This website presents high-resolution solar images accompanying our short publication, “Which Solar Structures Can Be Observed Using BAADER Accessories for Solar Observation?”, which you can download here as a german PDF file.

© All images by Wolfgang Paech unless otherwise indicated.

The animation on the left demonstrates that, at least for photographic H-alpha observation, the specified f/30 light path does not have to be maintained with absolute precision, as differences in contrast can be compensated for during image processing. However, this does NOT apply to purely visual observation. The animation shows the chromosphere at focal ratios of f/21, f/23, f/26 and f/30.

The animation shows a surge filament and the simultaneous formation of an emerging flux region at intervals of ten minutes.

SolarSpectrum filters are available with full widths at half maximum of 0.8, 0.7, 0.65, 0.5 and 0.3 Å. To achieve these narrow bandwidths, the filters must be heated and require an approximately parallel f/30 light path. Prices depend on the full width at half maximum and the clear aperture of the filter.

These SolarSpectrum H-alpha filters are available in various product series, including:

• Solar Observer Series 1, discontinued
• Series 1.5, Advanced Solar Observer
• Research Grade Filters RG 32 and RG 46

They differ both in their full width at half maximum and in their clear filter aperture, which ranges from 19 to 46 mm.

Since 2017, SolarSpectrum has supplied H-alpha filters from the SunDancer series. These filters are available with clear apertures of either 19 or 25 mm and with full widths at half maximum of 0.7, 0.5 or 0.3 Å.

These filters are also heated. However, the H-alpha line is shifted towards the red or blue wing of the spectrum mechanically by tilting the filter within the telescope’s light path.

Unfortunately, purchasing a SolarSpectrum filter alone is not sufficient. The filters require a prefilter positioned IN FRONT OF the telescope aperture. This prefilter limits the infrared heat radiation so that it remains below the operating temperature of the filter. At the other end of the spectrum, short-wave ultraviolet radiation must also be blocked, as it can destroy the sensitive etalon coatings of the filter within a very short period of time.

For this purpose, Baader supplies so-called D-ERF Energy Rejection Filter 110mm (8mm glass) (#2459243D , € 560,- ) , which transmit only radiation between 600 and 700 nanometres.

Baader therefore supplies three different telecentric systems that extend the telescope’s focal length by factors of 2x, 3x or 4x.

Starting with a focal ratio of f/15 for the 2x system or f/7.5 for the 4x system, the telecentric system produces a parallel f/30 light path while using the telescope’s full aperture. With faster focal ratios, the aperture should be stopped down until the resulting focal ratio is once again f/30. The distance from the lens vertex to the focal point is 200 mm. This leaves sufficient space behind the telecentric system for the H-alpha filter and any additional accessories, such as a 2-inch star diagonal or virtually any camera configuration.

Since 2017, Baader Planetarium has supplied the TZ-3 Telecentric System 2" – Research Grade (3x focal length) (#2459257 , € 445,- ) . It increases the telescope’s original focal length by a factor of three. For example, a telescope with an aperture of 100 mm and a focal length of 1,000 mm, corresponding to f/10, is extended to 3,000 mm. The resulting focal ratio is the required f/30.

For a stable connection between the telecentric system and the SolarSpectrum filter when using larger telescopes, Baader offers the so-called M68 Telecompendium for telecentric systems and FFC (#2459258 , € 440,- ) . An overview is available here.

Under the typical seeing conditions at our latitudes, the long focal lengths produced by telecentric systems can rarely be used to their full potential.

The focal length can therefore be reduced again BEHIND the SolarSpectrum filter using SolarSpectrum telecompressors. Depending on the distance between the reducer and the eyepiece or camera, reduction factors ranging from approximately 0.5x to 0.7x can be achieved. Fortunately, the Sun provides sufficient light, so inserting an additional optical element has no significant effect.

Since 2017, SolarSpectrum has supplied the Telecompressor 2" H-alpha 0.4x – Research Grade, for Solar Spectrum (#2459260 , € 366,- ) . It was designed for use in combination with the TZ-3 Telecentric System 2" – Research Grade (3x focal length) (#2459257 , € 445,- ) focal-length extender.

It is mounted directly on the eyepiece side of the SolarSpectrum filter and reduces the focal length previously extended by the telecentric system by a factor of 0.4 without loss of image quality. Its working distance of 74 mm is optimised for video imaging and for capturing the entire Sun with a corrected image field measuring 16 mm in diameter, which is sufficiently large for the small sensors used in video cameras.

A detailed description of how to use SolarSpectrum reducers is available here.

This website presents high-resolution solar images accompanying our short publication, “Which Solar Structures Can Be Observed Using BAADER Accessories for Solar Observation?”, which you can download here as a german PDF file.

© All images by Wolfgang Paech unless otherwise indicated.