Baader AstroSolar Filter Film - photographic ND 3,8 - 20 cm x 25 cm

A good base for self-built solar filters:

With the Baader Astro Solar film, you can watch and capture the sun with full contrast. It offers also better protection against UV rays than simple glass filters.

This photographical filter foil lets approx 1/6300 of the light pass through - 16x more than the visual foil. (ND 3.8 vs. ND 5.0)

It is intended for solar photography with long focal length where the visual foil is already too dark.

The photographical foil can also be used for visual purposes in combination with narrow-band contrast filters like the Baader Solar Continuum or the Baader K-Line filter.

In this case, additional to a strong neutral or contrast filter, a UV cut filter is necessary! Suitable filters are linked as recommendations. 12.5% types are meant to be used with the Solar Continuum Filters, whereas the ND 1.8 types can be used without it.

The Baader Astro Solar Foil has been awarded as the astro product of the decade in the USA.

The following characteristics have made this possible:

Optimal protection: The foil is covered on both sides with a filter layer, not only on one side. Every layer can contain micro-holes that bypass UV rays. With a layer on both sides, this is not possible any more.

Exceptional optical quality: The Astro Solar foil as an optical performance that is superior to e.g. Mylar foils. This is proven by an independent test. Compared with glass filters, the Baader foil is superior, too - in every section, it has a diffraction-limited performance. What is more, the foils is colour neutral. It does not give a green or yellow colour.

Very tough: A glass filter may break and a foil may rip. But the Baader Astro Solar Foil is, because of its special molecular structure, extremely tear-rigid.

The colour of the sun through the foil

The sun is depicted in a neutral cool white tone. It is a tale that the sun would appear in blue. The neutral tone allows views full of contrast and is described by many observers as "very pleasant". Especially at higher magnifications, this allows successful observations.

Some astronomers prefer a warm orange or yellow colur. This colour does not represent the reality and is - from our point of view - not optimal for maximum contrast and finest details, but in combination with this neutral-colour foil, one can experiment with differnt colour filters and can choose the best. Thus you are not fixed to one colour.

An example for photographic use:

This group was captured with the Baader Foil (photographical version) and a Baader Solar Continuum filter. Instrument: TS 127/1200mm achromatic refractor.

Such high-resolution pictures are only possible with a good objective and a good solar filter. There are many pictures like this that have been made with the Baader Astro Solar foil.

Images from a comparative test

Interferometrical Test


Reference
Ideal picture - Strehl 1.01
(only theoretical)




Baader AstroSolar
close to the optimum -
like a good objective




Mylar Solar foil
irregularities are obvious. This would be
neither a good filter nor a good objective



Star test


Reference
Airy disc - 99.9% Strehl
(only theoretical)




Baader AstroSolar
94,1% inside the Airy disc
Comparable with a very good objective




simple mylar solar filter
57,2% inside the Airy disc
not diffraction limited any more