Wednesday, 16 January 2013

Multiple Exposure–Digital SLR–Stacking

I have a Canon EOS 350D digital SLR camera. I have had this camera for a number of years and I am very happy with it’s performance.

I am an amateur photographer. That means I occasionally get out an take a few photo’s with my camera. When we bought the camera, we had a couple of goals in mind.

  1. Easy to use in full auto;
  2. Good range of full manual options;
  3. Good images;
  4. Cost.

I should have added a couple of extra criteria since it was replacing my old SLR Ricoh KR10M camera (camera died and it was going to cost more than a new camera to fix it). The other criteria should have included … I could use my old Tamron Macro lens with the new camera and all of my Hoya filters … oh well, you live and learn.

For the filters, I just bought a 52mm – 58mm step down ring from eBay for the princely sum of $2.80, so that wasn’t a problem. My lenses are another problem for another day (and another couple of thousand dollars).

But I digress.

In the good old days of analogue photography, you could create multiple-exposure images by opening the shutter several times on the same exposure. This would overlay the different scenes over the top of each other. With care, you could come up with some pretty good creative works.

With digital photography, however, this isn’t possible in the camera (well, not entirely true, some DSLR have this feature, but they are few in number).

The alternative is to take several photos on the DSLR and then use an imaging tool (like Photoshop) and load each image into a single image as separate layers. This is called “stacking”.

The most straight forward way to do this is to open each image and then drag the background layer into the receiving image. Alter the layer transparency for each image so that it ends up with an equal level of transparency over all.

Say you have three images. IMAGE_01.JPG, IMAGE_02.JPG and IMAGE_03.JPG. where image 1 is the first one taken and image 3 is the last one.

  1. Open IMAGE_03.JPG in Photoshop … nothing more to do with this layer.
  2. Open IMAGE_02.JPG in Photoshop, CTRL-A (select all) CTRL-C (copy).
  3. Close IMAGE_02.JPG
  4. In IMAGE_03.JPG, CTRL-V (paste).
  5. Set the layer transparency of the 2nd layer to 50%
  6. Open IMAGE_01.JPG in Photoshop, CTRL-A (select all) CTRL-C (copy).
  7. Close IMAGE_01.JPG
  8. In IMAGE_03.JPG, CTRL-V (paste).
  9. Set the layer transparency of the 3rd layer to 33%

When you finish, you will have three layers that have averaged equal transparency. The idea is to divide 100 by the layer from background to calculate the correct transparency.

  • Layer 1 (background) = 100 / 1 = 100%
  • Layer 2 = 100 / 2 = 50%
  • Layer 3 = 100 / 3 = 33%
  • e.t.c.

Anita in 3 layers

The above image is a series of three pictures taken of my daughter as she ran along the balcony.

F-stop f/4
Exposure time 1/250 sec
ISO 100
Exposure bias 0
Focal length 28mm
Flash mode none
Capture servo

I took eight shots in all on my tripod and with no remote control.

Using the same principle, I also stacked with 5 images and 8 images in the series.

Anita in 5 layers

5 steps

Anita in 8 layers

8 steps

I don’t think that 5 or 8 steps adds any real value to the image, so 3 is good for this picture, but you can see that 5 and 8 work using this transparency calculation.

Because the camera was mounted on a tripod, the immobile elements of the image appear crisp and clear.

I’d like to take another go at multiple exposure where the object is running across the field of view, rather than diminishing in the field of view.

On a side note, in the bottom left-hand corner of the image … our sheep was completely motionless. Lazy sheep.

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