Drogenberg

Astrophotography

Hoegaarden, Belgium

EQUIPMENT REVIEWS

All reviews represent my personal opinion after extended usage of the material - I have no connections to any vendor or brand.

Baader Semi-Apo Filter 2" (Images: Baader)

I purchased the Baader Semi-APO filter mainly for photographic usage in combination with the achromatic refractor 120mm Startravel from SkyWatcher. It effectively reduces the purple secondary spectrum around brighter stars. The biggest advantage that this filter brought me was the anti-light-pollution effect. I knew it was supposed to do so because this filter is not only a cutting of the purple part of the spectrum but also removes the Sodium (Natrium) lines of High-Pressure and Low-Pressure Sodium lights. In addition the infrared part is cut off also.

The effect was: longer exposure times and a higher background contrast.

Pictures above: this is a series of exposures taken with the 135mm Nikkor pre-AIS at F2.8 with the filter mounted before the objective.

From left to right: without filter / without filter and processed / with filter / with filter and processed.

For some reason the filter introduced a reflection from the (very very) bright star Capella. The halo of Capella itself is smaller with the filter. Also the contrast (before processing) seems higher with filter then without. Part of the orange background is reduced.

Pictures below: test images of Regulus with diverse telescopes, Semi-APO, UHC and IDAS LPS D1 filter. On the Travelstar divers objective masks were applied to decrease the aperture.