Additionally there is one camera that is noticeably below the others, the M2 rated at 10.0.
I ran the data through Grok and asked the question:
looking at the data from the 11 cameras, what if the outliers were eliminated? would there be any practical difference between any of the cameras?
Grok:
Identifying and Eliminating Outliers
Using standard statistical methods (IQR rule) on this small sample, there are no formal outliers — the data is tightly clustered with a range of 1.0 EV total.The two most extreme values are:
- Lowest: 10.0 EV (1961 M2)
- Highest: 11.0 EV (two instances: 1962 M2 and 1990 M6)
If we conservatively treat these as potential outliers (e.g., due to measurement variability, slight meter positioning differences you mentioned, or individual camera condition/age-related prism/fogging issues), and remove both extremes (10.0 and one 11.0 for symmetry), or just the single lowest (10.0), the remaining values become much more consistent.Remaining values after removing the 10.0 EV outlier (most logical single outlier, as it's the only one noticeably below the main cluster):
- 10.4, 10.9, 11.0, 10.8, 11.0
- Mean: ≈10.82 EV
- Range: 0.6 EV (10.4 to 11.0)
- Standard deviation: ≈0.22 EV (much tighter than the original ~0.37 EV)
If we also drop one of the 11.0 values (to exclude both ends), the core cluster is even tighter:
- Roughly 10.4–10.9 EV range
- Differences shrink to ~0.5 EV max
Would There Be Any Practical Difference Between the Cameras?
In real-world use — especially for Leica M rangefinder shooting — no, there would be essentially no meaningful practical difference once the outlier(s) are set aside.Here's why:
- The remaining spread (0.5–0.6 EV at most) represents a luminance change of roughly 35–50% brighter/dimmer at the extremes.
- In photographic viewfinder contexts, differences below ~0.3–0.5 EV are typically subtle at best, and often imperceptible in normal shooting (especially with eye adaptation over seconds of viewing).
- User reports and comparisons across Leica M film bodies (M3, M2, M6, etc.) frequently describe viewfinder brightness as "similar" or "equally bright" between well-maintained M2 and M6 examples, with only larger variances (0.5+ EV) noted when comparing older vs. newer or cleaned vs. uncleaned units.
- The M3's slightly lower measured value (10.4) aligns with some anecdotal reports of it feeling marginally dimmer in certain conditions, but the difference is rarely called game-changing — especially since the M3's higher 0.91× magnification trades some brightness for better focusing precision on longer lenses.
- Larger reported differences in Leica community discussions (e.g., M6 sometimes described as "brighter" than vintage M2/M3 due to coatings or prism design) tend to be subjective or tied to flare resistance rather than raw brightness, and even those are often debated as negligible in side-by-side use.
Bottom Line
If we disregard the single clear low outlier (10.0 EV, possibly an anomalous measurement or a camera with minor internal haze/dirt), the remaining Leica M cameras in your test show viewfinder brightness clustered so tightly (within ~0.6 EV) that practical differences in everyday shooting would be negligible to nonexistentfor most photographers.You'd be hard-pressed to reliably tell them apart in real use — especially given normal eye adaptation, varying ambient light, and the fact that Leica M viewfinders are prized for staying consistently bright and usable regardless of lens aperture (unlike SLR finders). Any perceived differences would more likely stem from magnification style (M3 vs. M2/M6), frameline clarity, flare behavior, or individual sample condition than from these tiny measured EV variances.
