Besides, what is a fixed focal length? a fixed focus lens is a lens whose focal length does not vary, unlike a zoom, which has it, a lens group that is movable …
(My) Short story …
When I started the photo it was with a trans-standard zoom that I had chosen, a 28-105. I chose it for its practicality and its versatility. Its diaphragm aperture of f3.5-f4.5.
Big fan of landscapes (and at the time too reserved for shooting people outside my family only), I exploited the goal generally between f / 8 and f / 16. There have been few times when I photographed people. When I did, I included them in the scenery without making the choice to detach them from the environment, simply by opening my diaph .. One day, I went to 28-75 (usually it is more a 24-70 which is proposed in opticians) with an opening to f / 2.8: a goal more “expert”! By practicing 75 mm and opening full on pictures of family members I understood that the choice of a large opening was important in this type of exercise. More and more I became interested in people photography. I was less apprehensive to photograph them, so I looked for that famous “thing” that could make the difference.
The world of photography has long favored the 50mm that opens at f / 1.8. Economical and light, he convinced me that the fixed focal length had sacred assets. Optical quality is better than zooming and opening is much more important! This is indeed the right focal point to become familiar with this type of lens. The 35mm is even to consider if one wants a wider angle of field, and mandatory if one is in APSC because the coef multiplier Nikon is 1.5 and 1.6 at Canon).
Fixed focal length has the advantage of making the photographer creative because he must constantly ask the question of framing while moving to have a tight plan moving forward or wider when backing. This can be a disadvantage but it is essential if one wants to progress. The major advantage of the fixed focal length is its brightness, which is not found at equivalent focal length on a zoom. Indeed the openings are larger and start around f / 1.0, f / 1.2 for some. The most common are openings that start at f / 1.4.
But why? What’s the point? The interest of such objectives is to be able to trigger in low light without having to use a flash or to put forward the subject by blurring the background. Have you heard of the background blur called “bokeh”? Bokeh? The term comes from Japanese boke which means blurry. The bokeh intensifies according to the weakness of the depth of field.
Here are some photos with a reduced depth of field to emphasize the subject. The larger apertures of the lens should be used and the background should not be too close for your subject to be far from the background. The longer the focal length, the greater the effect. To obtain an equivalent effect with short focal lengths you will have to be much closer to the subject. The mode to use is the “A” mode for Aperture, or Opening in French, if you want to work in semi auto. The M mode, for manual, also allows you to control the opening and in addition the speed.