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Archive 2012 · lens repair, modification and disassembly guide thread
  
 
Edgars Kalnins
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p.7 #1 · p.7 #1 · lens repair, modification and disassembly guide thread


here is the link to the mirror image of my creation at this stage:
http://www.flickr.com/photos/portreti/9024447028/



Jun 12, 2013 at 09:16 AM
sebboh
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p.7 #2 · p.7 #2 · lens repair, modification and disassembly guide thread


Edgars Kalnins wrote:
I have been trying to adapt the Contax T2 Sonnar 38mm f2.8 on my sony nex-3. It has been done before, but it seems to me that the focusing abilities were limited or sacrificed for simplicity or other considerations. So far I have only attached the lens temporarily to check the quality of images. My skills being as they are I ended up removing the mount plate from my sony camera and selotaping the lens onto it! Close-ups look satisfying to me and I will update once I have some images at infinity.


image quality looks good! can you post a picture of what the lens looks like removed from the original body?



Jun 12, 2013 at 02:31 PM
Edgars Kalnins
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p.7 #3 · p.7 #3 · lens repair, modification and disassembly guide thread


I will as soon as I take it off sony nex. I got it as new old spares - without a body - alongside contax T3 and Yashica T5 lenses. It comes housed in a primitive helicoid. It seems fragile and focusing is not very smooth but it is better than nothing. I have yet to disassemble the other lenses, but T2 seemed the easiest to adapt.
The seller still has one used yashica T5 left: http://www.ebay.co.uk/itm/YASHICA-T5-LENS-/251284907831?pt=UK_Replacement_Parts_Film_Camera_Parts&hash=item3a81bf6737
probably not worth for you considering the shipping costs.



Jun 12, 2013 at 11:04 PM
JimBuchanan
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p.7 #4 · p.7 #4 · lens repair, modification and disassembly guide thread


OK, here's my version of the Contax G28 converted to Leica M mount, minus rangefinder focusing:
http://farm3.staticflickr.com/2891/9118299086_8838d40ef3.jpg
I originally, had a MD 50/2.0 because it was 49mm filter thread smaller diameter. I had a working solution except for the aperture, but the 50mm helical gave way too much focus travel. I also had problems machining as the helical was made out of plastic. So, it went on the shelf.

Then, on a whim, I bought a $40 MD 28/2.8. The focus helical and aperture matched up to the G28, so why not. The MD 28 also had a 49mm filter thread, and the helical turned out to be real aluminum.

The lens assembly sits back so deep into the Minolta 28 body that attaching a filter maybe problematic, but there really isn't any need for a lens hood. I infinity adjusted to maximize corner performance on the NEX-7, which means wide open hard stop infinity is a hair short of infinity. I typically don't shoot infinity scenics wide open, but at least f/4. I don't remember the G28 as having any field curvature, but there could be that symmetrical lens/corner sensor filter problem manifesting itself as field curvature.

The G28 minimum focus distance correlates well with the distance scale on the Minolta lens. Because the aperture movement was about the same radial distance between the G28 and Minolta aperture ring, I was hoping for some correlation there, but nope. That's why most lenses have the aperture cam, the original in the middle, replaced with a new piece that will operate the G28 aperture.
http://farm6.staticflickr.com/5546/9116071583_192f5fc7e7.jpg
http://farm6.staticflickr.com/5486/9116073495_7f19c6c116.jpg
The aluminum helical was machined to give more room on the bottom for the aperture finger to reach up to the G28, and the top was surfaced in order to inlay the G28 optical unit into the helical.
http://farm3.staticflickr.com/2881/9118296976_66fa1ed2f9.jpg
http://farm3.staticflickr.com/2861/9118297710_47bca6d6e2.jpg
A quick check of aperture ring accuracy showed a doubling of exposure time with the move from f/2.8 to f/5.6 on the Minolta aperture ring.

The couple of caveats aside, the converted lens is M mount for widest application, the focus and aperture rings turn in the right direction, no lens hood is needed, great Minolta mechanics and the package turned out to be reasonable in cost.



Jun 23, 2013 at 05:23 PM
sebboh
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p.7 #5 · p.7 #5 · lens repair, modification and disassembly guide thread


looks great jim!

the long focus throw of the 55mm helicoid is why i needed to attach a new piece to the optics as well as the aperture ring on my conversion. having an accurate focus scale sounds nice, but i wouldn't want to give up the close focus possibilities. can't believe the helicoid on the md 50/2 is really made out of plastic! btw, are you only using one screw to hold the optics in the helicoid or just one for the picture?



