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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Mon Feb 26, 2024 6:50 pm Post subject: Disassembly of Lens Groups in Canon FD Fixed Focal Lenses |
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Herbert wrote:
Firstly, I apologise if this basic topic has been covered, but searching this forum didn't turn up anything. I would like to open my Canon FD 24mm / 28mm / 35mm / 50mm lenses, which are up to 50 years old, and thoroughly clean the dust from the lenses. The following service manuals are certainly helpful:
https://www.fou-du-canon-f-1.net/wp-content/uploads/2017/03/repair-FD-part-1.pdf
https://www.fou-du-canon-f-1.net/wp-content/uploads/2017/03/repair-FD-part-2.pdf
I am mechanically skilled, but so far it has been portable hi-fi equipment (e.g. portable CD players and Walkmen) that I have maintained or repaired. What interests me most when disassembling are the lens groups. Dust can also get in there, I assume, unless the lenses are cemented together. In the linked service manuals, Canon only supplies ready-made groups as spare parts, stating that these are individually adjusted by hand at the factory. However, it is also possible that Canon wanted to save labour hours in this way. But I would like to know what is usually adjusted within a lens group. Because when I watch videos of the disassembly of a 50mm nFD, there is no explicit mention that an adjustment within a lens group seems to be necessary. Shim discs are also missing. But I assume, 50mm is a less complex design than 24mm https://www.youtube.com/watch?v=A2cf_UeGfzU
However, I can see that the repairer places marks so that the lenses along the Z-axis are not twisted at an angle.
What do you have to pay attention to when disassembling such a lens group?
Greetings, Herbert |
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RokkorDoctor
![Level 3 Level 3](rating3.gif) Joined: 27 Nov 2021 Posts: 1389 Location: Kent, UK
Expire: 2025-05-01
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Posted: Mon Feb 26, 2024 9:03 pm Post subject: |
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RokkorDoctor wrote:
I know that Minolta in their service manuals for the AF lenses had a diagram for each lens where every element was given a priority number. The ones with priority 1 (I seem to recall it was 1) have the greatest impact on image quality when they are rotated.
If the lens failed the IQ test it was advised to take that element and rotate it 120 degrees, or 240 degrees, and mount it in whichever rotated position the lens gave the best IQ.
To be honest, this is all from memory as those Minolta A-lens service manuals that were once downloadable for free are now behind a (modest) paywall, so I can't check now. I would buy them if I worked on Minolta A-lenses, but I never do.
The service manuals for the earlier Minolta ROKKOR lenses that I do have, have no such element identifications. Those lens cells are not listed as available spares either ("NO SUPPLY").
If you take a cell apart I would somehow mark the elements and make note of their relative rotation. _________________ Mark
SONY A7S, A7RII + dust-sealed modded Novoflex/Fotodiox/Rayqual MD-NEX adapters
Minolta SR-1, SRT-101/303, XD7/XD11, XGM, X700
Bronica SQAi
Ricoh GX100
Minolta majority of all Rokkor SR/AR/MC/MD models made
Sigma 14mm/3.5 for SR mount
Tamron SP 60B 300mm/2.8 (Adaptall)
Samyang T-S 24mm/3.5 (Nikon mount, DIY converted to SR mount)
Schneider-Kreuznach PC-Super-Angulon 28mm/2.8 (SR mount)
Bronica PS 35/40/50/65/80/110/135/150/180/200/250mm |
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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Tue Feb 27, 2024 4:14 am Post subject: |
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Herbert wrote:
Many thanks!
I found those at elektrotanya:
https://elektrotanya.com/minolta_70-210-f4.pdf/download.html
https://elektrotanya.com/minolta_50-f1.4.pdf/download.html#dl
So, for lens groups, the rotation of an element is much more crucial
than the distance between the elements? What is the background?
Found this on wikipedia about astigmatism im lenses:
https://en.wikipedia.org/wiki/Astigmatism_(optical_systems)
All the best, Herbert |
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RokkorDoctor
![Level 3 Level 3](rating3.gif) Joined: 27 Nov 2021 Posts: 1389 Location: Kent, UK
Expire: 2025-05-01
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Posted: Tue Feb 27, 2024 9:09 am Post subject: |
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RokkorDoctor wrote:
No, distance between elements is also crucial, but they should be preserved if you use the same spacers and don't accidentally reverse them (some spacers have a bevelled edge to match the curvature of the surface of the element; reversing the spacer can mess that up as two bevelled edges may look similar but they can be subtly different). _________________ Mark
SONY A7S, A7RII + dust-sealed modded Novoflex/Fotodiox/Rayqual MD-NEX adapters
Minolta SR-1, SRT-101/303, XD7/XD11, XGM, X700
Bronica SQAi
Ricoh GX100
Minolta majority of all Rokkor SR/AR/MC/MD models made
Sigma 14mm/3.5 for SR mount
Tamron SP 60B 300mm/2.8 (Adaptall)
Samyang T-S 24mm/3.5 (Nikon mount, DIY converted to SR mount)
Schneider-Kreuznach PC-Super-Angulon 28mm/2.8 (SR mount)
Bronica PS 35/40/50/65/80/110/135/150/180/200/250mm |
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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Tue Feb 27, 2024 11:19 am Post subject: |
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Herbert wrote:
Again, many thanks! Could a tutorial be found, not only for Canon FD but to give an impression, how those spacers look?
