Apodizing Filter for an SCT - do they work?

apodization - [optics] The modification of the amplitude transmittance of
the aperture of an optical system so as to reduce or suppress the energy of
the diffraction rings relative to that of the central Airy disk.

Del Johnson


"Brian Tung" wrote in message
...

What exactly does "apodize" mean, as a verb?

Brian Tung

On Thu, 10 Jul 2003 17:54:46 +0000 (UTC), (Brian Tung) wrote:

What exactly does "apodize" mean, as a verb?

It is commonly used in the literature as a verb: to apodize an image; apodizing
an image, etc. It just means applying apodization, a filtering operation in
frequency space. The classic example of apodizing a signal is applying a Hanning
window when computing an FFT in order to eliminate the discontinuities at the
edges of the time domain sample.

There is an IRAF function, APODIZE, to do just this when working with mosaics.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:

On Thu, 10 Jul 2003 17:54:46 +0000 (UTC), (Brian Tung) wrote:

What exactly does "apodize" mean, as a verb?

Apodize : to cut off the foot

On Thu, 10 Jul 2003 18:10:46 +0000 (UTC), (Brian Tung) wrote:

So, just to make sure, the term does not have any
application outside the realm of diffraction rings and Airy discs?

Not at all. It is used in all kinds of signal processing, spectroscopy, NMR, and
lots of other things that perform frequency-domain operations.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

In message , Brian Tung writes
Del Johnson wrote:
apodization - [optics] The modification of the amplitude transmittance of
the aperture of an optical system so as to reduce or suppress the energy of
the diffraction rings relative to that of the central Airy disk.

Thanks, Del. So, just to make sure, the term does not have any
application outside the realm of diffraction rings and Airy discs?

It's used widely in just about all signal processing fields and
especially in aperture synthesis and radar. Usually to mean weighting
down the higher spatial frequencies in a controlled manner to minimise
the discontinuity of the graph of frequency response of a system at the
point where finite aperture prevents further measurements.

Also the term is widely used in 1-D signal processing where it is a lot
more accessible with various choices of weighting leading to different
trade-offs.

Simple cases for a function in a rectangular window and various
apodising functions should be included in most signal processing
textbooks.

Regards,
--
Martin Brown