Baader 7.5 nm Solar Continuum Filter (540 nm) - 2" Filter Thread

Baader 7.5 nm Solar Continuum Filter (540 nm) in 2" Cell

For Visual and Photographic Observations of the Sun

The Solar Continuum Filter is practically a narrow band photosphere filter for solar observation in white light. It provides the highest contrast in the photosphere of the sun. The filter works as a monochromator: suppressing the effects of the atmospheric turbulence and delivering images that are significantly sharper.

Lens systems - including those of apochromats, catadiopters or eyepieces - are traditionally optimized for the spectral range around 540 nm, since this is where our eye has the highest sensitivity. This narrowband filter therefore blocks everthing with the exception of the spectral range in which a lens optic works most sharply and with the highest contrast. The effect is greatest on achromatic lens telescopes; but there is also an effect on apochromatic telescopes, catadioptric systems, and even pure mirror systems by reducing air turbulence.

As a monochromatic filter, it is ideal for use on monochromatic cameras and can even provide a tremendous gain on pure color systems.

With a colour camera, as with deep-sky narrow-band photography, it is less effective as only the green pixels are used. Thus, although you still benefit from the improved image sharpness of the telescope that is optimised for green wavelengths (and the reduction of the influences of air turbulence), with a colour camera you cannot fully exploit the better image quality compared to monochrome cameras, as you are effectively working with reduced camera resolution.

Compared to the previous model with 10 nm half-band-width, this filter has a half-band-width of only 7.5 nm, which increases the contrast even more. It thus replaces both the previous Baader 10 nm Solar Continuum filter and the stacked 1.25" Filter BA2458392. The single filter is so good that stacking is no longer necessary - the contrast gain of a single 7.5 nm filter makes stacking unnecessary, and this performance is now also available in 2".

The Baader 7.5 nm Solar Continuum filter is also be included in the scope of delivery of the Cool Ceramic Herschel prism Mark II, which is in preparation.

The Baader 7.5 nm Solar Continuum also offers all the advantages of the CMOS-optimized Baader filters:

Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio

Reflex-Blocker coatings, for largest ever freedom from halos, even under most adverse conditions concerning aux-optics

Identical filter thickness to existing standards, with utmost care for parfocality

Blackened edges all around, with filter-lead-side-indicator in the form of a black frontside outer rim, to additionally eliminate any reflection due to light falling onto the edge of a filter

Each filter coated individually, with sealed coating edge (NOT cut out of a larger plate with coatings left exposed)

Life-Coat™: evermore hard coatings to enable a non-aging coating for life - even in a most adverse environment

Photo by a customer

Our customer Utz Schmidtko (Hannover region, Germany) took a very detailed photo of a sunspot on 11.07.2023 with the help of this filter, which we would like to share with you:

Object: Sunspot in white light

Telescope: TS PHOTOLINE 130 mm f/7 EDT Triplet APO Refractor
Light reduction: Herschel wedge with ND3.0 filter and polarizing filter
Contrast enhancement: Baader Solar Continuum Filter
Camera: ZWO ASI178MM

Please click on the image to get a larger version (original image).

Congratulations on this beautiful image and fingers crossed for more!