Long Exposure Simulation - Bedford Camera Clubbedfordcameraclub.co.uk/wp-content/uploads/2016/04/Long-Exposur… · Long Exposure Simulation Ian Whiting 31st March 2016 Typically

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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)