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Old April 14th, 2002, 01:33 AM   #1
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lens flare?

I have 2 questions:

1. Is there a way to eliminate lens flare completely and always?

2. And how does one know if the lens is not flawed? Heres the scenario.

I am filming the back of a black chair straight on, and there is a tall lamp behind the chair and you can notice a smudge on the back of the chair in the image. So not to confuse anyone one, the line up is like this. lamp, chair, camera. I tried cleaning the filter, then removing the filter but still the smudge is there. So I took the lens off and cleaned both parts with a lens cloth and still the smudge is apparent. I put a CD cover on top of the lens hood. It extended about 3 inches further out and boom, lens flare (smudges) were gone. Ok so I know how to remove them temporarily, but how do I know the lens isnt smudged inside? or that I didn't clean the other side or the body side well enough? or is this normal with all lenses?
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Old April 14th, 2002, 03:28 AM   #2
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Hi,

Flare is an optical defect that is produced anytime light passes from one medium to another (air to glass). Flare is controlled by multi coating on the optical surfaces. Many cheap filters are non coated or single coated or coated on only one surface. Multi coated filters are more expensive but do a much better job. Lens hoods go a step further and physically prevent the light from striking the optical surfaces. Standard hoods can only do a limited job. Why? Most of us use a zoom lens. The hood is only really effective at the widest zoom setting. If the hood were designed to be effective at max zoom, when you pulled back you would be shooting the inside of your hood. So, hoods work but have limited effectivness. What do we do? Just what you did. Hold a hand, card, reflector etc between the light source and the lens. You could also try to control the light or change it's placement. Pros use matteboxes that adjust back and forth for the different zoom settings. Flags and eyebrows can also be attached to the box to help eliminate flare.

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Old April 14th, 2002, 08:59 AM   #3
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What you are seeing is not uncommon. The direct light from the lamp that hits the lens is probably many thousand times brighter than the light reflecting off the black chair back, so even a modest amount of internal reflection of the lamps rays can be brighter than the chair back and show up in the image.

Reduce the problem by controlling the lighting, subject matter, and camera angles, and use flags and the like to eliminate hot sources 'seeing' the lens. YOu do nto see this in most professional shots because they avoid the problem.

As for whether or not the lens is flawed, compare it to another similar lens under the eame conditions. (If yocan't find an LX1 lens, try a similar camcorder.) If your XL1 lens is substantially worse, have it chacked by Canon. But if comaring it to another cfamcorder, watch other variables such as overall image contrast, the camcorder noise level, and other system parameters.
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Old April 14th, 2002, 03:04 PM   #4
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To add to the other responses above -

If you move your camera and the smudge stays in the same place on the screen then it's probably something on the lens. If the smudge moves when you move around the camera then it's most likely attributed to the placement of a light source.

Lens flares can be very heard to spot through the viewfinder. So checking with a field monitor and waving your hand in front of the lens (directly flagging out a potential source of a flare) will help you spot them.
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Old April 15th, 2002, 02:24 AM   #5
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And some more...

If you are getting a hit from a shiny surface another option is to use dulling spray, on the shiny surface not the lens, Ha! Ha! Don't spray too close or too much, start off with a little at first until it is no longer a problem.

Another good accessory is Black Wrap. It's black foil. You can attach it to your light to use as a flag to flag the light off your lens or you can attach a strip of it to your lens hood as a cheap French Flag.
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Old April 15th, 2002, 06:46 PM   #6
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more about lense flare

I put a UV filter on my 3x wide angle and I get the worst glare ever. I take off the filter and its gone. Did I mention that the UV filter is by Canon?

Can I just say it sure is hard just to take the camera and record a little footage. Lights! Camera, wait... Lights! Lights! wait Lense filters...wait Lights! uh...action?
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Old April 15th, 2002, 07:13 PM   #7
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Try a better quality UV filter, such as a Tiffen... you always get what you pay for. You may need to reduce glare to the UV on a 3x lens with an "eyebrow" sunshade or a deeper matte box.
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Old April 15th, 2002, 07:42 PM   #8
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Hi,

if you must use a UV I've had the best luck with B+W and Heliopan filters. Tiffins and Hoyas are not as expensive and almost as good. Most of the Canon filters are not multi coated, just single coating.

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Old April 15th, 2002, 10:12 PM   #9
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You're not alone with your lens flare problem. Flares are one of the biggest time consuming items in most productions, especially dramatic productions where a flare is really not acceptable.

French flags and, as has been mentioned, black wrap, are the best tools to control flares. Black wrap has the advantage in that it can be shaped to block exactly the culprit source. But be careful with either of these - since the XL-1 EVF is overscanned, unless you are monitoring the image in an underscanned monitor, you are likely to end up with a piece of the flag or wrap showing somewhere along the edge of the frame. The next best thing is to use flags, not at the camera, but placed somewhere between the light souce(s) and the lens.

I'm currently editing a little dramatic feature. Even though we took great care to control flares, now that we are in the edit room looking at big monitors, we can often see all the flares we missed. Often we just have to edit around them.
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Old April 15th, 2002, 10:49 PM   #10
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all cameras?

I was wondering if this is a problem with all cameras and all lenses or just more so with canon's xl1 stuff?
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Old April 15th, 2002, 11:17 PM   #11
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To varying degrees, it's a problem with all lenses. Some are specially coated to minimize flare but there's no way to eliminate it. Glass is glass no matter how good it is.
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Old April 16th, 2002, 02:49 PM   #12
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Flare can show up where you have good contrast capability with the lens and image sensor. Noise in the image can hide the flare, a bit like hiding a golf ball in tall grass. A clean dark black can show flare just like the same gold ball on the green. If the lens produces poor contrast, flare may be hidden in the rest of the murk. As noted above, pros setup their shots to avoid flare causing situations when possible.
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