About
Astronomik Nebula Filters
The following pictures may give you a glance of what the different
filters do. Therefore a certain area of the sky was taken with and without
filters. The performance of the different filters is clearly dependant on the
object itself, because the best filter will always be the filter best suited
for the emission lines of the object. However, darkening of the scattered
background light as well as the spectral selectivity of the filter is clearly
visible by these examples.
The following data are valid for all of the pictures:
Nikon D70 Digital Camera at 1600 ASA, objective 85mm, F/2.5. These are
highly compressed parts of the original pictures. They were taken under a
typical suburban sky, with medium background light. All pictures are raw, just
the internal noise reduction of the camera was activated. Due to the spectral behavior
of the filters the pictures are more or less colored - simply just a small part
of the spectrum is able to pass the filter. If you use them for photographic
purposes, you should take only the grey values or you have to be very careful
with the colors produced. However, in this case we have left the color in just
to give you an overview of the filter colors.
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30s exposure without filter. The sky background is clearly visible,
this is the maximum possible exposure time. |
Picture taken with CLS-filter (CLS = City Light Suppression), also 30s
exposure. Background is really darker, the contrast is remarkably improved. Because
of the broad spectral pass of the filter the faintest star limit is not much
worse than without filter, but one will get a greenish color. With this
filter you can achieve an expansion of the exposure time by a factor of two
to three. |
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Same picture taken with UHC-filter, also 30s exposure time. The filter
has narrower spectral band pass, which leads to a more darkened background
and now also to a loss in the limiting magnitude of the faintest stars. But
if you compare the intensity of the Orion nebula, you will find nearly no
difference to the pictures before. |
Same filter, but 90s of exposure. Now the limit in faintest star
magnitude is like the 30s-exposure without filter. Sky background becomes
visible again. The Orion nebula is visible well structured - thjs is due to
the two spectral bands of pass, one in the blue/greenish and the other one in
the deep red. |
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Picture taken with the H-beta filter, 30s exposure time. The extremely
small spectral pass takes most of the light intensity, background is really
black now. The color is blue due to the wavelength passed around 486nm. |
Again H-beta-filter, but 180s exposure time. H-alpha parts are clearly
missing in the Orion nebula, which can pass the other filters. |
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30s exposure with H-alpha-filter. Only the far red can pass this
filter, therefore the picture is colored red. Just the brightest stars are
visible here, but look at the Orion nebula: it is still as nearly as intense
as without filter. |
Again H-alpha-filter, but 180s exposure time. Background is still
dark, but the Orion nebula is now visible to the outer regions. Beside the
left bright star at the top the flame nebula becomes visible at a very faint
level. |
More information on Astronomik filters you will find at the
manufacturers site http://www.astronomik.com
and measurements on spectral performance of the filters at André Knöfel:
http://www.astroamateur.de/filter