The Geometric Image Analysis feature can be used to model extended sources in ZEMAX. It can be used to analyze useful resolution, display distortion, and calculate geometric efficiency for planar extended sources centered at any field point on the object surface.

You can examine the image analysis capabilities of ZEMAX using the Cooke triplet design. To open a Geometric Image Analysis window, select the menu option, "Analysis > Image Analysis > Geometric Image Analysis". The plot of a letter "F" (the default extended source) will then appear as a spot diagram.

To show the image of a grid instead of the letter "F", click on "Settings" from the Geometric Image Analysis window menu bar. Change the "File" setting to GRID.IMA. Details of the IMA format used to generate extended sources can be found in the ZEMAX manual. You can also change the "Show" setting to False Color. This will simulate the display of the image of the extended source on a detector with a finite number of pixels. Click "OK" to re-generate the analysis with these new settings.

ZEMAX also includes a Geometric Bitmap Image Analysis which is similar to the Geometric Image Analysis feature except that it uses standard Windows bitmaps (BMP) files as the source. Red, green, and blue wavelengths are traced to detector pixels on the image plane or any other surface to create RGB images. Any three wavelengths may be traced for analysis in others parts of the spectrum. This feature may be used to analyze photo-realistic images, or custom targets created and saved in bitmap format. Large numbers of rays typically need to be traced to adequately sample the image.

Open a Geometric Bitmap Image Analysis window and change the settings as follows. Set the "Input" to ALEX200.BMP. Increase the number of pixels at the image surface by setting both "X-Pixels" and "Y-Pixels" to 100. Decrease the size of each pixel by setting both "X Pixel Size" and "Y Pixel Size" to 0.5. Lastly, increase the number of rays that are traced by setting "Rays x 1000" to 100 and then click "OK".

   

There is also a Diffraction Image Analysis feature which is similar to the Geometric Image Analysis feature except that it computes the diffraction image. The Diffraction Image Analysis capability uses the same IMA file format as the Geometric Image Analysis feature does. The ideal image is transformed to frequency space and multiplied by the optical transfer function, then transformed back to the spatial domain at the image plane to produce the diffraction image. This feature may be used to analyze small images where the MTF is constant over the field of view subtended, and diffraction effects would blur the structure in the image. Over-sampling and zero-padding of the image are supported to increase the resolution and number of pixels in the diffraction image without having to redefine the image file.

Open a Diffraction Image Analysis window and change the settings as follows. Decrease the size of the extended source by decreasing the "File Size" to 0.01. Increase the resolution of the extended source by changing the "Oversampling" setting to 10 X. Then, click "OK" to generate the analysis.