Last Updated
- 25th June 2013
It is great fun to
just shoot camera
produced
jpeg images,
especially for family events and social trips but for any
serious work, I prefer to shoot ONLY 'RAW' files. They provide
the 'optimum' starting base for image quality and by using the
correct software to post process them, I can control the final
output for printing.
There are limits as to the
amount of editing control that a camera can apply to the final camera jpegs
bearing in mind that some users will edit their own settings in the camera menu
(saturation/contrast/noise reduction/sharpness)
which may increase
the final camera jpeg image quality but also may decrease it. There is no doubt that post processing 'RAW' image files and 'tweaking' to
suit (resolution/noise/print size/viewing
distance) will deliver greater control and often
produce a more desirable result. Very often images are judged by
their appearance on a digital display (at various sizes) but in reality
they should be judged by their final print on the wall.
I like reading professional reviews, following certain 'gear'
forums and generally keeping up with the latest camera and lens
technology. Invariably at the core of most of these discussions
is the relationship between a new camera's digital sensor noise
versus the final image quality at high ISO ratings. However,
there is much more to image quality and in the real world,
the final quality of a digital image file is
determined by a number of factors which control it's production, not least -
-
The amount of available light in a
scene (low light considerations)
-
Noise
reduction
-
Camera exposure meter + digital sensor
-
Lens
quality
-
Subject
Distance vs. Resolution
-
Camera autofocus
system
-
Shutter speed
+ image stabilisation' limits
-
Tripod
considerations
-
The
processing mechanism
- prints - digitals displays
Light + Low Light
Light plays an important part in the ability of a lens to
deliver optimum resolution. With low light conditions and just
like your eyes, the lens will struggle to take in all the scene
data, especially in the shadows and dark areas. The lens has to
be opened up (wider aperture) to take in more light and
in the process the resolution that the lens delivers to the
sensor is usually weaker and especially if the subject distance
is increased. A lens tends to have an 'optimum' aperture for
'optimum' resolution and very few lenses will maintain that
resolution at wider (f1.4 - f2.8) apertures. To compound the
problem of using a lens at wider apertures -
low
light photography (e.g. night
street shots) demands a higher ISO rating (especially for
camera hand held shots)
and as it rises, towards ISO:3200 and beyond,
digital noise starts to creep into the
image and noise reduction is applied (in camera or in software post
processing) to reduce it's visibility. Even in good daylight, sport or wildlife
photography may also push up the ISO rating towards ISO:3200 if
the lens is forced to operate at a 'stopped down' aperture of
f5.6 towards f22 due to it's design, whereas a lens with a
'wider' aperture of f2.8 can keep the ISO rating lower as the
lens lets in more light.
Noise Reduction
In light conditions where the
camera
sensor and the lens push the ISO rating of the camera up from
the preferred ISO:100 towards the less preferred ISO:3200 (or
higher) the resulting digital sensor noise
invariably has to be reduced either in-camera or in software
post processing. Any applied noise reduction will
impact on the resolution in the image, push it too far and the image becomes
mushy and loses it's resolution when viewed or printed at 100% - keep it too low
and the noise remains visible. There is a fine balance regarding the amount of noise reduction
versus the final image quality that can be applied in relation to the
size of the printed or digitally displayed image
and the
final 'viewing' distance.
Exposure Meter + Digital Sensor
The accuracy of the camera's exposure metering system is
essential to determine an accurate exposure setting for the
light in a scene. In normal light conditions, the correct
exposure will provide the best conditions for the sensor to
deliver it's optimum resolution and
dynamic range. Some sensors
have a very high dynamic range that can operate in a large
number of lighting scenarios whilst others struggle. However in
light conditions that are VERY uneven like a dark foreground and
a bright skyline, the exposure metering might struggle to
balance the two and invariably errs on the side of a bright
foreground and a blown sky where any cloud outlines have been
lost in the data captured and usually cannot be recovered
in-camera or in software post processing. The photographer
will take exposure meter measurements of both the foreground and
the sky and select an exposure reading in-between which
invariably will be an under-exposed reading (for the
foreground) which in turn weakens the final image
resolution. To work around this dilemma, some photographers will
use a
graduated filter
to darken (only) the skyline which balances out the
overall exposure reading and avoids the under-exposure of the
foreground. The graduated filter is great for using for even
lines between the sky and the ground but if there are any high
trees or building in the skyline, then their tops in the sky
tend to be darker than their base in the foreground - even soft
graduated filters struggle to avoid this.
