Surveyors Tape Reflects in HID Lighting

[DiverRush]

At work we use fiberglass open reel tape measures for surveying transect lines. Commonly when we get the video back from the field instead of being yellow in the video, the tape is overexposed and white from a distance but upon getting within 3ft the tape assumes it's normal yellow pigment. Camera is a Canon ZR80 in an Ikelite housing with 2 UK Light Cannon 100 HID Pro lights. Anyone know of a way to solve this problem? Would a different colour of tape be less likely to overexpose?

 

[TheBigPhillyFish]

It sounds like your having a white balance problem. I am not to familiar with the camera you are using. I have a few questions that could help us identify your problem.

What kind of water green or blue?
Are you using the video light filters in the Light Canon 100's?
Does your camera offer manual white balance? If not what white balance presets does it offer?
Does the tape measure have a matte, semi-gloss or glossy finish?

 

[DiverRush]

Hey BigPhillyFish,
Green water up here in B.C.,
No filters on the lights just those diffusers that come on the lights
Camera is pretty basic, guessing no WB or AWB but I can check when it gets back from the field.
Tape has a glossy finish so I think that may be where the problem is.

 

[ArtF]

Diverrush

THis is just speculation on my part but here goes-- Perhaps the fiberglass tape has some retroreflective properties, so your HID light is reflected directly back towards the camera when the rest of the world is mostly low reflectance.

A visual experiment you might do is see what the reflectance into your eye is when a flashlight is (how bright does the tape look) directed at the tape from a position near your face versus when the flashlight is held way off to the side and still hits the tape (does the tape look just as bright?).

Good luck

Art

 

[DiverRush]

ArtF,

It looks as though the tape may have some retroreflective properties. From examining some video footage taken of the tape from an angle has almost no reflection but if the camera is more directly above the tape it reflects the HIDs. I will have to try an experiment with the camera just to make sure this is the problem. Would the solution be trying to find an open reel tape measure that isn't retroreflective at all?

 

[ArtF]

DiverRush
If it is retroreflective then finding a tape that is not would solve the problem. The other approach which MAY NOT be practical would be to move the illuminating HIDs as far away from the camer as possible. Retroreflective means that the light goes back in the direction it came from (e.g. towards your HID). However, the angular sensitivity of the tape might be too broad for you to get the HIDs far enough from the camera lens to do any good.

Good luck!

Art