Camera lens and aperture teardown: interactive 3D teardown

All 6 steps

1. 1Remove the bayonet mount

   Take out the 4 cross-point screws round the metal bayonet mount with the PH000 screwdriver, pressing down firmly so its tip does not slip out of the head, and lay each screw in its own tray well. Then lift the mount ring straight up over the rear group and set it face up on the cloth.

2. 2Take out the rear optical group

   Set the lens spanner wrench’s two pins in the slotted retaining collar’s two slots and turn it anticlockwise, about two turns, until it is free, then lift the collar out. The rear optical group, three groups of glass in one black cell, then lifts straight out: hold it by its edge and stand it on the cloth.

3. 3The 9-blade iris and the aperture ring trap

   With the rear group out, the iris shows: 9 thin matt-black blades between a base plate and a cam ring. Each blade turns on a pivot pin in the base plate, while a second pin rides in one of the cam ring’s 9 curved slots. Turn the aperture ring from f/1.4 to f/16 and it turns the cam ring with it: the pins glide along the slots and all 9 blades swing in together, one click a stop, each stop half the light. Then lift the aperture ring off slowly and pick out its click-stop ball and spring with tweezers. Avoid this trap: Two things go wrong here. Oil on the blades, from over-greased helicoids or a careless cleaning, makes the thin blades stick to each other and to the plates: turn the ring to f/16 and they hardly move, so every photograph is shot nearly wide open. They must be washed dry, never oiled. And the aperture ring’s click stop is a 1.5 mm steel ball pressed up by a small spring: pull the ring off fast and the spring flings the ball across the bench. Lift the ring slowly over the cloth, catch the ball, and put ball and spring straight into the tray.

4. 4Mark and separate the helicoids

   Lift off the rear barrel, which carries the brass key that keeps the inner helicoid from turning. With the focus at infinity, draw a paint line across the inner and outer helicoids. Then turn the outer helicoid anticlockwise: it climbs the inner one’s thread, 10 mm a turn, through the 7 mm of the focus range and on until it lets go after 13 mm. Mark that exact point on both threads the moment it separates: the thread has 4 starts, and only the marked one brings infinity back.

5. 5The light path through the glass

   All 7 elements, the iris and the two helicoids spread along the optical axis, front up. Parallel light from above enters the front convex element; the front groups bend it in, the iris sits at the narrow waist between the front and rear groups, and the rear groups bring every ray to one focal point 42 mm behind the last glass, where the image forms. Stopped down to f/4, the iris cuts off the outer rays and lets in a beam 12.5 mm across.

6. 6Re-thread the helicoid at its mark trap

   Lower the outer helicoid onto the inner one with the two start marks lined up, so its thread meets the marked start, and turn it clockwise: it takes up at once and runs down 13 mm in 1.3 turns until the infinity lines meet. Turn it through the focus range, 7 mm out to 0.45 m and back, to check it runs smoothly. The rest of the lens goes back in the reverse order: press Reassemble. Avoid this trap: The helicoid’s thread has 4 starts, a quarter turn apart, and the outer barrel takes up on any of them as smoothly as on the right one. Lowered on without its start dot over the inner’s, it goes on one start round and threads down until the infinity lines meet, but a whole thread pitch higher: 2.5 mm in this lens (our model’s thread). At the infinity mark the glass is still 2.5 mm out, so the lens focuses no further than about 1.1 m, its distance scale is wrong all the way, and the helicoid has to be unscrewed and threaded on again. Line the start dots up before the threads touch; if they were never made, try each start in turn, a quarter turn round, until the lens focuses to infinity at its infinity mark.

What you need

• PH000 cross-point screwdriver · a JIS tip if the lens has JIS screws
• Lens spanner wrench · adjustable, with fine pins
• ESD tweezers · for the 1.5 mm click ball
• Fine paint marker · for the alignment marks
• Lint-free cloth and a parts tray · for the glass and the small parts

Questions

Safety

Work on a clean, lint-free cloth with clean, dry hands, and touch glass only by its edge: skin oil etches coatings. Never oil the iris. Fungus spreads between lenses, so a lens with fungus is opened and cleaned apart from the others. Broken glass edges are sharp.

• Lithium-ion batteries: never bend, puncture or pry a battery with metal. A damaged cell can go into thermal runaway: it smokes, catches fire and can explode. Discharge it below 25% first; if it swells, hisses, smokes or gets hot, stop and move it somewhere safe.
• Static (ESD): work on an anti-static mat with a grounded wrist strap; a spark you cannot feel can kill a chip.
• Power off: switch the device off and unplug its charger before you open it, and disconnect the battery before touching anything else inside.

About this teardown

3D Spatial Reconstruction: Models are engineered from factual hardware measurements to visualize internal layouts, screw lengths, and hidden cable traps before you open your device. Always verify cable routing on your specific hardware revision.

The lens is a generic manual-focus 50 mm f/1.4 of our own design, not any one maker’s model. It follows the classic double-Gauss layout most fast 50 mm lenses use: 7 elements in 6 groups, three in front of the iris and four behind it, two of them cemented. Its glass is a prescription we optimised ourselves for a 50 mm focal length and 42 mm of back focus, so the rays in step 5 are traced through it surface by surface.

The f-number is the focal length divided by the opening seen through the front glass (the entrance pupil): 50 mm ÷ 1.4 = 35.7 mm at f/1.4, 50 mm ÷ 16 = 3.1 mm at f/16. The iris itself is about 1.25 times smaller, 28.7 mm and 2.5 mm, because the front groups magnify it; the 3D sizes the blades’ opening that way. The owner’s brief had the iris opening itself at 50 mm ÷ N, which is the entrance pupil, not the iris.

Real lenses differ in the details: some use 6 or 8 blades, mount screws from #000 to #00, and two or three helicoid barrels. Here the outer helicoid turns in the fixed rear barrel, whose brass key keeps the inner one, with the glass, from turning (the bearing it turns in is left out), and the rear group stands 6.5 mm proud of the mount. The screw size, the 1.5 mm click ball, the 10 mm thread lead and the forces are our estimates, and the 3D runs faster than real hands do.

The wrong-start trap’s figures are our model’s: a 10 mm lead over 4 starts puts the next start a 2.5 mm pitch away, and on this lens’s distance scale 2.5 mm of extension is about 1.1 m. In that trap the red line round the barrel is where its edge comes down to at infinity on the marked start.

Sources: Nikon: the Gauss-type 7-element Nikkor-S 50 mm f/1.4, Canon Camera Museum: FL 50 mm f/1.4, 7 elements in 6 groups, DXOMARK: Zeiss Planar 50 mm f/1.4, 7 in 6 groups, 9 blades, Wikipedia: f-number, N = f/D, US patent 3,055,282: iris diaphragm, blades on pivot pins moved through cam slots, Richard Haw: marking helicoids before they part, and grease that oils the blades, Richard Haw: helicoid alignment and the infinity mark; mark where the helicoids part, as a lens put back together in the wrong position will not turn properly, MFlenses forum: a helicoid has several starts and must go on the right one, marked at infinity; otherwise turn it a start round and try again, MFlenses forum: the aperture ring’s click ball and spring, Price source: Neewer HW-05 lens spanner wrench, $24.99, Price source: Micro-Tools lens spanner wrench, $69.95, Price source: Brooklyn Film Camera, lens CLA for 50 mm and shorter lenses, $125–165.

The 3D models, drawings and text are our own. The device shown is a generic one of our own design, not any one maker’s model.