Astronomik filter).
The Astronomik CCD Halpha filter #2 for two incident angles. The curves show progression in pass-band when the angles of incidence of the f/8 beam are varied from 0° to 5° (simulate approximately the marginal rays of a f/5.6 telescope). The dashed line indicate the position of Ha.
Relative transmission curve of an Astronomik CCD SII filter. The red dashed line indicate the position of Ha line (at 6563 A). The magenta lines indicate the position of [SII] doublet (at 6719 and 6730 A).
|Name||Astronomik - H-Alpha 6nm CCD Filter - 31mm Round Unmounted|
|Custom Stock Status||Ships in 3-5 Days|