Adjustable Telescope Solar Filter, 86-117mm, Baader AstroSolar Film

The Johannes Scientific Adjustable Solar Filter is a front-mounted objective filter made with genuine Baader AstroSolar film. It slips over the front of your telescope or telephoto lens and adjusts to fit any tube with an outer diameter between 86 mm and 117 mm, so you can safely observe sunspots, solar transits, and the partial phases of a solar eclipse. Because it mounts ahead of the optics rather than behind them, sunlight is filtered before it is ever magnified.

Will it fit my telescope?

Measure the outer diameter of the front of your telescope tube or dew shield, not the aperture of the objective lens. Those two numbers are different, and the fit depends entirely on the tube measurement. If it falls between 86 mm and 117 mm, this filter fits.

Many 70 mm to 90 mm refractors and compact Maksutov telescopes land inside this range, along with a number of large telephoto camera lenses. Measure before ordering rather than going by your telescope's aperture rating.

Specifications

Safety warnings

Read this before every use. Telescopes and telephoto lenses magnify the Sun's rays. Unfiltered sunlight through a lens can cause fire, burns, damage to cameras and optical equipment, and permanent blindness.

1. Inspect the film before every session. Never use a filter that is torn, scratched, creased, or shows pinholes of light when held up to a bright lamp.
2. Always mount the filter in front of the objective lens. Never use a filter that threads in behind the optics, where the Sun's rays are already concentrated.
3. Confirm the filter is seated firmly and cannot be knocked or blown off before you look through the eyepiece.
4. Never remove the filter while the telescope or lens is pointed at the Sun.
5. Never look at the Sun directly, or through a finder scope, without proper protection. Cap or remove your finder scope before observing.
6. Supervise children at all times during solar observation.

Frequently asked questions

How do I know if this fits my telescope?
Measure the outer diameter of the front end of the tube or dew shield with a tape measure or calipers. Anything between 86 mm and 117 mm will fit. Your telescope's aperture rating is not the number you need.

Can I use it on a camera telephoto lens?
Yes, as long as the outer diameter of the lens barrel at the front falls within the 86 mm to 117 mm range. It fits over the outside of the barrel rather than threading into the filter ring.

Is it safe to look through?
Yes, when the film is undamaged and the filter is mounted securely on the front of the telescope. Baader AstroSolar film is made specifically for solar observation. The safety depends on the condition of the film and the security of the mount, so inspect it before every use and replace it if it is damaged.

Can I use it during a solar eclipse?
Yes. Keep it on for every partial phase, from first contact through to the end. Removing a filter during totality is something only experienced observers should attempt, and it must be back in place before the first sliver of the Sun reappears.

Can I photograph the Sun through it?
Yes. The filter works for both visual observation and imaging, and it produces a neutral, near-white solar disk rather than the orange cast you get from many glass filters.

What will I actually be able to see?
Sunspots and their surrounding penumbrae, granulation on the solar surface under good seeing, planetary transits, and the full progression of a partial eclipse. This is a white-light filter, so it does not show prominences or flares. Those require a dedicated hydrogen-alpha telescope.

Does it work on binoculars?
Only if each barrel measures within the fit range, and only if both barrels are filtered. Never look through binoculars with one side unfiltered.

How should I store it?
Keep it in a dry place, away from pressure and sharp objects that could crease or puncture the film. Store it flat or in its original packaging rather than loose in a bag with eyepieces and accessories.