Transcript Slide 1

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