The following is a FAQ on the Leica IIIc, with answers prepared after a joint British-American "visit" to the Leica factory in Wetzlar. You can find the complete report (British Intelligence Objectives Sub-Committee Report No. 1436, on "The 'Leica' Camera'") on Peter Grisaffi's site, in all of its gruesome detail, right down to the age breakdown of Leica workers, and without my asinine commentary. The questions are mine; the answers are from the report, based on site visits and interviews with Ernst and Ludwig Leitz. It's hard to read the report as anything other than a blatant... er... courtesy call, but it does answer some fundamental questions.

Question: How does the Leica IIIc vary from the IIIb?

Answer: The Leitz Company is now producing only the Model III C Leica Camera, this having by development, superseded the Model III B. The Model III C differs from the III B in several aspects, although it is functionally similar. It is approximately 1/8" longer, it has an integral top plate and range finder cover, and the main body is now a single pressure die casting, which together with two other pressure die castings for the top and bottom of the unit forms a complete chassis for the assembly of all the other component parts. In the later models the focal plane shutter blind rollers have been fitted with ball bearings. The outer case of the Leica although 1/8" longer is formed from extruded tube as was the case in the III B and earlier models. The coupled range and view finder has not been altered in any way.

Comment: Die-casting provided significantly improved rigidity in the camera body, which is important especially for high-speed wideangles.

Question: What did Leitz make and what did it subcontract?

Answer: Leitz make in their own factories practically all their requirements, including the leather cases for cameras and accessories. Of the items bought out, the castings come from Mahle of Stuttgart, slow speed shutter mechanism from Gauthier of Calmbach, shutter tape from Soenecker & Pfaff of Wupperthal Barmen, and blind material from America through their associated company in that country.

Comment: The comment about shutter blinds in particular is interesting, because the material is now subcontracted to a company in Switzerland.

Question: What kind of machines were being used at the plant?

Answer: In the machine tool side the following machines were noted:- Steinel Drilling Machines, Lindner Thread Grinder, Deckel Engraving and Horizontal Milling Machines, Lorch Lathes, Sooda Automatics, Mikron Gear Hobbers and Hauser Jig Borer. The chasing lathes were by Hille. The general machining of mall precision parts followed very closely the usual procedure in this country.

Question: How did they cut multi-thread helicoids in the bad old days?

Answer: The cutting of the multi-start thread in the focussing mount of the Sumitar [sic] and the Elmar lenses was carried out on a converted Lorch Lathe. The conversion of this machine by Leitz was extremely ingenious. The component to be screw-cut was screwed on to an attachment on the head-stock of the lathe by a chucking-thread already cut in it. A single tool was employed in the tool post. The whole head-stock was then caused to oscillate backwards and forwards by a thread attached to the back of the head-stock engaging with a chasing nut which was in turn engaged and disengaged at the end of each stroke by a yoke which also operated four glass-mercury switches. These switches operated a solenoid attached to the drive counter shaft which, in turn, operated a reversing clutch in the drive. The head stock was caused to rotate for some ten revolutions in a clock-wise rotation which moved it forward by the chasing thread on it engaging with the chasing nut. At the end of this forward stroke the chasing nut disengaged and then re-engaged with the next thread, the counter shaft also re- versing, causing the head-stock to rotate in an anti-clockwise direction on the back stroke for some ten revolutions. As the head-stock oscillated backwards and forwards at each successive movement it engaged with a conveniently disposed paul which engaged with a ratchet connected to the feed on the tool post and at each backward and forward stroke the tool was automat- ically fed in. The extent of this was shown by a clock indicator attached to the tool post slide. The device worked well and was almost "fool -proof" to operate.  

The male 5 start thread was cut first on one lathe of the type just described. The female member was cut in an identical manner but to suit the male thread. A certain amount of play was purposely left between the two, when dry, but after both had been well washed out in paraffin a liberal application of special grease was applied and they were assembled together. The special lubricant caused them to have a very fine "velvety" feel when moved in or out. As male and female members are machined to suit one another it is very doubtful if any two complete units are dead alike as regards inside and outside diameters of threads. Mr. L. Leitz agreed that this was so but added that once a lens focussing mount was assembled it became a unit for good and it did not need to be interchanged with parts from another complete lens mount.

Comment: It is interesting that people attack Soviet and Japanese lenses for using grease to take up the machining "slack," as that was Leitz's classical method of attacking tolerances and smoothness.

