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Passive Autofocusing For Visual Telescopic Systems Abstract System Flow Chart Stars have been always been a source of fascination to man. To observe these stellar bodies, NASA and other large international space organizations have developed telescopes with extremely powerful optics, controlled by sophisticated hardware and complex software. However, the majority of stargazers are hobbyists with relatively cheap telescopes and mounts that need to be manually controlled and focused. Handling a telescope is no easy feat. Setting up a telescope, orienting it, and carefully tracking the desired celestial body is a tedious process that requires much patience. Our project minimizes the amount of work required to focus an image, by automating this process for the user. This is accomplished using the following microcontroller-based closed-loop feedback system: The imager feeds the image from the telescope into MATLAB, which calculates its sharpness measure. This value is sent to a microcontroller, which moves the focus motor via an H-bridge for a calculated duration in the predicted direction of better focus. This process is constantly repeated until successive sharpness measures are close enough to assume that the image has converged to the point of maximum focus. Orion Accufocus motor moves LPI attached to telescope Autostar Imaging Software captures and saves images to computer ADVISORS AUTHORS Dr. Saleem Kassam Mr. Siddharth Deliwala Harsh Jain, EE ‘07 Vishaal Persaud, EE ‘07 Neha Sharma, EE ‘07 (i,j) j i The Muller & Buffington Sharpness Measure sums the squares of the intensity values (I) of all the pixels in the image and generates a sharpness value (S) for it. For a focused star image, whose energy is concentrated over a few pixels, a high sharpness value is obtained. On the other hand, if the same star image is poorly focused, it will yield a lower sharpness value since the same energy is now diffused over more pixels. Results MATLAB picks latest image using Muller and Buffington's sharpness measure Focus value sent to Microcontroller Yes End Yes Is current focus value almost equal to previous focus value? No Is focus value less than previous focus value? No Direction of focus motor reversed and step size reduced Direction of focus motor and step size remain unchanged Generic Plot of Image Sharpness Vs. Distance along Focus Axis Microcontroller moves motor using the new values for the movement parameters System Block Diagram GROUP 10 S = ΣΣ System initializes 2 I Muller & Buffington Values (From Matlab) Imaging the body becomes even more exasperating due to the replacement of the eyepiece with an imager. The user now has to rely solely on the images displayed on his computer screen, which are subject to finicky software settings. The imager also provides a smaller field of view, which, combined with the extreme magnification of the imager (~200x), causes even the slightest vibration by the user’s touch to displace the point source (such as a star or a planet) from its field of view. Additionally, the image needs to be re-focused when the imager replaces the eyepiece, as they have different optics. For an amateur telescope hobbyist this much need for precision may prove discouraging. Muller & Buffington Sharpness Measure Distance along Focus Axis DEMO TIMES Thursday April 19th, 2007 Times: 1.00pm-3.30pm System Specifications •Focuses a point source image in under 3 minutes •Runs continuously and autonomously in real-time •Selects the latest image for processing but not while focuser is in motion •Terminates when image is focused and resets upon keyboard input •Easily portable and can be operated using a 9V battery