Shadows / Flicker

Hello,

I’m just starting out with iStopmotion and just trying out a few setups. I have a 5DII camera so did try out the beta to test that camera directly, but the DSLR a bit complex and pricey from my son to play, ad there were difficulties with the narrow DoF - overkill for a starter setup for sure.

We then tried the iPod app and that worked okay but was there was a bit of a delay, so we decided to try a fancy webcam - the Logiteh C920 that my wife uses for Webex, hoping it would give us a the nice crisp picture, but be more portable than the DSLR and not have the lag of the iPod App.

I immediately noticed some horizontal shadows scrolling down the screen. I’ve tried several setting but don’t seem to be able to get rid of them. I’m not sure what I should be changing? Is this to do with the lights, software config, or the position of the lights and webcam.

I’ve posted a couple of second clip on youtube to demonstrate. The clip also shows the setup -
http://youtu.be/tghdUcuQLg8

Any pointers would be appreciated.

Thanks

Nick

2008 15" Macbook Pro, 1440 x 900 native screen resolution
Mac Mavericks
Webcam Settings App
Logitec C920 webcam
Lloytron L855BH Studio Poise Halogen Hobby/Desk Lamps -
http://www.amazon.co.uk/gp/product/B002MF66NQ/ref=oh_details_o03_s00_i00?ie=UTF8&psc=1

My guess is that your lighting is interfering with the frame rate of the Logitec webcam. Maybe your are using LEDs as bulbs, they get switched on and of very fast, or halogen bulbs, they also tend to flicker at the frequency of your power line (e.g 50hz). Your eye won’t notice the flickering but web cam captures the frames at a similar speed and therefor “sees” the switch on and offs of the lighting in a single frame. I am sure you won’t see the flickering anymore if you try to capture with pure sun light. My suggestion is to change the bulbs in the lighting to something with a tungsten filament.

I think Achim is right, that’s what it looks like to me too. I didn’t realise LED bulbs flicker (unless you’re using pulse width modulation to dim them as per RGB LEDs to make all the colours). I’m wondering if bouncing and filter the light through scrim etc would be enough to mix up the light wave phases so that there is always some light ‘on’ as it were every time the camera shutter is open?

Thinking some more about it, a phase inverter could be a good idea when running lamps that are subject to flickering (incandescent and arc lamps stay ‘warm’, not sure about fluoros some flicker for sure but some photography/video fluoro lamp sets with multiple elements might compensate for for phases not sure)

I am not sure if all fluorescent lamps help to avoid this problem. Even in the wikipedia there is a section about this flickering problem relating to video graphing: http://en.wikipedia.org/wiki/Fluorescent_lamp#Flicker_problems

In my experience fluorescent lamps where always the cause of flickering. So I avoided them where ever I can. Things may have changed here I have to admit. Also the cameras I used where able to control the shutter speed and therefore you can bring it to a lower speed than the flickering which then average the lighting just like your eyes does.