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Double Gauss Lens
In the following article I present my own version of a "Gauss Lens". The classic design of a Gauss lens consists of two groups of lenses placed symmetrically; in each group we find a positive meniscus followed by a double. The opening diaphragm is located between the two groups.
There are countless variants of Gauss lenses, as can be seen in the following links.
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https://en.wikipedia.org/wiki/File:DoubleGauss2text.svg
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https://en.wikipedia.org/wiki/File:DoubleGauss3text.svg
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https://en.wikipedia.org/wiki/File:DoubleGauss4text.svg
One of the easiest ways to start designing a Gauss lens is by Scott Sparrold at this link. The double Gauss is a lens used above all as a photographic lens. In another post we already saw that the photographic lenses meet certain conditions, which I take into account when developing my system.
Figure 1. Classic scheme of a Gauss lens.
The Gauss lens I present has a focal length of 50 mm, f/2.8, k=1.3, the BLF is almost half of the EFL (in this case it is -3% of the EFL) and the FOV is 40º. FIgura 2 shows the report and the characteristics of the system.
Figure 2. Gauss system report.
In the graph of the MTF vs Field I have chosen as the resolution line the 40lpp/mm test, revealing that we started with a 78%-79% resolution and finished close to 70%, both in the sagittal line and in the southern line. The minimum is found in the southern plane, in the 17º field, where it falls to 53%. The contrast line is maintained above 94% all over the field.
The Spot Size RMS is 3.187, 5.90 and 10.33 microns for the fields of 0º, 14º and 20º respectively. The Airy disc has an approximate value of 4.4 microns, which means that the point size for the 0º and 14º fields is very good. Although the 20º field has a dot size, a good resolution can be expected.
The system is achromatic, as we can see in the diagram of the Chromatic Focal Shift, being the value of the maximum range of focal displacement 30.9 microns.
The Ray Fan graph tells us that the aberrations are well compensated, but indicates that the system is affected by the lateral color. Looking at the "Lateral Color" graph we see how the system is outside the Airy disk for the F-line, while the D and C lines are inside.
In the DPO the same is observed, with the 0º field being the best corrected, while the 20º field shows that the D line is slightly deviated with respect to the other two. The OPD scale is noteworthy, only 5 waves.
The system distortion is 1.5% in the 20º field and the field curvature less than 0.10 mm.
The relative illumination in the 38º field is higher than 80%. In the simulated image you can see how the illumination is practically uniform and the resolution is good.
It is possible to reduce the size of the Spot Size RMS by introducing some vignetting into the system. The aperture diaphragm needs at least 5.22 mm to avoid vignetting. Leaving the aperture at 5.2 we get the following result:
As shown in the image, the dot size in the 38º field is half and the relative illumination is practically the same. The percentage of field without vignetting is approximately 96%.
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