Fred Miranda
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 p.1 #1 · Beyond 1m: Getting the Summilux 35 f/1.4 Pre-ASPH to Focus at 0.62m | |
Leica 35mm f/1.4 Summilux Pre-ASPH "Germany" - Modded to Focus Down to 0.62m (the True RF Limit)
I've gotten a few requests to show the mod I had done to my Summilux 35mm f/1.4 Pre-ASPH "Germany" to let it focus closer than the stock 1m minimum. Here's the full writeup.
The idea...
Most people assume the Leica rangefinder's practical minimum focus is 0.7m...that's the number Leica standardized on for M-mount lenses. But that's not actually a hardware ceiling. The real geometric limit of the rangefinder mechanism, given the base length and patch magnification on M bodies, goes closer than that. 0.7m is a convention, not a wall.
So this lens was engineered (very carefully) to rotate past the stock 1m mark all the way down to 0.62m, right at the actual limit of what the RF can resolve accurately. Now when I want to get in tight, I just rack it to the MFD hard stop, align the subject to the patch (works the same in live view), and I get a perfectly sharp image at 0.62m.
Credit where it's due: Yuri @yukosteel treated this as a fun project rather than just a repair job, and kept pushing to get the functionality right.
What actually has to be ground...
For the RF patch to stay 100% accurate through the extended range, you can't just file down a stop and call it done. Two areas need work:
1) The section shown in the photos below: this is what lets the ring physically travel past 1m.
2) The rangefinder cam itself: this has to be reshaped following the correct angle, or focus accuracy falls apart as you get closer.
Here's the part that trips people up: extending the mechanical travel isn't the hard part. The hard part is that as you push closer, RF misalignment increases 'progressively', it's not a fixed offset you can just compensate for once. The cam surface was cut assuming the stock travel range, so past that range it no longer matches the follower's expected path. Fixing that means grinding the inner RF cylinder to correct the follower geometry, not just extending the outer cam edge.
Why this is harder than the 35 Summicron "SR Reissue" mod...[Link]
Some may compare this to the close-focus mod done on the 35/1.4 Summilux SR Reissue, but the two jobs aren't really comparable in difficulty.
On the SR Reissue, the RF cylinder edge is already curved...so a technician can visually approximate the existing curvature and continue it outward. It's like knowing a curve follows Y = X^1.5 and just extending the same formula further along the graph. You have a reference to extrapolate from.
This Summilux is the opposite problem. The RF cylinder is "flat", with no existing curve to extend. The technician has to accurately originate that curvature from scratch, starting right at the edge, with zero built-in reference to guide the grind. Any error compounds instead of self-correcting the way it would on a curve extension.
Other work done...
While it was apart, I also swapped the stock plastic focus tab for a brass one (painted black, will patina naturally over time), sourced here: eBay listing: https://www.ebay.com/itm/366137492715
Opening the lens: for reference...
For anyone curious how to get into the Summilux 35mm f/1.4 Pre-ASPH:
1. Disconnect the hood.
2. Set the aperture to f/5.6, grip the front element, and unscrew the core counterclockwise.
3. Partially unscrew the three flat bolts in the focus ring: 2.5 turns on each, no more.
4. Remove the focus ring. There are bolts underneath securing the focus tab.
Note: torque and thread engagement can vary slightly across production runs of this lens, so treat "2.5 turns" as a starting point and go slow.
A couple of honest caveats...
This is a one-way mod: Once the cam and cylinder are ground, there's no going back to stock geometry. Don't do this to a lens you might want to sell as unmodified later.
Verify, don't just eyeball it: Patch alignment can look correct while actual focus is subtly off if the new cam curve isn't matched perfectly. I'd recommend checking against a focus target/ruler at 0.62m rather than trusting the viewfinder alone, especially wide open.
Here are a few images that should tell the story of this mod more clearly than I can in words:
Final work: tech showing off the new MFD of 0.62m. Look how far that is from the original 1m
The section shows what lets the ring physically travel past 1m
Swapped the stock plastic focus tab for a brass one (painted black, will patina naturally over time)
plastic versus metal tab
Tech team working on the grinding process. :)
Close-up of tech team working on the grinding process
Tech team working on the cam grinding process
Tech team working taking precise measurements
Tech team enjoying a well-earned coffee break. Job done!
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