Sunday, 20 November 2011

Fluorescent lighting

For many this means: Fluorescent lighting = "Kinoflo". Problem is that Kinoflo = $$$$$$$.
However, there are much cheaper alternatives available which use the same bulbs. Here are two examples. The light in the middle is a fluorescent photo light widely available on e-bay and also from other outlets. In Germany there are two companies which make reasonably priced fluorescent lights: Walimex and "Fotowerkstatt Mainz". There are also a couple of Chinese manufacturers on ebay. All in all there is not much in these lights except a transformer and that's it. These lights use special striplights from Osram which have a very high colour rendering index of over 90% and daylight balanced colour temperature (Dulux 954 55W tube). The quality of the light is exactly that of daylight and can be mixed with it. It looks very natural and soft. It's time for a lighting example:

Here, a small two-tube fluorescent light (2x55W) was placed underneath the candles the left. The second light source was an overhead fluorescent light fitted with a paper lantern and covered by a black bin-bag at the back to avoid light spill on the wall.
The light inside of the paper lantern is a fluorescent bulb produced in China and has a CRI of over 90%. It's 125W which is about the same light output as one redhead (without the heat of course!). Here is one shop on ebay which sells it but it's widely available now.
The bulb is also available in 150W. Important is that you buy the bulb with an actual power rating of 150W. It's basically a pretty large energy saving bulb with a special coating to achieve the CRI of over 90%. The boom arm is made of aluminium and I've mounted the plug directly on the aluminium with a earth connection to the aluminium. The counterweight is a bag filled with old books. I prefer books because in case the bag bursts it won't cause any damage to the floor. The stand is an Adam Hall loudspeaker stand which is very lightweight and is 3m tall. My second stand is a standard disco lighting stand where I have attached an aluminium arm. Same idea but a bit heavier.
Here is a test film using this overhead light as the only light source. Improvised by Tommy J Brennan and Shanta Roberts. The film WEBCAM CONNECTION uses the overhead light in the two first two scenes. In the first scene it's above Tommy and in the second scene it fakes the ceiling light.

Follow focus for Lumix GH1

After weeks of experimenting with different follow focus systems I've settled for this one.
The problem with cheap follow focus systems is backlash. With most of them the backlash is so large that it's impossible to do precise focussing. The main reason for the backlash is the 90 degree gear between the white knob and the lens gear. The follow focus system I have found uses a worm gear which has virtually no backlash at all.
The follow focus can be obtained from ebay, for example here. There is also a nice review on YouTube (thanks, Alan). However, the gears coming with this follow focus are pretty horrible because they are very hard to tighten. Better are the gears which are shown in the picture and are also widely available on e-bay.
In terms of the rod support: I have modified the rail system to allow hand camera operation. For this purpose I bought a flash adapter for a medium format camera. It has a nice large mounting plate, a large grip and it is very easy to attach it to the camera. I could have screwed the quick release plate directly on the flash adapter but that was not very stable so I used a bracket from B&Q and added a standard camera thread. All in all a weekend of plumbing. Bottomline: having a good rod support system saves loads of time. A warning: don't buy the Indian rod support systems. They are pretty horrendous and you need to buy expensive extras to have a complete system.
The lens I'm using on the camera is a 28-70mm f/2.8 Olympus OM with m4/3 adapter. For shallower depth of field I have a Canon FD f/1.4 with m4/3 adapter. For wide angle shots I'm using a Samyang 14mm F/2.8 EOS with m4/3 adapter. Because of the adapters you can buy all these high quality FD/OM/... lenses which are much more robust than the plasticky Panasonic lenses and they are just mechanical with no electronic parts. These lenses also cost a fraction of the auto focus lenses. This gives also a very long battery lifetime for the GH1 of about 4 hours.
Films made with this camera setup:

