SCOUT REGt. SCOPE assembly
Not exactly Lee Enfield but this is a bit of a follow-on from Hopmanhenks querie about his signalling telescope. They don't tell you this in the books and the photos have been reproduced so many times that they're useless. But on all but the very last spares for the Scout Reg telescope, the front lens, the Object Glass, came in two parts. The last spares supplied, made by a little company from High Wycombe, were cemented doublets.
The problem is that by default, being two separate lenses, there are now 4 ways that you can reassemble the two lenses. And you've guessed it right ....., 3 of 'em are wrong! I'll tell you how to do it correctly. The first is to look at both lenses and you MIGHT have a little 'V' vee or saw cut shaped notch on the edge of one or both. On the other hand , you might not, which is a bit of a bugger really. But if you have these, then you're half way home and dry because while it COULD mean that these notches face each other, it might not! But try it first anyway.
I am going to assume that you haven't got these notches cut or ground into the edges. Look at the lenses and you'll see that one is
PLANO-CONCAVE - that is flat on one side and slightly concave or dished on the other side and the other lens is
DOUBLE CONVEX- that is with a convex or outwards facing curvature. One of the convexes is very shallow and the other is visibly pronounced.
The flat side of the plano concave lens is the rearmost lens and the flat side MUST face the rear.
The MOST SHALLOW face of the double convex lens now fits snugly into the concave dish of the plano-concave lens. Now, with the two lenses perfectly cleaned in methylated spirit, insert them, flat surface facing the rear, into the brass housing and secure them with the counter cell or inner locking ring.
That's it really but the problem comes when the two convex surfaces are pretty well identical. And THIS is where the problems start. Because if you insert the wrong curvature into the plano concave dish, the glass will meet at the centre and can easily mark it. And being in the centre of the field of view, ruin the lens unless you know someone who can polish the marks out...then that affects the curvature of the lens and on it goes..... So this is what I have done since I learned the trade, back when adam was still a lad at school.
Put a tiny little dob of water into the plano concave dish then put the most likely side of the double convex lens in place and see how far the water spreads. Remove it and then put the other side in and look. THE SIDE THAT SPREADS THE WATER THE FURTHEST is the correct side.
Have you all got that? Good. All go away and do it and we'll meet up after lunch to discuss the finer points of the optical path. I bet that there are thousands out there that are wrong. And if yours has a blurred inner or outer edge, this is the likely problem. Go on and amaze your friends with your new found forum knowledge