Question: Are Leica III lenses cammed the same way as Leica M lenses?

Answer: The pitch of the 5 start thread in the focussing mount of the Sumitar was 6.210 mms., but in the case of the Elmar a pitch of 6.00 mms. and also 6.138 mms. was employed. To ensure lineality between movement of the lens and the coupled telemeter a slight cam is machined on the end of the male member of the multi-start thread which engages with the roller which actuates the winging prism of the telemeter. The greatest depth of this cam face does not appear to exceed .007".

Comment: The camming surface described here is a method for avoiding having a separate helicoid for the Elmar. It is also exactly the same method used to make Leica CL lens rangefinder couplings.

Question: How did they make prisms?

Answer: The manufacture of small prisms as used in the telemeter [rangefinder] were by mouldings cemented in fours and then gang-milled by diamond milling tools. They were then taken apart and milled to the other face. Diamond tool milling machines are used for slotting the hypotenuse. Smoothing and polishing was achieved by normal type poker-arm machines. Edging was carried out on small lens in the telemeter by diamond wheels. These wheels are made for Leitz by Jung of Berlin.

Question: What was the percentage transmission in the beamsplitters?

Answer: The small reflecting mirror in the range finder is very lightly alluminised, the degree of deposit being just sufficient to give an equal degree of brightness to both the directly and indirectly received images when seen through the range finder eyepiece.

Comment: This means that if you are really handy, you can buy a 50% aluminized beamsplitter from Edmund Optics and install it yourself.... yeah, right!

Question: What were the steps for applying the satin chrome finish?

Answer: Sandblast, hot cleaner without current, cold cleaner with current, warm rinse, followed by cold rinse, hydrochloric dip, copper flash, cold rinse, sulphuric dip, cold rinse, bright nickel-plate, warm rinse, hydrochloric dip, bright chrome, drag-out rinse, cold rinse, hot rinse, and dry.

Comment: So "bright" marks may be polishing... or they may be the brighter nickel finish showing through.

Question: Why were Leicas so expensive?

Answer: The Model III C takes longer to assemble than its predecessor, 33 hours as compared with 29 hours, but there is no doubt that as an engineering job it is far superior. Sub-assemblies were batched in tens and assembly practice was very similar to that employed in most instrument factories. Special jigs, fixtures, and tools were employed where-ever possible to assist rapid and accurate assembly. Female labour was used for the minor assemblies, the male labour being employed mainly on shutter and range finder assemblies and on testing.

Comment: This is an absolutely huge amount of labor. It only takes 22 man-hours to build an automobile, which has thousands of parts. Of course, they had no robots in Wetzlar.

Question: Was there any change in the shutter from the IIIb?

Answer: The main design of the shutter is in no way basically changed; only slight modification of various components to suit the new assembly. In the assembly of the shutter fast- range escapement one component after another was tried till one was found that worked in a fairly satisfactory manner and then various minor alterations were made to it by filing, and in some cases, a light tap with a small watch-makers hammer. The skill of the operators was undoubtedly the chief asset in the efficient assembling of this shutter. The slow speed escapement of the shutter is made by Gauthier of Calmbach.

Comment: The shutters must have been built to very low tolerances if it took a filing and a small hammer to get some examples of it going.

Question: How did they calibrate shutters before electronics?

Answer: The timing of the fast range of the shutter is carried out with the aid of a stroboscope of somewhat antique design. By means of this the 1/200, 1/500 and the 1/1000 speeds are checked. The stroboscope consists of a revolving drum placed horizontally, with 33 horizontal slits in its surface, illuminated from inside by a lamp of approximately 20 watts. The drum is driven by a belt from an electric motor which may be controlled by a rheostat. The drum is also coupled to a speedometer in order that its speed may be set. The correct speed for the drum to rotate at was 280 r.p.m. The camera is held on a wooden block in such a manner that the light from the rotating drum falls on the blinds of the focalplane shutter. The shutter is then fired and a series of
stroboscopic lines are seen in the aperture. If the shutter is correctly set these lines appear vertically but if the shutter is incorrectly set the lines will curl down either to the left or to the right according to whether the shutter is set too slow or too fast.

The checking of the lower speeds was only carried out on the 1/20 second and 1/4 second ettings by means of a revolving series of lights. The various speeds of the shutter were not accurate to the measurements on the shutter control knob and this fact was acknowledged by the Leitz executives. who pointed out, however, that the results obtained were quite good enough for all general requirements.

