So last time we looked at time lapse of the wheel and now we will take a look at long exposure.

A long exposure is when you are allowing the sensor to be exposed to light for an extended period of time. Anything moving like cars driving down the street with the lights on will become blurry… At least that’s what we want. Normally when you take a photo it can be a fraction of a second in a well lit room. But if you turn the lights off to get the same photo you would need to increase the time the sensor is recording and thus anything moving will blur, or if you use the same settings as the lit room picture, your picture will simply be black.

In DSLR photography we have 3 settings we can control to adjust the amount of light reaching the sensor.

• ISO: Is an old standard from the days of film photography which is how the film will chemically react to the light. These days its all digital but the principle is the same. In digital terms its how the sensor will react to the light. The lower the ISO (ie ISO 100) the more light is needed to make a clear exposure and also the cleaner the picture. The higher the ISO (ISO 6400) much less light is needed but then also the grainier the picture has become.
• Shutter Speed: Is how long the shutter curtain is open exposing the sensor to light. The quicker the shutter speed the more still the picture will be. But the slower the shutter speed is you start to get blurry images and you will likely need a tripod.
• Aperture: Is controlling how much light is coming into the camera, in a normal camera lens this is normally thorough an iris. The larger the opening of the aperture the more light is received

That turned into a little photography 101! To finish, these three setting used together can create different effects in photograph. If you have a quick shutter speed you can adjust the ISO and the Aperture to make your picture expose correctly look great (depending on your lighting arrangement).. There is a wonderful book written by Bryan Peterson called Understanding Exposure I recommend if you want to learn more about exposure and photography.

Now how does this work with the Rasepberry Pi! Well 1st we need to consider what we have on the camera and understand its limitations. We don’t have an aperture to control its fixed at f2.3. The best ISO we can get from the camera board is ISO 100. Also the Shutter Speed wont go any slower than 6 seconds as its limited by the firmware.

So we want to make a long exposure. We want to take it at night to get those trailing lights! Then we will need the following things.

• Configured Raspberry Pi with Raspbain (updated)
• Camera board
• Tripod (or something you can stick the camera too so its not moving)
• Connection to the pi..
• If you are working through a window you need something black to surround the camera to stop reflections)

In my example (below) I had set up the camera on a tiny tripod I had and put it against the window. I then used the following command to take the picture.

raspistill -hf -vf  -ss 2000000 -ISO 100 -sh 50 -br 50 -sa -75 -o wheel.jpg

A quick brake down of all the options are :

• -hf -vf : I had my camera upside down so these settings are for horizontal and vertical flip.
• -ss 2000000 : shutter speed at 2000000 nano seconds or 2 seconds.
• -ISO 100 : because we have exposing the sensor for 2 seconds we need to have the lowest ISO number so that the quality is crystal clear and that the light does not blow out. If we used a higher ISO number with this shutter setting the picture would be brighter.
• -sh 50 : Sharpness (optional) controlling the sharpness of the finished image.
• -br 50 : Brightness (also optional) controlling the brightness of the finished image.
• -sa -75: Saturation (again optional) controlling if the image is color bright or washed out.
• -o wheel.jpg: output with the file name.

Here is the image I manged to get

In this image example using ISO 100 and Shutter speed as 2 seconds we can use this as a reference to what would happen if we started to fuss with the options.

• If we just simply change the Shutter speed to 4 seconds the lights in the image would become brighter but the light trails would get longer as we are recording more of the movement.
• If we put it to 6 seconds then the lights would loose all color and would turn white!
• If we changed the image to 1 second the trials would be shorter the image would get darker.
• Returning the Shutter speed to 2 seconds if we made the ISO 200 the image would become a little more grainy and brighter but the light trails would remain the same as the image above.
• If we set the ISO to ISO 800 the image quality would be really grainy and the image would be almost white. But the light trails again would be the same as the 2 second Shutter speed is always the same.

Best thing to do is sit down next to your pi and play around with the options until you get what you feel is right.

