G7X front lens scratch: tech advice needed!

Discussion in 'Technical Troubleshooting' started by GregNouveau, Jul 6, 2025.

  1. GregNouveau

    GregNouveau New Member

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    Hi guys!

    After some advice from "people who know": I am a mech-tronic engineer, so I can fix loads of things....but my knowledge of camera optics is basically zero!

    I have a G7X, which works fine, but the glass front lens has a 4mm long scratch on the outside.
    I guess previous owner rubbed it with something that had a bit of grit on it, maybe?

    The scratch is upper right as you look at the screen: it is only in shot when zooming in about 70%, but some lens flare is evident prior to this point.
    Now this is not the end of the world, as the camera is intended for Youtube video and a music video, but I would like to rectify it if there is a cheap easy solution.
    I have emailed Canon asking if they can supply a replacement part: this would be the best solution, as I have already managed to remove the lens with no issues, and put things back together ok!
    I guess that getting someone to polish it out somehow is not a viable option, as the scratch seems a little too deep for that.

    My other option is the reason for my reaching out on this forum:
    if I can find a suitable glass lens, could I simply replace the scratched one?
    This where I need your help!
    What is the spec of the glass lens: I know that I'd need to replace it with an identical (or very similar?) spec lens.....but I'm wondering what effect a different one would have?
    Would the pictures come out ok, but with an altered focus / zoom?
    The front of the camera says "Canon Zoom Lens 4.2x IS". I know what this means.
    The other part is a little puzzling to me: "8.8-36.8mm 1:1.8-2.8" Again, I understand what this means: adjustable length and exposure.
    But what effect would putting a different lens on the front have on these figures?

    I'm guessing that the 8.8 to 36.8mm is basically the distance between the CCD and the actual lens, as you zoom in and out?

    When I removed the lens, it seemed to be a plano-convex type, and was approx 24-25mm diameter.
    Again, I guess the focal length is critical, but how do I find out the spec of the actual glass lens fitted to the G7X?
    Is there some standard spec 25mm lens that several manufacturers use on their compacts?
    I see that this is a rabbit hole I'm going down!

    Any help much appreciated!
    Obviously, the best solution is that Canon sell me a lens and I can fit that: job done!
    But experience tells me that it's just not gonna be that easy: I reckon Canon will say " Sorry, the lens is part of the complete lens assembly and cannot be supplied on its own. The cost of the assembly is £450 +VAT and there is a flat rate £450 service charge!!".....or words to that effect! lol!

    What can you tell me, guys?

    TIA.
    G.
     

  2. johnsey

    johnsey Site Moderator Staff Member Site Supporter

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  3. GregNouveau

    GregNouveau New Member

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    Yeh, that's a lot to pay for something that is working on my camera! There is a youtube video that shows how to replace the whole lens unit: looks a lot more involved that just the outside glass..... :)
    If I can get a lens that is physically close in dimensions to the canon original, surely it must work in the same way, regarding focal length, etc?
    It's not too difficult to maybe buy a replacement, fit it and see whether it works?
     
  4. GregNouveau

    GregNouveau New Member

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    I've been researching this and found the following on Google:

    "The Canon G7X series cameras (like the G7X Mark II and G7X Mark III) feature a built-in Canon Zoom lens with a focal length of 8.8 – 36.8 mm, which is equivalent to 24 – 100mm on a 35mm camera. This lens offers a 4.2x optical zoom and has a maximum aperture of f/1.8-f/2.8. The lens construction includes 11 elements in 9 groups, with various aspherical and UD elements to minimize aberrations."

    Reading this, I can kind of understand why the lens assembly is so expensive: "ELEVEN elements in NINE groups"!?

    And there's me thinking that it was just my scratched lens, another one inside the tube, and then the CCD!! lol!

    This does make me think that the front lens is a smaller part of the equation, and therefore changing it will have less overall effect?
     
