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Archive 2012 · lens repair, modification and disassembly guide thread
  
 
LightShow
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p.5 #1 · lens repair, modification and disassembly guide thread


sebboh wrote:
since there are number of people on the forum that like to do their own lens repairs and even convert lenses to other mounts, i thought it might be nice to start a repository for info on what people have done and how they've done it.

so anybody that has documented a lens conversion, repair, or simply a disassembly please post it here.

i'll start with how to remove the optical cell from the contax g 28mm f/2.8 biogon since a number of people expressed interest in how i am doing my ongoing conversion of the lens into the helicoid of a
...Show more
Thanks again for posting this, The 45's aperture mechanism differs slightly from the 28, but otherwise looks the same.

Well I have 2 lenses apart, now to combine the two.
sebboh, you said elsewhere that you had a drawing for the spacer, was that for the NEX or M mount? As I'm planning an M mount for mine, is this the type of adapter you are planning? And if it isn't, which one?
http://www.ebay.com/itm/6-bit-SM-to-M-adapter-for-Leica-Voigtlander-LTM-M39-50mm-75mm-lens-for-M8-M9-/200702156156?pt=US_Lens_Adapters_Mounts_Tubes&hash=item2ebac7dd7c






Thanks in advance.



Apr 08, 2013 at 09:55 AM
sebboh
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p.5 #2 · lens repair, modification and disassembly guide thread


LightShow wrote:
Thanks again for posting this, The 45's aperture mechanism differs slightly from the 28, but otherwise looks the same.

Well I have 2 lenses apart, now to combine the two.
sebboh, you said elsewhere that you had a drawing for the spacer, was that for the NEX or M mount? As I'm planning an M mount for mine, is this the type of adapter you are planning? And if it isn't, which one?
http://www.ebay.com/itm/6-bit-SM-to-M-adapter-for-Leica-Voigtlander-LTM-M39-50mm-75mm-lens-for-M8-M9-/200702156156?pt=US_Lens_Adapters_Mounts_Tubes&hash=item2ebac7dd7c
http://i.ebayimg.com/t/6-bit-SM-to-M-adapter-for-Leica-Voigtlander-LTM-M39-50mm-75mm-lens-for-M8-M9-/00/s/NTI0WDc5Ng==/$(KGrHqF,!k0E9Oq3TgkmBPZYpj5wv!~~60_3.jpg

Thanks in advance.


yup, that looks just like the adapter i was planning on using for the mount. i haven't gotten my drawings back from the machinist on the g28 design yet, but i was planning on doing a g45 myself this week. since i actually trimmed down the filter ring on the g45 for my previous conversion of it i'm planning on incorporating the rokkor's filter ring into the design.

for the front piece that will attach to the g45 optics and the rokkor helicoid i'm making an aluminum ring with an inner diameter of 40.21mm (to snuggly fit the contax g 45mm optics) and an outer diameter of 49mm. the thickness of the ring is 3.77mm in the center with a step down to 2mm thickness at a diameter of 44mm (the rokkor filter ring will lay in this inset). the fabricated ring will have 4 evenly spaced holes tapped for 0-80 screws at a diameter of 43mm to fasten the optics to it (i'm using 0-80 screws rather than the original screws because i didn't want to pay for a tap for whatever crazy metric size those screws are). finally there will be 4 evenly spaced countersunk holes at a diameter of 45.8mm to attach the aluminum ring to the helicoid with the original screws.

for the new mount i'm making an aluminum ring with an inner diameter of 39mm and an outer diameter of 58.9mm. the ring will be 7mm thick. on the helicoid side i'm cutting a 2mm deep inset at a diameter of 56.9mm (going all the way into the center) this inset will be the part that is screwed flush to the helicoid while the thicker outer part of the ring will keep the rokkor aperture ring from coming out. 4 evenly spaced deeply countersunk holes will be placed at a diameter of 48.4mm to attach the ring to the helicoid. i'm planning to make a 1mm inset with a diameter of 51mm on the other side for the m-mount adapter to fit into and then choose the best location for screw holes tapped at 0-80 to attach the m-mount. it looks like this will mean i need to mill out a little slot for the mount locking pin on my aluminum ring, so if you want to make this quicker you might want to forget the inset and just make this aluminum ring 1mm thinner.

note: i don't have precise measurements on for infinity focus here, so i'm leaving myself some slack to adjust the lens for infinity afterwords.