A metronome was used in checking the one second escapement.

Comment: The method they were using to check the fast speeds is remarkably similar to the home-built shutter testers that use a record player to turn a wheel of black-line markings. The comment about the slow speeds is interesting; the IIIc was just not capable of efficient precision-setting of slow speeds. Today it's all done with computers.

Question: How did (do) they make shutter curtains?

Answer: The fixing of roller blinds and tapes on the focal- plane shutter was carried out on a very ingenious fixture. The body of this fixture is all metal and accommodates the two roller blinds and apes on pivots ensuring that the blinds and tapes are of the right length and fixed at exactly the right distance apart. After the blinds and tapes have been stuck to the rollers they are allowed to dry for at least 48 hours before being assembled into a camera. In every possible operation special jigs and fixtures are used to increase speed and uniformity of production.

Question: How did they deal with flange-to-film alignment?

Answer: The checking of the lens flange of the focalplane for squareness is carried out by a focalplane ollimator which is located by the lens flange and directs a beam of light on to a polished reflecting surface which is located on the focal plane. Lack of squareness and an accurate measurement of the extent of the error is at once visible on the graticule of the collimator. When correction is necessary a specially adapted vertical milling machine is used to correct the orientation of the base of the camera body which corrects the lens flange. If small errors in squareness occur which are not sufficient to warrant machining, the lens flange is packed with a small shim. The correct istance from the front of the lens flange to the film pressure plate, located at the back of the focal plane is 28.80 mms. which is the equivalent to 1.134". Checking of the measurement was made by a special fixture and a clock indicator.

Comment: The IIIc did not take the curvature of film into consideration (but why would you with f/3.5 lenses?). Machining must have required some pretty big error if shims were the minor solution. Just as with the M cameras, there is no measurement for the front film rails. Interestingly, for quite some time, Japanese makers have used machining as the primary method of fixing film-plane alignment.

Question: How did they set the rangefinder alignment?

Answer: The setting of the position of the telemeter prism to correspond to infinity is carried out by the aid of a rotating disc fitted with alternate colour filters which are illuminated from behind, the whole being fixed in the roof of the assembly shop. The measurement from the lens flange to the centre of the telemeter actuating roller with the telemeter set at infinity is 0.750 mms.

Comment: The exact testing apparatus is unclear, but it appears that the focusing target is on a distant rooftop, rather than inside the same building.

Question: How did they test lenses before the dawn of MTF?

Answer: The Summitar lenses were tested for definition by projection at a focal length of 51.68 mm. and were stopped down to 3.2 aperture throughout the test. The total backward and forward movement was also checked by a clock coupled to the lens mount by a pivoted lever movement. The mounts shown by the clock were very closely checked with the readings of the footage scale engraved on the focussing mount. The projection test was in the form of a fine interlaced vertical and horizontal graticule, interspaced with fine figures and letters which were compared with a known standard ngraved on a vernier attachment mounted on the screen on to which the image of the graticule was projected.

Comment: I have seen a picture of the first part of this in a Minolta Autocord instruction manual. I am unclear as to what exactly the clock referenced in the second part was.
 
Question: What was the final test?

Answer: Each completed camera is tested finally by taking a number of black and white photographs between 1.25 to 10 metres. The result is checked with individual lens, a standard speed film and a metol hydroquinone developer being used. The tests are compiled for lens performance reference.

Question: How many were they making? Who got them?

Answer: In November 1946, the production of Leica Cameras was 1100 per month of which 89% was allocated to the American forces, 6% for French forces and 5% for German sales. A small proportion of the American 89% was available for the British forces in exchange for Rolliflex cameras.

Although the the camera was in great demand production was limited owing to shortage of materials, particularly optical glass. Stocks of brass and other metals appeared to be high.

Question: What were 1946's lens selections?

Answer: Through the shortage of optical glass, lens manufacture was confined to the f/3.5 5 cm. (standard) and 3.5 cm. (wide angle) and the f/4 9 cm [Elmar] and f/4.5 13.5 cm. lenses.

Comment: That's about the best test there is.

Question: What did the British think of Leicas after the war?

Answer: The team came away with the impression that the Leica camera is still worthy of its pre-eminent position and that the skill of the craftsmen is very much in evidence in the Leitz factory.