Tutorials & Guides

A Quick Guide to a Rangefinder’s Effective Base Length (EBL)

Effective Rangefinder Base length

I recently published my thoughts on the Voigtlander R2a and R3a two great cameras that have one major caveat – their short rangefinder effective base length. I’m now in the process of putting together my thoughts on the Leica M3 (edit: you can find my M3 review here), a camera that’s biggest technical advantage is possibly its especially long rangefinder effective base length. Short of repeating myself by explaining what rangefinder effective base length means in the M3 post, I thought I’d put together a short post to detail the basics of the subject.

Rangefinder base length is the space between the camera’s rangefinder window and the viewfinder. It is the difference between two corners of a triangle, the third corner being the subject the camera is focusing on. The longer the base length, the longer the space between two corners of the triangle, the more accurate the rangefinder is.

To make things slightly more complicated the rangefinder’s base length needs to be multiplied by the magnification of the viewfinder to give something called the “Effective Base Length” – commonly abbreviated to “EBL”. This effective base length, as a specification on paper can give a good idea to how easy it will be to focus the camera accurately. The longer EBL the more precise focusing can be achieved… though there is a little more to the story than that.

Calculating a Rangefinder’s Effective Base Length

First we need to know the two specifications required – Rangefinder base length and viewfinder magnification. The most common Leica viewfinder has a 0.72x magnification, meaning what you see through the finder is 0.72x lifesize. Largely speaking these cameras have a base length of 68.5mm – though there is some variance apparently.

So, if we take the one number and multiply it by the other:

0.72 x 68.5mm = 49.32mm

So the effective base length of the most common Leica M rangefinder is 49.32mm

Compare this to these aforementioned Voigtlander R2a and R3a cameras. These cameras have a shorter base length of 37mm and have rangefinder base lengths of 0.68x and 1x respectively.

0.68 x 37mm (R2A) = 25.16mm
1 x 37mm (R3A) = 37mm

So the R2A has an EBL of 25.16mm and the R3A an EBL of 37mm. In short, neither the Voigtlander R2A or R3A have as precise a rangefinder as most other M-mount rangefinder cameras. And this is despite the R3A having the advantage of a 1:1 rangefinder.

At the other end of the spectrum we have the Leica M3. The M3 has a rangefinder base length of 68.5mm (like most leica M cameras), but with that longer base length it also has a high 0.91x viewfinder

0.91 x 68.5mm = 62.33mm

The Leica M3 Actually has the longest effective base length of any m-mount Leica rangefinder giving it an on-paper advantage for focusing m-mount lenses.

Some cameras, the “Barnack” Leica’s included have separate rangefinders and viewfinders. The benefit of this is that the rangefinder can have a magnification greater than that of the viewfinder. Most Banack Leica’s have an rangefinder base length of 39mm, which is nearly as short as that of the aforementioned Voigtlanders. The difference with the Barnack Leica’s is that the rangefinder magnification is 1.5x.

1.5 x 39mm = 58.5mm

Which puts them close to the Leica M3 in terms of their effective base length.

The bigger picture

So what does this mean in real life? Well, in my experience, it means a little less than many out there in the world of the hyper-critical-internet would have you believe – and more importantly it means something different to different people. There is no arguing with the fact that a shorter EBL is a disadvantage when shooting longer or faster lenses – the RF patch just doesn’t seem to pop as obviously when focus is found when compared directly to a longer effective base length rangefinder camera. But, I’m just not sure it’s quite the deal breaker some people suggest.

The ability to focus and shoot long or fast lenses accurately with a rangefinder comes down to a combination of things alongside its rangefinder’s effective base length. These include: size of the viewfinder, clarity of the viewfinder, size of RF patch, clarity of RF patch, whether or not the RF patch has solid edges, whether or not the RF and VF are combined, a steady hand, appropriate shutter speed, quality of eyesight, how well lit the subject is, subject distance and subject movement etc. Yes, a long RF EBL will help, but the other pieces of the puzzle also need to be in place for success. A camera with a longer EBL will possibly increase chances of success, but so too might practice and experience. Some of these variables might also affect or be a concern to some people more or less than to others.