Lens Quality
Unfortunately (so far) I have not had the pleasure of
using a perfect lens. All my lenses have certain
imperfections, and not just
the kit lenses, I have some lenses which are very expensive.
Lens resolution is a complicated business to judge, even by
reading the reviews and the technical charts. One person's most
excellent kit lens is another's nightmare. A lens has limits,
like
diffraction,
depth of field
amongst others and
it is learning those limits through constant use that eventually
delivers excellent image quality for the photographer. Lenses of
the same focal range vary in price and it is a rare case indeed
when an in-expensive kit lens can out resolve and deliver less
imperfections than a professional grade lens. However, I found this
interesting -
"Most
importantly, even though MTF charts are amazingly sophisticated
and descriptive tools — with lots of good science to back them
up — ultimately nothing beats simply visually inspecting an
image on-screen or in a print. After all, pictures are made to
look at, so that's all that really matters at the end of the
day. It can often be quite difficult to discern whether an image
will look better on another lens based on an MTF, because
there's usually many competing factors: contrast, resolution,
astigmatism, aperture, distortion, etc. A lens is rarely
superior in all of these aspects at the same time. If you cannot
tell the different between shots with different lenses used in
similar situations, then any MTF discrepancies probably don't
matter. Finally, even if one lens's MTF is indeed worse than
another's, sharpening and local contrast enhancement can often
make this disadvantage imperceptible in a print — as long as the
original quality difference isn't too great"..............read
more
Subject Distance vs. Resolution
Every lens, even a zoom lens at varying focal lengths
has it's established distance limitations for maintaining
optimum resolution. For sure the optimum aperture setting plays
an important part BUT recognising the distance limitation
is paramount. If the primary subject or that distant landscape
is pushed too far back and beyond the optimum resolving limit of
the focal length used (prime or zooms) then as the print
is enlarged the quality of the image may appear mushy. Cropping
the image (e.g. a distant eagle in the air to see more of
it's head detail) can stretch the quality of the image even
further. Most photographers' quickly establish the distance vs.
resolution capabilities of a lens and maintain a strict
methodology in it's use thereof.
Camera Autofocus System
The camera's autofocus relationship with the lens fitted is
paramount. As we move forward with digital sensors which have
larger numbers of pixels which are smaller in pixel size, the
accuracy of the autofocus required becomes more focused, if you
will excuse the pun. Learning the little wrinkles of your
camera's autofocus system and also using lenses in manual focus
is a continual learning curve, especially if you also use other
cameras in your photography.
This is an interesting tutorial about autofocus - "A camera's
autofocus system intelligently adjusts the camera lens to obtain
focus on the subject, and can mean the difference between a
sharp photo and a missed opportunity. Despite a seemingly simple
goal—sharpness at the focus point—the inner workings of how a
camera focuses are unfortunately not as straightforward. This
tutorial aims to improve your photos by introducing how
autofocus works—thereby enabling you to both make the most of
its assets and avoid its shortcomings"
-
read more
Shutter Speed
+ Image Stabilisation Limits
Shutter speed has to be taken into consideration, especially
when photographing moving animals, people and trees waving in
the high wind. If you set the shutter speed too slow the image
will probably be blurred or at the very least sharp enough in a
small print size but blurred in enlargements. However there are
occasions when a slower shutter speed can blur a background but
capture the moving subject very sharply but this involves
panning the camera to match the subject's speed when the shot it
taken. Image stabilisation built into a camera body or a lens
has shutter speed limitations before a 'hand held' shot will
blur the captured image. The photographer has to learn those
limitations, especially for 'hand held' night street shots where
there is a combination of balancing for 'hand holding the camera
and also taking into account the movement of a car, person,
animal or even back to waving trees in the high wind in the
shot.
