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Canon XL and GL Series DV Camcorders
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Old May 20th, 2007, 10:25 PM   #1
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Oil on lens! Yikes!

I was doing a shoot for a commercial last night and a chainsaw sprayed chain oil all over my lens! I immediately cleaned it off, but am worried about the coating on the lens.

Is there any way to tell if the oil stripped the coating off of my 20x lens? Everything appears to be OK but how can I know for sure? Would I be able to tell by shooting a high contrast tester, or can I tell by simply looking at the lens?

The first thing I did this morning was order a UV filter to try to prevent something like this from happening in the future.
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Old May 23rd, 2007, 01:56 AM   #2
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Good call on the UV filter. I've had mine on for a year now with no incident till this weekend. I was shooting a live band and had a drumstick come into my flare hood on the first set and a bass headstock on the second. I'm ordering another as backup.
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Old May 31st, 2007, 01:37 PM   #3
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lens coating

i also made a post asking how to know if the coatings been damaged but no one replied. i'd kinda like to know as well, maybe i'll have to take it in to the place i purchased it.
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Old June 1st, 2007, 01:47 PM   #4
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Easy one that.......

Remove hood and hold the lens so that a good light source strikes the surface of the lens obliquely, with your eye on the other side, ie. so that the light bounces off the lens straight into your eye. If there is any damage to the coating it will stand out like a sore thumb as a change in the reflective surface.

If you try this with a perfectly coated lens (make sure it's REALLY clean) you should see no difference across the entire surface. Damaged coating shows up as irregular patches where the coating has gone or been damaged.

Depending on the type of coating, the surface may show a slight gold/ green colouration depending on the light source, if you see blotches on that, it's cactus.

Camera makers should plaster this across the front page of every manual "Fit a UV filter pronto" (but one could argue that the manufacturers could fit one before it leaves the factory!).

Should you see damage to the coating, don't immediately throw yourself off the nearest tall structure, it may not be terminal (to the lens/ camera). The effects may not even be visible on the recorded image dependant on type of coating, lens and resolution of sensor. As a "work round" to damaged coating that DOES show on the recorded image, it may actually be preferable to remove ALL the remaining coating rather than have blotches (this is as opposed to replacing the lens or having it re - coated [which is probably totally impractical]).

Lenses worked quite happily for many decades before coatings were even dreamt up. A non - coated lens front element may lose a tad of contrast but most people wouldn't even notice - I think you'll find that un - coated UV filters out - sell fully coated by 10 to 1!

Cheers,

Chris
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Old June 1st, 2007, 04:54 PM   #5
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Originally Posted by Chris Soucy View Post
Lenses worked quite happily for many decades before coatings were even dreamt up. A non - coated lens front element may lose a tad of contrast but most people wouldn't even notice - I think you'll find that un - coated UV filters out - sell fully coated by 10 to 1!
Yes, but one of the primary advantages to having a coated lens is that you will have fewer issues with flaring and internal reflections. Putting a UV filter on your lens can only increase reflections within the lens, because of the distance between the front lens element and the filter. These reflections are made even worse by the uncoated filters you're talking about--in fact, using an uncoated filter almost negates the entire point of the coating in the first place. You're putting cheap glass in front of expensive glass, and in many ways you're throwing away a lot of the advantages that come with the expensive glass. You might as well stick a crappy lens on the camera.

If you're in a high-risk situation (like shooting around a chainsaw or flying drumsticks, for example), the use of a UV filter is pretty justifiable, but just leaving it on at all times is probably a bad idea. I realize that what I'm saying goes against conventional wisdom, but conventional wisdom isn't always based on actual wisdom. :)
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Old June 1st, 2007, 08:59 PM   #6
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Hi Jarrod.........

It was not my intention to promote the use of un - coated filters, simply to point out that an awefull lot of people actually do and think nothing of it (and don't notice the effect it has).

As for not leaving a good quality coated filter on all the time - well, given that one can never predict the un - predictable (well at least, I can't) and that without one mounted, instead of cleaning a 30 buck filter I'm cleaning a 500 buck lens element, I, personally, will go with the filter every time.

There are occasions when it just has to go, but they're few and far between.

Just my PO.

Cheers,


Chris
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Old June 1st, 2007, 10:08 PM   #7
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I definitely hear what you're saying, Chris. It's hard for a lot of people to accept the risk of a cracked or oil-splattered lens when a cheap filter can help you avoid such situations. As you say though, most people are indoctrinated with the whole "leave your UV filter on all the time" idea from the moment they buy a camera, without ever realizing that cheap glass will lessen the overall optical performance of the lens. I like to point this out when the occasion arises, because the "UV filter always on" position is so ingrained in people's minds.

One is left with a decision: should one use the lens as it was designed to be used and accept the higher risk of damage, or should one at least partially eliminate that risk by sticking some cheap glass on the front and sacrificing image quality. It can be a tough call for some shooters, and ultimately one just has to determine if the improved image quality of a naked lens is worth the risk. For me and the way I shoot, filterless lenses (unless shooting in a potentially risky situation) make much more sense--to me, the risk is worth it. That's not necessarily true for everyone, perhaps.
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Old June 2nd, 2007, 09:33 AM   #8
 
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Originally Posted by Jarrod Whaley View Post
It's hard for a lot of people to accept the risk of a cracked or oil-splattered lens when a cheap filter can help you avoid such situations.

... without ever realizing that cheap glass will lessen the overall optical performance of the lens.
So the answer to all this is: Don't buy "cheap" filters.

I can provide footage with and without a filter that no one could distinguish which one was which.

Invest in a quality filter, put it on the lens and leave it there!
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Old June 2nd, 2007, 09:57 AM   #9
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Some very thoughtful and thought-provoking replies here, on what may seem like a minor consideration. Mind if I tag on a question?

