Exercise – Focal length and angle of view

My Nikon D3000 has a sensor size of 23.6 mm x 15.8 mm which means that a photo taken with the same focal length on a full frame 35 mm camera will be approximately 1.5 larger than the photo taken on the D3000. The crop factor is actually 1.483 (35 divided by 23.6), but 1.5 is perfectly fine for my mathematically challenged brain.

The brief is to look through the viewfinder, keeping both eyes open and adjust the lens until the image in the view finder is the same as the one seen with the other eye. I took all the photos from my deck overlooking my neighbour’s apple tree with the bird house  – he spends much more time in his garden than I do! On a fixed focus 35mm camera this point should be at 50mm, however on my 18-55mm kit lens, I found that I had to switch out to my 55-200mm lens before I could come up with a match. This could be due to my poor eyesight and my progressive lenses though. I found a match at 68 mm. So to avoid confusion, I am not going to include this photo as the course manual has warned me that this would probably not work with a digital camera.

I switched back to the 18-55mm lens and set my camera to 32mm which is approximately similar to a 50mm on a full frame camera and took a reference photo, again keeping both eyes open. Then I set my camera to 18mm, the widest focal length, took another photo and then swapped back to the 55-200mm lens and took the final photo at 200mm.

Exercise 01 - 32mm

32mm f8 1/160 200 ISO

Exercise 01 - 18mm

18mm f8 1/160 200 ISO

Exercise 01 - 200mm

200mm f8 1/40 200 ISO

I then printed the 3 images and went back to the position where I took the photos. I then held up each print, moving it forward or backwards until the scene was similar to what I was seeing with the naked eye and got my husband to measure the distance from the photo to the front of my glasses. The distances were as follows:

  • 32mm was 30 cm – this distance was comfortable to look at the print
  • 18 mm was 19cm – this distance was not very comfortable, just tolerable for a short while
  • 200mm was 177.8 cm – this distance was very comfortable for me

I’m a bit puzzled why the last measurement isn’t closer to the actual focal length as the other two measurements are, but that might be due to my eyesight.

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