Consistent Lighting Conditions

[pjbateman]

Hi there,

I am about to begin research in image forensics, and will be taking photographs of the exact same scene and angle from several different cameras. In order to do this fairly, I need the conditions to be the same for all cameras so that a fair comparison of the images can be made.

I have managed to find a room that has no windows, so the lighting is at least away from sunlight - however, the room has fluorescent lighting which I am lead to believe is on some kind of cycle, which will ultimately cause some degree of variation to all of the images (depending on when the images were taken in relation to the cycle).

My question is, does anyone know what type of lighting I should purchase to avoid this problem? The lights cannot be on any sort of cycle so that the EXACT same lighting conditions are maintained for all the cameras - the cheaper the solution, the better!

I've seen the following on amazon.co.uk but I am not sure if these lights will solve the problem:

http://www.amazon.co.uk/Ex-Pro-Produ...53WH77CZ5103XK

Thanks in advance for any help anyone can give me!

pb

[Frog]

Well, what you want to do has already been done multiple times. Here at this site
http://www.photographyreview.com/samplephotoscrx.aspx and I know dpreview also has a consistent set up for all the cameras they test.
As for the consistent light, I'll let the studio shooters chime in.

[pjbateman]

Well, what you want to do has already been done multiple times. Here at this site
http://www.photographyreview.com/samplephotoscrx.aspx and I know dpreview also has a consistent set up for all the cameras they test.
As for the consistent light, I'll let the studio shooters chime in.

Thanks for your help. Yes, this setup is very similar to what I am looking for. I guess the key lies in finding a cheap but consistent light source. I hope someone is able to offer some advice on this later.

Thanks again,

pb

[another view]

the room has fluorescent lighting which I am lead to believe is on some kind of cycle, which will ultimately cause some degree of variation to all of the images (depending on when the images were taken in relation to the cycle).

Old fluorescent was 60 cycles per second, but new fluorescent with electronic ballasts and T8 (1" diameter) lamps are 20,000 cycles per second - so this isn't an issue anymore. By "old" I mean magnetic ballasts (the big heavy ones, hence the name) and T12 lamps which are 1-1/2" in diameter. Also, T8 lamps are available in much higher quality color (as well as daylight options which are something different than accuracy) which would probably be helpful. If you're in the US, look for a Philips F32T8/TL950/ALTO or equivalent and a fixture to power it (I'm in the biz...).

Incandescent halogen is not a good choice - they typically have a diode that acts as a half-wave rectifier (as I understand it) that essentially turbo-charges the lamp. Some people can see it - I have seen it with a small percentage of lamps; it flashes at 60 cycles per second because that's the frequency of AC power we have (120v, 60hz). No ballast involved, but the same problem.

Outside of fluorescent, you may want to look at quartz work lights. They're energy hogs but they are consistent and provide accurate light, from a color standpoint.

[pjbateman]

Old fluorescent was 60 cycles per second, but new fluorescent with electronic ballasts and T8 (1" diameter) lamps are 20,000 cycles per second - so this isn't an issue anymore. By "old" I mean magnetic ballasts (the big heavy ones, hence the name) and T12 lamps which are 1-1/2" in diameter. Also, T8 lamps are available in much higher quality color (as well as daylight options which are something different than accuracy) which would probably be helpful. If you're in the US, look for a Philips F32T8/TL950/ALTO or equivalent and a fixture to power it (I'm in the biz...).

Incandescent halogen is not a good choice - they typically have a diode that acts as a half-wave rectifier (as I understand it) that essentially turbo-charges the lamp. Some people can see it - I have seen it with a small percentage of lamps; it flashes at 60 cycles per second because that's the frequency of AC power we have (120v, 60hz). No ballast involved, but the same problem.

Outside of fluorescent, you may want to look at quartz work lights. They're energy hogs but they are consistent and provide accurate light, from a color standpoint.

Thanks for all your help!

