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flagman 04-21-2005 04:49 PM

Cleaning an L lens
 
Hi All

Is it possible and easy to clean the glass on an L lens? I've recently bought a 100-300 5.6L that doesn't take a clear picture, even with a tripod. The photos look like there's something smeared on the lens. There's nothing obvious on the 2 visible outside elements, otherwise I would have seen it, so I'm thinkng there maybe something inside. How feasible is it to attempt to open and clean all the elements?

Thanks in advance

Andy.

mlopes 04-21-2005 05:06 PM

Re: Cleaning an L lens
 
Hi Andy, considering that your lens is still under the warranty period, my advice is to contact your local store or local brand support in order to check what's the problem. I believe that opening and cleaning the lens by yourself should always be the second choice.

BR's
Mario

green 04-21-2005 05:22 PM

Re: Cleaning an L lens
 
I believe that opening and cleaning the lens by yourself should always be the second choice.

Nope, it shouldn't be a choice at all.
If you manage to dismantle the lens, there a very little chance you'll manage to put it back together. But if you do manage to do all this, you'll just even more dirt into the lens. Lenses are manufacture in stricly control environement and should be repair in that same environment.

mlopes 04-21-2005 05:28 PM

Re: Cleaning an L lens
 
Yes, you're write Donadio... at least i personaly couldn't put it back together again ;) i've tried once with a calculator and the result was not very good ahaha.

DiaAzul 04-21-2005 08:46 PM

Re: Cleaning an L lens
 
It's unlikely that you are suffering from anything on the outer surfaces of the lens as they are typically out of focus when taking pictures and so don't contribute a great deal to smearing effect. What you may notice is a loss of contrast or flaring if there are marks or scratches on the lenses.

There is a good chance that one or more of the elements has been knocked out of alignment. It is unlikely that you will be able to make any adjustments yourself without the necessary optical workbench and clean working environment. A lens is a precision instrument and as such needs the correct tools in order to ensure that it is reconstructed with the correct lens alignment. Best to send it back to the manufacturer for them to do the necessary work.

flagman 04-22-2005 12:44 AM

Re: Cleaning an L lens
 
Thanks for all your comments. I have come to the conclusion that it isn't a good idea to open it up. I bought the lens second-hand, though, so getting it repaired/cleaned under warranty is not an option. I guess the inner lens could be mis-aligned. The effect is sort of like motion-blur and is reduced but still visible at small apertures. Does anyone know the likely cost of getting it checked/repaired?
Thanks
Andy.

AdrianW 04-22-2005 02:45 AM

Re: Cleaning an L lens
 
Unfortunately the UK is probably the most expensive place to get something like this fixed :(

I suppose the real question is, what's wrong with it... I'm wondering about mould inside the lens, although I'd expect that would be magnified with narrower apertures.

Take the caps off the lens, shine some light at a sheet of paper and look through the lens. Do any of the elements seem cloudy or blotchy - if so, it's mould.

Still looking at the sheet of paper, if you look through the lens does the image circle appear to be a perfect circle, or is it ellipsoid? If you've got an ellipse chances are there's an element out of alignment.

Another option would be a sticking aperture blade - with the lens on the camera shine a light into the lens and use the depth-of-field preview button. Look at the aperture, is it a regular shape? If not, it's an aperture fault.

That's the end of my lens diagnostic skills I'm afraid!

flagman 05-03-2005 07:14 PM

Re: Cleaning an L lens
 
Thanks for these tests, Adrian, they are very helpful, at least a place to start.
Sorry for being dense, but can you just clarify exactly how I do these tests:
Mould test - Do I look straight through the lens or have it attached to the camera and through the viewfinder? And is the light shining through the paper into the lens or just onto the paper from the same side?

Andy.

flagman 05-04-2005 12:15 AM

Re: Cleaning an L lens
 
I've uploaded a few pictures here, if anyone could use them to disgnose the problenm, I'd appreciate it.
Same focal lengths, aperture and shutter speeds used. Tripod and cable release used.
Shot 1, taken with a 70-200 F4L:
<a href=http://homepage.ntlworld.com/gameandwatch/70-200b.jpg>Shot1</a>
Same Shot with the faulty lens, a 100-300 5.6L:
<a href=http://homepage.ntlworld.com/gameandwatch/100-300b.jpg>Shot1</a>
Shot 2, taken with a 70-200 F4L:
<a href=http://homepage.ntlworld.com/gameandwatch/70-200a.jpg>Shot2</a>
Same shot with the 100-300:
<a href=http://homepage.ntlworld.com/gameandwatch/100-300a.jpg>Shot1</a>

Andy.

flagman 05-04-2005 12:42 AM

Re: Cleaning an L lens
 
I hope double and treble posting is allowed :)
I run those 3 tests and my limited skills would diagnose: inconclusive. There is no obvious mould, although the central 80% of the round image through the paper is VERY slightly darker than the outer 20%. The ellipse/circle test doesn't really show an ellipse but it does seem that one side of the camera-end of the lens remains visible from most angles, when the other side disappears as you move the lens around. I don't know if this means there's a mis-aligned element? Perhaps my previous post with sample images helps?

Andy.


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