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Astronomik OIII |
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The best focal ratio for the use of this filter is 1:4.5 to 1:6. The field of application is from 1:3,75 up to 1:15. Loss of transmission and colour displacements, that appear at other filters, emerge with the Astronomik filters only at extreme light intensive focal ratio of 1:3 and bigger. So you can see widespread objects in the whole field of view and not only in the middle. The OIII filter is to be used from a aperture of more than 6" (15cm) on. At smaller instruments there is not enough light available for a sensible use. Many experienced Deep- Sky- observers rather use the OIII filter at instruments with more than 10" (25cm) despite the smaller field of application than the more versatile UHC filter. Due to the well- known high optical quality of the glass substrate you will see with the Astronomik OIII filters still the needle-sharp stars, that you know to from your instruments.
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The red lines are the most important lines from artificial light pollution. The green lines are the most prominent emission lines for nebulas. The grey curve is the human eye´s night-sensitivity. The blue line is the transmission curve of the filter. |
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The Astronomik OIII filter is designed for visual observation
of gas nebulas and planetary nebulas. Due to the extreme small band pass
of the two OIII- lines, the filter will produce a relevant increase of contrast
even under best observing conditions. At faint super nova remnants and faint
planetary nebulas the Astronomik OIII filter often makes the gain, that decides
if the object can be seen or not.
