Best Way To Stop Light Changes!

[Guest stevey]

As I said, disable auto iris on the camera.

[Axejacket]

Essentially the fluorescent tube never emits a constant colour temperature. At different points on the mains cycle, it will emit a slightly different colour temperature, which in turn will reflected at different temperatures, after absorption by materials within the scene.

Hope this helps and good luck

B)

Matt i dont dispute or critisise your theory there at all, its not an explanation ive come across before and ive never seen a similar fault either which is where my question comes from.

If your theory is correct then how come it doesnt happen to all DC powered cameras in flourescent lighting situatuations? Ive fitted hundreds of DC fed cameras in such situations without problem?

I think Matt is almost certainly right here, or at least it's the best explination I've come accross.

I have installed many of the same model of camera in to diferent locations and they often behave differently. I can only assume it must be down to the supply at the site etc. as stated.

In one installation in to a chain of shops, in two sites the "breathing" or "hunting" effect was very bad yet, with the same model camera in other stores (that appeared to be no different) the effect was not noticable. They are all 12vDC fed and are Sony HDD fabrications.

If it is possible to resolve with an alternative supply, Matt - what do you mean when you refer to lock it?

[Matt the Teckie]

Hi chaps,

I used to work at Sensormatic in a QA function for some 6 years before going to work at Baxall for a while doing PM and Apps, hence plenty of experience of this issue. I'm not suprised you've not seen this Ian, you usually only get to see this effect if the scene is PURELY lit with fluorescents. Normally the scene has a little sunlight which allows the camera's AWB to sort itself out. The auto white balance also limits this effect if there are lots of colour in the scene (let me know if this need explaining further.... I have flip charts!). The effect is more evident when the camera's looking into a bland scene, try it in your workshop.

When refering to "lock", I mean Line Lock. It was traditionally used to ensure that all cameras trigger at the same time. Without it, the cameras triggered at different points. Now consider the monitor connected to a desk switcher. The monitor is locked to the sync pulse of camera 1 and displaying the picture just fine. When the desk switch flips to the next camera, its sync pulse isn't where it should be (because the camera triggers at a different point in time). So the monitor get all confused and loses its frame hold until it picks up the sync pulse again. The effect you see is a brief picture roll. If you engage line lock and set the cameras to trigger at the same point on the AC cycle, the sync pulses become syncronised. As the desk switch moves from one camera to the next, the sync pulse remains in the same place so the picture does roll. Pretty much all AC powered camera have this facility.

matt

[Matt the Teckie]

Oops, got that carried away rambling on I forgot you answer your your question.....

If your camera can be powered using AC then yes, you can probable resolve your problem. If its DC only, you might just be scuppered unless you can introduce a significant amount of incandescent or high bandwidth light and lots of colour.

Hope this helps

matt

[Guest stevey]

Or you could just smash the lights and hope that the camera can see in low light

[Matt the Teckie]

THAT's the spirit Stevey.....

You could always fore-arm smash the customer if they don't like it too...

Especially if they try to sell you a cheap lens.... ;-)

[Guest stevey]

That was a joke. Honestly, try a lens that has a low refractive index if all else fails.