Introductory Exercises

The first part of The Art of Photography involves a series of exercises dealing with focal length, focus, aperture and shutter speed. I have spent my time today reading through this introductory material, and developing ideas and a plan for each exercise so that I can go out shooting tomorrow.

I found the first exercise 'Focal length and angle of view' quite confusing at first. I already knew about crop factor and it's implications with regards to what you see through the viewfinder, but I wasn't entirely versed in the concept of a 'normal' focal length - that is, one that represents the scene through the viewfinder at the same size as what you see with your naked eye. The normal focal length for a camera with a crop factor of 1.5x (as with my D50) is 33mm (50mm - the normal focal length of a full frame camera - divided by the crop factor). However, the view in my viewfinder is not the same as with the naked eye until a focal length of around 55mm. My tutor offered an explanation on the forums:

It's a question of magnification. To fit the same scene on to the smaller sensor it has to be reduced more.

I/O=M

In order to reduce the image height I of the object height O to occupy the same proportion of the frame on the smaller sensor the magnification must change.

I still don't have an understanding, but I intend to do more reading and research on this topic while I continue with the course. With perseverance it should become clear soon enough!