Examine the rear of every 'normal' F/1.4 RE Auto Topcor lens (58mm and 50mm GN) and you will find a segmented flange extending out beyond the edge of the Exkata mount. On early lenses this flange has an arc length of about 60 degrees and when mounted in the camera body is centered at about the 4 O'clock position. On later lenses (starting with the 3rd generation?) the flange became much shorter and extended around the mount approximately 180 degrees. Lacking any definitive information, I had always assumed this flange was some sort of a light baffle to block some stray flair anomaly, unique to this lens only. It is present only on this, the fastest, of all RE Auto Topcors.

It turns out that the purpose of this flange has nothing to do with optics, rather it's function is more pragmatic. On these lenses the rear convex surface of the final lens element extends beyond the protection afforded by the metal mounting tube. Without the flange, a lens placed face up on a flat surface would rest on the surface of this protruding glass. The flange tilts the lens at a slight angle and keeps the glass from contacting dirt and grime on the resting surface. Apparently the later lenses had a new optical design that reduced the curvature of the rear lens element and the length of the flange could be reduced.

The images below show the three versions of this flange.

A later lens. The flange is now about 180 degrees with an extension of approximately 1 mm.

The GN lens. The flange is the same as the one shown to the left.

An early lens with the 60 degree flange extending out approximately 2.5 mm.

The images above illustrate the purpose of the flange. At the left, the lens is resting on a surface  with the flange positioned to overhang the surface edge. Note that the lens is tilted slightly to the left indicating that it is resting on the curved glass of the rear element. To the right the lens is positioned such that the flange is in contact with the surface, protecting the glass at the rear.

Another oddity that always bothered me concerned the rear plastic lens cap. The normal cap does not fit properly when mounted to early lenses with the longer flange. Also, I had noted that a few rear caps I have are deeper than the normal ones. I had always assumed the deeper ones were offered with the later lenses since this is the type that came with a new 50 mm F/1.4 GN lens. But then I finally figured out that the deep ones fit the lenses with the long flange. So now I believe deep rear caps were made specifically for the early 58 mm F/1.4 lenses. Why the deep cap for the GN lens that didn't need one? I have no idea unless it was Topcon's practice to ship all F/1.4 lenses with a deep cap regardless of whether or not is was necessary.

The image below shows the two types of rear caps side-by-side--the normal one to  the left and the deep one to the right..

This is trivia in it's purest form--interesting, but with little practical value.

On the bottom of every Topcon RE Super/Super D camera body are two screw-in caps: one to cover the access to the Motor Drive coupling disk, and one to retain the Exposure Meter battery in it's holder. Both of these caps have slots machined in them to allow a coin to be used as a sort of 'screwdriver' to assist in loosening or tightening these caps. But over the years these caps changed in subtle ways.

I have identified three different variations I have designated Types 1, 2 and 3. The Type 1 caps were mounted to the very early bodies and had a short (10 mm) slot with a single 'breather' hole in the center on the battery cap. Apparently Topcon discovered this short slot provided insufficient engagement of the coin, and edges of the slot were becoming 'chewed up' when the coin slipped out of the slot. This led to the Type 2 caps with a longer (12.5 mm), and deeper, slot. A single 'breather' hole was retained for the battery cap. Then came the Type 3 with an additional 1 mm in slot length, but now with two 'breather' holes. Why this change? Maybe the single 'breathing' hole tended to get clogged up, or perhaps the cap came in contact with batteries from some manufacturers and sealed the hole. In any case, the Type 3 was the final evolution and was retained through the Super Dm models.

The below data is only a guess as to association of cap type to serial numbers:

Type 1--Serial numbers below 4610000
Type 2--Serial numbers between 4610000 and 4619999
Type 3--Serial numbers greater than 4620000 and all Model 71 and Super Dms

Since the Motor Drive cap was probably not removed on most cameras, it may represent the original type.

The only value I can think of for this information is if you are restoring an old Topcon and want it to be pure. In that case very early bodies should have the Type 1 and late models should have the Type 3. In any case both the Motor Drive cap and the Battery cap should be of the same type.

Below are images of the three cap types along with a drawing showing the configuration of each.

The underside of the Battery caps. Note that for the Types 1 and 2 the 'breather' hole is in the center of the '+' polarity symbol and may be difficult to see. Also note that for the Type 3, the polarity symbol is on a slight pedestal while the 'breather' holes are outside. This is probably to allow the cap to contact the top of the mercury cell without sealing off the 'breather' holes.

The outside view of both the Motor Drive and the Battery caps. To the left is the type 1, in the center Type 2 and to the right type 3. The Battery caps are in the upper row.

The diagram at the left shows the differences between the three types of caps. The length of the slot probably the best method of classifying a cap as either a Type 1 or a Type 2. Two 'breather' holes always indicates a Type 3.