White box = line pattern

[temjeito]

Hey, guys. I'm new to photography--started snapping pics for SOTD and wanted to learn/do more to make them look better. Recently I put together a "white box" using poster board and a few clip lamps. But when I take pics in the box, I get weird wavy lines, like an interference pattern. I'm using an iPhone, and I can see the lines in the "viewfinder" before I snap the picture, so I'm guessing this is an issue with the iPhone camera sensor not being able to handle the amount/wavelength/pattern of light.

Just wanted to check if anyone had experienced this, or knew of a fix for it (other than using a "real" camera, which is my next step).

Here's a few pics to show what I'm talking about:

View attachment 353908

 

[Edcculus]

what is your light source? Is it direct or are you diffusing it? If diffusing, what are you filtering through? What is the background paper made of?

Also, what version iPhone? My iPhone 5 camera is MUCH better than my old 4. That being said, Ive found all iphones (and camera phones for that matter) are very poor low light performers. They are awesome outside, but are really bad inside. It may be that you just need more light in your box to help the sensor out. I've even found that I need TONS of light when doing makeshift product photography inside. Since I don't have a studio setup, I have to bombard it with just about every light I have available.

You also may find that you could get better results in your box if you use daylight temerature (5000K) bulbs. I think the iphone defaults to white balance in daylight, not tungsten or fluorescent.

Hope that helps!

 

[Mr Bob]

You're indeed observing beat interference. This is coming from your shutter speed in relation to the line frequency in that they are slightly different in frequency (whether fundamental or harmonic), and/or they are out of phase. They way to overcome this is by getting your shutter speed away from the line frequency or multiples, i.e., 1/60s, or 1/30s or 1/120s (there's more to it, but that would get results). The iPhone camera (phone cameras) works more like a TV camera. It does not have a shutter, but rather captures images at some fixed rate. I think that fixed rate is causing beat interference with the line frequency through your lighting source.

Edcculus' suggestion of pumping up the light sounds like a good solution. Perhaps this might change the iPhone capture rate?

 

[temjeito]

what is your light source?

two lamps with CF bulbs (one is 5000K, one is 5500K).

Is it direct or are you diffusing it? If diffusing, what are you filtering through?

Direct

What is the background paper made of?

The box itself is white posterboard, and then I taped a piece of "ultra-bright" printer paper to the back and bottom to give a curved background surface. The fact that the paper is a different hue from the posterboard is frustrating me, as is the visibility of the line between the tape and the posterboard, so I may take it out and consider alternatives.

Also, what version iPhone?

It's a 5
Here's a couple of shots of the setup, one with the lamps off and one with lights on:

 

[Rocinante]

two lamps with CF bulbs

Fluorescent bulbs are the problem. The current from a fluorescent bulb fluctuates in intensity like a sine wave, and the color temperature changes along the way. The solution is to use a slower shutter speed.

Better explained here: http://photography-on-the.net/forum/showthread.php?p=790596

Hope that helps.

 

[fast14riot]

Fluorescent bulbs are the problem. The current from a fluorescent bulb fluctuates in intensity like a sine wave, and the color temperature changes along the way. The solution is to use a slower shutter speed.

Better explained here: http://photography-on-the.net/forum/showthread.php?p=790596

Hope that helps.

+1

Turn your camera app on and hold it right up to a florescent tube and watch the screen. Mix the lighting, ditch the CFLs and screw in some tungsten burners. Adjust your white balance accordingly. To slow the shutter speed, try moving the lights further away, double the distance and the output is 1/4 the intensity, and dial down your iso to 100 or so. I'm an android guy, so I don't know if your iphone can do this or not. I use my camera on my phone a ton, though!


-Xander

edit: if you're going to use CFLs make sure they are fully warmed up before shooting, atleast 30 minutes.

 

[Mr Bob]

Fluorescent bulbs are the problem. The current from a fluorescent bulb fluctuates in intensity like a sine wave, and the color temperature changes along the way. The solution is to use a slower shutter speed.

Better explained here: http://photography-on-the.net/forum/showthread.php?p=790596

Hope that helps.

The issue described in the article results in changes to the color temperature over the period of the mains frequency. The effect will be more pronounced with low power florescent lighting. Using a slower shutter averages the change in color temp over time, producing consistent white balance results. The described effect will produce changes in color temperature from one shot to another, however, this is not the cause for the banding temjeito is experiencing.

In his second post, he indicated that he is using CF bulbs. CF bulbs use electronic ballasts which operate at well above the mains frequency, or any shutter speed most cameras can achieve. The high frequency signal of the ballast might well be modulating a 120Hz (or 100Hz) line component that makes it through the cheap ballasts, but the RMS value of the 120Hz will be insignificant compared to the 120Hz rectified signal used in the magnetic ballasts of traditional tube florescents. The amount getting through may or may not produce the effect described by the link, and would likely be dependent on a number of factors.

I do not know how the camera phone captures images... whether it sums frames or integrates light over time, but the bands in the images look like beat interference. Either increasing or decreasing shutter speed should reduce the effect, staying away from 60Hz harmonic related shutter speeds. I would also try to move the lights farther away from the subject. The line frequency that is present in the light emission of the CF bulb is small. Moving the light source slightly farther away would reduce the banding while keeping adequate lighting as the line freq is significantly smaller than the modulating frequency.

 

[Rocinante]

Good info, Mr. Bob. I hadn't looked closely enough into the modern CF bulbs. They sound quite different from the old tube fluorescents, for photography purposes anyway.