Solar Filter FAQs

Here we answer some questions that arise frequently from our customers. If your questions are still not answered, please email us and we will respond as soon as possible.

SOLAR FILTERS

What is the difference between visual and photographic Baader film?

Can I use visual film for photography? - Yes

Can I use photographic film for visual observations? - No


You can use visual Baader film for visual astronomy as well as for photography. The difference is that the photo film lets through 16x more light than the visual film does. So this means that your equivalent exposures will have to be 16x longer with visual than with photo film, but with the ample light of the Sun, that is usually not an issue.

The photo film CANNOT be used for ANY visual work - not even briefly to focus the Sun through your camera. To use photo film, you will have to use additional ND (neutral density) filters to reduce the Sun's glare during focusing. You could also use your visual film for visual observations and for focusing, then switch to the photo filter for photography. On a video camera, you can use the photo filter directly if you use the LCD screen (and not the viewfinder) for framing/focusing.

Do you sell off-axis or full-aperture solar filters?

Our 63mm, 110mm and 140mm filters have an on-axis design. Because of the on-axis design, these filters are not optimal for reflector telescope designs (Newtonians, Maksutovs or Schmidt-Cassegrains) since most of the Baader film will overlap with the telescope's secondary. But if you've got a refractor, these filters are perfect! The 180mm, 200mm and 225mm filters, however, have an off-axis solar filter aperture, so these will work very well with reflectors as well as with refractors.

Do you sell filters larger than 225mm ID (inner diameter)?

Not at this time. Also, note that the 225mm filter does not imply that this will work for an 8" telescope - it is meant for slightly smaller scopes where the outer tube diameter does not exceed 225mm (just under 9").

Can you make a solar filter of size X for me?

Sorry. We cannot make special-request filters in sizes and designs other than what we already offer.

Should I make a full-aperture or reduced-aperture filter?


A full aperture filter has an advantage of more light capture - nice, especially for long focal length telescopes (like SCTs), but by no means necessary. However, full aperture filters are also reputed to provide higher contrast, higher resolution (since you're 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. In most instances, an aperture of 3-4 inches should be adequate.

Is it easy to replace the Baader film if required on your solar filters?

Very. Just unscrew the retainer ring on the filter cell to strip out the old Baader film and glue on a new one. The filter film on the 63mm filter cannot be replaced unless you glue the film to the inside of the filter cell upon replacement.