Tripod Considerations
A tripod can be used to assist in producing 'optimum' image
quality by keeping the camera and lens 'rock steady' but there
are technical considerations to take into account. The ability
of any camera or lens 'image stabilisation' mechanism to operate
when fitted to a tripod, (e.g. IS may required to be switched
off) the method of pressing the camera
shutter button,
even a hand press can create tripod movement whilst a camera
self timer, remote cable or wireless shutter operation are
preferable.
Some wind conditions might vibrate a tripod enough to spoil the
resolution in the image, especially if it is a long exposure and
the weight ratio of the tripod in relation to the camera/lens
used is wrong because the tripod is too lightweight and not
suitable. Most photographers who have a lightweight tripod for
hill walking, invariably use a heavy back pack or other heavy
object (bag of stones) to tie under and to the tripod to add weight to it,
causing the tripod legs to be firmer on the ground.
The Processing Mechanism - Prints - Digital Displays
The 'RAW' image file retains the maximum data to produce the
optimum image quality. There are post processing actions that
will impact on the final image quality, such as correcting lens
distortion which inevitably results in cropping out a section of
the image. Other include, cropping (in-camera or PP),
correcting lens imperfections, adding software graduated
filters, adjusting the exposure and/or texture to parts of the
image and conversion to a jpeg image file which compresses and
reduces the available image data. Most of this work cannot be
seen in reasonably sized prints (tiffs or jpegs) even up
to A3 with 16Mpixel digital cameras but could impact on larger print
or digital display sizes, especially if there is some HDR software post
processing in there. Some camera manufacturers are fully aware
of the limitations of their cameras and lenses, especially fixed
lens cameras and they will recommend maximum print size
limitations to ensure the resolution and image quality is not
over stretched. Problems arise when the user (digitally)
pixel peeps the image at 100% size which is way beyond the
manufacturer's print limitations and expects the same image
quality. Viewing distance (digital and print) plays an
important role in all of this, stand further back and the
display or print can be larger, stand closer and the display or
print should be of a size to match the viewing distance.
A 'Raw' file converted to jpeg will reduce the data level,
especially if the image is re-sized and reduced in % capacity
for the web. When images are re-sized for the web, many
photographers forget to re-sharpen them at the time. This often
leads them to think that the image is sub standard.
Re-sharpening will improve the images but re-sharpening them too
much can often lead to artifacts or halos such as
compressions as well as
the possibility of
jaggies
(known as the stair case effect) in non
vertical/horizontal lines
appearing in certain
areas of the web image
- in the end it is always
about
balance in post
processing an image for display or print at the correct and
expected viewing distance.
Some photographers
prefer to use lenses that
are designed to soften an image and in many cases there are
photographers who produce 'Photo Art' and 'Fine Art' prints, who
use
post processing
to soften and even reduce the amount of material in their images
for effect.
When post processing a 'RAW' image file some photographers will
add a
software graduated filter to the sky to darken it
down to put more detail in the clouds, they may even add a colour and it works very well,
although in some cases the software (and hardware)
graduated filter will not only darken the sky, it also darkens
the tops of trees and houses or hills.
Many photographers will use a software graduated filter in
reverse and apply it with increased exposure (in the filter
area of coverage) to a dark
foreground to lighten it.
Some may even use an adjustment
brush to dodge, burn and create different lighting effects but
invariably this weakens the enlargement capabilities of the
image as very often the adjustment artifacts become more visible
in a larger frame size, especially around the adjustment edges.
It takes great skill in software to make digital adjustments to
images and a great deal of patience to apply the adjustments
correctly to produce flawless print enlargements. These days you get
what you pay for, so if the software is expensive, there is
usually a very good and sound reason.
Many professional artists use software that can
dodge and burn
as well as masking and layering the 'RAW' image file -
Check out the
Adobe CS Tutorials for more on dodging,
burning, masks and layering and for photographers
who wish to take post processing to an even higher step, check
out
Corel Paint and Tablets.