A "Canon lens coating issue"!? Not on an L-series!
That is fungus and needs a professional service if inside (I have seen 2 incidences of fungal growth from optics used in far north Queensland here in Australia necessitating a complete disassembly of the lens, and that is costly). Fungus is common in tropical/moist conditions, moreso if the lens has been stored in a humid environment. If there is fungus up front, chances are, it could have penetrated deeper.
This optic is a much valued staple to my walking kit (and as you point out an equal performer to the heavier 2.8L version). The 70-200 f4L can fetch for up to 2/3 original value for a mint specimen — mint meaning no scratches, dents, scuffs or fungus. The ULD CaF2 inner element is chief among its costly features. I would be looking at a bit of heavy bargaining if the fungus is a concern, even though a mid-range Av will yield a most likely 'no show' in images. In common with the standard Canon optics vs the L-series, it is by far a much better performer than the 100-300mm 'pedestrian' Canon.
Last edited by Poisson Du Jour; 07-13-2009 at 02:44 AM. Click to view previous post history.
Do I spot a hint of sarcasm in that last comment....
A follow-up for anyone who's interested.
I tested the lens extensively with and without my 1.4X TC and shooting all sorts of conditions - low light, into the sun, angle to the sun without hood, close focus, infinity focus, etc. I have no source for comparison but the images struck me as being very good in terms of contrast, sharpness, flare, and quite acceptable. So, I don't intend to deal with the fungus before my Colorado trip but will see what's involved in cleaning it up afterwards. I had sent my co-worker the link to this thread and I guess he read this and did some on-line research. In any event, we came up with a fair price so I have a lens to take with me on my trip.
Do take care of it before too long, though.
Originally Posted by Fotoguy20d
The fungus itself could continue growing and, worse, the damage done by the fungus to the glass (etching) will probably increase with time.
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Having had a 100-300 f4.5-5.6, I can highly NOT recommend it. Autofocus is fast, but inaccurate, image quality is marginal until stopped down to f 11.
How is a 100-300 f/4.5-5.6 even close or equivalent to a 70-200 f/4.0L ? They're not even the same lens whatsoever. I don't even majority use Canon but I know a stupid comparison when I see one.
Originally Posted by bob100684
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.
That does indeed look like fungus. This could be caused by water splashing onto the coating (and subsequently not dried) which creates an ideal place for the fungus to grow. Lenses also do not like humid environments and fungus often goes hand in hand with high humidity. Other problems like internal corrosion can also happen in these environments but this is greatly reduced by the weather sealing present on the "L" lenses.
I would test the lens to see how it performs. Shoot it on a full frame camera and see if there are any noticeable faults in the image - something that you will be unhappy with. (please do this with a freshly cleaned sensor to avoid headaches!). Sometimes these marks can be polished out but it will never be the same as you are taking some of the coating off the glass with even the finest of polishing compounds. Lens elements are expensive not only for the part but the amount of labour time required to install and calibrate to factory specifications.
Prevention: Store lens in case with dehumidifying material - silica gel. You can get it online in big packs for very little money. Also, stick a high quality Sky or UV filter on the front of the lens. You can get a 67mm B+W/Schenider filter for a reasonable price and it will protect against front element fungus, scratches and even some potential breakages!
if you have any questions, please send them along to me:
Last edited by andrewkirkby; 07-26-2009 at 10:21 PM. Click to view previous post history.
That is fungus, but that lens; in that condition will probably take great pictures anyway. Use it and when not in use; put it on a windowsill under the sun. After a couple of weeks you will have a care free lens.
If the fungus has eaten away the coating then your pictures will probably be useless. Your pictures will be sharp but the colors will look off and wrong where the coating is gone. Tread carefully.