Category Archives: Getting To Know Your Camera

Getting To Know Your Camera

Exercise – Focal Length and Angle of View

I skipped the the first part if this exercise, due to the suggestion that it was unlikely to work with a digital camera.

Firstly I had to determine my camera’s standard focal length. The camera is a Nikon D5100 and according to the manufacturer has a cropped imaging sensor and therefore a crop factor of 1.5X. This would therefore give it a standard focal length of just over 38mm. I then¬†mounted an 18-105mm Nikkor zoom lens onto the camera for this exercise.

The scene I decided to capture lay just outside my rear balcony. A new apartment block just completed in construction. Something of an eyesore actually, but useful at least as something quite definite in form and easy to measure against. The camera was mounted on a tripod for a repeatably stable from which to take the next series of photos.

First photo was at the cameras’ standard focal length – 38mm

38mm

When this photo was printed and then held at enough of a distance so that it appeared to be the same size as its subject, I measured this to be 35cm.

The next photo was at its’ widest angle of view – 18mm

18mm

I found this photo when printed had to be held at such a close level I think I ended up cross-eyed! It wasn’t practical to make a measurement, but I would say length somewhat shorter than my nose, about 4 cm

And the last photo at the narrowest field of view (or longest telephoto length) – 105mm

105mm

This photo had to be held at just beyond an arms’ length away to make the comparison, at about 95cm (does that mean I have short arms?).

When I printed these photos out on A4 sized paper I wasn’t sure whether to do so with a borderless reproduction, or as the print software determined a “100%” print size to be, which had quite a wide border. I opted for 100%. The images had to be straightened slightly in software. I very rarely print my photos, so it really was quite interesting to have actual photos in hand, even if they were printed on plain copier paper.

Link to higher resolution TIFF image files

Shutter

The shutter is a device, mechanism or electronic function in a camera, be it still or video, which limits the amount of time in which light is exposed on the focus area or plane, whether that be an electronic light detector or a frame of film. Typically it consists of a thin mechanically driven plate that moves in and out of the path of light. Often it sits just in front of the focal plane or focusing area.

Being able to control the shutter speed determines a number of effects in the resulting image:

  • The most important being that of the ability to stop or freeze action. Typically, the faster the shutter speed, the less obvious the effect of motion blur, especially of subjects moving at high speed. High shutter speeds also generally limit the amount of light falling on the focus area, useful for controlling exposure in brightly lit environments.
  • Slow shutter speeds are useful in situations where there is a need to boost or increase the amount of light falling on the focusing area, as in low-light conditions. A drawback to this though is an increase in motion blur, especially if the camera is not mounted on a stabilising device like a tripod. Slow shutter speeds also can be used for artistic effect, as when there is a need to suggest the motion of a subject.
https://i0.wp.com/upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Focal-plane_shutter.jpg/266px-Focal-plane_shutter.jpg

A mechanical focal plane shutter – source: wikimedia.org

 

 

 

 

 

 

 

 

sources: wikipedia.org

Aperture

The aperture of an optical system is a measurement of the size of the iris or light opening and therefore of how much light is allowed to the reach the point of focus. It does not refer to the mechanism itself that controls or determines that same size.

The aperture is measured in f-stops with small f-stop numbers indicating when the aperture is set at its’ widest opening, and small f-stops when set at it’s smallest. A wide aperture allows the maximum transmission of light through the optical system to the focus point, where as a narrow aperture allows for less light to reach the focus point. The effect of these aperture changes, wide to narrow and vice-versa on an image are two-fold.

  • One is the effect varying aperture sizes have on light gathering power. Wide apertures allow for greater light-gathering power in low-light situations, as would be useful in dimly lit or night-time environments, whilst narrow apertures limit the light gathered, as would be useful in artificially brightly lit or daytime¬†environments.
  • The other is that the field of depth, or apparent depth of focus in an image is either shallow deep, depending on the aperture size. Wide apertures give rise to shallow fields of depth, where only a small proportion of the image is in clear focus, whereas narrow apertures give rise to deep fields of depth, where most of an image, front to back is in clear focus.

The aperture in a camera system is controlled by an aperture mechanism. This is a device, usually made up of multiple interleaving blades, whose position is adjusted to determine a given f-stop number. The typical range of f-stops for a lens can be between f/1.4 and f/16.

 

https://i2.wp.com/upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Aperture_in_Canon_50mm_f1.8_II_lens.jpg/237px-Aperture_in_Canon_50mm_f1.8_II_lens.jpg

An aperture mechanism for a 50mm lens. source: wikimedia.org

 

source: wikipedia.org

f-stop Number

This is the ratio between the focal length of a lens and diameter of its’ aperture (or light entrance pupil) and is expressed by the equation:

 

 

Where N is the f-number, f is the focal length, and D is the aperture diameter.

f-numbers are typically measure in full-stops, where each successively larger stop number halves the light gathering area of the lens, as in the series; f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11f/16

source: wikimedia.org

f-numbers in full-stop increments

f-stop numbers can further be divided by halves or thirds.