AstroSolar® Photo Film 3.8 is only intended to be used by well-experienced Astro-imagers. AstroSolar® Photo Film 3.8 is not intended to serve for protection during visual solar observation. Also PhotoFilm is not necessary for imaging the sun with camera- or tele-lenses, or in the prime focus of most telescopes. The resulting exposure time would be much too short, respectively the results would cause severely overexposed images. Instead, you can use AstroSolar® Safety Film 5.0 with a modern camera up to a focal ratio of ca. f/15 to f/20 – even at ISO 100.
AstroSolar® Photo Film 3.8 solely is used in conjunction with astronomical telescopes – and only in connection with fast digital video cameras. This combination is highly apt to capture finest solar surface detail and granulation at extremely high magnification – but enabling ultrashort exposure increments measured in milliseconds – in order to “freeze” atmospheric turbulence (lucky imaging technique). The results are quite outstanding as can be seen in the image gallery and in the customer reports.
Do not use AstroSolar® Photo Film 3.8 until you are convinced to having gained sufficient experience with the hazards of Solar videography while using regular AstroSolar® Safety Film 5.0.
PhotoFilm OD 3.8 consists of the same optically treated carrier film with just diffraction limited properties as our AstroSolar® Safety Film with optical density 5.0. The density of the adjacent multiple coatings however has been reduced for Photo Film in a very controlled fashion. OD 3.8 constitutes the border line, to still offer an absolute minimum of eye safety, in case someone would handle with the film and – in spite of extensive care – would accidentally catch up a split second view of the intense solar energy near focus. Still every amount of precaution must be undertaken to avoid just this to happen.
Sadly AstroSolar® Photofilm OD 3.8 may not be used for visual solar observation – not even in combination with additional neutral density filters nor other filters of any kind. Reason being: none such filter combo has been tested by any licensed authority for eye safety. Surely such combinations may exist and they may produce magnificent and interesting views with sufficient reduction of solar energy across a safe enough spectral passband. However – as a manufacturer – we would be obliged to warrant for sufficient eye safety and provide safety evidence for an innumerable amount of possible filter combinations each having it´s own certification.
For this reason we must leave it with the clear statement that we do not approve of any other use for AstroSolar® PhotoFilm than described above.
Many astronomical Oldhands have asked repeatedly in recent years to produce an even brighter version of PhotoFilm in order to achieve even shorter delivery times. Unfortunately today nobody could or should offer such a product with his mind in peace. Just 20 years ago Carl Zeiss could afford to offer single side coated (and pinhole prone) photographic glass filters stopped to OD 3.5 – and offer them without any excessive warnings nor safety measures for photographic use with slow emulsion based SLR-cameras. In the contrary – the only warning read: “pinholes are common in solar filters. If found objectionable opaque with sharp brush and black paint”. Modern times product safety regulations do not allow to offer so bright and single side coated solar filters anymore.