Sensor 'Final' Resolution (Image Quality vs Noise)
Diffraction
Field of View
Depth of Field (Section of Scene in Focus)
'Full Frame' Image Perspective
The 3D Effect + Bokeh
Resolving at Distance
Dynamic Range
Post Processing
The smaller the focal length (e.g. 12mm)
The
larger the focal length (e.g. 300mm)
of the
lens the narrower the angle of view from the front which in
turn draws in and compresses the entire scene,
including the perceived distances between objects in the scene and
their relationship with each other towards the lens - this is known as compression distortion. It is irrelevant what camera sensor the lens is fitted to and
whether the final image 'field of view' is cropped by the sensor
and/or later in post processing, the lens NATIVE (e.g. 300mm)
focal
length,
depth of field scale, compression distortion and characteristics remain the same.
A 50mm lens on a 35mm 'full frame' sensor
camera is considered to produce a 'natural eye' viewing of a scene where
there is neither extension or compression distortion - the scene is neither moved outwards from or drawn into the lens.
This is because the 'diagonal measurement' of the sensor is nearest
to that of the 'native' 50mm focal length of the lens.
A
smaller sensor, for instance the Micro 4/3rds 2x crop digital sensor
in my GF1 camera has an imaging aspect ratio of 4:3 on a 17.3mm x
13mm sensor imaging area of measurement with 12 mega x 4.3 micron
'pitch' sized pixels. To achieve the same image resolution with a
35mm 'full frame' digital sensor camera, the full frame camera with
an imaging aspect ratio of 3:2 would have to have approximately 46
mega x 4.3 micron 'pitch' sized pixels on its 36mm x 24mm sensor.
However, that is not the entire story and conclusion, as the smaller
the pixel micron 'pitch' size the greater the loss of image quality
at higher ISO ratings (e.g. ISO:400 plus
as
per current 2011 technology)
which would equally apply to the 12Mp Micro 4/3rds digital sensor as
well as the 46Mp 'full frame' digital sensor. Most photographers
seek a 'balance' for image quality versus higher ISO ratings and
this is where the smaller compact digital sensors have a problem as
their ability to maintain a reasonable number of pixels and yet
reduce the pixel micron 'pitch' size is restricted because of the
smaller sensor area. This is one of the reasons that compact camera
manufacturers are reducing the pixel numbers and increasing the
micron 'pitch' sizes of pixels on their sensors, typically Canon
with their 10Mp sensor, G12 compact camera. A 'full frame' digital
sensor can be 'balanced' more effectively, for example my Canon 5D MK
1 DSLR with 12 mega pixels x larger 8.2 micron 'pitch' sized
pixels to achieve excellent image quality and resolution at those
higher ISO ratings and it is no surprise that the March 2012,
new Canon 1D-X 'Flagship' DSLR has a digital
'full
frame' 36mm x 24mm
sensor
with 18.1 Mega Pixels with 6.9 micron
'pitch' sized pixels.
The
smaller the sensor and/or the larger the number of pixels, determines an aperture diffraction limit where the lens resolution
commences to weaken as the lens aperture is closed down - typically
around f5.6 on the GF1 Micro 4/3rds sensor and f13.2 on the Canon 5D
MK 1
'full frame' sensor.
The
smaller the digital sensor in overall measurement size the greater the 'depth of field'
characteristics - this equates to as many as 1-2 aperture stops or
more of a
difference (e.g. f2 with a smaller sensor equals the f4 of a full frame sensor)
dependent on how small the sensor is in relation to 35mm full frame.
The
smaller the digital sensor in overall measurement size the less
dynamic range is available.
Perspective
distortion is a warping or transformation of an object and its
surrounding area that differs significantly from what the object would
look like with a
normal focal length,
due to the relative scale of nearby and distant features. Put
a 25mm lens on a Micro 4/3rds camera and
due to it's native wider angle, it will tend to move
the
If you have enjoyed this article - please donate to my Charity of Choice - The Sick Kids
Richard Lawrence
|
entire scene,
including the perceived distances between objects in the scene and their
relationship with each other (extension distortion) further back from the lens and
also achieve a wider view at each side. The 
he photographer will find that the control of the
'depth of field' becomes increasingly more difficult when the 'primary
subject' is further away from the lens as a smaller sensor tends to have
a much larger depth of field at any given aperture to that of a 'full
frame' sensor. The 25mm lens will produce a 50mm 'field of view' but as
before, it
STILL retains the depth of field, the extension distortion and the focal
and natural characteristics of a 25mm lens. It becomes a
serious issue when the overall scene has
greater gradients of depth in it and the bokeh effect desired, cannot be achieved.
As I have already mentioned, this starts to
manifest itself as a real problem when the 'primary subject' is at a further
distance from the lens - a Micro 4/3rds sensor delivers a
much larger 'depth of field' with a 25mm lens at f2 and especially at f4
and
cannot match the shallower 'depth of field' control of a 50mm
lens at f2 and a more gradual 'out of focus' effect at f4 on a 'full frame' sensor.
Also with a smaller compact camera, it is invariably the case that the
25mm lens does not have a '