"Astrophotographers amateur getting beautiful and detailed photographs tricolor of deep sky objects that exceed those recorded by professional observers only 20 years ago.
CCD sensors have quantum efficiencies which can reach 90%, with a high resolution and a large field can show details also very weak.
sensors of these cameras are made of silicon (Si), they cover the wavelengths of ultraviolet (UV <400 nm), visible (VIS 400-700nm) and infrared (NIR) up to about 1100nm as shown in the diagram above: spectral regions covered by the various filters including red (R), green (G), blue (B), the luminance block with infrared (L) and luminance without blocking infrared (Clear C). This also shows the sensitivity curve of the sensor Kodak KAF3200ME. The curves R, G, B, L and C refer to those filters Astrodon series E.
Astrophotographers professional use CCD sensors very expensive made of different materials to allow greater sensitivity in the infrared range in addition to the data from silicon. For example, images in the bands J and K are taken at 1250 and 2200nm respectively.
The photometric filters available covering the region of the near infrared (NIR) that is between 700 and 2800nm, while the infrared (IR) is located in longer wavelengths.
images tri-color shooting by placing a red filter (R), a blue filter (B) and a green filter (G) between the telescope and CCD camera monochrome. Then the three images are added together and processed with special software to obtain a final color. The images in the three colors are usually taken at a lower resolution (binning) to allow shorter exposures. The low-resolution images in color are used to "" œcolorare "" the high resolution image obtained in the luminance channel. This combination provides the high resolution image LRGB.
The NIR region remains largely unexplored by amateur astrophotography. Probably this is due to the fact that silicon sensors seem insufficiently sensitive in this region. Perhaps it is also true that no one knows what can be photographed in these wavelengths. The photograph in narrow bands has become popular only recently allowing even amateur photographers to obtain images similar to Hubble. The images in the infrared can never follow the same evolution becoming a new tool for everyone astrophotographers?
Let's see what you can get with photography in the infrared (NIR): ITALY
- photograph Tri-color entirely in the region of the near infrared (NIR)
- study objects obscured by dust in the Milky Way, as IC342 that are difficult to photograph in the wavelengths of the visible
- to study faint emission nebulae in red (ERE)
- discover stars and nebulae of other details that are obscured by light emission wavelengths in the visible range, the H-Alpha, the SII, OIII or other elements
- to combine images in RGB and NIR of globular clusters to emphasize the appearance of cooler stars
- to minimize the effects of light pollution from mercury vapor lamps and sodium ul> The NIR filter set is similar to that LRGB. The luminance is a filter NIR broadband whose transmission starts to 700nm. The filters NIR1, NIR2 and NIR3 match the filters B, G and R wavelengths and increasing (FIG. 2).
Even the filter NIR3 has a very broadband and the final shape of the transmission curve is defined by decrease of the quantum efficiency of the sensor used. Eg. in FIG. 3 shows the transmission values obtained when the filters are used in conjunction with a sensor KAF3200ME. The transmission curves are obtained from the resulting final transmission curves of the filters and their curve of the quantum efficiency of the sensor (QE.
The filters Astrodon LRGB allow to use a single exposure time for the three colors having the same efficiency (see the description of the filter set LRGB for more information). The same approach was used to design filters NIR but taking into account the sharp drop in quantum efficiency that is detected in the NIR region. Tests carried out on a star with G2V a sensor and a KAF3200ME RC 12.5 "" gave the following weights for NIR1, NIR2 and NIR3: 0.85: 1.00: 1.21. As seen the filters require NIR exposures that are greater than the RGB filters.
filters for NIR are tri-color unique in that they provide the opportunity all'astrofotografo amateur explore objects that can not be taken with RGB filters. The group IC342 / Maffei is an excellent example: in fact only recently, in 1968, Paolo Maffei has managed to discover these galaxies They were obscured by dust in the Milky Way. If the giant galaxy Maffei1 was not obscured by dust, losing well magnitude 5, it would be one of the brightest objects in the night sky, along with M31 and M33. These objects are located directly beneath the double cluster (NGC869, NGC884) in Cassiopeia. Figure 4 shows a tri-color in the NIR Maffei1: is one of the few amateur images of this object.
The ability to switch over to the emission nebulae can be detected from the images of M17 in Sagittarius, shooting in a NIR left and right in the VIS (FIGURE 5). Note how many more stars are present in the image NIR that the recovery in VIS failed to detect.
The shooting technique NIR can also be used on globular clusters. Figure 6 shows the cluster M3 resumed in LRGB (left) and tri-color NIR (right). The colors are more distinguishable in the image in the VIS (left) due to the hot blue stars detected by the blue filter set LRGB. However there are still many details in the image observable NIR. Thanks to the fact that the various filters are all parfocal for most of the optical systems, there emerges the possibility of interesting studies. You can study any combination of filters: you can take a picture, for example tri-color BGNIR2 to capture light from the stars blue warmer and cooler red ones more efficiently than it would using a traditional red filter. And this is just one example of use. "