Cleaning the insides on a lens

Discussion in 'Digital SLR' started by Siddhartha Jain, Nov 2, 2005.

  1. While cleaning my Sigma 24-135mm I noticed a small dot on the last but
    one lens element. On close inspection it seems that a tiny insect
    crawled into the lens and died on the glass element :( Now its stuck
    there!!

    Any idea how easy/difficult it is to reach that spot? I found several
    screws on the back of the lens but am not enthusiastic about opening up
    this lens as it is my primary lens unless I know what I am getting
    into. Also, I doubt if there are any Sigma service centres in India.

    Thanks for any help,

    - Siddhartha
     
    Siddhartha Jain, Nov 2, 2005
    #1
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  2. Live with it! Any attempt to dis-assemble the lens has a very high
    chance of ending in tears. The effect of the bug on image quality is
    almost certain to be immeasurably small.

    David
     
    David Littlewood, Nov 2, 2005
    #2
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  3. Don't mess with it. There are just far too many little parts in there
    that all need to be returned to their exact original positions. That little
    bug is not likely to impact on the images (a few test will show that, try
    photographing a gray card). If there is a real problem, get an estimate
    from a camera repair person.
     
    Joseph Meehan, Nov 2, 2005
    #3
  4. All I see is a small black dot on my photographs so I am not in panic
    yet. I guess I will just live with it and replace the lens with
    something better and faster in a few months.

    - Siddhartha
     
    Siddhartha Jain, Nov 2, 2005
    #4
  5. It is highly unlikely that the small black dot on your photographs is
    caused by a speck inside the lens; the latter would be so far out of
    focus as to be wholly invisible. Far more likely (assuming, from the NG
    you have posted in, that it is a DSLR) that there is a quite separate
    dust spot on the sensor.

    David
     
    David Littlewood, Nov 2, 2005
    #5
  6. Siddhartha Jain

    Lorem Ipsum Guest

    It's Karma!
     
    Lorem Ipsum, Nov 2, 2005
    #6
  7. It sounds like something on your sensor. If you have another lens, I'll
    bet you will see the same spot. Lenses don't focus on bugs inside the lens
    very well. :) At most it is likely to show up as a very fuzzy difficult
    to see blob.
     
    Joseph Meehan, Nov 2, 2005
    #7
  8. Siddhartha Jain

    G.T. Guest

    Yeah, I have a substantial speck of dust inside the front element on my
    70-200L f/4 and it's nowhere to be seen in my photos.

    Greg
     
    G.T., Nov 2, 2005
    #8
  9. Siddhartha Jain

    Mike Berger Guest

    A lot of people in this newsgroup have said that Sigma lenses
    tend to have bugs.
     
    Mike Berger, Nov 2, 2005
    #9
  10. Siddhartha Jain

    frederick Guest

    You are getting plenty of warnings not to try. (and it might be just
    sensor dust causing the spot - as pointed out).
    I'm not disagreeing with them.

    But if you do want to give it a try, then it might not require removal
    of the mount. Rear element assemblies usually unscrew as one piece in
    their barrel - you may need a lens spanner - don't try just jamming
    something down to the notch to try and lever it around as you will
    likely slip and break something.
    Sometimes the gap is not wide enough between the rear element group
    barrel and the inner edge of the mount - and the mount will need to be
    removed.
    To remove the mount, as well as the obvious screws, there are usually a
    couple of very small screws (assuming lens is positioned front element
    down) under the electrical contacts. Unscrew and remove these - as
    otherwise you risk damaging the ribbon cables as you attempt to remove
    the mount. The electrical contacts stay with the body of the lens as
    you remove the mount.

    Don't drop anything down the lens once you have removed the rear
    element. If you do, it will likely end up in the middle of the lens
    around the diaphram - and you may have turned a relatively simple job
    into a big one.

    Note that there are probably spacer washers with positioning lugs under
    the mount. The screws holding the mount on are not usually positioned
    symetrically - they only go one way. Make sure when reassembling that
    all washers are replaced and positioned in the correct rotation. If
    something doesn't want to go back into place, then don't force it.

    If everything turns to custard, then the following method should be used
    only as a last resort:
    http://www.hermes.net.au/bayling/repair/lens_20b.jpg


    Good luck.
     
    frederick, Nov 2, 2005
    #10
  11. Tom Nakashima, Nov 2, 2005
    #11
  12. Siddhartha Jain

    Bob Guest

    If it doesn't bother the pictures - leave it!!

    I once opened a lens just to see what was in it, and now it's a big dust filled
    mess! Remember the kid that took apart the alarm clock and never got it back
    together? That was me... although I'm better at it now!

    The lens I played with was just a scrap lens from a copy machine, but there is
    no way to keep the dust out once opened, unless you have a clean room...
     
    Bob, Nov 3, 2005
    #12
  13. Siddhartha Jain

    Rich Guest


    Unless you have a particularly dust-free environment, and the idea of
    replacing precision-fit lens elements in aluminum tube doesn't bother
    you, I'd avoid it. The saddest thing will be if someone tries to
    "drop" a lens element back into place only to have it lodge sideways.
    Then the real fun begins. Having disassembled and reassembled lots of
    these things, it's not something you'd want to do if you have no
    experience. The worst thing is that if the lens has any flint (it
    will) or ED elements. They are fragile and can get edge chipped
    easily.
    -Rich
     
    Rich, Nov 3, 2005
    #13
  14. Hmm .... that's something I've been dreading - dust on the sensor. Need
    to run some tests to figure out where and how much dust is on the
    sensor. And with all the responses I've got regarding the lens, I guess
    I am not attempting to open it or anything of the sort.

    Thanks,

    - Siddhartha
     
    Siddhartha Jain, Nov 3, 2005
    #14
  15. Siddhartha Jain

    frederick Guest

    It is most unlikely that the "bug" is on an inside surface of the rear
    element group - as the tube itself is effectively sealed. It is probably
    on the front element of the assembly, and should be reasonably easily
    accessible - without disassembling the rear element group itself.
     
    frederick, Nov 3, 2005
    #15
  16. Oh, now you disassemble and reassemble lenses? Jeez, what a moron!
     
    Randall Ainsworth, Nov 3, 2005
    #16
  17. Siddhartha Jain

    redbelly Guest

    He could also take a photo with no lens at all. If it's dust on the
    sensor, it'll still show up.

    Mark
     
    redbelly, Nov 3, 2005
    #17
  18. I thought of that, but I suspected the problems of exposure might
    complicate the situation.
     
    Joseph Meehan, Nov 3, 2005
    #18
  19. Siddhartha Jain

    Rich Guest

    Not if someone put an expensive ($7000) lens away in a closet for 8
    years when it was freezing cold from being outside. What do you
    supposed the interior of the lens was like? Had to be disassembled,
    cleaned and reassembled.
    -Rich
     
    Rich, Nov 3, 2005
    #19
  20. Siddhartha Jain

    phk Guest

    Not only is it physically difficult, requiring specialized tools, but
    unless you re-assemble it in a very dry environment, internal humidity
    will cause fogging if you take it out in the cold.
     
    phk, Nov 3, 2005
    #20
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