The main purpose of this instrument is a high precision full disk imaging of the photosphere in order to derive sunspot and faculae areas and positions as well. Other scientific objectives are studies of the underlying photosphere before, during and after chromospheric flares, hunting for the mystery white light flares at the begin of a new solar cycle and providing a data set for developing an automatic determination of sunspot relative numbers by image segmentation techniques. The obtained time series will also continue the support of the Debrecen Photoheliographic Data by daily synoptic images.

The KPT is based on the Kanzelhöhe Photoheliograph (PhoKa) which went into operation in 1989 and was described in detail in Pettauer, T.: 1990, in L. Deszö (ed.), The Dynamic Sun, Publ. Debrecen Heliophysical Observatory, Debrecen, p. 62(1990).

Unlike the old Kanzelhöhe Photoheliograph (PhoKa) which needed an enlarging eyepiece system to fit the solar disk image approbiate onto a 13x18 cm² planar film, is the chip size (15x15 mm²) of the proposed CCD cam model even too small for the acquisition of the full solar disk in the primary focus of the superb Jena AS objective lens which should remain in use. Therefore considerable changes of the telescope design in order to adapt for the relatively small detector and image sizes were required. Downsizing the primary focus image with an eyepiece lens would be an option, but a calculation of the optical parameters showed, that this combination would need a field lens and would increase the aberations. The alternative was to insert another positive focus lens within the focus distance of the objective lens L1 and reduce the effective focus length (for details see figure 1). The back side of the Jena AS front lens (air gap side) carries a gold coating with a transmission less than 0.1% to reduce the amount of light which enters the telescope to avoid image distortion caused by heating the telescope. The spectral range of the solar continuum is limited by an interference filter with a FWHM of 10 nm at a wavelength of 546 nm.

Figure 1: Layout of the Kanzelhöhe Photosphere Telescope. Choosing achromats for L1 and L2 reduces also non-chromatic aberations. The effective focus length of the complete system is about 1460 mm which corresponds to a disk size of about 13.7 mm in diameter. The diaphragms D1...D3 for the reduction of straylight were kept from the old system. An extra neutral filter N with a transmission of 10% became necessary to avoid very short exposure times (< 2 ms) and smearing which is specific to interline transfer CCD cams. The lens L2, the interference filter IF, the neutral filter and the CCD cam are fixed in an inner tube which is inserted from the back end into the main telescope tube. The focus control is made manually by shifting the lens L1 back and forth with a worm gear.

Figure 2: A 3-D ray trace sketch of the Kanzelhöhe Photosphere Telescope visualizes the physical setup of the instrument.

Figure 3: The whole photosphere telescope system is mounted piggy-back on the main patrol telescope cabinet.