tracey medcalfe photography | You're Smarter Than Your Camera - Lighting - Double Exposures

You're Smarter Than Your Camera - Lighting - Double Exposures

October 30, 2015  •  Leave a Comment
You're Smarter Than Your Camera - Lighting - Double Exposures
Good morning and welcome to the third October blog on lighting! In this interesting technique for you to will help your understanding of light combining natural light with flash, and it is pretty cool :-).  The technique is relatively simple to try, but may take a bit of practice to master.  So without further ado, here we go! 

Enjoy and thanks for reading,

How to Capture a Well Lit Subject Combined with Ambient Background Light?
Lets say you want to take a photograph of a subject, but its quite dark, it is difficult to expose correctly for the subject without using flash, but if you use flash, you will lose all the ambience of natural nighttime light behind the subject.  I love this technique and the challenge that comes with it.  You are essentially creating two separate exposures on the camera sensor.  One is created with the flash and the other with the ambient light.
Flash Sync Speed
I mentioned this last week, but lets just take a look at the technical detail before we go into the process.  Without boring you with too much technical information about the camera, I want to let you know that the shutter speed you use with a flash, is limited by your camera 'Flash Sync Speed' this value will be around 1/200 of a second or so.  You cannot increase the shutter speed beyond this if you are using flash.

Stop reading now, if that's all you want to know :-).  A short's all about the curtains that open and close in the camera and the speed of those curtains that limits this.    The drawing below shows what is happening with the curtains during slow shutter speeds and fast. In the slow shutter speed example, the front curtain opens to expose the sensor and the sensor is exposed for a period of time and then the rear curtain closes.  In the second example, the front curtain opens, but before it has fully opened, the rear curtain starts to close and so there is a moving slit of exposure that travels along the sensor.  The part of the sensor that is exposed is show in yellow on the diagram.
Lets now think about flash.  For flash to work, the sensor must be fully exposed otherwise, we would see some of the curtain on the sensor shown as a black section.  So the shutter speed can only be as fast as the instance where the camera has fully opening the front curtain and hasn't started to close the rear - this is normally around 1/200th or 1/250th of a second shutter speed.
Back to the Technique...Taking the Shot
The flash is positioned off to 45 degrees from the subject as mentioned in the last blog and next it's best to test the exposure of your subject.  The shutter speed should then be reduced to very slow maybe 1/6th of a second.  But hey, I hear you, don't I need a tripod?  Well, not necessarily!! The flash will freeze the subject and the reduction in shutter speed will allow the ambient light to be recorded by the sensor and in many instances, it is better if this isn't recorded as sharp.
Below are some examples I created whilst playing around with our halloween decoration

I created the images below with a flash and shutter speed of 1/8th second.  The background lights are spider lights and are about 1 yard behind the ghost lantern.  The flash fired and froze the lantern, but the slow speed allowed the ambient light from the spiders to be recorded.  I also moved the camera slightly as I was exposing and this gave the direction of the ambient light recorded.

In fact in the last image, the ghost was also illuminated.  This resulted in the ghost being party captured as frozen, by the flash, but party as ambient giving a 'ghostly' spread of it's image!  
Don't Forget about the Bulb Setting
Remember long ago in the shutter speed blog (I think it was April) you come across the term 'painting with light'?  By using a light source, which could be anything from a firework to a torch, the photographer creates an exposure of an image on the camera sensor.  This is a great time of year to have a go with this setting...make sure you use a tripod.

A quick reminder - The bulb setting on your camera is normally at the slowest end of the shutter speed dial and one press of the shutter release button opens the shutter to expose the sensor and then another press closes it.  So basically you control the shutter speed.
Next Time
Next month is the final month for 'You're Smarter Than Your Camera' boo hoo!!!  We will continue with a huge month dedicated to a few aspects of your camera that we haven't already covered, such as bracketing, spot metering and fast shutter release.  Here is your opportunity, do get in touch if you would like me to cover something I haven't already.
Also....don't fret :-) I will continue blogging in 2016, and will talk about the content next month. 
Your Challenge
Have a go getting an image with this week's special always, I'd love to see any results!
Thanks so much for reading and as always, I would love to hear any comments or questions you have.  
Have fun with your photography,
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