A Guide to Choosing Astronomy Eyepieces for Binoviewers

Baader AstroSolar Visual Solar Filter Film (ND 5) - 3" (76mm) Square Piece

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Our Product ID: OFIL-BP-ASOLV-030
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Pre-cut Baader AstroSolar film piece

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  • Pre-cut Baader AstroSolar film piece
  • An image of the Sun captured using Baader AstroSolar film. Photo credit: Radoslaw Ziomber.
  • Example of a home made solar filter for a telescope using Baader solar filter film
  • Example of a home made solar filter for binoculars using Baader solar filter film
  • Example of a home made solar filter for a camera lens using Baader solar filter film

Please Note: For safety reasons, we do not accept returns of Baader film. Please make sure that you order the right type and size for your needs.

Product Details

Baader AstroSolar Safety Film - 3" x 3" (76mm x 76mm) square piece. Other film sizes referred to in the description below are all sold separately.

A. Information About Our Pre-Cut Baader Solar Filter Film Pieces

We offer Baader AstroSolar Safety Filter Film pieces in a visual optical density (OD) or neutral density (ND) of 5.0. This implies that the filter film will block 99.999% of the solar intensity; in other words, it has a transmission of 0.00001 or 0.01% only.

This is suitable to make your own:
(i) Solar viewing glasses or observing card (for direct solar viewing without the use of optical equipment), or
(ii) Front-mounted solar filters for telescopes, binoculars, spotting scopes, or large camera lenses.

Baader sells their AstroSolar Safety Film in just three sizes (A4 7.9x11.4" sheet, medium 19.7x39.4" roll, and extra large 46x46" roll). Since 2003, we have been providing amateur astronomers and photographers worldwide with Baader film in many sizes and at excellent prices. Besides the original A4 sheet and medium roll, we also offer Baader film in smaller 1.5", 2", 2.5", 3", 4", 5", 6", 7" and 8" square pieces.

B. Baader AstroSolar Safety Film - Brief Overview

In its September 2000 issue, Sky & Telescope magazine proclaimed Baader Planetarium's AstroSolar Safety Film to be "the new standard in solar filters." AstroSolar Safety Film provides white light views of the Sun that are unmatched by any other front-mounted solar filter or material.

The views through AstroSolar Film display fine solar details, including fine penumbral detail in sunspots, solar granulation, and lighter colored faculae. The solar disk is set against a dark background, free of the haze and scatter that is common in typical 'mylar' films or inexpensive glass filters. The performance of AstroSolar is even more remarkable when considering its very low cost. When combined with Baader's tips for a simple do-it-yourself filter mount (see below), anyone can construct a complete low cost, high quality, white light solar filter for any telescope, binoculars, or camera lenses.

What is even more important - with AstroSolar Film the Sun appears in its real color - neutral white (with only a slight bluish tint). Other films and glass filters produce a blurry bluish or reddish/orange/yellow solar image, thereby cutting part of the spectrum. Especially with an orange sun, it is very hard to see faculae regions which are visible predominantly in the blue portion of the light spectrum.

Due to its neutral color balance, AstroSolar Film can be used with various other color (or interference) filters which allows the observer to concentrate on certain spectral passbands for investigations of different layers within the solar "atmosphere." It is also possible to further improve the stability and sharpness of the solar image through the use of the Baader Solar Continuum Filter (sold separately). Views of granulation and faculae are particularly enhanced through the use of this continuum filter, in combination with AstroSolar film. Users of achromatic refractors will be particularly pleased with the performance using this additional filter.

Please note that you cannot see solar prominences with white light solar filter film such as this - that requires the use of sophisticated and significantly more expensive narrowband solar filters or specialized solar telescopes.

C. Making Your Own Solar Filter

While many commercially made solar filters are available, either using Baader AstroSolar or other film types, it is fairly easy and much cheaper to make your own custom solar filter for your telescope or camera. Instructions for making a simple solar filter cell are included with the film piece you purchase (the instruction sheet can also be downloaded from the link below). Baader AstroSolar film filters must be mounted in the front of the telescope. A simple Google search for solar filters will show you dozens of sites with examples of filters other amateur astronomers have made, along with some excellent photos of the Sun shot with this filter material.

