Adventures in Adaptation: Jupiter-12 on Sigma fp Shouldn't Work

I bought a Sigma fp basically on virtually nothing but the strength of this tweet:

You see, the Jupiter-12 is cheap, it's cheerful, it's hated by many… and it's one of my very favorite lenses. It's also pretty much impossible to fit on non-Leica cameras because its rear element sticks so deep into the camera body. Seriously, this lens is bizarre.

Basically, the Jupiter 12 fits my Ricoh GXR M (designed to accomodate deep rangefinder lenses), and it fits a true Leica (ditto), and a Sony a7 (hisssss) and that's… about it.

If a camera fits a Jupiter-12, it'll fit just about anything else I'd like to throw at it.

And I really wanted a full frame camera for my lens collection. But the "reasonable" Leica is $2600+ used.

So you can imagine my excitement. Especially since the Sigma fp has incredible high ISO performance, is small and sleek, isn't a Sony, and even features a built-in system for handling color shift on vintage lenses. Oh yeah, and it's about 1/3 the cost of the "lower end" digital Leica I've considering.

There's just one teensy little problem.

I let myself be dazzled by the pretty pictures.

I didn't fully read, or absorb, the Japanese tweet featuring the Jupiter 12 mounted on the Sigma fp. The poster said:

sigma fp + shoten lm-lsl + amedio adapter + Jupiter-12 35mm F2.8

That's not one adapter (or one adapter and an L39-M screw ring)… it's two. Two whole adapters. 

1. Leica M to Leica L (the Sigma fp is in the L alliance) — and a pricey one with a helicoid
2. Amedeo adapter… what?? turns out it's a specialty adapter for Contax/Nikon RF lenses to Leica M

…oops.

They weren't using an L39 screw mount Jupiter-12 like I have.

They adapted a Contax mount Jupiter-12.

I started worrying. So off to Google I went, to see if anyone else had discussed mounting a Jupiter-12 successfully on their Sigma fp. In short, the answer is No.

The only evidence that it may be possible are the tweets from @camedak. Everyone else reports the lens is too deep, it hits the IR cut filter and can't reach infinity focus.

But @camedak tweeted this picture and labeled it as Jupiter-12:

And it's sharp. And while it may not be focused on infinity, it includes infinity. And doesn't have grain suggesting a super-high ISO to compensate for a super-stopped-down lens.

So……… does that mean I have to get a second Jupiter-12 copy, in Contax form?

Let's talk flange distance:

• Leica M flange distance: 27.8mm
• Contax RF mount flange distance: 34.85mm
• Difference: 7.0mm

My LTM Jupiter-12 lens must, by logic, sit 7mm closer to the imaging surface in order to focus.

So… if the Jupiter-12 is 1 to 6.9mm too deep for the Sigma fp, a Contax model just might make the difference?

I'm not 100% certain this thinking is correct.

The thing is, the vast majority of adapted lenses work fine because they don't protrude backwards anywhere near as much.

Generally, all you have to know is: does the lens you're adapting want a bigger flange distance than the body you're adapting to? It does? You're golden! You can always add depth. That's why mirrorless bodies are perfect for adaptation.

But the flange distance for Leica M is 27.8mm — and the regular Jupiter-12 is a Leica Thread Mount lens, adapted by the world's thinnest ring of metal — and the flange distance for L-mount bodies, like the fp, is 20mm.

27.8mm is greater than 20mm. By quite a lot! Logically, all Leica-like lenses should fit and focus on a Sigma fp.

But the Jupiter-12 doesn't.

Perhaps another 7mm away and it will.

It would be an expensive experiment if I didn't already have both Contax/Nikon rangefinder adapters. But I do. (Because I initially bought the wrong one for a different lens.)

And it turns out the Contax-mount Jupiter-12 is a third or less of the price of its essentially-free-to-adapt cousin.

I was just the only bidder on a Contax Jupiter-12 that's actually located in the US. $59 plus shipping.

Hopefully it'll arrive next week.

We're about to find out.

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