What do you guys do to clean your lenses and filters? I don't mean give them a wipe with optical cloth, but really clean them. I have the 20X, plus a handful of expensive 4x4's. Can I use alcohol? I've never done anything to clean them, except use the aforementioned optical cloth. I know the lens is coated, but what about the 4x4s? They are glass, not resin or plastic. Would alcohol damage them?
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Old June 2nd, 2007, 02:17 PM   #10
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Originally Posted by Jay Gladwell View Post
So the answer to all this is: Don't buy "cheap" filters.
Yes and no.

Even with a well-made, quality filter, you're still adding extra glass to a lens. If the designers of the lens had intended for there to be an extra element on the front, they would have put it there. They give us the option of adding filters, but the availability of an option does not automatically mean that the use of that option is the best course of action in every single situation.

Quote:
Originally Posted by Jay Gladwell View Post
I can provide footage with and without a filter that no one could distinguish which one was which.
"No one" is sort of a blanket statement. If you can't see the difference, it doesn't mean that someone else can't.

You have to remember that it all depends on who is looking at your footage, and also upon what kind of footage we're talking about. In many cases, there may be no major optical disadvantage to leaving the filter on the lens. In other situations (such as in bright lighting conditions), the difference can be pretty dramatic.

Quote:
Originally Posted by Jay Gladwell View Post
Invest in a quality filter, put it on the lens and leave it there!
For some users, yes, this is decent advice. But remember that any filter will lessen the overall optical performance of your lens, because the lens is optimized to be used exactly the way it is as it comes from the factory. Again, you are sacrificing optimal performance for peace of mind. For many shooters, this is a sound decision. For many others, it is not.

In my opinion, there is never any situation in the field of video/film production in which advice like "always do x thing every single time you shoot" is valid in every case. You have to evaluate things on a case-by-case and/or shooter-by-shooter basis if you want to do the best work you can possibly do. The minute you accept a specific procedure or idea as a given is the minute you you stop thinking critically about your process. Sometimes the difference between "great" and "just OK" can be a very subtle thing at first glance.
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Old June 4th, 2007, 01:22 PM   #11
 
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Jarrod, you up to a challenge?

You pick the subject, within reason (me being in Miami), it can be interior or exterior, or both. One shot (from camera on to camera off) without a filter and one with a filter. I'll shoot both clips using the XL2 with the stock 20X lens.

I'll bet you can't tell the difference between the two shot.
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Old June 4th, 2007, 02:40 PM   #12
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Jay--I think one shot is going to be too small a sample for us to call this a scientific experiment, but I'll bite. Why not.

How about an outdoor shot, in the afternoon on a clear day, of a colorful and detailed subject, with the camera facing in the direction of the sun--the sun doesn't have to be in the shot, obviously, just out of the shot but in the same general direction in which the camera is pointed. For simplicity, just set the focal length at the widest setting and set the iris to f1.6.

Make sure you use the exact same camera settings in both shots.

Everyone else--Can I possibly get someone who knows their optics to back me up a little bit here? :)
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Old June 4th, 2007, 04:38 PM   #13
 
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One would think if any "one" shot would show the difference, what you've described would. It's like you're trying to set up the worst possible scenario.

Just for argument's sake, what do you think the difference would be if the camera were turned away from the sun, the way the vast majority of video is shot? What then?
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Old June 4th, 2007, 05:07 PM   #14
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Basic scientific methodology aside, I've suggested this particular kind of shot because the entire gist of what I've been saying hinges on the idea that in many situations a UV filter on your lens will not have much of an adverse effect on the image, whereas the effect will be pretty noticeable in others. If I had suggested a shot where little to no effect is likely to be seen--since our entire data set consists only of two shots from one camera set-up--then I'd have to be a pretty massive moron, wouldn't I? :)

Of course you're way less likely to get a flare if you're pointing the other way. Depending on what you decide to shoot and how you shoot it, even following my suggestions, we still may not see much of a difference. That doesn't necessarily mean I'm wrong, it might just as well mean that the experiment was procedurally flawed. Even if this experiment ends up supporting my claims, I'll still say it's a flawed experiment.

If I concluded that the moon was made of cheese based on a single observation of it in which that seemed to be the case, would that mean that I could empirically state that the moon is made of cheese? No. :)

If we really wanted something much closer to proof, one way or the other, we'd need shots taken in tons of situations, and everything would have to be done in a very controlled way. There are reasons why scientists work that way. :)

Anyway, knock yourself out. Let's see how the footage turns out. :D In the meantime, if you search this very site, you'll see that plenty of very experienced people say the same thing I'm saying--that leaving a UV filter on your lens at all times is not necessarily the best idea for every shooter and/or every situation.
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Old June 4th, 2007, 09:02 PM   #15
 
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Originally Posted by Jack Barker View Post
Would alcohol damage them?
No, do not use alcohol.

To be safe, only use materials that have been made and approved for the cleaning of coated, optical surfaces. Use them (liquid or dry) sparingly and only when needed (if it ain't dirty, don't clean it!).

Remember dust particles can bond with and/or absorb other materials, such as oils or other unsavroy chemicals, as they float through the air. More times than not, those particles can/will come to rest on your lens without your knowledge. As they sit on the coated surface, those oils/chemicals will eat into the coating on the lens. You may be able to clean off the particles, but you will never be able to remove the spots left behind by the chemical reaction with the coating. I've seen it happend on too many lenses.

Another consideration is without protection you must clean the lens more often. Every time you clean your lens you remove a minute layer of coating. Over time, and with multiple cleanings, your lens and image will suffer due to the fact that you have lessened the quality of the glass by removing the very coating that was put there to improve the image in the first place.

The choice is yours.
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