[vsnet-chat 4790] 7Kx4K camera at Sonneberg Observatory

[Peter Kroll <pk@stw.tu-ilmenau.de>]

In response to:

     I was wondering if Peter Kroll could explain the rationale behind
using such a short focal-length lens for this survey camera.

\Brian


Yes, I could: The combination of this 7kx4k camera with this 3.5/30
fish-eye objective is, simply, the very first use of this chip for sky
surveys.

Sky surveys -- or better "patrols" as we call our regular (photographic
-- so far) sky survey -- aim at regording large portions of the sky, or
even the whole sky, as frequent as possible, as deep as possible and as
accurate as possible (depending on the scientific purpose). Quite clear
that all these goal cannot be achieved simultaneously. 

That's why we are working towards a hierarchical sky patrol, consisting
of between 2 and 4 levels of monitoring:

Level 1: Complete coverage of the whole sky with one exposure very
frequent (some 5 min.) down to about 9m.

Level 2: Large fields (some 10 deg) with a sky coverage of once per
night down to about 15m.

Level 3: Smaller field (a few deg) with a sky coverage of once a
week/month down to 20m.

Level 4: (optional) Deeper than 20m.

In this sense, the camera's first light concerns level 1. In order to
cover the whole sky with this chip (84 x 48 mm) one simply needs such a
lens (in this case a Russian ZODIAK 1:3.5/30 mm; this means 8mm
effective aperture only!). Of course, a more powerful lens (1:1 or so)
would be extremely helpful, but we haven't it at the moment. (Does
somebody know from where we could get not very expensive ones?)

We are very happy to have this big chip available now, even for a very
moderate price (less than 50k$ for the whole camera). As soon as we get
more funding, more cameras will be build to set up the higher levels.

The reason for a hierarchical sky patrol is, e.g., to register transient
events, and, this is a serious problem at least in Middle Europe, to
distinguish air plane flashes from real astronomical objects. On our
wide-field photographies such flashes appear very frequent, and one can
uncover them only when a chain of "new stars" can be seen. -- This is
the case in all-sky-images! From these images one would be able to
predict false stars in the other deep images. 

This for short about the rationale behind...

Peter

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Dr. Peter Kroll                 E-mail:         pk@stw.tu-ilmenau.de
Managing Director               URL:    http://vsnet.stw.tu-ilmenau.de
Sonneberg Observatory           Phone:           +49 (0)3675 / 81214
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