You can construct a full aperture filter or a smaller off-axis filter for your telescope. In most cases, an unobstructed filter size of 3-4 inches in diameter should be sufficient. Make a larger or full aperture filter if you have a long focal length telescope and/or plan to observe with high magnifications which dims the image. Larger filters also provide higher contrast, higher resolution (since you are using a larger aperture, the theoretical resolving power is higher), and are more comfortable to use (since you get a larger exit pupil) when the conditions are good. On the flip side, a smaller aperture provides steadier images when seeing conditions are turbulent, which is most often the case in most places.

D. Appearance of Baader AstroSolar Film

At first glance, Baader AstroSolar Film appears to be like a thinner version of ordinary aluminum foil. You will often notice streaks, bends or dents on the Baader film you receive. Sometimes, it also appear that the film might be slightly "warped." This is absolutely normal and natural, and it does not imply that the filter film is defective. The optical and mechanical properties of the film are not compromised. Please also note that the "flashlight test" is not a good way of inspecting this film. Putting it right against a very bright light will show a very mottled and non-uniform appearance, but again, this is normal and does not indicate a problem with the film piece.

E. Eye Safety

AstroSolar Film is essentially free from pinholes since, unlike even the most expensive glass filters, it is coated on both sides. Hence, the chance of two pinholes overlapping each other is extremely small. Pinholes do appear, but to 1 out of 10000 only, in optical density 2.5! This is because pinholes act as diffuse sources of light, not point sources. Baader AstroSolar safety film has been approved for eye safety by the National Bureau of Standards in Germany, the PTB. Unlike any other solar filter on the market, AstroSolar is CE-tested according to EG-Norm 89/686 and EN 169/92 (notified body 0196). All processes connected to this product have been thoroughly tested. Coatings are inspected constantly for consistency to ensure your eye safety!

F. Technical Specifications

- AstroSolar Safety Film is a specially manufactured streak and blister-free foil only 0.012mm thick.
- The film is manufactured by Baader Planetarium, Germany.
- The base material is not cheap Mylar. The quality of the solar image is immeasurably better than can be achieved by using so-called Mylar "rescue blankets" or similar materials.
- The basic development of this precision film was made in laboratories for nuclear and particle physics. Due to its absolute homogeneity, the foil attains the optical performance of high quality plane-parallel glass filters.
- High density coatings on both sides of the foil ensure a highly uniform filtering capacity without pinhole effect, resulting in an extremely contrasty solar image with neutral density characteristics. The Sun appears in its real color - neutral white - not blue or orange.
- The coating of AstroSolar Safety Film is subject to constant quality control. Its reflective property (reduces intensity of sunlight by over 99.999%, i.e., by a factor of over 100,000 in the case of visual film) and security for direct solar observation is tested repeatedly by the PTB (German National Bureau of Standards for Eye Safety).
- One layer of this foil is sufficient for the construction of a safe, high resolution solar filter.

(Source: "Baader AstroSolar Safety Film" and "Original Baader AstroSolar Safety Film" information sheets, distributed by Baader Planetarium Astronomical Instruments, Germany)

G. Cleaning AstroSolar Film

We strongly recommend that you store your completed filter in a container to protect it from dust and damage when you are not using it. Similarly, protect any unused filter material so that it is in new condition when you need it. Fingerprints on the metallized surface are to be avoided under all circumstances. It has the same consequence as putting fingerprints onto a telescope mirror.

Since your AstroSolar filter will be open to dirt and dust, the coating may require cleaning after extended exposure. If the dust is loose, you may be able to blow it off with compressed air or an airbulb, both available in camera stores. Since the coating is harder than regular aluminum coatings applied on mirror surfaces, it can be cleaned with a solution of dishwater detergent and distilled water. Obtain sterilized cotton wool (as used for eye application), available in pharmacies. Normal cotton wool as used for cosmetic purposes should NOT be used!

Use careful, gentle strokes. For each stroke, a new portion of cotton should be used, soaked with the cleaning solution. This helps to avoid scratches in the metal surface due to dust grains picked up by the cotton.

Check the cleaning result by holding the cleaned filter up to the Sun. If scratches or pinholes show up, exceeding a combined uncoated area of 10 square mm, the film is regarded as unsafe and must be destroyed. Tiny pinholes can be covered with a black felt-tip marker. If the filter becomes very dirty, we encourage you to replace it, rather than risk damage in the cleaning process.