Focal length and angle of view

Enough reading, time to get out with the camera!  At least I had picked up early on that the crop factor for my camera is 1.5 so determined the setting for the first photo in the series of 3 should be 33mm on the zoom lens.  However, on framing the first shot I realised from the viewfinder information that there were some peculiar settings – lesson here; when you have been experimenting with the camera in conjunction with the manual always return all settings back to your normal values!  This also applies when returning home from any shoot.  Anyway, with 3 shots in the bag returned to print them out ready for the second part of the exercise.  Back outside returned to my carefully selected memorable view point, a convenient manhole cover.  It took me a minute or two to calibrate my eyeballs but found having a large van in the pictures helped considerably as it provided a very good reference.  Not so easy was taking the measurements from eye to picture; if you have access to a measuring stick for spacing seeds in the garden it makes life easier!

Focal length 33mm - DSC_5138The first picture, lens set at roughly 33mm focal length (actually recorded as 32mm in Lightroom) returned a viewing distance of 40mm.





The second picture, wide angle setting of 24mm, returned a picture to eye distance of 24mm.





The third shot, telephoto (thought I had it set at 70mm but LR shows 66mm), gave a picture to eye distance of 80mm.




For the standard focal length shot there is good correlation between the lens setting and the eye to picture distance, given the rather rough measuring method.  This accords with the fact that the with both eyes open the central angle of view is 40-60 degrees which gives a focal length similar to the camera standard focal length.  Again, the wide angle lens setting corresponds to picture to eye distance.  However, the telephoto setting figures show a discrepancy in the trend.  Nevertheless, the results correspond to the findings put forward in the exercise notes and suggests a good deal of similarity between the optics of the camera lens and our eyes, albeit the camera sees what it sees within the limits of the technology and there is considerably more processing in the case of the eyes/brain partnership.


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