For the present time we use a 80 mm photographic objective for Messier 20 images demonstration.The objective is stopped at f/5.6 in manner to reduce the geometrical aberrations and thus to obtain very fine stellar images. A filter R is interposed between the objective and camera CCD to reduce also chromatic aberrations. Audine camera is equipped with a KAF-0401E CCD. We use of the DRIZZLE command of Iris.

Figure 11. The figure shows one of the 15 dithered frame obtained to test the drizzling technique with short focal length photographic objective. The FWHM is of 1.2 pixel. Integration time is of 60 seconds.

Figure 12. Left, the classical average of the 15 diphered frames (simple shift and add technique). We show here only a part of the initial image. The result is zoomed 4 time compared to the starting format. Right, the result of the drizzling composit algorithm (scale parameter = 4). The resolution improves is very significant (more than 50%) !

Figure 13. It is necessary to adjust the parameters of the diphering for an optimal result. Left, the value of pixfrac (pixfrac=0.2) is too low what produces holes. Center, the number n of images is too weak (n=3). Right, the parameters are nominal (pixfrac=0.6, n=15, scale factor=4). Remember also that the pixfrac parameter should be slightly larger than the inverse scale factor value. For example if the scale factor is 2, a good value for  pixfrac is 0.6 (1/(scale factor) = 0.5).

 

Figure 14. It is still possible to improve the result slightly. Top left, the image at output of the diphering processing. Top right this image was deconvolued by method of the maximum entropy (MEM command under Iris). Bottom left, we used a modified version of the Richardson-Lucy algorithm (wavelet multiresolution regularized Richardson-Lucy restoration). Bottom right, a scaled image, extracted from the Buil-Thouvenot Atlas, realized with an Epsilon Takahashi 160 telescope (focal length of 560 mm). The comparison with our image test made with a simple 80 mm photographic objective is instructive. All the images are processed with Iris software.


Figure 15. Click on this image to see the result of the diphering technique in full format (1500 X 1000 pixels). The scale parameter scale is here equal to 2. The resolution reached is that which one would have with a 135 millimeters objective, but the field of view is that of an optics of 80 millimeters focal length ! This is a fundamental property for survey programs.

Figure 16. Another example: The M11 region captured with a standard 55 mm focal length photographic lens and with an Audine equipped with a KAF-1602E CCD (1520 X 1024 pixels). We have combined 18 diphered individual images (180 seconds exposure each at f/5.6). Click on the thumbnail image to display the final result (1.2 Mb). This image has a format of 3000 X 2000 pixels and contains a huge quantity of information (14X 9.3 field of view).

 


Goto index page                                                  Previous                                                   Next