Two spots with one laser beam in images

[Fernando]

Hello everyone. I have a question about Optics and I place here because I don't know if there are a specific thread.

I am using a laser beam to calibrate position of several cameras. But instead of to have one spot in the image I have two spot. One of them is smaller of the other.
I presume that the smaller one is some kind of reflection, maybe in the material, maybe in the optics of camera.

The focal length of camera optics is 9mmm and resolution is 1600 pixels.

Have someone any idea of the cause of this reflection?

Have someone eperienced something similar?

Thanks a lot in advance!

 

[pixel]

I think we would need some more detail about the setup, and a photo of the spots would help.

 

[Fernando]

The laser is pointing to a painted metal surface and in parallel to laser and similar distance is located the camera. The resulting image of the camera have two laser spot. one es very big. The other spot is close to the first one and much smaller.

Sorry, but I can't upload the image because i don't have a url to share. The images are stored in a local repository.

Any explanation will be welcome. :-)

 

[berkeman]

The laser is pointing to a painted metal surface and in parallel to laser and similar distance is located the camera. The resulting image of the camera have two laser spot. one es very big. The other spot is close to the first one and much smaller.

Sorry, but I can't upload the image because i don't have a url to share. The images are stored in a local repository.

Any explanation will be welcome. :-)

Do you see two spots with your naked eye too, or just in the camera image? It's probably just internal reflection inside your camera optics...

Just make a screen shot of the image on your computer display and paste it into a JPG file using Microsoft Paint or something similar. We need to see the image tobe of more help.

 

[Fernando]

Thanks berkeman.

Maybe, also I think that can be a reflexion in camera optics.

Or a second reflexion in a deeper layer of the paint. The first layers of paint can have some index of transmission until the layer of a second reflexion.

I can't reproduce the effect for the moment because I waiting for new lasers but I have the images of previous experiments in my computer. The problem is that I don't find the tool or button to add a picture in the message. Only to add a url.

 

[berkeman]

Click the UPLOAD button to upload a picture to your post...

 

[Fernando]

Ah! Ok. I haven't seen that button

That is the image. I need only the main spot of the laser but there are a secondary reflection...

 

[berkeman]

Do you have any pictures with the lights on?

 

[Fernando]

No. That is illumination that we are using. We only need the laser spot so only use environment lighting.

 

[Domullus]

Move the camera up and down and check if the distance between spots changes in the image. If there is some reflection from camera optics, the smaller (reflected spot) should jiggle randomly and disappear when your main laser beam hits the lens on optical axis. If you distance is almost constant and smaller spot does not jiggle, then it means the second spot is not caused by the camera :)

 

[Fernando]

Thanks Domullus. Great idea! I will try it.

 

[pixel]

Or a second reflexion in a deeper layer of the paint. The first layers of paint can have some index of transmission until the layer of a second reflexion.

I don't think it is this since any reflection from the back of the paint would be diffuse and the second spot you're seeing is sharp. I agree that it's most likely ghosting flare in the camera lens. A coated lens will usually eliminate such artifacts unless the light source is very bright, as is the case here.

 

[Khashishi]

My guess is that it is a reflection between surfaces in the compound lens.

 

[Domullus]

Most often when I see two beams instead of one I check the mirrors in the beam deliverysystem. These maybe inserted upside down (coating side down). Mirrors have coatings only on one side and other side is substrate. If you are not careful you can easily mix the sides. When this happens you will get two reflection one from the coating (bright) and other from the substrate (weak). Flip the mirror and problem solved :)

 

[Fernando]

Thank you, Pixel. I think that this is the best solution. Using coated lens.

Thank you, Domullus. But the only mirrors in the laser beam are inside the laser and I can't dismount it.