Jun 23, 2013 at 10:37 PM
JimBuchanan
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p.7 #6 · p.7 #6 · lens repair, modification and disassembly guide thread


Thanks! One screw for illustrative purposes only. As you know, there 2 sets of 3 threaded holes. One set for the Minolta front lens assembly and one to secure the front housing/filter threads. Because I got a good inlayed fit of the G28 optics rim, I used just 3 screws to hold both the optics and front housing. One of the photos shows the G28 optic rim right in the middle of the screw radius, so 3 notches with a round file had to be made in the optic rim in order for the screws to make it thru.

I'm more than happy with 12 inches MFD of the G28/Minolta, and that's to the film plane so 9 inches from the lens is macro enough for me. There is an example using the NEX6 on the NEX images thread.






Jun 24, 2013 at 01:09 AM
ISO1600
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p.7 #7 · p.7 #7 · lens repair, modification and disassembly guide thread


Thinking out loud here, but i'd be interested to see a size comparison and shootout between the above converted G28's and a native MD 28/2.8.... :P




Jun 24, 2013 at 01:52 AM
sebboh
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p.7 #8 · p.7 #8 · lens repair, modification and disassembly guide thread


ISO1600 wrote:
Thinking out loud here, but i'd be interested to see a size comparison and shootout between the above converted G28's and a native MD 28/2.8.... :P



i don't have the MD 28/2.8 on hand, but on camera it's an inch longer than my converted g28. i'll post a picture of the coverted g28 next to an MC 55/1.7 (which is smaller than the MD 28/2.8) both on NEX adapters later tonight. i could do a shoot out of the g28 vs the MD W 28/2 some time later.



Jun 24, 2013 at 02:18 AM
sebboh
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p.7 #9 · p.7 #9 · lens repair, modification and disassembly guide thread


JimBuchanan wrote:
Thanks! One screw for illustrative purposes only. As you know, there 2 sets of 3 threaded holes. One set for the Minolta front lens assembly and one to secure the front housing/filter threads. Because I got a good inlayed fit of the G28 optics rim, I used just 3 screws to hold both the optics and front housing. One of the photos shows the G28 optic rim right in the middle of the screw radius, so 3 notches with a round file had to be made in the optic rim in order for the screws to make it thru.

I'm more
...Show more

that sounds pretty good, i does the md 28mm focus that close or is that with a helicoid adapter?



Jun 24, 2013 at 02:22 AM
LightShow
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p.7 #10 · p.7 #10 · lens repair, modification and disassembly guide thread


Looks nice Jim, thanks for posting.


Jun 24, 2013 at 07:24 AM
 

Search in Used Dept. 



sebboh
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p.7 #11 · p.7 #11 · lens repair, modification and disassembly guide thread


ISO1600 wrote:
Thinking out loud here, but i'd be interested to see a size comparison and shootout between the above converted G28's and a native MD 28/2.8.... :P



here's the closest i could do to a size comparison for you:
http://farm4.staticflickr.com/3670/9124785204_ab0bb6ba7a_o.jpg
both lenses are focuses to infinity and attached to their e-mount adapters.

i don't have an MD 28/2.8 so the lens on the right is the MC PF 55/1.7 (which was the lens i used as a donnor for my conversion). the 55/1.7 is 37mm long whereas the smallest version of the MD 28/2.8 is 43mm long.

here's a picture to put the size more into perspective:
http://farm4.staticflickr.com/3754/9122562367_8e7a744793_o.jpg
from left to right the lenses are: leica m 40mm f/2 c-summicron, jupiter-3 50mm f/1.5, leica m 50mm f/1.4 summilux pre-asph (version II), g28 frankenzeiss, rokkor MC PF 55mm f/1.7, olympus zuiko pen f 42mm f/1.2, contax 35mm f/1.4. all the lenses have e-mount adapters attached except for the jupiter-3 and summilux (i only have two m-mount adapters).



Jun 24, 2013 at 07:48 AM
ISO1600
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p.7 #12 · p.7 #12 · lens repair, modification and disassembly guide thread


awesome example pictures. The G28 looks to be an awesome lens, and you've successfully crammed it into a nicely smaller package.


