340/500/1375 mm
, f/4.0, film size 90 mm x 90 mm, field of view 82 mm x 82 mm (Ø 116 mm) = 3.4° x 3.4° (Ø
4.8°) which differs a bit by using different plate- and film holders, instrumental angular resolution better than 10 µm = 1.5" so that
the apparent resolution is almost seeing limited to about 3" during long exposure times, thanks to the largely dimensioned primary mirror no visible
obstruction occurs over the whole field (theoretical intensity in 58 mm distance from optical axis is 90 % !). This instrument is mounted on a
heavy fork mounting and is equipped with
two 150 mm guiding refractors (f/15) and a 80 mm finderscope. It is housed in a
7 m dome on the observing site "Hoher List" in Eifel midlands (Germany). The
Observatory "Hoher List" is part of the
astronomical division of the University Bonn.
202/182/400 mm
, f/2.2 - f/2.5, film size 64 mm, field of view Ø 53 mm = Ø 7.6°; on a lens-flatted field, alternative film size Ø
86 mm, field of view Ø 80 mm = Ø 11.4°; on a curved field, instrumental resolution is better than 10 µm = 5"; (best measured
value 8 µm). Because of the poorly dimensioned primary slightly obstruction is still visible with the small film holder (theoretical intensity at 27
mm offset is 66 %) and strong obstruction is visible with the large film holder (theoretical intensity at 40 mm offset is only 38 %), so that it
will be used only for special proposes. This instrument is mounted together with the "Ohlmueller-Schmidtcamera" on a heavy German equatorial mount
(GEM) and is equipped with a 100 mm f/6 guiding refractor. It is housed in a 2 x 2 m removable garden house
on the observing site "Hoher List" in Eifel midlands (Germany) but also used as travel equipment for excursions all over the world.
140/200/250 mm
, f/2.0 - f/2.35, film size 45 x 45 mm, filed of view Ø 42 mm = Ø 9.6°; on a lens-flatted or curved field, alternative
film size Ø 86 mm, field of view Ø 80 mm = 18.2°; on a curved field, instrumental resolution better than 10 µm = 8". No
visible obstruction appears to the "small" field (theoretical intensity 21 mm off center 89 %!), on the large field an obstruction is visually
detectable (theoretical intensity at 40 mm offset 45 %). The large size cassette is commonly used only for
special porposes like large scale phenomens. It was built for the
Hale-Bopp excursion to discover
weak object structures far out in the ion tail. Mounting and
location like MPT-200.
f=500 mm, f/2.8
The "Heliotar" is a catadioptric lens build out of a Ø 200 mm main mirror, two Ø 200 mm meniscus
lenses (one with a central aluminized spot of Ø 120 mm) and two correction lenses which are placed in the central hole (Ø 85 mm)
of the main mirror. It's a system of 500 mm focal length at f/2.8 and constructed for medium size format (56 x 56 mm). Because of its special desing the whole system is only about 300 mm long and 225 mm in diameter. Cause of its strange design it needs a 200 mm long dew cap to 'baffle' much portions
of stary light out. Although the contrast seems to be poor and the instrumental resolution is only about 30 µm = 12". Obstruction occurs out of 30 mm off center. The "Heliotar" was mounted on a heavy GEM
during our Comet Halley exkursion to La Silla, Chile before it was sold in order to buy the "MPT-200".
Deltagraph (catadioptric astrograph):
Ø 300 mm, f=990 mm, f/3.3
The Deltagraph is a catadioptric astrograph. Because there is no schmidt-corrector like for classical schmidtcameras, the image abberations must be corrected by other means. In this case the aspherical primary mirror is corrected by
a three element corrector lens more ore less 'near' the focal plane. The large field of view (6x7 cm) is flat and placed inside the tube like it is known by schmitcameras. Therefore this instrument can not be used for visual observations. The image quality is outstanding and schmidtcamera like (about 5 µm at center, better than 20 µm at the extrem edges (r = 45 mm, theoretical values for spectral range of 400 - 700 nm)). Because of the large sized corrector a central spot of 125 mm in diameter is obstructed (wich is about 18 % of the total area), giving f/3.6 in total. Instrumental obstruction can be brought down to under 35 % for the extrem corners. This instrument was delivered in April 2001 and is now beeing prepared for principal testing. The first results look quite promising. A detailed test report will follow soon. A 6x7 cm vacuum cassette for rollfilm (120) is also under construction and for producing outstanding results we plan to move this instrument down to the southern hemisphere to a location in Namibia (Africa).
... to be continued later
last udate 27. May 2001