The room I am using is an unused office room, and it is hard to see exactly what the lights are... The whole office is pretty old, and I can sometimes see a bit of a flicker on the shadows of objects, so I can't trust these lights for the photography I've got planned.

Unfortunately I live in England, which might make it hard to get hold of the products you mention. I was hoping for a solution that would involve table lights or lights on a stand, so that I could turn the office lights off altogether and work with something I can trust...

Do you happen to know of anything cheap that will do the trick? I know next to nothing about lighting so I'm not even sure that what I am looking for even exists. I just need something preferably not on a cycle that will give me the same true light regardless of when the image is taken.

pb

[another view]

Standard, cheap incandescent will do that but avoid a Halogen PAR lamp (lighting geeks such as me call "light bulbs" lamps). These are the heavy glass lamps with a reflector that are commonly used outdoors. Halogen is also used with this kind of construction and very common indoors in retail and residential, etc. In any case, avoid any of these as I mentioned above.

Any other standard incandescent even including the quartz tubes I mentioned before will work. And actually since you're in Europe you'll have very good options available. We pay less for energy (although that's changing) so you folks have been working at energy efficient products for longer (side benefit is the 20,000 cycles per second that you need).

Sorry I can't be more help as some products are different in other countries and I haven't been to London in years... You may want to find a place that specializes in selling lighting for commercial products and they'll be able to help.

[SmartWombat]

UK is 50Hz, so more of a pronounced mains cycle.
If it's an old office I would guess old fluorescents.
Easy to tell, bring in an electric fan, spin the blades.
If you see a strobe effect and multiple blades, it's old 50Hz lighting.

Do you have to use continuous lights, or can you turn the room lights off and use a couple of flashguns instead ?

[pjbateman]

UK is 50Hz, so more of a pronounced mains cycle.
If it's an old office I would guess old fluorescents.
Easy to tell, bring in an electric fan, spin the blades.
If you see a strobe effect and multiple blades, it's old 50Hz lighting.

Do you have to use continuous lights, or can you turn the room lights off and use a couple of flashguns instead ?

I think turning the lights off and relying upon some other light source is going to be the best option... I will need to turn the flash off for all the cameras as some of them do not have flashes (i.e. cameraphones), and if some used a flash and some didn't, it would skew the results.

What are these flashguns you mention? I am guessing by the "flash" part of the name, the light is not always there, and it will output all of the power in 1 second, just before the image is taken... in which case, does it need to connect to the camera somehow? Not all camera's have an accessory tray...

I just need a couple of lamps (almost definitely not the right word) to go either side of the scene, as per the following picture:

http://ecx.images-amazon.com/images/...500_AA280_.jpg

But the lights need to emit a constant light that does not flicker. The reason being that the images would be different colours depending on when the image was taken in relation to the flicker/light cycle. All the images need to be taken using the EXACT same light, no matter when they are taken.

I have probably made this thread 1000x harder to solve than it should have been because of my lack of knowledge of lighting, but thanks everyone for all your help so far.

[Asylum Steve]

Wow. You're either really good at double-talk, or you do this for a living...

[SmartWombat]

I would say you could use 1/50th second exposure because that is one full brightness cycle of an ordinary mails lightbulb. But if your cameras don't have manual exposure control that's not possible.

So if you don't want flicker, because you're going to test cameras that don't have a flash connector - you will need special lamps.
Something like this perhaps http://www.warehouseexpress.com/prod...px?sku=1011577
Flicker-free is the important thing, I think ?

[freygr]

Good old standard tungsten lamps is what you need along with a variable transformer (autotansformer) for controlling the lamps, and a voltmeter to keep the voltage constant. The filament do not cool off between power mains cycles. If you can find them photo flood lamps were made for this application (called flat copy). Usually four lamps are used with the object placed in the center. The quantity and size of the object being photographed will determinant the placement and quantity of lamps needed.