Understanding the Original Leica I, II, and III

May 2026

Long before the M-mount existed, before the rangefinder window and the viewfinder were combined into one bright frame line, Leica had already invented the 35mm camera as we know it. The story of how Leica got from a fixed-lens experiment in 1925 to a mature interchangeable-lens rangefinder by 1933 is told in three model families: the Leica I, the Leica II, and the Leica III. Each one added something fundamental. By the time the III was on dealer shelves, the basic shape and controls of a screw-mount Leica were essentially settled.

This post sticks to the major revisions. Within each family there are letter variants — Ia, Ib, Ic, IIIa, IIIc, IIIf, IIIg and so on — that refined the basic design over the next thirty years. Those refinements deserve their own treatment, and they'll get one in a follow-up post. For now we'll cover what makes a I a I, a II a II, and a III a III.

Leica I (1925) — The Original

The Leica I was the camera that Oskar Barnack built around the idea that 35mm motion picture film, rotated ninety degrees so the frame ran horizontally, could be used to make small, light, perfectly usable still cameras. It debuted at the Leipzig Spring Fair in 1925 and quickly turned what had been a curiosity into a category.

A few things define the I:

• Fixed lens. The original I came with a non-interchangeable 50mm lens — first the Anastigmat, then the Elmax, then the famous Elmar 50mm f/3.5 that most surviving examples carry. The lens collapses into the body for transport.
• No rangefinder. Focus is set by feel and experience, using the distance scale on the lens. There's a separate viewfinder window for composition but you guess the distance.
• Horizontal-travel focal-plane shutter. Cloth curtains running across the film plane, speeds from roughly 1/20 to 1/500 of a second plus B (bulb).
• Brass body, vulcanite covering. Early production used nickel plating; chrome came a bit later in the run. These cameras are dense, beautifully made, and have aged extraordinarily well.

The Leica I established the basic ergonomics — bottom-loading, knob film advance, top-plate shutter speed dial, that distinctive round eyepiece — that the next thirty years of screw-mount Leicas would inherit.

Leica II (1932) — The First Rangefinder Leica

Seven years after the I, Leica brought out the model that most people picture when they hear the words "vintage Leica." The II added two things that changed the camera in a fundamental way:

• A coupled rangefinder. A second window appears on the top plate. Look through it, line up the two images of your subject, and the lens is in focus. The rangefinder is mechanically coupled to the lens helical, so turning the focus ring moves the rangefinder. This is the moment 35mm photography became precise — no more scale-focus guessing for a hand-held shot.
• The 39mm screw mount. The fixed lens is gone. In its place is the famous M39 thread — known today as LTM, the Leica Thread Mount — that defines an entire ecosystem of lenses still being made and used. The Elmar 50mm f/3.5 is now removable. So is everything else Leica and many third parties would build over the next two decades.

The II has two separate eyepieces — one to compose and one to focus. You shoot it as a two-step operation: focus through the rangefinder, then look through the viewfinder to frame. That's slower than a modern M, but it's the price of having any rangefinder at all in 1932.

Shutter speeds were unchanged from the I — top speed 1/500, no slow speeds below 1/20.

Leica III (1933) — Slow Speeds and a Few Refinements

The III arrived just a year after the II and took the camera in two important directions.

• Slow shutter speeds. A second, small dial appeared on the front of the camera, just below the rewind knob. It controls speeds from 1 second down through 1/2, 1/4, 1/8 — all the speeds the I and II simply didn't have. Now you could shoot indoors without a tripod for the first time on a Leica.
• Diopter adjustment. The rangefinder eyepiece gained a small knurled wheel under the rewind knob that lets the user dial in a correction for their own eyesight. A small thing, but a big quality-of-life improvement for anyone who wears glasses.
• Strap lugs. Eyelets for a neck strap, finally. The I and II had to be carried in a case or ever-ready holder; the III could just hang around your neck.

By the III, the layout that survives all the way through the IIIg in 1957 — knob advance, separate rangefinder and viewfinder windows, shutter dial on top, slow-speed dial on the front, removable bottom plate for film loading — is essentially complete. Everything Leica did in the screw-mount era after 1933 is a refinement of the III, not a re-invention.

What All Three Share

From the I to the III, every Barnack-era Leica is built around the same basic camera: a small, dense brass body, a horizontal cloth shutter, bottom-loading film transport with a removable baseplate, knob film advance, and that unmistakable round-eyepiece look. Hold one and the construction quality is obvious. These were precision instruments built to be repaired and serviced indefinitely, and most of them have outlasted multiple owners.

None of them have a built-in light meter. None of them have automatic anything. The viewfinder shows you roughly 50mm of view at infinity — no frame lines for other focal lengths, no parallax correction. You compose by experience and you set exposure with a separate meter or a Sunny 16 rule. That's part of the appeal: these cameras force you to slow down in a way that almost nothing modern does.

Picking One Up Today

All three families are still very much around on the used market. As of May 2026 we track 214 Leica I-family bodies, 205 Leica II-family bodies, and 825 Leica III-family bodies across our active listings — the III family alone is the largest single pool of screw-mount Leica inventory on the site. Across all three, examples range from rough user-grade bodies under $400 to mint and collector-grade pieces in the thousands. Prices depend more on cosmetic condition and originality of the lens than on which of the three families it belongs to — a clean III isn't necessarily worth more than a clean II.

If you want to shoot one, the practical considerations are roughly:

• A working Leica I is a deliberate choice — no rangefinder means scale focus, which is more limiting than it sounds. Best for hyperfocal street shooting or anyone who already shoots with a Rollei or other scale-focus camera.
• A working Leica II is the lightest and simplest of the rangefinder Leicas. If you're shooting outdoors at 1/60 or faster, the lack of slow speeds doesn't matter, and the camera is a joy to carry.
• A working Leica III is the most versatile of the three. The slow speeds open up indoor and low-light work, and the diopter glasses wearers and strap lugs make minimal carry easier.

Whichever family you pick, expect to have it serviced before you shoot a roll. The shutter curtains on these cameras are eighty to a hundred years old at this point, and the cloth dries out, the lubricants gum up, and the slow speeds drift. A good CLA (clean, lubricate, adjust) from a Leica specialist is roughly $250–$400 and turns a sticky old shutter into a precise instrument again. Many of the dealer listings on this site advertise recent CLAs, and that's a real value-add — read the descriptions carefully.

In a follow-up post, we'll get into the letter variants — what makes a Ic different from a Ig, why the IIIa was a milestone, what the IIIf and IIIg added, and which of those variants are the sweet spots for buyers and shooters today.