Simple Steadicam for DSLR

For a shoot (where I was running backwards through the woods) I made a simple steadicam which works very well.
A steadicam is basically a pendulum which adds inertia to the camera movement. It's suspended directly underneath the camera, here just with my hand and arm. The two exercise weights at the bottom add the inertia. The longer the boom and the heavier the weights the smoother is the movement. Because the DSLR is pretty light the weights at the bottom need not to be that heavy to pull the camera in a vertical position. What is trickier is the rotational movement of the camera which is prevented by having two weights sideways on a metal bar. Ideally, the rotation could be even more dampened by a soft suspension. It's not that optimal to hold the pendulum directly with your hands. It would have been better to have a handle sideways but I never managed to build that. As long as the camera is held pretty loose in your hand also the rotational movement is pretty smooth.
I use 1kg of exercise weights but could add a second set (after more time in the gym!). These are from a set of exercise weights I got from Argos. The aluminium sheet at the bottom and the screws are from B&Q. The tripod was just a cheap still camera tripod which conveniently had this quick release mechanism attached to it which lies quite nicely on my hand and acts as a bearing:

How to merge MPEG4 with AC3 audio

Sony Vegas 11 has an annoying bug, namely that the Sony AVC encoder won't export audio. Solution: render out AVC without audio and then render out a separate AC3 audio file and merge them using MP4Box.
  1. Download GPAC and install it on your computer.
  2. Extract the H264 from the MPEG4 file:
    MP4Box -raw 1 attr_2_resiliance03_sonyavc.mp4
    assuming that stream 1 contains your H264.
  3. Merge with AC3 audio:
    MP4Box -add attr_2_resiliance03_sonyavc_track1.h264 -add attr_2_resiliance03.ac3 merged.mp4
That's it. And it's even streamable for flash.
Update: this bug only shows up if the audio rate is higher than 192kbit/sec.

Saturday, 17 September 2011

Colour rendering index

The colour rendering index is a percentage measure of the quality of a light source in terms of colour reproduction. For example, a sodium lamp has a colour rendering index of 0 because when you shine it onto an object you cannot reproduce its colours. It's just yellow, isn't it? Tungsten bulbs or daylight have a colour rendering index of 100 and serve as a reference to other light sources. More strictly the black body radiation is the reference but tungsten light is a good approximation (a more nerdy definition is here). Note that the colour rendering index is not identical to the colour temperature! The colour temperature defines the temperature of the radiator. So, roughly a light bulb with 3200K colour temperature has that temperature!
So, why don't we just use tungsten light? Because it's terribly inefficient. Most of it's output is in the invisible range which is basically heat (think of the 3200K). Anybody who has blown up fuses with red-heads or burnt him/herself knows what I mean.
What are the alternatives? There are quite lot. The only problem is that most other sources have CRI of <100%. For filming a CRI of 90% or higher is required.
The oldest alternative are the so called HMI lights which have roughly 90% CRI. These are gas discharge lights. In the old days these were really just the HMI lights but now you have a large range of discharge lamps with a CRI of well over 90%. They are often called metal halide lamps, for example, the Osram Powerstar D. See my post about HMI style lights. Lights of this type are often used in fashion shops because they need to reproduce colour faithfully.
Three phosphor fluorescent striplights also have a colour rendering index of over 90%. People associate them usually with Kino flos. However, many companies make them now -- and much cheaper. For example, Fotowerkstatt Mainz or Walimex. All fluorescent lights use basically the Osram Dulux 954 55W tube. The rest is just a box with barn doors.
On the left there are fluorescent lights from the Fotowerkstatt with the Osram Dulux tubes in it, mixed with HMIs to create a sunny daytime atmosphere. Here for the film BIG BOOTS. When you watch the film, the lights are on the right of the window which was covered with ND filters to reduce the incoming light by 2 stops. The room was basically lit by the fluorescent lights and the HMI while the ND reduced the incoming light so that the windows won't burn out.
The colour rendering index of both light sources is above 90%. The colour temperatures are actually slightly different but add a bit of texture to it.

