Recently I was filming a green screen with the Canon C300 set to 720 50p and 50Mbps, the results on FCP 7 were the best I have seen for a long time. I put this down to the 50Mbps CBR 4:2:2 which is a far cleaner image than 4:2:0. What about that shallow depth of field, how does it affect green screen, I must admit the last time I filmed green screen with a large sensor camera was with the Panasonic AF101 and the results were
less than spectacular.
Looking back at the AF101 I think it suffered in two accounts, lack of resolution (800 lines max) and 4:2:0 shot with AVCHD set to 28Mbps.
Shallow depth of field actually enhances green screen work as it gives a better overall diffusion to the screen itself taking out the odd wrinkle here and there.
Lighting is also critical when it comes to using green screen, six tips for less hassle are as follows…
1. Light the green screen (GS) as evenly as possible using as much diffused light as possible, the last thing you want with GS is hotspots.
2. Use the cameras ZEBRA to check for hotspots.
3. Bring the subject as far forward from the screen to avoid green spill.
4. Expose for the green screen first then adjust the lighting for the presenter, the last thing you want is an under or over exposed background.
5. Make sure you tell the presenter NOT to wear anything green and check how green his/her pupils are, if they are too green use a blue screen instead.
6. Film the presenter straight to camera as the best resolution of your lens is to the centre, move him/her to the left of frame later in post.
Green screen can be tricky to say the least, I have found that sticking to a medium close shot gives you the best results while a wide shot can give varying results from acceptable to unusable. One of the major bonuses of LED lighting is HEAT FREE lighting, I used eight LED lights for this chroma key set-up and the room temperature stayed constant throughout the 2 hour shoot.
CN600 seen above with 3200K filter in place.
Lighting is the key to a good green screen and I now use LED lighting to light my screen and presenter. Most LED lights are about 5200K to 5600K daylight balanced which does not affect the “greenness” of the screen itself though you do need to use at least one LED light at 3200K to give your presenter a nice back light.
I was recently sent one of these new CN-600SA LED lights to test, one of the new generation LED lights using moulded plastic and has a far smaller footprint than previous metal constructed LED lights.
I love the “V” lock mount that now comes standard on most LED lights allowing cable free lighting a God send for anyone using lights in public places. LED lights are a must for wedding videographers who use lights to film the speeches as long as you also use “shot bags” to weigh down the lighting stands.
The CN600 LED light costs £300 new and the UV160 “V”lock DSM battery both from H Preston Media.
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