View Single Post

Replacement Focus Tab
Old 02-09-2017   #1564
michaelwj
----------------
 
michaelwj's Avatar
 
michaelwj is online now
Join Date: Feb 2013
Location: Brisbane AUS
Posts: 1,508
Replacement Focus Tab

For such a brilliant lens, the thing that always got me (after the flaring hood problem was solved) was the dinky plastic focus tab. It's almost like the lens was made to a budget, which was exhausted before the focus tab was thought of. I have a few issues with the tab;

1) It's not really that deep, so I don't get a great feel from it. Unlike the more modern or older 'infinity lock' lens tabs which have are tighter radius and a deeper surface.

2) It breaks easily. When you see how it is secured, it's amazing any of them lasted so long. There is just not enough plastic to ensure it doesn't break. I think this limitation (having to secure it with a screw) influences the shape - it can't be deeper or either there isn't enough material for a strong(ish) attachment, or on the other hand it would protrude too far and hit a surface when you put the camera down.

3) Directly related to 2), Leica in their infinite wisdom will no longer sell the part to independent repairers. In fact, the only authorised repair service in Australia said that Leica won't sell the part to them and it would have to back to Germany to get replaced. At a minimum cost of 300 Euro. Plus shipping. Minimum!

So given all of that, I thought I'd make my own. I wanted it to fit securely using the existing screw (not glue on like some replacements are - how inelegant is that!), requiring no modification to the lens. I also wanted to get the shape of the focus tab as close as possible to that of the 21mm Super Angulon which I believe has the best shape tab. It is also similar to the modern lenses and older ones like the 35mm Summaron for example. I also wanted it to have a weak point so it breaks rather than the lens.

I'm currently of prototype #2. Here is a shot of the first prototype and the original tab to compare the shape of the tab.



You can see the original (broken and glued back together) is relatively shallow, while my prototype v1 is deeper with a tighter curve. Mine is also metal (this one in Stainless Steel, v2 in Maraging Steel), so I need less material for the screw while maintaining strength, allowing it to maintain a low enough profile. v1 had a few issues though. Firstly the "wings" were a bit long and thin and it made manufacture too tricky so for v2 they were shortened and the depth increased. Secondly I was planning on tapping a thread for the screw, but it proved to be too secure and difficult. Basically there would not have been a weak point and the lens would have broken before the thread gave out.

Here is a shot of prototype #2



You can see I've made the changes to the "wings". What you can't see is that I've changed from tapping a thread on the inside to gluing a nut to the inside. The aim is that the glue here breaks before the lens does in the event of an accident, and then it can be simply glued back on. Nothing broken.

Changes for v3 (and hopefully final version). The 2 dowels and the nut need to be moved 0.5mm down (towards the rear of the lens). At the moment, it attaches a little bit too close to the front of the lens - you can almost see it overhanging. It doesn't get in the way, but is not elegant enough. It should and can be better. Apart from that, I'm super stoked with it (that means over the moon for non Aussies). It gives a way more positive feel, where I always felt like my finger was going to slip out of the original one. It's like a new lens.

Once I have the final design down, I'll make a batch (likely in Bronze) and offer them for sale in the classifieds here. At the moment I'm piggybacking other jobs, so don't really get to choose the material... They'll cost about US$50, which is the same as some plastic ones that I've seen on the bay.

I *think* the 35mm v4 summicron has the same shape, but I'm not sure 100%

(This was also posted on LUF)
__________________
Cheers,
Michael
  Reply With Quote