By Ked · May 2026
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 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-five years. Those refinements deserve their own treatment. For this post we'll cover what makes a I a I, a II a II, and a III a III.
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:
The Leica I established the basic ergonomics that the next thirty-five years of screw-mount Leicas would inherit: bottom-loading, knob film advance, top-plate shutter speed dial, and that distinctive round eyepiece.
One important intermediate variant deserves a mention: the Leica I Model C (1930) introduced the 39mm screw mount, what we now call LTM. The original I Model A (1925) and the Compur-shuttered I Model B (1926) both had fixed lenses; the Model C is where interchangeable lenses first became possible on a Leica. Sometimes called the "Schraubgewinde" Leica, it's a key transitional body between the fixed-lens I and the rangefinder II.
Two years after the screw-mount Model C, Leica brought out the model that most people picture when they hear the words "vintage Leica." The II combined the now-established 39mm thread mount with a fundamental new capability:
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.
The III arrived just a year after the II and took the camera in two important directions.
By the III, the layout that survives all the way through the IIIg in 1957 is essentially complete: knob advance, separate rangefinder and viewfinder windows, shutter dial on top, slow-speed dial on the front, and a removable bottom plate for film loading. Everything Leica did in the screw-mount era after 1933 is a refinement of the III, not a re-invention.
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 through a removable baseplate, knob film advance, and that unmistakable round-eyepiece look.
Loading film means trimming the leader first: the film slides into a removable take-up spool and is slipped through a narrow throat at the bottom of the camera. A modern factory film leader is too short and doesn't quite work. You trim the film leader with scissors into a long tongue before loading. It is a one-minute procedure every Barnack owner learns, and trimming templates are cheap and widely available if you'd rather not eyeball it.
Hold one of these cameras 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, a self-timer, or automatic anything. A self-timer shows up later, on the IId and IIId letter variants, on the final red-dial sub-variant of the IIIf, and as standard equipment on the IIIg. The viewfinder on the I, II, and III shows you roughly 50mm of view at infinity, with no projected frame lines and no parallax correction. That's true of these three base models specifically. The IIIg, the last of the screw-mount line, would later become the only LTM Leica to get a much larger, brighter viewfinder carrying projected, parallax-corrected frame lines for 50mm and 90mm.
All three families are still very much around on the used market. As of August 2026 we track 166 Leica I-family bodies, 202 Leica II-family bodies, and 856 Leica III-family bodies across the 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 near junk bodies under $400 to mint and collector-grade pieces in the thousands. Prices depend more on cosmetic condition and originality than on which of the three families it belongs to. A clean III isn't necessarily worth more than a clean II.
Fair-price data pulled August 26, 2026. Of those, here's a fair-price snapshot of body-only asking prices. Kit/bundle listings, special editions, and black-paint premiums are excluded, since a bundled lens or a rarity premium skews what a plain shooter body actually costs. Each "family" row pools the base model with its letter variants (the I row includes the Ia/Ib/Ic covered above, the II row includes IIc/IId/IIf, and the III row includes IIIa through IIIg), so treat this as the broad-strokes view; the letter-variants post breaks individual variants like the IIIf and IIIg out on their own:
| Family | Fair price (median) | Fair range (middle 50%) | Body-only listings |
|---|---|---|---|
| Leica I | $1,582 | $816–$2,588 | 137 |
| Leica II | $571 | $372–$972 | 99 |
| Leica III | $696 | $450–$1,048 | 569 |
If you want to shoot one, the practical considerations are roughly:
Whichever family you pick, expect to have it serviced before you shoot a roll. The shutter curtains on these cameras are ninety 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 genuine value-add, so 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.