UV Coating? on products.

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Patryk
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Hi Guy's,

I'm after some advice, I've been filming many headlights on a turn table recently and i've ran into a problem of these rainbow colours appearing on the products? I can't figure out what is causing this and how to remove it? I've attached an example where it's very obvious.

Any help or suggestions would be highly appreciated.
 

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I have a polarizing filter although when i use it it doesn't eliminate it completely, only shifts the effect if that makes sense? Like from one place to another. That's right, it's not glass, most of the time it is acrylic or another form of hard plastic.
 
I used to be involved in spectacle manufacture and we used to check for over tight glazing of glass lenses into metal frames by viewing the lens through crossed polarizing filters, this showed up and stress points, if you viewed an acrylic lens this way it showed an effect just like that which you are getting.
Can you only see it when filmed or can it be seen by eye? (I know nothing about film cameras)
Yes rotating a polarizing filter will alter the pattern.

Edit. Posting at the same time as Chris. :)
 
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I think you are seeing stress patterns, the use of polarized light allows the stress patterns in the "Glass" to show up.
This http://www.vishaypg.com/docs/11212/11212_tn.pdf illustrates it , how you stop it -no idea
The solution here is cross polarisation - you must fit a linear polarising screen (filter) to each light, and use them in conjunction with the polariser on your camera lens.
You need to do one light at a time, and rotate the screen until the stress marks have disappeared, then repeat with each light in turn.
Fiddly, but it works.
 
First thing to try is without the polarising filter which is probably doing very little to help reflections anyway. Note that polarisers don't work on metallic surfaces and reduce reflections only at a narrow range of angles like 30-40 degrees to the surface (google Brewsters Angle).

A quick and dirty fix for that image might be to use the local adjustment brush in post-processing and take out the colour (de-saturate). Might be okay, might look weird, but very easy so worth a try.

Did you find the comments helpful in your other thread? Forum etiquette would be to acknowledge that ;)
 
Thank you all for the replies. Definitely many points for me to consider and take a look at. By the looks of it there is no easy solution to this. So far like mentioned by HoppyUK i've been desaturating the effect in post which removes it but still sometimes looks a bit weird due to the shapes, i guess i'll just have to live with it in a way :D
 
Thank you all for the replies. Definitely many points for me to consider and take a look at. By the looks of it there is no easy solution to this. So far like mentioned by HoppyUK i've been desaturating the effect in post which removes it but still sometimes looks a bit weird due to the shapes, i guess i'll just have to live with it in a way :D
You don't have to live with it, you just have to make a business decision, whether to spend the time and money on getting good photos that will increase your sales, using the method I outlined to you (and also Richard's suggestion, which will add the finishing touches) or whether to just produce the same poor standard as your competitors.
I know about the problem because I had to overcome it, on similar products in the past, and I've also been looking at crap photos of car lights because I thought about replacing the headlights on my shogun (until I saw the price) so I know that you CAN get perfectly good STILL photos if you want to. My method won't work if you're using your turntable to produce 360 photos though.
 
The CPL on the lens is what is causing this to be visible. What is happening is that polarized light is traveling through the plastic (like a fiber optic cable), and it is refracting along internal stress lines that are usually invisible. The light that is high and far camera left is the source as it is (more) inline with the end/edge of the plastic where the refraction is occurring.

All light is polarized to some extent, and reflected light more so, so you can't eliminate that cause. You also cannot filter it out by using a filter on the lens as it is in no way consistent/uniform. You can move the light source so that the light is not being transmitted through/along the lens so much (i.e. move it more forward). You can use direct lighting rather than bounced light to reduce the amount of polarization (if that is contributing). And you can remove the CPL so that the light reflected/emitted isn't filtered by wavelength (direction). Or some combination of all of those.
 
This whole thread is the result of asking a question on a forum, and then not engaging.

Amongst the many answers to @patryk_beben original query was to use a polariser (both on the source one on the camera), patryk took half this advice on board (the easy half) and it’s caused him this issue.

So he comes back here with half a story about a new problem. :banghead:
 
I don't think double polarizing will work in this case. In fact, double polarizing is the method to use in order to emphasize this characteristic/effect in plastics. If it were a coating on glass it would probably work, but I don't think it is (it's too wavy/irregular).
 
I accept that polarisation is used primarily to show the stresses, but I've used it to hide them, it's all about the angles, ans there can be problems when the subject has a complex shape.
But, this seems to be of interest only to us, the OP seems not to be interested..
 
I thought about replacing the headlights on my shogun (until I saw the price)

A bit off topic, but maybe you could just replace the bulbs themselves with some of those 50%, 90% brighter bulbs - just the 50% ones made a really good improvement on my car for night driving around lanes, I dont want to add to the local road kill (badgers, deer), hence the upgrade.
 
A bit off topic, but maybe you could just replace the bulbs themselves with some of those 50%, 90% brighter bulbs - just the 50% ones made a really good improvement on my car for night driving around lanes, I dont want to add to the local road kill (badgers, deer), hence the upgrade.
Already done that, and they are still pathetic.
I think the problem is that the car is worked far too hard, it's basically a farm vehicle and also something that takes me to my shooting clubs and competitions, in all conditions. The plastic headlamp covers seem to be permanently misted up inside, and not so good outside. It may be possible to cure the problem by taking them apart but I'm not sure that this is even possible, and certainly not by me, so I thought it might be best just to replace them - but I didn't allow for Mitsubishi's pricing policy:) so they will have to stay as they are.
 
I
Already done that, and they are still pathetic.
I think the problem is that the car is worked far too hard, it's basically a farm vehicle and also something that takes me to my shooting clubs and competitions, in all conditions. The plastic headlamp covers seem to be permanently misted up inside, and not so good outside. It may be possible to cure the problem by taking them apart but I'm not sure that this is even possible, and certainly not by me, so I thought it might be best just to replace them - but I didn't allow for Mitsubishi's pricing policy:) so they will have to stay as they are.
I may have spotted an opportunity here @Garry Edwards...The OP provides you with some shiny new headlights and you take some pics of them for him! :)
 
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