Apr 08, 2013 at 08:49 PM
LightShow
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p.5 #3 · lens repair, modification and disassembly guide thread


Thanks for the discription, the 2nd reading made more sense than the first, and it's given me a few ideas to think about.
I look forward to seeing your pics of the build.



Apr 09, 2013 at 02:30 AM
sebboh
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p.5 #4 · lens repair, modification and disassembly guide thread


LightShow wrote:
Thanks for the discription, the 2nd reading made more sense than the first, and it's given me a few ideas to think about.
I look forward to seeing your pics of the build.


it's harder to think about without pictures. hopefully i'll have it made by the end of the week/beginning of next week.



Apr 10, 2013 at 10:28 PM
LightShow
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p.5 #5 · lens repair, modification and disassembly guide thread


I'm really looking forward to seeing it come together, I will be starting mine next weekend.


Apr 11, 2013 at 12:24 PM
sebboh
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p.5 #6 · lens repair, modification and disassembly guide thread


alright, everything seems to fit well enough mating the g45 to another 55/1.7 and i have infinity focus tuned nicely:





focus goes down to around 1' or a few inches with the helicoid. i love the feel of this helicoid!

i kept the rokkor filter thread for this lens, on the g28 i'll probably get rid of it.





and here's a shot of both helicoids fully extended:







Apr 17, 2013 at 06:29 AM
sebboh
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p.5 #7 · lens repair, modification and disassembly guide thread


i was lazy on the aperture control levers, i just bent them out of christmas tree ornament hooks.

the one that attaches to the lens i just epoxied to the one on already there:





the one on the helicoid i screwed into place where the original rokkor one had been. you can see them connected in place here:





f/2 falls nicely at the f/1.7 marking and f/16 is at the f/16 marking. click stops at 1/2 stops appear to fall nearly at real half stops.
here's a picture of the aluminum ring that attaches the optics to the helicoid too (as described in a previous post):





the rokkor filter ring goes on top, then the optical block goes on and screws into the threaded holes visible in the picture.

the problem with this design is that you have to take the optical block out to remove the filter ring and tune infinity focus. i designed it this way for style to insure that the zeiss name plate could remain visible and intact, but it seems a bit silly now.



Apr 18, 2013 at 01:26 AM
JimBuchanan
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p.5 #8 · lens repair, modification and disassembly guide thread


Very Nice!

I have a MD 50/2.0, with 49mm filter, waiting for a G28.

Problem I'm having is the rising price for these G lenses, and the cornerfix type requirement for NEX cameras. Can anyone refresh my memory of this on the NEX-6 specifically?



Apr 18, 2013 at 03:49 AM
carstenw
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p.5 #9 · lens repair, modification and disassembly guide thread


It is more like the 5N.


Apr 18, 2013 at 06:37 AM
LightShow
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p.5 #10 · lens repair, modification and disassembly guide thread


Thanks Derek for posting some details on the swap.


Apr 18, 2013 at 06:50 PM
 

Search in Used Dept. 



sebboh
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p.5 #11 · lens repair, modification and disassembly guide thread


JimBuchanan wrote:
Very Nice!

I have a MD 50/2.0, with 49mm filter, waiting for a G28.

Problem I'm having is the rising price for these G lenses, and the cornerfix type requirement for NEX cameras. Can anyone refresh my memory of this on the NEX-6 specifically?


in pictures with the g28 on the 5N and 6 i don't notice any need for cornerfix while it most definitely needs it on the 7. there might still be a little shift on the 5N and 6, i'm not the most sensitive person to it.




Apr 18, 2013 at 06:58 PM
sebboh
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p.5 #12 · lens repair, modification and disassembly guide thread


after actually looking at test pictures through the range of apertures, it looks like the click stops actually fall somewhere between 1/3 and 1/2 a stop. i added clicks beyond f/1.7 and f/16 on the dial to get the full range of apertures.


Apr 19, 2013 at 08:29 AM
LightShow
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p.5 #13 · lens repair, modification and disassembly guide thread


sebboh wrote:
the problem with this design is that you have to take the optical block out to remove the filter ring and tune infinity focus. i designed it this way for style to insure that the zeiss name plate could remain visible and intact, but it seems a bit silly now.

If you are beyond infinity(I assume), you could just add shims between the mount and the lens.
I Like that the old name plate is used, makes it look original.

I do have a question or 2...
Did you cut down the G filter threads that hold the name ring?
I'd like to get closer to the final thickness of the rings, how thick is the shim needed?
Out of curiosity, how accurate is the focus scale?



