The Schmidt 400/300/615 camera	Aldo Radrizzani, one of the best italian astroimagers

Film imaging is no more a good choice in the modern era. But for me the real reason not to use film is that Aldo has yet imaged all that can be imaged, from an observing site in the mountains and so I cannot do better from my polluted backyard. Moreover Kodak have just discontinued Tecnical Pan, the only film that can exploit the great resolution of this telescope. Moreover all know that CCD cameras can gather far better results than film. For all thise reasons, I've thought to digitalize the Schmidt camera, a non simple task for many reasons.
First of all a CCD camera with a lot of pixel was necessary, but with the uncommon characteristic to be compact enougth not to introduce a significant obstruction in the optical path: remember that in a Schmidt camera the focal plane is exaclty in the middle of the tube. In the beginning of 2006 there were not many cameras that satisfy all thise requests, so a choosed one with a Kodak Kaf-6303e sensor, with about 3000x2000 pix of 9 um, in black and white, with a maximum quantum efficiency of about 65%.
Once found the camera, the curved focal field problem must be solved: with film the solution was bending the plate by means of a curved support. The CCD -unfortunately- cannot be bent and the optical solution was a simple plano-convex lens nearly in contact with the ccd chip surface, at only 1 mm distance, realized by Romano Zen. The glueing of the lens in the right position was made by the CCD camera manufacturer. And so the camera cannot be used anymore on other optics! The optical correction is very good on the whole field.
Another big problem was the CCD camera cooling, necessary to gain the best performances. The Peltier cells used to cool the ccd chip cool on one side and heat on the other side. This heat would accumulate inside the telescope tube and in some time it would distort the optics. Luckily the chosen ccd camera is provided with a liquidi cooling system that can conduct the heat out of the optical tube, where then is dispersed in the air with a heat exchanger and a fan. The liquid is maintained circulating with a pump. To avoid that in the winter the liquid can freeze, I've used ParaFlu liquid, a glicol-ethilenic and water mixture that freeze at about -40°C.

The motorization of the mount
This mount was conceived about 30 years ago, when GO-TO mounts were only a dream. But now a mount without a go-to motorization would not be fully exploitable.in an observatory. So I've added an AstroElectronic FS2-40V controller and Secm8 motors. The modification was not easy because the old declination movement was realized with a tangent arm that permit only a few degrees of motion. This was substituded with a gear wheel and a worm gear, kindly offered by my friend Ivan Mariotti.
The mount is really a heavy weight, all the complex of mount, fork and tube weight nearly 600 kg! For the dismounting from the dome of Aldo, the transport and the re-mounting I've to thanks a lot many strong friends, among which Alberto Brunati, Alberto Gianni, Alessandro Gambaro, Antonio Paganoni, Stefano Simonelli,, and others, without whom I've neved succeded.
The filters
The CCD camera has a black and white detector and to obtain color images (or narrowband images) some filters with generous free aperture (50mm) were necessay. Another requirement is the thicness that must be exactly the same (+/-0.01 mm) to assure the parafocality. A filter wheel was not a feasable solution because it would have obstructed the optical path. So I've designed a magnetic filter holder, a mechanical jewel made by my fiend Franco Martegani. Now I've a LRGB set and a H-alpha 6 nm, all from Astronomik.

Guiding
The guiding scope is the same used by Aldo, an achromatic refractor of 120mm f/13. Differently from Aldo that have always guided by eye using the eyepiece, I obviously prefer to take advantage of technology, and I use an autoguider. Now I'm using a modified Vesta Pro webcam with a b/w sensor and a 0.5x focal reducer. This system fully accomplish to the task. The commands are imparted with a relais-box.
The observing site
To maximize the useful observing nights I've built the observatory in the more confortable site: my backyard. Unfortunately I live in the center of a 16.000 people city in the middle of Pianura Padana, the more industrialized region in Italy, where the light pollution is abundant and where the Milky Way is NEVER observable, neither in the clearest and more transparent nights. The limiting magnitude in the best nights is about 4,5. The option to build the observatory in the mountains, farther to be by far a lot expensive, whould not allowed me to exploit the instrument all the clear nights.

South-East view. Note also the 310 mm Newton Maccagnan piggybacked on the Schmidt.	The observatory during winter after a snaw fall (December 2009).	The desperate situation with the light pollution... this is one of the worser places on Italy. Click for scale.

The observations
The possible activities of a fixed observatory are many, a lot more that those possible with a telescope to be mounted and dismounted all the nights. The activities spans from very deep sky images, of the H-alpha nebulas and of the galaxies. Other observations are photometric studies of the variable stars and asteroids, and ,more, tje astrometry of asteroids and comets. For this reason I've obtained the Minor Planet Center B39 code.
In the future I'd like to piggyback a 30 cm Newton reflector, and the observations will widen also to high resolution on planets and Moon.

Other DSC (Digital Schmidt Camera)
With the advent of the digital imaging, many Schmidt cameras has been converted. In August 1998 Aldo Radrizzani conducted me to visit a DSC at the Cote d'Azur Observatory, in Calern, in Southern France. The Schmidt camera with a 90 cm front lens and 1,5 m mirror was instrumented with a Loral 2Kx2K sensor and was mainly used of asteroid search, by means of the drift scan method. Unfortunately now this telescope was abandoned. Here are some DSC links.
Links:

• Cote d'Azur Observatory, Schmidt camera
• CCD Imaging With A Schmidt Camera, by Mike Harlow
• A field corrector and a flat Schmidt camera, obtained modifying a commercial Meade Schmidt-Newton telescope, by Tanaka Kazuyuki
• David Levy published on Sky and Telescope, July 2006, pp 106-107, an article about his 40 cm Meade Schmidt camera, digitized with a modified SBIG STL-11000. Unfortunately no additional information is available from his website (up to 12/1/08).
• Osservatorio Astronomico di Treviso, DSC by Fabrizio Marchi
• Commercial DSC: A&M, on Astrotech website
  
• Commercial DSC: ASA, Astro Systeme Austria

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