QHYCCD ColdMOS QHY174M cooled CMOS 2.3 Mpx camera
This package contains a Moravian G2-4000 monochrome CCD camera along a...
The value FWHM (width of the bandwidth at half maximum of the transmission curve) is 5nm. In the construction of dichroic filters, narrow band, you are reached often a compromise between a value of FWHM very low (sharp bend) and a transmission peak as high as possible. For this the filter Custom Scientific H-alpha 3.5nm has a peak transmission of 72% while the Astronomik 13NM has a transmission peak near the 95%. The Astrodon 5nm, despite having so a sharp turn, currently reaches a peak transmission of 90-92%, which is quite remarkable. For example a Astronomik 6nm not get on average 84%.
The bandwidth of dichroic filters narrow band moves to lower wavelengths with optical short focal ratio. A filter H-alpha very narrow band designed for a perspective f / 10 may not provide much signal when used with a view f / 3.3 given that the bandwidth of the filter may have shifted under the length of emission dell'H- Alfa of 656.3nm. Astrodon 5nm filter has a bandwidth wide enough to support change optical configuration as described above without transmission loss.
Recently, Custom Scientific has offered the market a filter H-Alfa 4.5nm that overcomes the problems of the previous model. The figure below shows two shots of the Crescent Nebula (NGC6888) obtained with a filter Astrodon H-Alpha 6nm (right) and with a filter Custom Scientific H-Alfa 4.5nm (left). The images were taken the same night in sequence, with the same instruments and consist of 6 exhibitions 5 minutes each then processed in the same manner with Maxim DL. You may notice the greatest contrast provided by the filter Astrodon right. The rectangle is drawn in the same region to use the Maxim DL: The table shows the highest value of the mean and standard deviation of the signal, resulting in greater contrast filter Astrodon.
|H-FILTER ALFA b> td>||MEDIA ADU td>|| SD td> tr>|| Astrodon 5nm td>|| 16279 td>|| 5919 td> tr>|| CUSTOM SCIENTIFIC 4.5nm td>|| 13114 td>|| 5265 td> tr> table> div>|
Many Astrophotographers use filters H- Alfa, SII and OIII to obtain images similar to the Hubble. The photo shows an example of what can be achieved by shooting a region of the nebula North America with a Takahashi FSQ106N and a CCD sensor KAF3200.
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