I thought I've always read that the aldis was pretty useless. I can't image having to lean foward and put my eye up to a telescope in the middle of a dogfight. If you're that far away, aren't you too far to be shooting?
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Wab
Well Wab,
I think your right about the 1st edition but it was magnified. when they took out the magnification 1v3 to 1v1 and changed from cross hairs to circles, it made all the difference.
"In 1915 Martlesham Heath tested an optical sight submitted by the Aldis Brothers of Sparkhill, Birmingham. It consisted of a 559 mm (22 in) metal tube containing lenses giving a magnification of x 3 and a cross-hair aiming mark. The new sight was mounted on the cowling of a Be.2c with a Lewis gun on the upper wing, and firing tests were carried out at ground targets. The sight proved more accurate than the ring and bead, though on one occasion the pilot nearly flew into the ground whilst looking through it! The sight was then tested in air fighting manoeuvres. Magnification of the field of view often made it difficult to locate the target quickly. Another problem was that the front lens was prone to fouling by oil from the engine, and it was also no longer possible to estimate target range by comparing the wingspan with the ring diameter. Hugh Aldis was therefore asked to submit a sight without magnification, but with a circular graticule which could be used for range-finding, and possibly, deflection. A spring-loaded oil flap was fitted, and leather-lined adjustable clamps mounted on short sturdy brackets were supplied.
"Production Aldis sights were issued to selected front-line squadrons for operational trials in mid-1916. Pilots found the Aldis superior to the ring and bead, and news of a secret new gunsight soon spread to other squadrons. The Aldis was said to possess almost magical powers, and at a time of high casualties the authorities did nothing to dispel these rumours.
By 1917 the Aldis had become the standard British sight for fixed guns. It was usually mounted on the right side of the engine cowling, with the ring and bead on the left. A smaller version was used on large guns such as the Davis and COW, and a version for anti-aircraft guns had a prism which could be clipped into the field of view, giving a set deflection of 30 degrees."
Some also had the ring and bead mounted directly on top of the Aldis sight like in the Camel.
The sight could be used as little as 5" and as far as 12" away. In a few planes the sights were put right through the windshield and in some case's the windshield was just removed.
Here is a good write up about a few of the wwI sights, the Aldis is "part 7"
http://forum.axishistory.com/viewtopic.php?f=84&t=17649 
