FD 70-150 front lens element removal?

[franklin_h1]

<p>After being neglected for quite some time i just noticed my fd 70-150 4.5 lens now has a couple of small spots of fungus forming on the inside of the front lens.<br>

I'd like to remove the front element and clean up and was hoping for some removal instructions before i blindly start trying to remove things.<br>

From what i can see, it looks like i'll have to remove an outer ring with a spanner tool, but from there i'm not sure. Does the small ring with the canon name inscription screw out as well? If so what is the best/easiest method to remove that? Any other screws hiding under the sliding lens hood?<br>

Any help appreciated and my thanks in advance</p>

 

[alan_swartz]

<p>Franklin,</p>

<p>My philosophy is to go ahead and share what I have learned about these things, rather than simply say, "Don't take your lens apart--you'll probably ruin it." I leave it to you (and others) to judge their skill levels and the risks they're willing to take. So here's the official disclaimer: <em>you can certainly destroy your lens if you don't know what you're doing . . . or even if you do know and you slip with the spanner!</em><br>

<em></em> <br>

Legalities aside now, you jinxed my 70-150. I went to have a look at it and it too has a few mold spots and one spidery haze. Someone has already had it apart, too. Oh well, I spent something like $14 for it, so no big deal.</p>

<p>So instead of a guesstimate, I went into it and here's the story. Mine is an FDn lens--I don't remember whether this was made in a breech ring version.</p>

<p>The spanner comes off first. That lets the hood slide off.</p>

<p>Under the hood are three screws. Remove them completely so that you can sight through the holes. Note the bright dimples made by the screw points, as well as the orientation of the name ring with respect to the focus/aperture index mark on the lens. You'll need to return this group to the proper position.</p>

<p>Place your rubber ring cup on the name ring. The ring itself does not unscrew, but you have to turn it to unscrew the entire front group, ring, glass, and all. The front element is a cemented doublet.</p>

<p>Now you have access to the rear of the front group and the front of the first zooming group. My spots are on the little zooming group, and they did not come off. The coating is damaged. The baffle that holds this group has spanner slots. It is plastic, so if you decide to go further, take care with the spanner wrench. Mark its position before unscrewing it. Two groups come out with the plastic. Two more groups stand between you and the diaphragm, and even those have damage in my lens.</p>

<p>That's as far as I have gone. When you reassemble, it looks like the front group can go deeper into the barrel than its normal position. As far as I can tell, the only effect that would have would be to alter infinity focus slightly, since the front group does the focusing. There may be no other adjustable infinity stop; if so, this would be the adjustment. But sight through those screw holes and put it back just where you found it. By combining your rotational index and the depth of the dimples in the holes, you should return it precisely to its original position.</p>

<p>Hope yours cleans up OK!</p>

[franklin_h1]

<p>Thanks Alan for the detailed step by step, thats the info i was hoping for.(and the words of caution, sorry about your lens)</p>