From the start, the Astronomik OIII filter has been very specifically designed for the visual observation of gaseous and planetary nebulae. The extremely narrow pass band of the two OIII lines brings a substantial contrast gain to these lines even under the best observation conditions. On faint super nova remnants and faint planetary nebulae the Astronomik OIII filter will often make the difference as to whether the object can bee seen or not!
The optimal aperture ratio for the use of the filter is f/3 to f/15 with apertures of more than 6" (150mm). Transmission losses and chromatic distortions, which arise with other filters, occur with Astronomik OIII filters only when extremely bright aperture ratios of f/3 and more come into play. Thus, the Astronomik OIII filters can expand the view of dispersed objects, generally speaking, to the whole visual field of view of the eyepiece and are not limited to only the center of the eyepiece.
Since enough light must be available to make use of the OIII filter, it is best to use this filter with apertures of more than 6" (150mm). Many experienced deep-sky observers with apertures of more than 10" (250mm) prefer using the OIII filter instead of the more versatile UHC filter. Due to the high optical quality of the Astronomik OIII filter substrate you will see the same needle-sharp stars as you would from your telescope without the filter in place.
This filter is not for solar observation.
Price does not include shipping from Germany, which is separate from the possible free shipping from us to you. You will be notified of these shipping charges prior to payment being taken.