Jun 24, 2013 at 05:50 PM
LightShow
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p.7 #13 · p.7 #13 · lens repair, modification and disassembly guide thread


The size won't be much different, because the optics still have to be the same distance from the sensor @ infinity, the only real changes will be the overall diameter, and the improvement in manual focusing.


Jun 25, 2013 at 03:29 AM
sebboh
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p.7 #14 · p.7 #14 · lens repair, modification and disassembly guide thread


LightShow wrote:
The size won't be much different, because the optics still have to be the same distance from the sensor @ infinity, the only real changes will be the overall diameter, and the improvement in manual focusing.


indeed the length is exactly the same as the g28 was prior to conversion. the diameter is larger because i'm partial to rokkor scalloped focus rings. you can certainly get smaller diameter helicoids that would work (i bet the helicoid in the OM 50/1.8 would work well).



Jun 25, 2013 at 04:40 AM
ISO1600
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p.7 #15 · p.7 #15 · lens repair, modification and disassembly guide thread


i meant smaller in comparison to a normal MD 28/2.8.


Jun 25, 2013 at 02:38 PM
ZoneV
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p.7 #16 · p.7 #16 · lens repair, modification and disassembly guide thread


I bought a lens with supposed separation. Cause it was a old rare Edixa 85mm/1.9 I found no lens diagramm.

http://www.4photos.de/camera-diy/Edixa-Edixar85m-1024.jpg


But after I disassembled the lens front, I could clearly verify that it was delaminated:

http://www.4photos.de/camera-diy/Delamination-Blume-1024.jpg


Cause I supected the lens to have Canada Balm as glue, and not modern UV curing glue, I used my tested method for DIY lens separation repair. I heated the lens in an oven at 150C, and it gets full separated.

http://www.4photos.de/camera-diy/Linse-Backofen-1024.jpg


Cleaning with isopropanol alkohol.
And my new idea using not expensive optical glue, but cheap "UHU glas" worked just fine!

http://www.4photos.de/camera-diy/Linsen-Delamination-Reparatur-1024.jpg


Now the lens works fine - without the defect visible in the bokeh in some images

http://www.4photos.de/camera-diy/Edixa-85mm-1.9-Objektiv-1024.jpg





Jun 29, 2013 at 10:52 AM
ISO1600
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p.7 #17 · p.7 #17 · lens repair, modification and disassembly guide thread


I'll admit, I haven't scanned every page in the thread, but I've got a Nikon 300/4.5 EDIF that could benefit from some regreasing of the Focus Helicoil.
I am lost when it comes to this.
Seeing as this is an IF telephoto, I am worried that the process may be somewhat complicated.



Jul 01, 2013 at 03:53 PM
ZoneV
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p.7 #18 · p.7 #18 · lens repair, modification and disassembly guide thread


I suppose there is no focus helicoil when its a internal focus system. IF systems are more like zoom lenses with a bearing moving in cam tracks.


Jul 01, 2013 at 05:59 PM
ISO1600
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p.7 #19 · p.7 #19 · lens repair, modification and disassembly guide thread


ahh yeah, that makes sense.
Hopefully one of two things will happen:

1) Somebody will be awesome and have experience in this exact situation,
2) When I get to Korea, I'll find a repair place in Seoul that can handle it affordably.

I think it will most likely wind up being door #2.



Jul 01, 2013 at 06:11 PM
Edgars Kalnins
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p.7 #20 · p.7 #20 · lens repair, modification and disassembly guide thread


Here are 3 Zeiss lenses from the famous compact film cameras (Contax T2 and T3 and Yashica T5). I added the modern C-Biogon for size comparison. I attached the Tessar 35mm and Sonnar 38mm to my Sony Nex-3 for a couple weeks. It was only a temporary experiment and I used insulation tape for this purpose. I am sure it affected the results somewhat. I was quite pleased with results at close distances but often straggled to get good pictures from medium distance to infinity. It might have been my "adapter" or possibly the lenses were designed this way. I hope someone more patient and resourceful makes better adaptations and tests them properly!


Zeiss 35mm family (5) by lowlightlove, on Flickr

here the Sonnar 38mm and C-Biogon are at MFD

Zeiss 35mm family (6) by lowlightlove, on Flickr

the rear element of the modern lens is quite a bit larger (not easily seen)

Zeiss 35mm family (1) by lowlightlove, on Flickr



Jul 04, 2013 at 12:02 AM
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