I hope this helps in working out how to make a long exposure and if you have the time/money please do check out Bryan Petersons Understanding Exposure its a really great read for those starting out in photography

Please do feel free to comment with your examples of Raspberry Pi Powered Long Exposures!

I am a massive fan of photography and especially time lapse photography so when I spotted a Christmas market setting up a Ferris wheel across the road from my 7th floor office, I jumped for the most logical (and quiet) tool for a time lapse. The Raspberry Pi!

Here is a super quick write up of what you would need and also what I did (and did wrong) on this little adventure.

What you need:

• Raspberry Pi + power, sd-card, case etc… Installed with raspbain
• Pi Camera board
• Some sort of tripod (but this can even be hot glue and something that stands up)
• Mass storage device – USB stick or Hard drive (powered)

Step One: Find a location to shoot

I was indoors so I have to find a window where I could set the camera up. I had to consider the reflection so it was a good idea to make everything black. I have the Camera mount from pimoroni which is black and with black screws.  otherwise I just covered everything else in a black cloth.

This image is an example of reflection in action (sucks!)

If the time lapse is at night then try and reduce the light behind the camera so you don’t end up with a massive network cable in the sky!

Step Two: Setup the camera and make a test shot

I used my laptop to SSH into the Raspberry Pi where it was so I could walk away and leave it running without any screens or keyboards waiting to trip anyone up.

To test the camera was working I made my 1st shot using the following command:

raspistill -o /home/pi/test.jpg

which gave me this image (without the reflection)

(the blur is water on the window nothing I can do but can look interesting with light intersecting it)

I had to rotate the camera and flip the image so that everything looked as it should  on the output screen. You could just turn the camera but where is the fun in that.

raspistill -hf -vf -o /home/pi/test.jpg

hf = horizontal flip, vf = vertical flip

Now we are cooking!

Step Three: Attach mass storage device and MOUNT IT!

First make a new folder

mkdir /media/timelapse

Then you can plug in your hard drive and type the following command (assuming sda1 is the drives Identifier)

mount /dev/sda1 /media/timelapse

This now means the anything on the hard drive can be seen in the folder /media/timelapse and in turn you can save to /media/timelapse and it would be on the hard drive.

Yeah well this is important and where I slipped up. When running a pi with the desktop environment any USB stick or hard drive you connect would be mounted automatically. So half way though the timelapes I had to unexpectedly restart the pi… and forgot to re-mount the hard drive!

Why did I use hard  drives instead of cloud or online storage… My office wont allow this device to be connected to our network.

Step Four: Start the timelapse

There are a few ways to do this..

• You could use bash scripting with cron tab: Tutorial from raspberrypi.org
• Python: Tutorial from raspberrypi.org (scroll down a bit)
• Raspistill with the -tl option: Tutorial from raspberrypi.org

I went with the -tl option.

My command looked like this –

raspistill -hf -vf -o /media/timelapse/wheel_%07d.jpg -tl 30000 -t 604800000

so -tl is 30000 milliseconds (30 seconds) meaning it will take a picture every 30s for -t 604800000 (7 days), the file name has %07d which means the file name will have 7 digits for example: wheel_0000001.jpg this will increase until wheel_9999999.jpg

So at this point check its all working and your happy!

Step Five: Ignore and get on with life

Note: I did not use any magic lenses or changed any settings to adjust for lighting. All that I am experimenting with now.

Step Six: Compile your photos

Ok so this is where I cheat and don’t use the raspberry pi. The data you would be pushing to make the finished video is massive, especially when your compiling 7 days worth of photos at 30s interval’s.

I found a neat tool for MacOS called Time lapse assembler. Its a simple application where you point it to a directory tell it the frame rate and quality, have a couple cups of tea and its done.

I used this app because while the pi is capable of compiling the time lapse when you start running into the 1000s of files, then its just better and safer to use a desktop system like a Macbook.

Step Seven: Upload and share

Well that’s a given right!

In the end this is a quick overview of what I did. I would totally recommend you to read the tutorials on the raspberrypi.org/resources page I mentioned before as they do a really great job to show you by example how this can work.

Please feel free to leave a comment with how you get on or any questions. Share your results also!