During the first half of 1942, US Navy SBD bombers had problems with their bomb aiming scopes fogging over, which reduced the accuracy of their bombing during several early war operations. Was this resolved by better scopes, improvements to the existing scopes or replacing them with reflector sights?
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1$\begingroup$ Astronomers use heaters to keep their lenses from fogging up. Would not be surprised if this was also the solution. $\endgroup$– Juan JimenezMar 30, 2022 at 1:45
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1$\begingroup$ This answer on quora to a similar question suggests it was fixed in the SBD-5 by using a reflector based sight instead.. $\endgroup$– Mr RApr 11, 2022 at 3:57
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$\begingroup$ @JuanJimenez A good telescope would not have a heater because the heater would cause turbulence that would ruin the image. $\endgroup$– Anonymous PhysicistJul 17, 2022 at 3:16
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$\begingroup$ @AnonymousPhysicist You are mistaken. It's called a dew heater and they are very commonly used. optcorp.com/collections/dew-heaters $\endgroup$– Juan JimenezJul 18, 2022 at 13:50
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$\begingroup$ @JuanJimenez "Good" was a key word there. Those are for small hobbyist telescopes. Humidity is low at good locations: en.wikipedia.org/wiki/Teide_Observatory elt.eso.org/about/location maunakeaobservatories.org/maunakea-is-unique $\endgroup$– Anonymous PhysicistJul 23, 2022 at 3:07
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1 Answer
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The fogging problems were solved by switching from a telescopic to a reflective gun sight.
From The Dauntless Dive Bomber of World War Two by Barrett Tillman, chapter 1:
The SBD-1 through the -4 were equipped with a three-power telescopic sight, a holdover from the open-cockpit aircraft of the thirties. The pilot looked through the tube, lining up the crosshairs on the target while keeping a ball much like that of a turn-and-bank indicator centered in its groove. The centered ball told him the aircraft was level in the dive, otherwise the bomb would go off on a tangent when released. The drawback to the telescopic sight was its tendency to fog over in a dive from high altitude because of a sudden change of temperature, and the resulting condensation clouded the lens. The windscreen was also prone to fogging, and pilots said the tubular sight was inadequate for aerial gunnery since it severely limited the field of vision.
The answer was a reflector gunsight nearly identical to those used in fighter aircraft.
Beginning with the SBD-5, Mark VIII reflecting gunsights were installed, as were heaters for the windscreens. These measures eliminated the problem and were instrumental in improving bombing accuracy. But they were not available until 1943. ”
An image of the Mk. VIII reflecting sight mentioned, provided by the US Air Force Museum:
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2$\begingroup$ There is something wrong here because telescopes can be reflectors. Both mirrors and lenses can fog. Modern high quality mirrors are made of the same glass as high quality lenses, but with a thin metal coating. The cause of the fogging is the heat capacity of the glass. $\endgroup$ Jul 17, 2022 at 3:15