Much worse are LED lights. They have often a colour rendering of less than 80%. This is because they have strong blue component which is not very flattering on faces. I've used LED lights in documentary making but I wouldn't use it in fiction, certainly not on faces. It is well known from theatre that blue light brings out blood vessles and makes faces look ugly. Actors will hate them.

cheap ND filters off ebay

For my GH-1 I bought recently cheap ND filters off ebay.
Then the shoot. It was a typical Scottish day: some times it was really overcast and sometimes pretty sunny so that I had to use sometimes the ND4, ND8 or even both on top of each other. These filters I've used have a lilac kind of colour tint. In order to correct in post I shot a white sheet of paper and then put the different filters on. Below is the result.

The ND4 filter adds especially more blue to the image whereas the ND8 adds both blue and red to the image but in slightly different proportions. Pretty annoying. The other option would have been to have 4 different custon WB settings in the camera which the GH-1 won't allow. Bottomline is that I'll tape a greycard to my clapperboard! Taking every time a white balance just takes too much time.

Saturday, 13 August 2011

"HD" monitors for HDSLRs

There are loads of monitors out there for HDSLRs which claim to be high def. What turns out is that most of them take an HD signal but then down convert it to standard definition.
For example,

They both offer so called HD. But if you look at the actual resolution, you get just 800x400. This is not even standard PAL resolution.

In addition many Canon cameras scale down to standard resolution while filming. As far as I know it's only the 7D which provides full HD all the time.

My personal bottomline is: I rather buy a camera with a proper viewfinder than trying to find an external monitor which is sharp.

Thursday, 11 August 2011

HMI style lights

This is a film light which has about the same light output as a red-head but at only 150W power consumption. It uses a bulb which is used in HMI lights. The parts are:
- Lanzini, Alaska display light. They are the lightest and available from many places but any other for 150W MH bulbs will do.
- par 56 barn doors. They fit exactly around the light
- aluminium U shaped bar & self tapping screws (see picture below):
- Calumet rapid adapter which allows mounting the lamp on a standard tripod

Important is that the bulb has a colour rendering index (CRI) of more than 90%. The Osram Powerstar bulbs are generally best and are indistinguishable from daylight on camera. They have a colour temperature of 5200K which is the same as daylight. They work nicely as a fill against the ceiling in a INT/DAY scenario and also as a source of sunlight. If used in interior shots it is recommended to balance the camera also to daylight and wrap half C.T. blue around practical lights which are usually too bright anyway.

Wednesday, 3 August 2011

How to capture audio under Linux?

I needed to capture audio from a video running in a flash player. Here's what I did:
Created .asoundrc in my home directory:
pcm.fileout {
   type empty
   slave.pcm "tee:default,'/tmp/out.raw',raw"
   # 48000 S16_LE 2ch (aplay -t raw -f dat)
Started firefox from the command line:
FLASH_ALSA_DEVICE=fileout firefox
Converted the raw file it to a wav file:
sox -r 48k -s -b 16 -c 2 out.raw out.wav
...assuming that it's 48kHz sampling rate, 16bits and two channels stereo.

Tuesday, 26 July 2011

ssh login with public key

One of the Linux projects I'm working on requires a public key login via ssh.
Simple I thought and generated a key with  
Then copied it over with
and tried to log in with the key. However, then I got this error message:
ssh error: agent admitted to failure to sign using the key
After endless googling I found out that it has something to do with ssh-agent.
This can be temporarily disabled by adding
in front of the ssh command and I'm able to log in. There's clearly something wrong with ssh-agent but this fixes the issue. I then started ssh-agent by hand on the server and client with ssh-agent bash and could then run ssh-add on the server to store the passphrase as well.

Monday, 25 July 2011

GH-1 hack GOP=5

I bought off a hackable GH-1 off ebay and optimised its firmware with the well known "ptool3".

