2 The instrument concept

The telescope that has been used in the experiment is a Meade 2080 Schmidt-Cassegrain F/10 with a focal length of f=2032 mm. The images of the Moon were captured with a PXL211 CCD: it uses a Texas Instruments TC211 CCD, $165\times 192$ rows by columns, with a pixel size of $16 \;\mu$m$\times 13.75 \;\mu$m. When the CCD is mounted at the focus of the telescope the scale of the system is of 1.6 by 1.4 arcsecs per pixel perpendicularly to the edge of the Moon and along it, respectively.

It is also well known that in the CCD the matrix of pixels is sent, one row at a time, to the serial register where the pixels are read sequentially. While the process of shifting each row or each pixel is very fast (of the order of 10^-7 s) in our low cost interface there is a bottleneck due to the A/D conversion of each pixel.
In order to freeze the effect of the atmosphere on the images of the lunar edge, it is necessary to overcome this limit. We adopted the approach of using a frame transfer technique so that more images of the Moon are collected in the same frame and it is possible to have an equivalent frame rate of roughly 20 Hz. The edge of the Moon is imaged in n of the lines which are on the side of the CCD opposite to the serial register. Here n is the number of rows of the CCD over the number of images of the Moon that we want to have on the same frame, s.
After the first exposure (of the order of t=50 msec), the image of the edge is shifted of n lines, which are then discarded. After s exposures, on the matrix there are s different images of the edge of the Moon (Fig. 2) and the pixels can now be converted into digital data.

  

Figure 2: An image with 6 frames of the edge of the Moon obtained without the anamorphic relay

In addition, for some of the measurements performed in this experiment, an anamorphic optical relay is inserted between the focus of a the Schmidt-Cassegrain telescope and the CCD.
It is known (Laikin 1973) that in the CinemaScope system, using a conventional 35 mm cinematographic film, the image projected is twice wider than its height. This is achieved by placing an anamorphic objective after the objective of the projector. The anamorphic objective is an afocal optical system usually made of cylindrical lenses: it shortens the focal length of the main objective in one nodal plane while leaving unchanged the focal length in the complementar direction. To avoid any problem of astigmatism, due to the presence of cylindrical lenses, the anamorphic objective should work in collimated light.
The anamorphic relay used in this experiment is made of a cylindrical tube (see Fig. 3) in which a 50 mm camera objective (collimator), the anamorphic objective and another 58 mm camera objective take place.

  

Figure 3: The anamorphic relay used in this experiment. From left to right one can see the collimator, the anamorphic objective and the second camera objective. The light from the telescope arrives from the left side while on the other side it goes to the CCD

With the anamorphic relay a double portion of the edge of the Moon (if the anamorphic relay is properly oriented) can be imaged on the CCD: inversely, turning the anamorphic objective upside down and rotating it around its axis of $90^{\rm \circ}$, the perturbation observed on the edge of the Moon can be expanded of a factor of 2.
We wish to point out that we have used very simple and low cost instrumentation which is nevertheless able to demonstrate with reasonable confidence the feasibility of our technique.