Is this fungus or dirt on my lens?

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ps2user

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Hopefully someone might be able to let me know if this is fungus or some sort of dirt in the lens? Unfortuntely its behind the rear glass element so cant get a cloth to get rid of it :(

Never seen fungus on a lens before, but i thought it being so big it would have fine lines growing out of the center? Also im not sure if its effecting the coating on the glass since you can see something like clouding around it.

Taken some photos with it at the back garden and couldnt see any issues with the pictures.
 

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I’m afraid it looks very much like fungus to me
 
Fungus does tend to be a bit more 'spidery' from my experience, although it could start like this I guess.

I also had a lens with a bug in it that looked just like this, but you could see it move around. Could be one that's died I guess.
 
Looks like the very beginning of fungus to me, probably wouldn't affect image quality (yet). If its new and active/ alive leave it in the sun or under a UV lamp for a few days which should kill it and stop it spreading. Depending on the lens and you comfort levels disassembling lenses it might be cleanable using some hydrogen peroxide although if it isn't affecting the image I would probably leave it as is unless you're really bothered by it as you run the risk of ruining the lens and or introducing dust in the process.
 
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It won't get rid of if it is fungus but you can stop or delay the spread by putting the lens in an airtight sealed bag with several large Silica sachets. that should help draw out any moisture inside the lens. May take a couple of weeks or so but that is another option
 
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Thanks everyone for confirming it's fungus.

Well it's a used lens I just bought. Thought I got a bargain since it cost £120ish for canon 70-300 IS DO since I like the compact size. The company is happy for a full refund or give me a partial refund of £20 making the it only £100ish. I quite like the lens, I'm thinking it's not a bad offer, but will take a few more shots to be sure it's good. I assume if I keep it's just a matter of how long in time before the fungus grows and causes an issue.

Would zapping it with UV just stop it from growing? I also presume that I will need to take the lens apart and clean it, which I've not done before. Is it worth £100 risk and adding a green band lens to my collection?

What would you do?
 
Not a bad price if you're happy with the lens.

Have you used a torch and looked through the lens from both the back and front to see if that's the only fungus/ debris? Sometimes infections can be difficult to spot on the edges of the inner elements. Also test images throughout the aperture range as it might show in images at smaller apertures.

I just watched a disassembly video for this lens and it's not something for a first timer imho.
Theoretically prolonged UV exposure should kill fungus so it won't spread further (just be careful as you can really damage your eyes with strong UV) and the silica beads trick suggested above should help as well.

One thing to note is it might be harder to sell on with fungus if you ever decided to do so but if it's just that one spot, it doesn't affect images, and the compact form was a deal breaker ( a decent non DO 70-300mm is usm is supposedly a better performer) I personally would probably keep it at that price.
I am a bit of a lens pack rat though...
 
ps2user said:
Thanks everyone for confirming it's fungus.

Well it's a used lens I just bought. Thought I got a bargain since it cost £120ish for canon 70-300 IS DO since I like the compact size. The company is happy for a full refund or give me a partial refund of £20 making the it only £100ish. I quite like the lens, I'm thinking it's not a bad offer, but will take a few more shots to be sure it's good. I assume if I keep it's just a matter of how long in time before the fungus grows and causes an issue.

Would zapping it with UV just stop it from growing? I also presume that I will need to take the lens apart and clean it, which I've not done before. Is it worth £100 risk and adding a green band lens to my collection?

What would you do?
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TBH, I'd be tempted to be a bit cheeky and see if they can do you a bigger partial refund - a decent, honest dealer shouldn't sell a knowingly infected lens (IMO) so in theory, it's worthless to them as it is.

Whatever you decide to do, keep the lens separate from the rest of your kit (when not in use!) and not kept fitted to your body (unless it's a body dedicated to the lens.) Keep it well ventilated and in sunlight to keep it under check.
 
Well that doesn't resemble any lens fungus that I've ever seen. But the pics are too low res to guess ...

What's with the bright centre & the dimmer but concentic 'halo' at one remove from it?

When I see lens fungus it's normally radially dendritic with a spidery texture, & whiteish ...

Better pics possible?
 
Thanks for the tip on keeping it separate to my camera and away from my lens.

Watched the videos on taking it apart and it's looks quite fun and challenging. Will give it a go when it affects photos, hopefully that's a long time to come.

Ordered a sterilising UV light and if it's fungus, hopefully it will kill it.
 
Agree with @droj, that isn't fungus. It's a dead insect. I've seen similar before. Needs cleaning out though. Not sure if it could cause permanent damage to the lens surface.
 
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