Here is my configuration file for ptool3 which I called "setd.ini". Just copy this file in the same directory as the ptool and select profile D.

With GOP=5 the camera generates an intra frame every 5 frames instead of every 25 frames. The other important numbers are Video Bitrate FHD/SH=40000000 and Overall Bitrate=41000000. It seems to be important that both numbers are pretty high but that the overall bitrate must be a bit smaller.

The actual bitrate is much smaller as the number suggests in the config file. Here is a highly complex scene with loads of movement -- taken from the play "The Red Dress" which premieres at the Edinburgh Fringe 2011:

The bitrate averages at 22Mbps which is well above the 17Mbps of the original setting. Higher bitrates show occasionally up but only in high contrast clips (shooting having tree branches against the sky) but rarely go above 30Mbps.
I record on SDHC 10 cards with 18MB/s writing speed.

Converting mov to m2t for Sony Vegas

A friend captured from a Z7 with some Apple-flavour software (I think it was FCP). That's what in the mov:
  Duration: 00:23:11.36, start: 0.511854, bitrate: 26575 kb/s
    Stream #0.0(eng): Video: mpeg2video (Main), yuv420p, 1440x1080 [PAR 4:3 DAR
16:9], 25000 kb/s, 23.98 fps, 23.98 tbr, 2997 tbn, 47.95 tbc
      creation_time   : 2011-07-14 10:48:07
    Stream #0.1(eng): Audio: pcm_s16le, 48000 Hz, 1 channels, s16, 768 kb/s
      creation_time   : 2011-07-14 10:48:07
    Stream #0.2(eng): Audio: pcm_s16le, 48000 Hz, 1 channels, s16, 768 kb/s
      creation_time   : 2011-07-14 10:48:07
The streams themselves are completely compatible with Vegas but the container causes problems because it loads the quicktime DLLs and they won't like mpeg2 for some reason. Essentially not a Vegas problem but an Apple problem. I decided to convert to m2t with ffmpeg:
ffmpeg -i -vcodec copy -an boots_noaudio.m2t
Note "-an" means no audio. With audio added to the m2t file Vegas 10 locks up. I guess ffmpeg is not generating a fully compliant m2t file. Instead I exported the audio as separate tracks:
ffmpeg -i -acodec copy -vn -map 0.1 boots_audio1.wav
ffmpeg -i -acodec copy -vn -map 0.2 boots_audio2.wav
...and loaded the 3 files into Vegas and then grouped them.
I had quite a lot of problems with ffmpeg generated files but this workflow works at least and there is no loss through recompression.

How to create streamable video with Sony Vegas

I faced the problem how to create mpeg4 video clips which play instantly with a flash player.
Sony Vegas can generate high quality mpeg4 video but it's not streamable. When played with a flash player it won't play until all the content has been downloaded. The problem is the so called "MOOV atom" which is located at the end of the mpeg stream but needs to be at beginning of the stream.
The project GPAC has a very nice command line tool called MP4Box which moves the MOOV atom to the front of the stream:
MP4Box -inter 500 myMPEG4file.mp4
One note about bitrates: keep them below 1Mbit/sec. Some providers throttle the bitrates of videos to 1Mbit/sec. So, if you want to be sure your video plays keep it below 1Mbit/sec.
In Vegas I usually use two pass modes:
Examples of stremable videos are here:

ME88 preamplifier

The ME88 is a pretty ancient shotgun mic from Sennheiser. It comes with a passive supply module which has just too little output power for most camcorders.
So, I built an active supply module instead:
I've just built it on a matrix board. The circuit is inspired by the transformer less amplifier of the AKG microphones:
I used the microphone on a couple of shoots with very good results, esp in the jogging scene of "Fried" and also on Joe McArdle's "A Mug's game".


Hi all,
this blog will be mainly technology related and will act as a communal storage space for anything I find out or find useful for others.