For my personal tastes I find focusing long/fast lenses easier with the like of a Voigtlander R3A than I do with some of the more elderly cameras in my collection like my “Barnack” Leica iiia. For me, a bigger, brighter more distinct viewfinder and passably good, solid edged rangefinder patch trumps the extra magnification in the rangefinder of my iiia. The fuzzy-ish rangefinder of my iiia works less well for me, as does having to focus with a small rangefinder then frame with a separate independent viewfinder; the sheer act of moving the camera from rangefinder to viewfinder for me feels a distraction from the process when such precision is required. I know for a fact that others would dispute this and claim the exact opposite reality for them, but this is really my point, what works for one person might or might not work for the next. The key – as always – is finding what works best for you and your shooting needs and requirements.

Cheers for reading


Links & References
Very useful reference chart on CameraQuest


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  • Reply
    January 24, 2015 at 5:06 pm

    Very nice and helpful article! Good work!

    • Reply
      Hamish Gill
      January 26, 2015 at 1:43 pm

      Cheers Harman!

  • Reply
    Matt Jacques
    April 3, 2015 at 7:27 pm

    Great piece, and an interesting read. I’m pretty new to rangefinders, but is another EBL advantage the accuracy of close focusing at or near minimum focus distance too? As a glasses wearer, I think lower magnification, high eyepoint viewfinders will be my lot (newer Zeiss Ikon seems to be recommended), but don’t want to completely erase EBL with a super low magnification finder.

    • Reply
      Hamish Gill
      April 5, 2015 at 5:52 pm

      Hi Matt,
      Yeah, longer effective base length is helpful wherever shallow depth of field is an issue. So with longer lenses, faster lenses and both especially so at closer distances.
      As far as magnification, rangefinders and eyepoint goes … It’s not quite as simple as it is with an SLR I don’t think.
      The Zeiss Ikon ZM – which would indeed likely be a good choice for a glasses wearer looking for a versatile camera – actually has the same magnification as the M7 et al. But it also has a longer EBL and a physically larger finder.
      In short, I can see the 28mm lines in a ZM, but not in a Leica, even though the magnification is of the finders is exactly the same.
      Of course, it also depends on how frequently, you would want to shoot 28mm … If you only want to shoot 50mm, even the M3 would suit. That has the highest magnification going, and I can still see the framelines with my glasses on.
      Another factor is of course how far your glasses are from your eyes.
      Does that help, or confuse matters? 🙂
      Sorry for the slightly delayed response … been a bit manic

  • Reply
    5 best place to buy film cameras in Tokyo {2015|advice} – marcuslow photography
    August 13, 2015 at 4:28 pm

    […] I wanted a Zeiss Ikon because my current main lens is the f1 noctilux. Although my current Bessa r3m is just solid good, the EBL (effective base length). In short, focusing at F1, i will need more EBL and Zeiss Ikon is definitely at the top end. You can read more about EBL here […]

  • Reply
    Michael Fortner
    August 13, 2015 at 6:18 pm

    The FED-2 has a rangefinder base of 68mm, beating out the Leica rangefinders (LTM or M mount).

    • Reply
      Hamish Gill
      August 13, 2015 at 7:31 pm

      Perhaps, but as I say, it’s not all about length. I can’t imagine the RF patch is as bright or has a solid edge?

  • Reply
    Brett Rogers
    March 19, 2018 at 11:11 am

    Dear Hamish,
    A very interesting read. Thanks for the effort you put in. I know how time consuming it can be to author this sort of content.
    I’m a little reluctant to blow my own horn but, as you clearly wish to delve deeper into the subject matter than most internet writers (a trait I thoroughly approve of, BTW) perhaps you might find some musings I wrote about the pre-war Contax II/III rangefinder system to be of some interest? You can see the relevant comments here:

    I suppose it’s inevitable when discussing the 35mm rangefinder that Leica features prominently. I will say, though, that in my humble opinion the Contax installation is both more accurate and technically superior. Also that the flawed, but fascinating, Kodak Ektra features a rangefinder effective base length that annihilates even the Contax with its gargantuan dimensions. Both types of cameras would be worthy of inclusion in any future discussion about the specifics of rangefinder design. For students of technical aspects of rangefinder theory and design I would refer them to the long out of print, but still, extraordinarily informative, publication Miniature and Precision Cameras, authored for Amateur Photographer by J Lipinski in the early 1950s. Good condition copies of this title are still available with a little searching.

    • Reply
      Hamish Gill
      March 20, 2018 at 9:31 pm

      Thanks, Brett! Interesting stuff – What are your feelsing toward my thoughts about solid edged rangefinder patches vs soft edged ones. For me this is the most important differential in practice. I just don’t get on with the soft edged ones nearly as well.

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