long exposure simulation - bedford camera...
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Long Exposure Simulation
Ian Whiting 31st March 2016
Typically a very dark ND filter, e.g. big stopper giving 10 stops of light reduction, is used to give a
very long exposure, e.g. 30 seconds to 5 minutes, to blur movement. This is often used to give
waterfalls or the waves on a sea a creamy smooth look or smooth cloud movement.
I was interested to know whether I could simulate a long exposure without recourse to a dark ND
filter.
My test was carried out with the Canon 5DMkII camera tripod mounted, raw images, manual
exposure and focus. Little wind, river flow is slow.
I took a number of images of a river and blended them in Photoshop. Images taken at about 1 per
second, thus a 12-image exposure was taken over 12 seconds and a 7-image exposure taken over 7
seconds etc. All images taken at same exposure, aperture ISO and focus.
In Photoshop choose File > Scripts > Load files into stack to open the image set as layers. Select all
layers except the bottom one, change opacity to 20%. I experimented with different opacity levels
but 20% worked best for all sets (I was using 7 to 12 images per set)
Lower layer opacity is 100% Other layers are 20%
The tripod worked well so there was really no camera movement but otherwise a mask could be
used on the static elements so that these were derived from just one image to avoid blurring them
or use Photoshop image alignment feature.
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Advantages / Disadvantages
ND filter Multiple images
Only one image to process Multiple images to be blended
Long exposure can "hide" moving people Photoshop to remove people from scene *
Possible colour cast to remove No colour cast
Dark viewfinder, focus problems Clear viewfinder and simple focusing
Calculate exposure, some trial and error Normal exposure used
£100 filter, £50 holder Free
Different strength ND filters at £100 each Simulate any density or duration for free
Carry it with you and fit onto camera No extra equipment needed
One shutter press and wait 60 seconds Press shutter 10 times (once every second)
No control during exposure Choose when each exposure is taken
Takes 60 seconds plus noise processing** Takes 10 seconds, no noise processing
Stores just one image Uses more memory card space (10 images)
Can see the result, retake if required Photoshop before being able to see result
You get what you get Selective blending control in post ***
I have used example 60 seconds V. 10 images, numbers may differ depending upon requirements. For instance to blur cloud movement you might need to take one image every few seconds. * can be done using averaging and/or masking. The result is more controllable and may look better
** long exposures can cause the camera to run a noise removal process, often this doubles the time
to take one image
*** control degree of blur, choose whether specific elements like trees and clouds have blur or not.
Use visual tricks like accentuating one still image over the top of the blurred images
Results
Examples used below include images with no static parts, static parts in the background and static parts covering some of the moving water. Only the first image in each set is shown, this image looks very similar to all the images in the set apart from where the water has moved, the waves and ripples etc will be a different position. No other Photoshop filters, e.g. Gaussian blur, were used in this test, the results are purely layers blended only by changing the opacity.
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First Image in Set Blended images
First image 1/160sec f/6.3 12 blended images
First image 1/160sec f/6.3 8 blended images
First image 1/160sec f/6.3 7 blended images
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First image 1/160sec f/6.3 8 blended images
First image 1/200sec f/6.3 8 blended images
First image 1/125sec f/11 8 blended images
Next steps to be done...
More testing can be done to refine the technique
Run a test alongside a ND filter to compare the differences. I suspect there may not be that
many a lot of the time. I assume the ND could generate smoother blends which might be
simulated with a small touch of Gaussian blur when using multiple images.
Try more images in a set, e.g. 30.
Where possible test with longer exposures per image, e.g. 1/30 sec, to get more natural blur.
But this might add blur to other objects, e.g. swaying tree branches, that you might
ultimately prefer to have left sharp (mask out to use just one sharp image for that area)