I knoiw that shooting in half light and the jungle, you always use a large aperture - like the battle sight because you need the light and ranges are usually short. So why we also have a No5 rifle sight with a small aperture as well as the large diameter is another mystery. I have to say that of all the hundreds and hundreds of No4's that I have ever seen and worked on, I have never noticed that there were two different aperture sizes.

The change, whenever it was, wouldn't have taken place without some extensive trials. But I can't find anything, even in the detailed EMER's!