In this video, the repairer dos not seem to care about the angle of the lens elements...
https://www.youtube.com/watch?v=5ChD4ecqzes |
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RokkorDoctor
![Level 3 Level 3](rating3.gif) Joined: 27 Nov 2021 Posts: 1389 Location: Kent, UK
Expire: 2025-05-01
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Posted: Tue Feb 27, 2024 9:06 pm Post subject: |
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RokkorDoctor wrote:
Herbert wrote: |
Again, many thanks! Could a tutorial be found, not only for Canon FD but to give an impression, how those spacers look?
In this video, the repairer dos not seem to care about the angle of the lens elements...
https://www.youtube.com/watch?v=5ChD4ecqzes |
Best tutorial/treatise that I know of is the book:
"Mounting Optics in Optical Instruments", Paul R. Yoder; Second Edition, 2008, SPIE
Unfortunately the book itself is rather pricey, but here are few synopses borrowing from Yoder's book:
https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/08/Synopsis-of-Yoders-Lens-Mounting-E.Milby_.pdf
https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/Synopsis-of-Paper-Michihisa-Onishi.pdf
https://spie.org/news/optomechanical-design-in-five-easy-lessons#_=_
The book itself is about 750 pages and goes much more into the detailed maths and all sorts of other issues related to optical mounting of lenses, prisms etc.
As I said, it is expensive but I have learnt a lot from it and I consult it frequently. _________________ Mark
SONY A7S, A7RII + dust-sealed modded Novoflex/Fotodiox/Rayqual MD-NEX adapters
Minolta SR-1, SRT-101/303, XD7/XD11, XGM, X700
Bronica SQAi
Ricoh GX100
Minolta majority of all Rokkor SR/AR/MC/MD models made
Sigma 14mm/3.5 for SR mount
Tamron SP 60B 300mm/2.8 (Adaptall)
Samyang T-S 24mm/3.5 (Nikon mount, DIY converted to SR mount)
Schneider-Kreuznach PC-Super-Angulon 28mm/2.8 (SR mount)
Bronica PS 35/40/50/65/80/110/135/150/180/200/250mm |
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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Tue Feb 27, 2024 10:45 pm Post subject: |
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Herbert wrote:
Many thanks! I will read at least through the pdfs
Quote: |
(some spacers have a bevelled edge to match the curvature of the surface of the element; reversing the spacer can mess that up as two bevelled edges may look similar but they can be subtly different) |
I took me some time to understand. Another term for bevel is chamfer.
I assume, the edge or chamfer of a spacer is milled to match the concave side of a lens?
Also, the bigger the chamfer, the deeper the lens could sit in the assembly (of course only within fractions of a mm) |
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RokkorDoctor
![Level 3 Level 3](rating3.gif) Joined: 27 Nov 2021 Posts: 1389 Location: Kent, UK
Expire: 2025-05-01
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Posted: Wed Feb 28, 2024 11:29 am Post subject: |
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RokkorDoctor wrote:
Herbert wrote: |
Many thanks! I will read at least through the pdfs
Quote: |
(some spacers have a bevelled edge to match the curvature of the surface of the element; reversing the spacer can mess that up as two bevelled edges may look similar but they can be subtly different) |
I took me some time to understand. Another term for bevel is chamfer.
I assume, the edge or chamfer of a spacer is milled to match the concave side of a lens?
Also, the bigger the chamfer, the deeper the lens could sit in the assembly (of course only within fractions of a mm) |
Yes, exactly; the chamfer can be milled to match the concave (or convex) side of the lens.
This means if a spacer between two lens elements has two chamfered edges to match the respective lens curvatures, mounting it the wrong way around will affect the lens spacing and potentially also the centring.
