Baader Solar Projection Screen (BSPS)

 Baader Solar Projection Screen (BSPS)

• Safe solar projection on refractors with star diagonals
• Simple observation of the Sun in white light – individually or in groups
• Quick and easy assembly of pre-cut cardboard parts with pre-mounted adhesive strips
• Also suitable for tracking control, e.g., for public outreach. Optimised for viewing from the side
• For operation, you will need (not included)
  • a lens telescope suitable for solar projection with a star diagonal/prism and at least 3 cm of backfocus. Recommended for focal ratios of ~f/6 or slower
  • eyepiece projection adapter with T-2 thread, e.g., the Baader OPFA - Eyepiece Projection adapter (I - VII) (various versions available)
  • a glass/metal eyepiece suitable for solar projection with an appropriate focal length to project a solar image at least 6 cm in diameter. The BSPS has been tested with Baader Classic Ortho/Plössl eyepieces.

Baader Solar Projection Screen (BSPS)

A safe way to observe the sun with small groups

The Baader Solar Projection Screen (BSPS) provides a safe way of solar projection and allows small groups to observe the Sun together. The projection screen is ideal for observing solar activity with sunspots in white light as well as following the course of solar eclipses.

It consists of a rear projection screen and a T-2 thread for connection to common eyepiece projection adapters. The screen was developed and tested with the Baader OPFA - Eyepiece Projection adapter (I - VII) (various versions available) . When used with the matching Baader Classic Ortho eyepieces on refractors with focal lengths between 250 and 1200 mm, it produces a solar image that fills the 9 × 9 cm projection surface. Sunspots, the limb darkening of the Sun, and the progress of eclipses can all be observed. The screen can also be used with other T-2 projection adapters instead of the Baader OPFA; however, in that case you will need to determine the required distances yourself.

Unlike traditional open projection screens, there is no risk of someone reaching into the light beam or even looking into the eyepiece. Rear projection enables a closed system. The screen can be connected to any telescope suitable for solar and eyepiece projection.

When the telescope is mounted on a tracking mount, the Sun can be observed comfortably for several hours. If the mount is not perfectly polar aligned, the Sun will slowly drift out of the field of view. From the drift direction, you can see during the day in which way the mount needs to be corrected and thereby improve the alignment while observing – detailed instructions for this can be found in the PDF of the operating manual.

The projection screen is particularly useful for public outreach, when many guests are taking turns looking through the eyepiece of a telescope equipped with its own solar filter: if the screen is attached to another small guide scope or finder, you can both check whether the Sun is still centered in the main telescope and at the same time show waiting guests what to expect.

Requirements

To use the Solar Projection Screen, you will also need:

• A telescope suitable for solar projection with a star diagonal/prism – ideally a refractor with a focal length of 250–1200 mm. The projection screen has been tested on telescopes with f/5 (90/500) and f/4 (VarioFinder 61/250) as well as on 150/1200 mm and 150/2250 mm refractors, each for several hours and at full aperture. To reduce the heat stress for the star diagonal, we recommend using telescopes faster than f/6, and to stop down telescopes with apertures larger than about 80 mm if necessary. You can see the entire Sun in telescopes up to about 1200 mm focal length; larger telescopes produce a higher magnification and show only a part of it.
• A variable eyepiece projection adapter with T-2 thread. The Solar Projection Screen was developed for the Baader OPFA. The diameter of the solar image depends on the distance to the projection surface.
  • The eyepiece projection adapter Eyepiece Projection adapter OPFA I – with 1¼" Nosepiece (#2458141) has a 1¼" connection;
  • The eyepiece projection adapter Eyepiece Projection adapter OPFA II – with 2" Nosepiece (#2458142) fits star diagonals/prisms with a 2" nosepiece.
  • If you use a Baader star diagonal/prism with T-2 connection, you can screw the eyepiece projection adapter Eyepiece Projection adapter OPFA IV – Basisversion with T-2i (#2458144) directly onto the housing and thus save backfocus.
  You may also use other projection adapters, but this may result in different image sizes. The solar image must be at least 60 mm in diameter.
• A heat-resistant eyepiece. In addition to the usually recommended Huygens eyepieces for solar projection (which are hardly available today in good quality), you can use the Baader Classic Ortho eyepieces with 6, 10, or 18 mm focal length or the 32 mm Baader Classic Plössl
• Most telescopes that provide sufficient backfocus for eyepiece projection can also be used with the Solar Projection Screen. The Solar Projection Screen requires about 30mm of Backfocus. Alternatively, the OPFA can also be screwed directly onto a T-2 prism such as Baader Zenith Prism Diagonal T-2/90 ° with 32mm Prism (T-2 part #14) (#2456005K) via the T-2 thread to achieve a very short adaptation.

Setup & Usage

The BSPS consists of the special projection screen, a T-2 thread adapter, and a pre-cut three-piece cardboard kit with pre-mounted adhesive strips for assembling the housing. Alternatively, you can download the STL files to produce a housing with protective cover from plastic on a 3D printer.

Remove all optical finders from your telescope, or cover the lenses of any optics that may still be installed.

Insert the eyepiece into the projection adapter, remove any T-2 extension tubes if necessary according to the instructions to adjust the distance, and screw the projection adapter onto the Safe Solar Box. Then insert both into your telescope with a star diagonal (on a refractor), point it at the Sun, and focus. Using the sliding focuser of the OPFA (or other variable eyepiece projection adapters), you can slightly adjust the size of the projected solar image. To center the Sun in the telescope, you can use the shadow cast by the tube or tube rings, or a dedicated solar finder.

The BSPS consists of the special projection screen, a T-2 thread adapter, and a pre-cut three-piece cardboard kit with pre-mounted adhesive strips for assembling the housing. Alternatively, you can download the STL files to produce a housing with protective cover from plastic on a 3D printer.

Remove all optical finders from your telescope, or cover the lenses of any optics that may still be installed.

Insert the eyepiece into the projection adapter, remove any T-2 extension tubes if necessary according to the instructions to adjust the distance, and screw the projection adapter onto the Safe Solar Box. Then insert both into your telescope with a star diagonal (on a refractor), point it at the Sun, and focus. Using the sliding focuser of the OPFA (or other variable eyepiece projection adapters), you can slightly adjust the size of the projected solar image. To centre the Sun in the telescope, you can use the shadow cast by the tube or tube rings, or a dedicated solar finder.

Note: To achieve focus on telescopes with a 1.25" focuser, the OPFA sometimes had to be screwed directly onto the Baader Zenith Prism Diagonal T-2/90 ° with 32mm Prism (T-2 part #14) (#2456005K)