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"Hacking" Contax 85/1.4 to focus more closely?
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PostPosted: Sun Mar 09, 2014 10:06 am    Post subject: "Hacking" Contax 85/1.4 to focus more closely? Reply with quote
With my 85/1.4 dissembled for repair, I saw that the focus helicoid is stopped by a protruding flange attached to the base of the lens, above the aperture ring. The two ends of this flange are supposed to be calibrated to stop the focus tube at infinity and 1m.

This may be stupid--but what if I cut away the one end of this flange to allow the helicoid to turn out of spec and the lens to focus more closely than designed? It should have some extra room before falling out completely.

Sorry for the atrocious photo but I mean the circled flange.

Just wondering out loud. I also have the Leica 80 1.4 and really like that it focuses down to 0.8m, and wish the Contax did too.



PostPosted: Sun Mar 09, 2014 6:58 pm    Post subject: Reply with quote
If I were you, I'd rather go for extension rings. Butchering a lens like this Zeiss is not a great idea IMO.


PostPosted: Sun Mar 09, 2014 7:03 pm    Post subject: Reply with quote
aoleg wrote:
If I were you, I'd rather go for extension rings. Butchering a lens like this Zeiss is not a great idea IMO.


+1


PostPosted: Mon Mar 10, 2014 6:51 am    Post subject: Reply with quote
Well, extension rings wouldn't be quite as convenient, and I'd want it to focus maybe 20 cm closer, not to do real macro photography.

That said, I'm just curious -- I don't think I'll actually do it. Smile


PostPosted: Mon Mar 10, 2014 11:59 am    Post subject: Reply with quote
Personally if it was a lens that I will keep for myself for sure and if it can be done without danger that the function in any way suffers than frankly I wouldn't hesitate. If there was a chance for resale I'd document very exactly what has been done.

Actually I just finished doing something similar to a Pen-F 1.5/60mm lens while changing it's mount to Leica M.
To change the mount it needed a new piece machined that covers the rear of the lens and it is this very same part that has the stoppers integrated. So I just positioned the stopper slightly different on the machined part, still without danger that the helicoid gets screwed apart it now focuses down to abt. 60 cm instead of to 80 cm.
However I did not ( have to ) alter any original part of the lens and anytime I can very easily swap back the original mount restoring original condition incl. original close focus distance.


PostPosted: Mon Mar 10, 2014 1:34 pm    Post subject: Reply with quote
Thanks for the response Kuuan. If you happen to have documented the process I'd love to see some photos.

On the Zeiss I'm pretty sure the stopper flange is integrated with the mounting base, so unfortunately no simple reversible surgery would be possible.

Another issue is I'm not sure how much close focus performance would improve... one might only get a little closer by cutting a big piece away?


PostPosted: Mon Mar 10, 2014 3:02 pm    Post subject: Reply with quote
I don't know about this particular lens, but when I've attempted something like this in the past it hasn't gone well. I recently tried it with a cheap Suntar 135mm, that one I could just remove a screw to test it, not far past where the normal stop was the aperture lever inside became disconnected. Another lens I tried the helicoid unscrewed.

Those stops are usually there for a reason.


PostPosted: Mon Mar 10, 2014 4:06 pm    Post subject: Reply with quote
aly324 wrote:
Thanks for the response Kuuan. If you happen to have documented the process I'd love to see some photos.

On the Zeiss I'm pretty sure the stopper flange is integrated with the mounting base, so unfortunately no simple reversible surgery would be possible.

Another issue is I'm not sure how much close focus performance would improve... one might only get a little closer by cutting a big piece away?


Hi Aly, you are most welcome!
I hope that the following will be enough to understand how is / was the case of the Pen-F lens.
Please see this photo of the original mount and mounting base / cover of the rear part of the lens and the piece to substitute it with I cut out on the right:


I had to manufacture this piece to be able to convert the lens to Leica M mount, see: http://forum.mflenses.com/pen-f-lens-converted-to-leica-m-t64879.html though one can also see there that the 1.8/38 is different, I had not looked into changing it's minimum focus distance but while doing the mount conversion of the 60mm it was too inviting to let it pass )

The rim of these parts slide below the focus barrel which, on it's inner side, has a stopper integrated. Turning the focus ring this stopper hitting the steps to the 'higher' part of the rim makes for the end of the focus throw. That is the focus throw is as long as the lower part of the rim ( as indicated by the badly drawn arrow )
The original mount allows for 180 degrees ( as indicated by the straight red lines ), I cut out longer, on the correct side, of course. Now total focus throw is between 205 and 210 degrees as indicated by the green line, that makes minimum focus distance pretty exactly 60 cm ( or a bit shorter ) as compared to the original 80cm. I was working cautiously and conservatively, first had cut out the same focus throw as original, checked, and then cut out more, one can well see a step that I left between 'original and extended'.
It was very easy to make out the point where the helicoid would have separated, it still is on the save side, I could have cut out about 10 to 15 degrees more.

hope this helps, andreas


PostPosted: Mon Mar 10, 2014 7:17 pm    Post subject: Reply with quote
Before you start modification of parts, or building new parts check whether the internal iris levers are long enough for the new minimal focus distance. When you unscrew a lens out of a focus helicoid these levers loose contact to the mount part at one point.


PostPosted: Tue Mar 11, 2014 5:23 am    Post subject: Reply with quote
kuuan wrote:

Please see this photo of the original mount and mounting base / cover of the rear part of the lens and the piece to substitute it with I cut out on the right:



The rim of these parts slide below the focus barrel which, on it's inner side, has a stopper integrated. Turning the focus ring this stopper hitting the steps to the 'higher' part of the rim makes for the end of the focus throw. That is the focus throw is as long as the lower part of the rim ( as indicated by the badly drawn arrow )


Thanks again Andreas. This is ingenious. I think I understand how it works but actually doing it is beyond my abilities! So the steps between the green and red lines -- are these to provide tactile feedback so that you know when the lens is focused out of spec? I.e. you have to turn a bit harder to go into "close focus" mode?

ZoneV -- I'd been already going through your DIY pages religiously. They're very inspiring.


PostPosted: Tue Mar 11, 2014 7:45 am    Post subject: Reply with quote
aly324 wrote:

Thanks again Andreas. This is ingenious. I think I understand how it works but actually doing it is beyond my abilities! So the steps between the green and red lines -- are these to provide tactile feedback so that you know when the lens is focused out of spec? I.e. you have to turn a bit harder to go into "close focus" mode? ...


haha, why going beyond your ability? Consider that I am living out of my suitcase right now in a country where few people speak English, the people I needed for the project certainly don't, and I don't speak the local language. It still can be done, actually it has been big fun Wink

I had to find where to buy the pieces of metal I needed





and a workshop with a turning lathe with someone who understood my drawing


to explain myself I even had made a paper model ( seen on top of my instruction sheet, under the vernier caliper )


the rest I did with locally bought rather primitive tools Wink



No, the step does not give any tactile feedback. It's just that I cut poorly and the rim was getting too low, so when I decided to cut out more for getting the close minimal focus distance I cut it higher again. Actually I also would not want any 'unusual' strain on the 'stopper' or any other part.
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