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Sunday, 4 April 2010

Focal lengths and different viewpoints

This exercise appeared to build further on earlier exercises around focal length. However this exercise was about exploring how perspective can be affected by the focal lengths and changes of viewpoint.

What is perspective?

I had a look on the internet and through my <books> to find a definition and came up with the following points

  • Perspective is the optical effect that makes objects in the distance smaller than those that are closer to you.
  • Perspective is about ‘distance’ the focal length alone doesn’t affect the perspective.


For the exercise my scene was Greenwich Park; and my ever willing (not so much really!) daughter as my model. Normally I would have played around with the manual settings for a more control over the exposure (aperture and or shutter speed) however it was a cold and overcast day with 4 year old model whose attention was more focused on feeding the squirrels than helping her dad with perspective experiments; therefore I elected to just put the camera in a program mode and relied on the camera to find suitable settings.

In hindsight I wish I had spent a bit more time on this; I would have preferred to have used smaller apertures to increase the depth of field (less background blurring) as I think that would have demonstrated the perspectives a bit clearer. I think that I should have increased the ISO too (I left it in an auto mode) which potentially would have allowed me to use faster shutter speeds (I took the images handheld). Because of that the settings are not as consistent as I have had before. That aside, the results of my findings tied in with course text and what I found in other references.

The idea was to take 2 photos one with a wide angle (short focal length) and the other with a telephoto (long focal length), however between each shot, change the viewpoint (distance) to keep the subject roughly the same size in the frame.

Image1 For this image I used a focal length of 250mm (55-250mm lens).

250mm f/5.60 1/30 sec ISO 200

Image2 For this image I used a focal length of 18mm (18-55mm lens).

18mm f/4.50 1/60 sec ISO 200

Wider angle (18mm) appears to make the girl in the foreground look larger.

Although the exercise didn’t ask for it, but I also added an image3 where I used a focal length of 55mm (using the 55-250mm lens) as a baseline between the Image1 and Image2

55mm f/4 1/60 sec ISO 200

Image1 & Image2 for comparison

In Image1 I found that the image was flatter. I noticed that the trees on the left appeared to be much closer (although blurred by the shallow depth of field which can create a sense of depth/distance in the mind) than Image2. The same set of trees in image2 are where the person in the red top is walking; appearing considerably further away.

Although image1 retains sense of depth because of the shallow depth of field, I feel that the perspective is flatter than in image2

This compression/flattening can also been seen with the bench on the left side of the image; not so much with image1 as the angle of view cuts out the bench altogether, but in image3 (55mm) the bench is still visible and it appears much more close to the foreground than in image2.

Something else the bench shows is its size; the bench is smaller in image2 than in image3 making it look further away. The perceptions being that as things get further away then the smaller they will appear. The book “The Photographer’s Eye by Michael Freeman” makes reference to this as ‘Diminishing Perspective’ and it being a form of linear perspective.

In image 2 I had to get quite close to my daughter to get her to a similar size in the frame with the 18mm focal length. I noticed from the image a sort of distortion to her that makes her look larger in the frame. What I also notice is the parallel edges of the path converging into the distance; creating a more linear perspective, and therefore a sense of depth to the image.

Final words

Deeper perspective = Image taken closer to foreground object / Wider angle of lens (Objects appear further away from each other)

Flatter perspective = image taken further away from foreground object / narrow angle of view (Objects appear closer together)

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