Baader Solar Projection Screen (BSPS)

Safe solar projection on refractors with zenith mirrors/prisms

Easy observation of the sun in white light – alone or in groups

Quick and easy assembly of the die-cut cardboard images with pre-applied adhesive strips

Also suitable as a tracking aid, e.g., for public relations purposes. Optimized for side viewing

For operation, you will need (not included):

A refractor telescope suitable for solar projection with a zenith mirror/prism and at least 3 cm of back focus. Recommended for aperture ratios of ~f/6 and above.

An eyepiece projection adapter with a T-2 connection, e.g., the Baader OPFA - Eyepiece Projection Focal Adapter (I - VII) (various versions available).

A glass/metal eyepiece suitable for solar projection with a suitable focal length to project a solar image at least 6 cm in size. The BSPS was tested with Baader Classic Ortho/Plössl eyepieces.

Solar Projection Screen
Safe Solar Observation for Small Groups

The Baader Solar Projection Screen (BSPS) offers a safe way to project the sun, allowing small groups to observe it together. The solar projection screen is ideal for observing solar activity, including sunspots in white light, and for observing the progression of solar eclipses.

It consists of a rear projection surface and a T-2 thread for connecting to standard eyepiece projection adapters. The screen was developed and tested with the Baader OPFA Eyepiece Projection Focal Adapter (I-VII) (various versions available). When used with compatible Baader Classic Ortho eyepieces on refractors with focal lengths between 250 and 1200 mm, it produces a solar image that fills the 9x9 cm projection surface. Sunspots, limb darkening, and the progression of eclipses are all clearly visible. It can also be used with other T-2 projection systems besides the Baader OPFA; however, you will then need to determine the necessary distances yourself.

Unlike classic open projection screens, there is no risk of someone reaching into the light path or even looking into the eyepiece. The rear projection allows for a closed system. The screen can be attached to any telescope suitable for solar and eyepiece projection.

If the telescope is used on a tracking mount, the sun can be observed comfortably for several hours. If the mount is not perfectly aligned with the north pole, the sun will slowly drift out of the field of view. By observing this direction during the day, you can determine which direction the mount needs to be corrected and thus adjust the polar alignment more precisely during observation – instructions for this can be found in the PDF of the detailed user manual.


If the telescope is used on a tracking mount, the sun can be observed for several hours. The projection screen is particularly helpful for public outreach when different guests are constantly looking through the eyepiece of a telescope with its own solar filter: When the screen is attached to a smaller guide scope or finder scope, you can see whether the sun is still aligned with the main telescope and simultaneously show waiting guests what to expect.

BSPS on Baader Vario Finder 10x60 on Vixen 90x1000
BSPS on Celestron AstroMaster 70 AZ
BSPS on Bresser AR 90/500
BSPS on Baader Vario Finder 10x60
BSPS on Baader Vario Finder 10x60 on Vixen 90x1000
BSPS on Celestron AstroMaster 70 AZ
Requirements

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

A telescope suitable for solar projection, including a star diagonal/prism – ideally a refractor with a focal length of 250-1200mm. The projection screen has been tested on telescopes with apertures of f/5 (90/500) and f/4 (VarioFinder 61/250), as well as on 150/1200mm and 150/2250mm refractors, each for several hours at full aperture. To minimize stress on the star diagonal, we recommend using telescopes with a faster aperture than f/6 and, if necessary, stopping down telescopes with an aperture larger than approximately 80mm. The entire sun can be projected onto telescopes with a focal length up to approximately 1200mm; larger telescopes magnify more and only show a portion of the sun.

A variable eyepiece projection attachment with a T-2 connection is required. 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 OPFA I eyepiece projection adapter – with 1¼" barrel (#2458141, €63) has a 1¼" connection;

the OPFA II eyepiece projection adapter – with 2" barrel (#2458142, €80) fits star diagonals/prisms with a 2" barrel.

If you are using a Baader star diagonal/prism with a T-2 connection, you can screw the OPFA IV eyepiece projection adapter – basic version with T-2i (#2458144, €55) directly onto the housing, thus saving back focus.

You can also use other projection adapters, but you may achieve different image sizes. The solar image must be at least 60 mm in diameter.

A heat-resistant eyepiece is required. In addition to the Huygens eyepieces typically recommended for solar projection (which are now rarely found in good quality), you can use the Baader Classic Ortho eyepieces with 6, 10, or 18 mm focal lengths, or the 32 mm Baader Classic Plössl.

Most telescopes that offer sufficient back focus for eyepiece projection can also be used with the Solar Projection Screen. The Solar Projection Screen requires approximately 30 mm of back focus. Alternatively, the OPFA can be directly screwed onto a T-2 prism, such as the T-2/90° Zenith Prism with 32 mm prism including eyepiece holder and plug-in connector (#2456005K, €136), via the T-2 thread to achieve a very short adapter.


Most telescopes that offer sufficient back focus for eyepiece projection can also be used with the Solar Projection Screen. Exploded View of the BSPS at the OPFA

Assembly & Use

The BSPS consists of a special projection screen, a T-2 thread adapter, and a pre-cut, three-part cardboard kit with pre-applied adhesive strips for assembling the housing. Alternatively, you can download the STL files to create your own housing and protective cover from plastic using 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 as needed 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. You can adjust the size of the projected solar image slightly using the OPFA's sliding focuser (or other variable eyepiece projection adapters). To align the sun within the telescope, you can use the shadow cast by the tube or tube rings, or a dedicated solar finder.

Setting up the Solar Projection Screen on the telescope.

The right combinations
Focal length of the OPFA telescope with the following extension tubes (included with the OPFA): Classic Ortho eyepiece
250 mm (Baader VarioFinder 10x60) 2x40 mm Classic Ortho 6mm, 1¼" eyepiece (HT-MC) (#2954106, €73)
400 mm (Celestron PowerSeeker 80/400) 1x40 mm
500 mm (Bresser AR 90/500) 2x40 mm Classic Ortho 10mm, 1¼" eyepiece (HT-MC) (#2954110, €73)
580 mm (Baader APO 95/580)
600 mm (Celestron ED 80/600) 1x40 mm
700 mm (Celestron Inspire) 70/700)
910 mm (Vixen 80/910 Mf) 2x40 mm Classic Ortho 18 mm, 1¼" eyepiece (HT-MC) (#2954118, €73)
1000 mm (Vixen 90/1000)
BSPS on Baader APO Travel Companion 95/580

Note: To achieve focus on telescopes with a 1.25" focuser, the OPFA had to be partially screwed directly onto the T-2 / 90° zenith prism with 32 mm prism including eyepiece holder and plug-in connector (#2456005K, €136).
... Technical Specifications
Baader Solar Projection Screen (BSPS)
Product Details

Item Number

2420400

EAN Code

4047825061058
Manufacturer
Baader Planetarium
Net Weight (kg)

0.00

Optical Properties

Required Back Focus

30mm
Sunlight Wavelength
White Light (integral light)

Mechanical Properties

Inner Diameter / Clear Aperture (mm)

T-2 (M42)

Solar Filter with Mount/Thread?

Yes