Apr 20, 2013 at 08:23 PM
sebboh
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p.5 #14 · lens repair, modification and disassembly guide thread


LightShow wrote:
If you are beyond infinity(I assume), you could just add shims between the mount and the lens.
I Like that the old name plate is used, makes it look original.


adding shims and getting them right at the infinity stop is still more work than taking the optical block and filter ring off, replacing the optical block without the filter ring and tuning infinity.


LightShow wrote:
I do have a question or 2...
Did you cut down the G filter threads that hold the name ring?
I'd like to get closer to the final thickness of the rings, how thick is the shim needed?
Out of curiosity, how accurate is the focus scale?


yeah, i cut down the threads for the previous conversion where it was in a rokkor 58/1.4 body, hence the need for the rokkor filter ring. otherwise i would have just made a big aluminum surround to strengthen the contax filter thread.

i believe the final combined thickness of the two rings comes to around 12mm, roughly 8mm in back and 4mm in front for my final design (i'm just guessing i didn't measure the final amount). there is a couple millimeters of wiggle room since the helicoid has the same handy infinity tuning adjustment as the rokkor 58/1.2.

the focus scale is accurate enough to use the dof scale for zone focusing and hyperfocal focusing, but i wouldn't trust it for much at larger apertures.



Apr 21, 2013 at 01:37 AM
m-a-x
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p.5 #15 · lens repair, modification and disassembly guide thread


Sebboh and dear fellow modders,

I am in the process of finishing my Frankenzeiss Mark II (again a G 45/2 inside of OM 50/3.5) - this time with Fuji X mount.

Now I am contemplating if I shall leave the aperture control fluid, or if I should make it klick in place.
To be honest, part of my uncertainty is that I am not sure how to find the exact aperture positions of the 45/2. Wide open is easy, but where exactly are F2.8, 5, 5.6, 8, 11 and 16
Is there an accurate enough way of determining them on camera with the exposure metering system?
Might be a silly question but how would you do that? Which metering settings, what type of lighting, and what's the procedure?
Thanks!



Apr 25, 2013 at 07:01 PM
wfrank
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p.5 #16 · lens repair, modification and disassembly guide thread


This might be a stupid answer, but I'll take a shot.

Using the cam metering system in a fixed lit scene (and fixed ISO of course); why not turn the aperture dial from wideopen til the time doubles? Usually the metering system allows for 1/3 stops of times and that would increase the precision in finding optimum F/2.8 from F/2.0. For real-world footage that should be more than suffice.

Then keep on doubling the time for each full stop to mark each position.

(typo control: F/5 in your post should of course be F/4)

Looking forward to a new legend at the FM board, Frankenzeiss II by Max :-)







Apr 25, 2013 at 07:31 PM
sebboh
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p.5 #17 · lens repair, modification and disassembly guide thread


m-a-x wrote:
Sebboh and dear fellow modders,

I am in the process of finishing my Frankenzeiss Mark II (again a G 45/2 inside of OM 50/3.5) - this time with Fuji X mount.

Now I am contemplating if I shall leave the aperture control fluid, or if I should make it klick in place.
To be honest, part of my uncertainty is that I am not sure how to find the exact aperture positions of the 45/2. Wide open is easy, but where exactly are F2.8, 5, 5.6, 8, 11 and 16
Is there an accurate enough way of determining them
...Show more

sweet!

camera matrix metering should be plenty accurate enough if you put it on a tripod and point it at a evenly illuminated white wall.



Apr 25, 2013 at 08:15 PM
sebboh
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p.5 #18 · lens repair, modification and disassembly guide thread


finally got the pieces mostly finished to for the g28 frankenzeiss:
rear spacer for attaching the mount and holding the aperture ring in place on the left and new lens barrel for holding the optics in place on the right:





outward facing sides:





inward facing sides (parts that connect to rokkor helicoid):





front piece attached:





rear piece attached:





focused to infinity:





focused to mfd:





i'm undecided on whether i should anodize the lens barrel, kinda like the silver look...



May 17, 2013 at 08:01 PM
LightShow
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p.5 #19 · lens repair, modification and disassembly guide thread


Those parts look nice!
You can always anodize later.
No name rings?



May 17, 2013 at 11:55 PM
sebboh
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p.5 #20 · lens repair, modification and disassembly guide thread


LightShow wrote:
Those parts look nice!
You can always anodize later.
No name rings?


the contax name ring and filter thread attach to the optic block and will sit inside the aluminum lens barrel.



May 18, 2013 at 01:49 AM
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