(centring of some lens elements with enough curvature is achieved by precision machined spacers and/or lens retainers, much along the same way for some elements centring bells are used for centring the element prior to edge-grinding to ensure its mechanical and optical centres are aligned) _________________ Mark
SONY A7S, A7RII + dust-sealed modded Novoflex/Fotodiox/Rayqual MD-NEX adapters
Minolta SR-1, SRT-101/303, XD7/XD11, XGM, X700
Bronica SQAi
Ricoh GX100
Minolta majority of all Rokkor SR/AR/MC/MD models made
Sigma 14mm/3.5 for SR mount
Tamron SP 60B 300mm/2.8 (Adaptall)
Samyang T-S 24mm/3.5 (Nikon mount, DIY converted to SR mount)
Schneider-Kreuznach PC-Super-Angulon 28mm/2.8 (SR mount)
Bronica PS 35/40/50/65/80/110/135/150/180/200/250mm |
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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Thu Feb 29, 2024 10:51 am Post subject: |
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Herbert wrote:
Many thanks for the explanation! |
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BrianSVP
![Level 2 Level 2](rating2.gif) Joined: 09 Jun 2023 Posts: 318 Location: Philadelphia
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Posted: Thu Feb 29, 2024 4:41 pm Post subject: |
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BrianSVP wrote:
Just be aware, as well, that the manuals you have linked in the original post are from 1971 and only cover the very earliest of the FD lenses. The so-called "New" FD lenses have radically different internal mounts - some elements are held in place by plastic clips rather than metal retaining rings, some are swaged-in in plastic housings, some use soft rubber gaskets as spacers, etc.
As far as rotational alignment vs spacing goes, the latter is far more critical, whereas worrying about the rotational position of an element group is like arguing how many angels can dance on the head of a pin. As the late SK Grimes would say, by the time the SLR era came around, the centering on lens elements was so good, it was "like it was done by God himself." That's why lens repairers can get away with using machinists' blocks when recementing doublets instead of using fancy collimating equipment- the elements are so symmetrical, that mere mechanical alignment is enough to ensure proper optical alignment, no matter what the rotational position.
Also if you look at the internal elements of almost any zoom or floating element lens while you zoom and/or/focus, you will see that the internal groups actually rotate as they go in and out. The reason they can do that is that the individual elements and groups are so symmetrical that the there is no optically-significant wobble on the position of their center point as they rotate about the center axis.
Also, also, a bevel and chamfer, while similar, are actually technically terms describing two different things. A bevel is a flat cut across two parallel surfaces, while a chamfer cuts across to perpendicular surfaces.
Image source: https://www.madearia.com/blog/chamfer-vs-bevel/
A rounded chamfer is called a fillet, and a rounded corner that went parallel to parallel would be called a demi-bullnose. |
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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Sat Mar 02, 2024 1:27 pm Post subject: |
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Herbert wrote:
Many thanks for the detailed explanation and thanks for the warning!
In fact, only one of my Canon FD's is covered by the documentation linked in the first post:
35mm 1:3.5 Manufactured June 1975
I t would be great to have documentations / service manuals for the following lenses:
FD 28mm 1:2.8 Manufactured July 1978
New FD 24mm 1:2.8 Manufactured January 1979
New FD 50mm 1:1.8 Manufactured June 1984 (But this one is covered in the repair video linked in my first post)
New FD 35-150mm 1:3.5 Manufactured July 1981 and September 1983 (I have two of them)
Many thanks! |
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ZoneV
![Level 3 Level 3](rating3.gif) Joined: 09 Nov 2009 Posts: 1632 Location: Germany
Expire: 2011-12-02
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Posted: Tue Mar 05, 2024 11:57 am Post subject: |
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ZoneV wrote:
Herbert,
Are you sure those lens groups in those Canon manuals are not cemented together?
From my experience I tend to say, on most consumer grade 50 years old photography lenses the rotation is not of big influnece on the image quality.
On older lenses or high end lenses this may likely be different. I think at Leica the rotation was oftem optimized, to get the very best results - but perhaps this was beyond what users would detect outside of astrophotography. _________________ Camera modification, repair and DIY - some links to look through: http://www.4photos.de/camera-diy/index-en.html
I AM A LENS NERD!
Epis, Elmaron, Emerald, Ernostar, Helioplan and Heidosmat.
Epiotar, Kameraobjektiv, Anastigmat, Epis, Meganast, Magnagon, Quinar, Culmigon, Novotrinast, Novflexar, Colorplan, Sekor, Kinon, Talon, Telemegor, Xenon, Xenar, Ultra, Ultra Star. Tessar, Janar, Visionar, Kiptar, Kipronar and Rotelar.
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Herbert
Joined: 07 Sep 2023 Posts: 26
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Posted: Thu Mar 07, 2024 10:46 am Post subject: |
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Herbert wrote:
At least in the nFD Cleaning tutorials/videos linked in my first post the lens groups are partially cemented together.
And where they were not, dust was able to creep in.
If they were completely cemented I assume this thread would not be needed.
I also assume that alignment within a group is crucial as the assembled groups rotate against each other
which naturally might give some play, even if engineering fit gives fractions of a mm:
https://en.wikipedia.org/wiki/Engineering_fit |
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