Astronomik OWB CCD Clip Filter for Sony alpha 7 cameras

Astronomik OWB Clip Filter

The OWB filter would usually not be designated as an "astronomical" filter. The intention is to enable converted digital cameras (without inbuilt IR-filter) in order to be used for ´terrestrial´ photography.

The OWB (Original White Balance) filter shifts the complete spectrum of a converted DSLR or mirrorless system camera in such a manner that the camera will not be exclusively usable for astro-photography. Therefore the decision, which in former times had to be made, whether to ´victimize´ a system camera in order to exclusively use it for astronomical tasks or accept the lower sensitivity on the red end of the spectrum, it is now a thing of the past and disencumber your purse, too.

Compatibility:

The Clip-Filter are sucessfully tested with the bodies Sony Alpha 7, 7r and 7s. (Astronomik will test other/future models and add them here.)

The manufacturer has made a short video which shows installation and removal of the clip-filter for Sony Alpha:



The filters are not suitable for Sony alpha 3000 to 6500 or Sony alpha NEX cameras.

Main use:

Digital cameras which have been converted for astronomical use by removing the inbuilt IR-filter or by substituting it with a filter with greater range for H-alpha, have a white balance that made them unable for ´terrestrial´ purpose. The spectral sensitivity of the camera will be changed by an OWB-Filter to the former range. In other words: The OWB pretend to be the conventional built-in filter!

Use of the Filter:

Adapting modified DSLR cameras or mirrorless interchangeable lens camera (removed or substituted inbuilt IR-filter) to achieve standard colour space in digital imaging via a special spectral curve.

Filter transmission curve:

The horizontal axis is the wavelength in nanometers (nm). 400 nm is deep blue, at 520 nm the human eye senses green and at 600 nm red. At 656 nm is the famous "H-Alpha" emission line of hydrogen.

The transmission in % is plotted on the vertical axis.

The red line shows the transmission of the filter.

Visual filters: The grey line in the background shows the relative sensitivity of the human eye at night. The maximum is at ~510 nm and drops to longer and shorter wavelengths. You can easily see, that you can´t see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity at 656 nm is 0% at night!

Photographic filters: The grey line in the background shows the sensitivity of a typical CCD sensor.

The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by see mercury (Hg) and sodium (Na), which are used in nearly all streetlights.

The most important emission lines from nebulas are shown in green. The most important lines are from ionized hydrogen (H-alpha and H-beta), double ionized oyxgen ([O III]) and ionized sulfur ([S II]). The square brackets indicate that these lines are forbidden.