Exercise: Focal Length.

The general aim was to study the effect of distance and focal length and to find the point at which the subject to the eye and view finder equalised.


Equipment used:

Nikon D700  – full frame.

24 – 70 mm f/ 2.8

50mm Prime f/ 1.8

70 – 200 mm  F/ 2.8 

Unfortunately I do not have access to a 35mm film camera as suggested for the exercise but was able to still work through the exercise to a point where I could understand the concepts of focal length.  The subject matter is somewhat dull but, once images are printed this week,  I will have enough features within the image to find distances between where subject and  image becomes  the same size.  

In the absence of an instant print to use, (printer arrives this week)  I adapted the exercise through the view finder.  I found that …

– with the wide angle lens (24mm) I had to move extremely close to the image until eye and view finder image equalised.

– With the 50mm I remained at the chosen fixed point as anticipated due to standard focal length.  i.e. Subject to eye and view finder were equal.

– With the 200mm I moved as far back as I possibly could (3.5m) and still the eye and view finder were not equal.  


I have now printed the images and my finding are:

50mm. This surprised me. I was expecting to remain in the original shooting distance but actually had to move back 50% of the shooting distance for the image to replicate the size of the subject.

24mm. I moved back to double the original shooting distance.

200mm. I moved forward to half the original distance.

This seems to be opposite to what I found with the looking through the view finder.


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