Focal length: | 120 mm |
f/number: | 12 |
Half field of view: | 10 degrees |
Wavelength: | 550 nm |
This clears out any previous lens data and prepares CODE V to "restart" and define a new lens. A confirming dialog box asks you to confirm the restart.
A title is actually optional, but it's a good idea. The title appears on most graphical and tabular output.
Landscape Lens
).
Note that below the entry area for the title is the place where we can enter the radius mode. We are using the default setting, which is to enter radii rather than curvatures.
You must specify at least one wavelength -- there is no default wavelength. Wavelengths area always entered in nanometers, regardless of system dimensions.
CODE V needs to know the system aperture (or pupil size) of your system. This can be entered in one of four ways, entrance pupil diameter (EPD), numerical aperture at the object or image (NAO or NA), or image space f/number (FNO); one of these must be entered, since there is no default pupil specifcation. The pupil specification defines the extent of the light bundles traced from each field point.
You can define the lens data in inches, millimeters, or centimeters. Since system dimensions (units) are defined on the same subscreen as EPD, we can make sure now that we are working in millimeters.
This positions the cursor at this line in preparation for entering the surface data.
You can double-click to highlight any field, then type a new value. You can also move between data fields with TAB (move right) and Shift-TAB (move left) keys, or move up and down with the vertical arrow keys or the up/down arrow toolbar buttons.
Surface | Radius | Thickness | Glass |
---|---|---|---|
1 | 30 | 3 | BK7 |
2 | 60 | 0 | |
STO | | 100 | |
Click the [Go] toolbar button or press the Enter key to enter the new surface data.
The results should be as shown below
Now is a good time to draw a picture of the lens and verify that it looks reasonable. Plots are generated in a seperate plot window.
You may have noticed that the value of 100 mm was not a very good guess for the distance from surface 3 to the image. We could try various values to achieve better focus (or enter the value shown as Back Focal Length), but there's an easier way. The paraxial image solve (PIM) can set the focal distance directly, without trial and error.
Note that after entering this solve the thickness is updated. Furthermore, redrawing the lens (using Display - Quick Lens Draw) will show that the lens is now in focus.
Most systems have a non-zero field of view, and in CODE V we predefine one or more specfic field or object points at which to do analysis and optimization. For an infinite object distance, semi-field angle (in degrees) is the most common field specification.
Field angles must be entered in increasing order and should be entered as a Y-Angle for symmetric optical systems.
Redraw the lens using the menu item Display - Quick Lens Draw and notice how each field has a set of three rays displayed, the central ray and two marginal rays.
The above plot was clipped from the plot window and converted to a transparent gif for display here.
We've done a fair amount of data entry, and the lens is a valid one (indicated by the prescence of non-blank first-order values on the bottom of the main Lens Data screen), so it would be wise to save our work in a disk file. The menu item File - Restore can then restore this file into memory at any time.
The thickness of the image surface is interpreted as the defocus from the nominal thickness of the surface before the image (in this case, that nominal distance is set by a PIM solve.)
We have chosen not to vary defocus in this lens, so we click [V/F] again to keep this thickness fixed.
We want to hold the effective focal length (EFL) to 120 mm.
Look in the CODE V Output window to see the results.
This display shows the tangential and sagittal field curves and the distortion, both as a function of field height on the vertical axis.
Look in the CODE V Output window to see the results.
Look in the CODE V Output window to see the results
where
Quick AUTO Run produces a default optimization that holds the system's effective focal length (EFL) to its current value. It generates a grid of rays from each object point and wavelength, and tries to minimize the RMS spot size of these ray bundles. It does this by changing the variables, while meeting any required constraints.
In this example, the stop is at the lens (since the thickness of surface 2 is zero). The optimization produces the best singlet lens for this application, but the lens is not very good.
At the end of this optimization (which may be repeated to try for additional improvement), you have completed the design of a landscape lens. The off-axis performance should be considerably improved over the singlet with stop at the lens.
Repeat the analysis steps.
Maintained by John Loomis, last updated 5 Dec, 1997