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Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd element
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PostPosted: Tue Jan 18, 2022 5:10 pm    Post subject: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd element Reply with quote
I just have been trying to clean some fungus on the nFD 4.5/75-150mm lens. If the fungus is limited to the space between front element and second element, it's pretty easy to dismantle and clean it - BUT when re-mountng the front element it needs to be centered! I'm pretty sure it can't be done properly without the corresponding instruments - nevertheless one of my copies with pretty visible fungus seems to do quite well after the cleaning.

So let's start. First we have to unscrew the metal ring betweem lens hood and lens barrel, using the corresponding tool:


After removing the ring, we can slide the entire hood towards the front, and finally take it off:


Now, on the front ring of the lens, three screws are visible. We can extract them:

When you shake the lens after removing these screws, you can hear/feel a rattling sound - something is loose, but doesn't come off. It's the front element (a doublet). It obviously has been made with pretty "loose" tolerances, allowing to adjust its centering with the three screws we just had removed.

Now we can screw out the front element, using e. g. a small screwdriver which "fits" into one of the letters on the front ring (just as shown here):


Finally the front element comes out, and the two surfaces may be cleaned:


Re-assembling is quite straightforward - the only thing to adjust apart from centering is the position of the front element. Since the 70-150mm does focus with the front element only, we can easily adjust "infinity", depending on how deeply we insert the front doublet. When it comes to the centering of the said front doublet, I just tried to put in all three screws equally.

Was it a success? Well, partly. There's still a trace of fungus between the inner elements, and of course I didin't have the instruments to properly re-center the front element. Nevertheless, I can't see any difference in corner resolution, compared to my other samples of the nFD 70-150mm. And contrast has increased, of course, since 80-90% of the fungus has gone.

S


PostPosted: Tue Jan 18, 2022 6:14 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
Like 1 small Like 1 small

stevemark wrote:
... it's pretty easy to dismantle and clean it - BUT when re-mountng the front element it needs to be centered! I'm pretty sure it can't be done properly without the corresponding instruments ...

... When it comes to the centering of the said front doublet, I just tried to put in all three screws equally. ...
S


For some lenses (probably not the nFD 4.5/70-150mm from the looks of it) there may be a couple of workarounds for this problem. I have never had to try this myself, so it may not work, but:

If it is possible to take out the problematic element/group with the set-screws / grub-screws undone only partially (i.e. with their threads still partially engaged) then:

- before taking out the element, take note of its exact rotational orientation
- for each set-screw take note of exactly how many full turns and partial turns it has been undone (to the nearest 5 degrees or so if possible). A bit painful, but it may work

then:

- re-mount the element in exactly the same orientation
- re-tighten each of the three set screws by their respective counted full and partial turns
- if necessary, then finish the final tightening equally across all three set screws

Alternatively, if the set-screws / grub-screws are flat-ended (not point-ended), and the element has sufficient clearance, it may be possible to extract the element after loosening up only one of the three screws and leave the other two screws untouched. Then, upon re-mounting the element in its original orientation, only the loosened screw is to be tightened up to get pretty close to the original centration of the element.

This won't be perfect, but perhaps it might be an acceptable compromise in absence of a full-blown centering setup Wink


PostPosted: Tue Jan 18, 2022 6:28 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
stevemark wrote:
...
Now we can screw out the front element, using e. g. a small screwdriver which "fits" into one of the letters on the front ring (just as shown here):

...


OUCH!!!

Get the correct tool. Smile


photo ebay seller yuenuli

Click here to see on Ebay


PostPosted: Tue Jan 18, 2022 6:32 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
visualopsins wrote:

OUCH!!!

Get the correct tool. Smile


photo ebay seller yuenuli

Click here to see on Ebay


I have a set of those exact ones! Really useful. Also great to hold up an assembled aperture assembly as you lower the lens' inner barrel down over it.


PostPosted: Tue Jan 18, 2022 9:54 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
stevemark wrote:
BUT when re-mountng the front element it needs to be centered!


Thanks for sharing this! I have got one of those laying around here awaiting cleaning. This may have saved me some headache.

stevemark wrote:
Since the 70-150mm does focus with the front element only, we can easily adjust "infinity", depending on how deeply we insert the front doublet.


As far as I understand the lens construction, the intended way to adjust infinity is found at the back of the lens. At least adjustments can be made there without risking to decenter the front element.



PostPosted: Thu Jan 20, 2022 6:11 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
RokkorDoctor wrote:

For some lenses (probably not the nFD 4.5/70-150mm from the looks of it) there may be a couple of workarounds for this problem. I have never had to try this myself, so it may not work, but:

If it is possible to take out the problematic element/group with the set-screws / grub-screws undone only partially (i.e. with their threads still partially engaged) then:

- before taking out the element, take note of its exact rotational orientation
- for each set-screw take note of exactly how many full turns and partial turns it has been undone (to the nearest 5 degrees or so if possible). A bit painful, but it may work

then:

- re-mount the element in exactly the same orientation
- re-tighten each of the three set screws by their respective counted full and partial turns
- if necessary, then finish the final tightening equally across all three set screws


Sounds pretty reasonable - but since I really didn't expect this kind of "centering on the finished lens" mechanism, it is too late for my lens ...

visualopsins wrote:
stevemark wrote:
...
Now we can screw out the front element, using e. g. a small screwdriver which "fits" into one of the letters on the front ring (just as shown here):

...


OUCH!!!

Get the correct tool. Smile


photo ebay seller yuenuli


I *do" have the correct tool Wink

In this case however it wasn't needed at all - the front doublet unit (which includes the front ring with engravings shown above) is made with such big tolerances that it actually wobbles around as soon as the three "centering" screws have been loosened. Which means it cab be turned very easily. In addition, the set of tools shown above sadly is rather slippery and usually doesn't work as advertised ...

S


PostPosted: Thu Jan 20, 2022 6:15 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
fdlenses wrote:

As far as I understand the lens construction, the intended way to adjust infinity is found at the back of the lens. At least adjustments can be made there without risking to decenter the front element.


This screws are for adjusting the correct distance between the Master lens (and coincidentally also of the entire lens, of course) and the sensor/film. This distance must be correct even before adjusting infinity.

Focusing, however, is done only by moving the front doublet. Adjusting infinity therefore must be done by adjusting the front group only.

S


PostPosted: Fri Jan 21, 2022 2:48 pm    Post subject: Re: Canon nFD 4.5/70-150mm: Fungus between 1st and 2nd eleme Reply with quote
stevemark wrote:
fdlenses wrote:

As far as I understand the lens construction, the intended way to adjust infinity is found at the back of the lens. At least adjustments can be made there without risking to decenter the front element.


This screws are for adjusting the correct distance between the Master lens (and coincidentally also of the entire lens, of course) and the sensor/film. This distance must be correct even before adjusting infinity.

Focusing, however, is done only by moving the front doublet. Adjusting infinity therefore must be done by adjusting the front group only.

S


Slotted holes instead of internal shims for the master lens register calibration? That looks like something that would be quite easy to knock out of alignment, even with that bucket full of thread-lock I can see applied Wink
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