Yes – provided that the eyepiece is suitable for solar projection. With unsuitable eyepieces, the cement between the lenses may deteriorate. In particular, older eyepieces sometimes use heat-sensitive Canada balsam.

Furthermore, an eyepiece with a plastic housing can suffer damage if the Sun drifts out of the field. Burn marks on the housing appear quickly as soon as the Sun moves out of the center.

Our Classic Ortho eyepieces have been tested for up to five continuous hours. Even with inadequate tracking, only the anodizing faded; the eyepiece itself was not damaged. We cannot provide information on eyepieces from other manufacturers.

You can use the BSPS with a Newtonian, as long as

• the telescope has got enough backfocus, and if
• the telescope can be used for solar projection.

Most Newtonians with sufficient back focus should work fine with our Solar Projection Screen! However, not all Newtonians may be allowed to be used for this purpose.

There are Newtonians where the secondary mirror may get damaged, or a 3D-printed plastic spider (or secondary mirror holder) may get soft, or even some where the secondary mirror is mounted onto the spider with heat-sensitive cement only, which might dissolve after a day in the sun. The merciless needs for cost saving have led to some pretty wild telescope constructions. Black plastic may get hot in the sun, even without any optics focussing the light on them... We simply do not know every telescope, and thus we can't give any warranties for all Newtonians. The BSPS itself definitely is not the problem and observing with it is absolutely safe for the eyes of users.

So, please consult the telescope's manual or its manufacturer if the telescope can be used for solar projection. We can't give warranties which the telescope's manufacturer does not give. If there is no information available – or no answer from the manufacturer, you will be using the telescope at your own risk.

In any case, solar projection with a Newtonian is possible, many people have done it. We have successfully tested it even with a catadioptric Celestron 114/1000 Newtonian on a tracking mount, but you must be cautious concerning following issues:

Especially do not try solar projection with an open-truss Newtonian telescope! There are Newtonians with such kind of open tube design which burned down simply because they weren't properly pointed at the Sun, as this one: https://web.archive.org/web/20250826011638/https://skyandtelescope.org/astronomy-news/mike-lynchs-explodingtelescope/

This event only happened because the suns energy could enter into the tube from the side, so that the telescope focus did not contact the secondary mirror but was pointing onto the telescope front ring beside the secondary. This same situation might even pose danger for people in the vicinity ot the telescope, when you are pointing the same open tube telescope at the Sun. As a result, the concentrated light coming from the large primary mirror may even focus outside of the telescope tube on the other side of the tube and cause burns on skin or incinerate nearby objects. A metall or textile cover around the tube (a tube-shroud) is absolutely mandatory for any open tube design, to avoid this situation.

And third: absolutely make sure that nobody can look into the telescope's tube from the front end while the telescope is pointing towards the sun.

In general, telescopes with very short focal length are not well suitable for solar projection, because even the projected solar image may become too bright for convenient views. We have tested lens telescopes with focal ratios from f/5-f/15 and all were working fine with the BSPS. Still we would recommend somewhat slower optics around f/8 for the most convenient brightness.

However  -  if you happen to own a sturdy Newtonian with the standard metal tube for the optical assembly, for which in the old days even a classic (open) solar projection screen was offered by the manufacturer as an accessory, then there is probably no heat problem existing at all, as long you can reach focus.

If however the manufacturer explicitly does not allow solar projection with the telescope, eye-safety will not be the real reason, but rather the telescopes front components may be sensitive to heat build up at the secondary mirror. So you may use even such a telescope successfully with the BSPS  and experience a great projected sun,  but – you do it on your own risk – for the telescope alone.

Yes – but you must adjust the distance so that the solar image is at least 6 cm in size. For this, you can use our T-2 extension tubes, for example.

Warning: With too many extension tubes, the image becomes very large; the T-2 thread will then vignette and the image will be cut off.

Basically yes. The same notes apply as for the use of a Herschel prism. We recommend telescopes and accessories made of metal, since we do not know which plastics are used and how heat/UV-resistant they are. We cannot give any further guarantees beyond those of the device manufacturer.

Our tests with 70/400 (f/5.7) and 90/500 (f/5.5) telescopes showed no significant heat load inside the tube. At the end of the tube before the focuser, the temperature was only about 5 °C above ambient (33 °C instead of 28 °C) – no danger for focuser, telescope, or baffles, especially as long as the Sun is visible on the screen. Cover the objective when not observing.

The situation is different at the star diagonal: here, the light cone is smaller and the energy density higher. Use a full-size diagonal/prism that utilizes the full aperture without additional baffles. Too-small mirrors (often in inexpensive prisms) can suffer damage at the housing from the solar energy (fading, deformation, embrittlement).

No – Amici prisms have a more complex beam path and are not suitable for solar projection.

No – spotting scopes usually cannot reach focus with an eyepiece projection adapter; in addition, they have complex internal focusing and too many components near the focal plane which would be damaged by the heat. They are not suitable for solar projection.

Some inexpensive telescopes with 1¼" focusers do not provide enough backfocus for eyepiece projection. In this case, screw the OPFA directly to our star diagonal #2456005 / #2456005K.

Yes – but the image will be larger and you will only see part of the solar disk.

In principle yes – the image will be smaller. If it becomes smaller than 6 cm, increase the distance with additional extension tubes. Note: Excessive distance will again lead to vignetting by the tubes; the image will then be cut off.

The screen is intended to be viewed from the side. When viewed directly from above, the image appears very bright – but not harmful. Stop down the telescope if necessary; even with a smaller aperture the image remains bright enough, and the heat load on the star diagonal is reduced.

Not necessarily, but a stable mount with tracking makes observation much more comfortable. Especially with the Sun nearly filling the field of view, it will drift out of the image quickly without tracking.

Yes. When used correctly and with an image size of at least 6 cm, the screen hardly warms up. The brightness is harmless due to the natural observation distance.

No. The BSPS allows observation in white light. For H-alpha structures such as prominences, you need a dedicated H-alpha filter system.

No. The back projection reduces image brightness so strongly that the Sun remains well visible, but the Moon (even full Moon) appears too dark.

Solar activity varies in a cycle of about 11 years. During solar minimum, there may be no or only very small sunspots for several days (last maximum around 2024/25).

No – due to the back projection the brightness is already significantly reduced. An additional sheet of drawing paper on the screen dims it too much.

No. Due to the back projection the image is somewhat softer, but the umbra and penumbra of large sunspots remain visible. For maximum sharpness, a Herschel prism with Solar Continuum filter is ideal, followed by objective filters made of AstroSolar film – however, both are not suitable for group observations at the telescope.