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Filter Clear Without Blocking Infrared Diam. 31.8 mm Mounted In The Cell.
The Clear filter (C) without blocking infrared has a transmission greater than 97% through the spectral region, transmission is reduced to 95% at 400nm only in blue. The filter C increases the luminance signal 45 % for the Kodak sensor spacing and the like.
If your aim is to get to 22 magnitude combining long exposures in "" luminance "", this filter C is the best choice (the other is bypass the filter ).
If your aim is to emphasize the bright colors of a galaxy, the filter luminance L, which is combined with spectrally filters RGB, is the best choice to eliminate the halo surrounding galaxies in the near infrared ( NIR) .This choice is even more desirable if systems are used to slow or with a meniscus or a corrector plate.
If you have a refractor or a telephoto lens, remember that the filter C also passes the UV. For this many refractors little chromatically corrected, often require a filter "" minus violet "" or "" Fringe-killer "" to remove the optical dispersion in the region of short wavelengths (blue-purple halo around bright stars). A filter size L partially these wavelengths and this is the best choice if you are using these types of instrument.
All filters are parfocal Astrodon:
most frustration nell'astrofotografia with CCD is that of having to find the correct firing position with the H-alpha filter: the narrow band filters keep out much light so you must use a very bright star to perfect the focus . All filters Astrodon Tru-Balance L, C, R, G, B, H-Alfa, OIII and SII are parfocal on optics with focal ratio less than f / 4.
This means you can adjust the focus using a filter C or G, install a filter H-Alpha and immediately proceed with the acquisition. This is one of the key advantages of the Tru-Balance filters Astrodon that made them cosŕ¬ popular in a short time.
The thickness of the filter determines how it can be parafocality: Tru-Balance filters are dichroic filters with very resistant treatments deposited on a single glass substrate highquality. The reduced thickness (3 mm) of this substrate is controlled accurately with error +/- 0.05mm. The change from lot to lot is less than 0.1mm, measuring slightly less than the critical areas of focus of a system f / 5. On request it is possible to select within various batches filters with less variation and then get a set of filters that have the exact same thickness (prices on request). "
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