  5. johnsey

    johnsey Site Moderator Staff Member Site Supporter

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    Well it is a built in lens unit which is meant to be every thing you need since this is essentially a high end point and shoot camera.
    With a DSLR you could just buy a new lens.

    I assume the glass part that is scratched would solve your issue, replacing a single glass piece as you say would be complicated on a small compact single built in lens unit, hence why you see it as a whole part to swap.
     
  6. GregNouveau

    GregNouveau New Member

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    It does seem that only a genuine replacement from Canon is the proper fix: I'm thinking that the lens itself is not just a plano-convex one?
    It's more likely to be an aspherical one! More science going on here than I initially reckoned with!
     
  7. Caladina

    Caladina Well-Known Member

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    two of the cheaper options, 1st, live with the imperfection and work around it or with it for cool flares
    2nd, see if you can get either a glasses (spectacle) maker to polish it out,
    my mum used to work in an opticians and one of my after school jobs was to cycle the glasses between the opticians and the makers, they would often polish out scratches back then
    with this you will loose any canon coatings.
    though they may want the lens on its own?

    likewise see what a camera repair shop can offer in way of polishing out the scratched glass

    aliexpress has those same front assemblies for around the $200 aus dollar

    next up will be getting an estimate from canon see what they want to fix it, either single lens replacement or assembly

    and the odd ball try it and see would be a windscreen UV chip repair fluid, it will fill the scratch but results i have no idea on
     
  8. Caladina

    Caladina Well-Known Member

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  9. GregNouveau

    GregNouveau New Member

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    @Caladina You know, all the above things have been on my agenda!
    Re: Canon. I did get a reply to my request to purchase a front lens: predictably, they cannot (will not) send me just the lens. I have to send my camera back to them, etc.....its gonna cost at least £500, so that's a no, then! ;-)

    I have determined that the scratch is only visible / in shot beyond a certain point when zooming, so i'm gonna be ok 80% of the time, at least.

    I have seen the £50 ebay G7's and was wondering as well if the lens assy's are the same / v.similar?

    I get the impression that the G7X was a re-design, not an update, though, so I'm apprehensive about the lenses being the same?
    The glass lens is basically a 1" diameter item, so I COULD fit any optically comparable lens from 22-25mm?
    But the £500 question is what ARE the specs of that lens: it does seem as if I could MAYBE fit an optically similar lens, maybe off one of the ebay cameras, and see what happens? Before I removed the lens, I wasn't sure what the situation was inside the lens assembly.

    I naively thought that it was the front lens, then another lens, and then the CCD. Research dug up all this "elements" business, achromatic, aspherical and plano-convex lenses..none of which I was aware of!

    What I DID deduce though, was that when that front lens is removed, the main part of the lens assembly is behind a well -sealed lens: whether this lens is part of the main assembly, or for protective purposes. I don't know.

    What it did tell me was that by removing the front lens, I hadn't damaged anything critical.
    Removing the front lens IS a much better way to clean the dust from inside the zoom mechanism that the guys who drill 5mm holes in the plastic and stick cotton buds in there!!!
    The fact that Canon were ok with the zoom setup does further convince me that the inner lens is where the delicate (expensive!)stuff starts!
    Dust can easily creep in past the tube sides, and the front lens itself is not actually hermetically sealed: it is just 6 x glue spots with a thin plastic self-adhesive ring over it in a very half-hearted attempt to keep dust out!

    So yes...I think I may take a punt on one of the ebay cams......

    Does anyone know if the lens info on the front of lenses has any hidden clue as to what part the actual front lens plays in the general scheme of things?
    Knowing the focal length of that front lens would be VERY heplful...... ;-)
     
  10. GregNouveau

    GregNouveau New Member

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    The windscreen repair resin is also something I could look into: if I drip a tiny bit of that into the scratch, it will blend it in a little, if nothing else?
    That way, I can retain the lens coating as much as possible, too.
     

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