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Infinity stop on 24mm f2 lens


Ian Rance

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<p>I have been using my new 24mm f2 lens for a few days now, but I note that it does not quite focus to infinity - it needs just a fraction more of a turn.</p>

<p>The focus ring says infinity, but the glass is not quite there. Are the two independantly adjustable? Where is the infinity stop inside this lens? If it reachable by just removing the F mount, I can do it, but I don't want to just tinker.</p>

<p>Thank you, Ian</p>

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<p>I think the lens was probably taken apart, (as in helicoid unscrewed), and then put back together one helicoid turn too soon. I have seen the same when I took apart a 50 f1.8 lens.</p>

<p>To fix it, you'll probably have to undo the lens, unscrew the helicoid, carefully stopping as it just comes apart. Once you have it just apart, make a small turn and then cry to catch the groove to get the turns back together again.</p>

<p>It took me several trys to get the correct orientation, when I tried it.</p>

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<p>Ian.... Did the 24/2 come from the camera shop you regularly use? Perhaps they should do it for you.</p>

<p>That said, Carey describes it well if you have to go in yourself. The hardest part, in my opinion, is keeping the aperture ring and stop-down linkage stuff straight. If you're comfortable with that from past experiences, have at it. Needless to say, work clean.</p>

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<p>Do not dismantle the lens or unscrew the helicoids. Typically if the inner helicoids are mated incorrectly (i.e. one turn too late or early), the focus is way off, not slightly off. The outer helicoid (to which the focusing ring is attached) has such a shallow pitch that there is normally only one way to *start* it when mating the two halves, and that is the correct way. But it has an infinite number of possibilities to where is can be *stopped* once it has been screwed in.</p>

<p>Assuming you have an AIS version ...</p>

<p>The adjustment for the infinity focus stop is reached by partially disassembling the FRONT section of the lens. The stop itself is a fixed "step" that is part of the knurled silver mounting ring, but the focusing ring (with corresponding "step" on the inner surface) is secured to the outer focusing helicoid by a thin brass "clamp ring" and three #0 JIS screws. By loosening the clamp ring and slipping the focus ring you adjust where these two "steps" meet (for both infinity and minimum focus).</p>

<p>I haven't worked on this particular lens, but do have the exploded diagram for it. The rubber grip needs to be removed, which should expose a tiny hole through which threads are visible. Typically, there is a small amount of red threadlocker on these threads that can be loosened by applying a drop of acetone in the hole (there is no screw). The focusing ring is in two halves, and you need to remove the front nosepiece section to gain access to the brass clamp ring. By loosening the screws of the brass clamping ring, you can slip the focusing ring clockwise a little bit, retighten the screws, and then you should be able to focus to infinity.</p>

<p>Usually in this scenario (not reaching infinity) you need to slip the ring far enough clockwise initially so that you can actually focus past infinity. You then focus the lens to correct infinity focus visually through the viewfinder, loosen the clamp ring screws once again (without moving the focusing ring), then slip the focusing ring counterclockwise until it hits the stop, and retighten the screws. Reattach the nosepiece and rubber grip, and you are good to go.</p>

<p>Caveat emptor. Might not be for the faint of heart. :-)</p>

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<p>Thank you for the comments.</p>

<p>Joe, yes it came from my local shop, but the price was very low so if they repaired it they would be out of pocket I think.</p>

<p>Michael, thank you for the comments. Reading through it, I do get the feeling that it may be beyond my skills. I would hate to render the lens inoperable or damage something.</p>

<p>I think I will save up and send the lens for a full service as and when.</p>

<p>Ian</p>

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<p>In case you are curious, I have attached a scan of the 24/2 "exploded view" showing the stops for infinity and minimum focus. This is the AIS version. The AI would be different internally, but similar in principle (fixed stops, adjustment via "slipping" the focusing ring).</p>

<p>Most of the small AI/AIS primes are similar in design to the 24/2.</p><div>00UnU7-181941784.thumb.jpg.7266bb7ec719bad5ea2dd1c340650c99.jpg</div>

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<p>I don't think it is the focus stop that is the problem. Unless one is extremely careful, and patient, it could easily scrap the lens.</p>

<p>Alternatively, if you see the value of photographing with the lens the $60 potential cost for the repair would be well worth it, for the enjoyment afterwards.</p>

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