Section 2 - Manufacturing tolerances, Mechanical and Thermal disturbing effects

After this, we started to examine how resistant these designs are against manufacturing tolerances and agains mechanical and thermal disturbing effects.

In the case of oil spaced lenses, the following parameters can be slightly different from the theoretical values:

Curvature radiuses
Lens member thicknesses

According to the computer simulations, an oil spaced lens is highly resistant to these problems. E.g. if we change a curvature radius of the lens e.g. by 1mm (a very irrealistic value!), the result is still very little, the lens performs almost perfectly. The situation is similar in the case of lens member thicknesses, even changing the thickness of a member with the same irrealistic amount, the performance hardly changes. As in these tests were tried tolerances that are many times larger than the real tolerances we use, we can conclude that neither of these problems could cause real performance problems for the lens.

It is interesting, that the fact of oil spaced lenses having less degrees of freedom also means that the manufacturer of the lens has less chance to make a really bad lens. If there are no parameters to change in order to ruin the performance, the average quality of the produced lenses will be excellent (as all currently existing oil spaced lenses we know about are in the high end category optically).

In the case of air spaced lenses, the differences of lens member thicknesses have about equally negligible effect on the performance, so in this respect the lens types are about equal. But in the case of curvature radiuses, the situation is completely different.

In the case of air spaced lenses, changing one of the radiuses surrounding the air space cause a severe problem in spherical aberration. (It is interesting to note, that similarly changing the other surface surrounding the air space, the problem can be corrected.) So, we can conclude, that air spaced lenses are many times (about 20x � 100x) more sensitive to the incorrect curvature radiuses surrounding the air spaces compared to oil spaced lenses. Though, in the case of the front and back surface of the lens (i.e. those surfaces that do not surround an internal air space) there is no difference between an oil spaced and an air spaced lens, both designs are insensitive to the changes of these radiuses. So, all in all, air spaced lenses are extremely sensitive to the radii of 4 of their surfaces (out of their 6 surfaces), and oil spaced lenses are insensitive for every surface radii. One score for oil spaced lenses!

Additionally, in the case of air spaced lenses, there are two more parameters that depend on parts that are manufactured to a limited precision: the thickness of the air space, and the parallel position of the surrounding surfaces. Both parameters depend on the three little metal spacers between the lens members. According to our simulations, the lenses are sensitive to the thickness of the air space, but the possible difference in the thickness of the air space has no tragical effects: some spherical aberration and also some false color can occur if the thickness of the air space is not optimal, but with standard tolerance in machining the metal spacers, the problems that can occur are not vital, until the surfaces surrounding the air space are parallel. On the other hand, the lens is extremely sensitive to the extremely small deviations in this parallel position, if one of the spacers is only a slightly thicker or thinner than the other two spacers, the result is really problematic: the lens starts to show a serious coma even on the optical axis. There is no similar problem in the case of oil spaced lenses, as the lens is homogenous internally and the oil immersion tightly keeps the surfaces together.

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