Claim 1 Full - frame
cameras are better for wide-angle work
Well, this is a no-brainer really. Look at the image above
- the full frame image is totally uncropped in camera,
unlike the other two cameras, so a wide-angle lens will
appear much wider on full frame than on a crop sensor
camera - end of story.
The focal length of the lens does not change irrespective
of what size sensor the camera has. A 28mm wide angle
lens for example is still 28mm on a camera of any sensor
size, but the field of view does change, so a much smaller
part of the image fills the frame on the crop sensor.
To all intents and purposes the 28mm lens acts as though
it has become 1.3x or 1.5x or 1.6x longer than it actually
is on the crop cameras. To differentiate this pseudo-multiplication
effect, we need to talk about effective focal length as
opposed to actual focal length. So a 28mm wide-angle on
a full frame camera is still 28mm x 1 = 28mm. On a 1.6x
crop camera it becomes effectively 28mm x 1.6 = 45mm.
Such a 45mm lens is not considered very wide angle at
all. This is why crop cameras are frequently supplied
with an 18-55 kit lens - as this gives a very useful equivalent
field of view to 28-88mm on a film or full frame camera
and makes a great walk-around lens.
One disadvantage of full frame sensors for wide angle
work is the fall off in light at the corners - vignetting.
The crop sensor has effectively had it's edges and corners
"removed" and is therefore working in the lenses
"sweet spot" for image quality.
Claim 2. Crop-sensor cameras are
better for telephoto work, where you can't get as close
to your subject as you would like.
Imagine that each of the sensors represented by the white
boxes in the above image held the same number of pixels
- let's say 10 million (or 10 megapixels) for example.
The 1.6x crop sensor - being much smaller, will require
it's pixels to be a little smaller and to be packed tighter
together in order to fit them all into the small space.
The density of pixels is therefore high. In theory, this
means that when photographing a bird or animal that is
hard to get close to, there is a telephoto advantage to
a crop camera.
Let's clarify this a little. In the image above, the blue
butterfly will have more pixels covering it if the sensor
has a high pixel density - as is the case in the 1.6x
crop camera. The 1.3x camera with the same number of pixels
(10 Megapixels) should be at a disadvantage due to lower
pixel density (same number of pixels but bigger sensor
area). A full frame 10 megapixel sensor should be even
However, to make things a little more even, manufacturers
have been able to put additional pixels on the big, full
frame sensors in order to fight back the deficit due to
lower pixel density.The 1DsmkII that I use has 16.7 megapixels.
Even so, it is still theoretically disadvantaged as you
can see in the table below when cropped to 40D size (a
high pixel-density 1.6x crop camera). It is important
to understand that it is the high pixel-density of the
crop camera that is providing a theoretical telephoto
advantage - not the crop factor itself. If a
large full frame sensor had enough pixels packed on it
to match the pixel density of the small sensor crop camera
it would not be disadvantaged in telephoto comparisons.
In the chart below, the 40D is a 1.6x crop camera, the
1DmkIII a 1.3x crop and the others are full frame.
in pixels/mm (both
horizontal and vertical)
when cropped to 40D size
1D mk III
1Ds mk II
* Notice how many more pixels
are available on the 40D crop camera.
Since this article was written, Canon have release the
7D camera with a massive 18Mp on a 1.6x crop sensor it
has the highest pixel density of any digital SLR (as of
September 2010). In theory this should make it very powerful
So in theory the crop camera has a big advantage
in telephoto work. Let's see if this actually born out
Expt 1. Images taken from the same camera
to subject distance
In the first experiment, I attached a 180mm macro lens
onto a tripod and (without changing the tripod to subject
distance throughout) I then attached the full frame camera
and took a shot at f8 and 1/1000 sec to eliminate any
chance of camera shake.The lens will work near its best
at around f8 and the reasonable depth of field that f8
provides should eliminate any minor focusing inaccuracies.
Full frame sensor camera image (Canon 1Ds mk II)
1.3x sensor camera image (Canon 1Dmk III) taken from same
distance with same lens as the first image.
1.6x sensor camera image (Canon 40D). Notice how this
uncropped image is much bigger than the others ? this
is because of the multiplication effect of the crop camera.
If I wanted to crop the image down to a single butterfly,
this image will require a much lighter crop - and will
retain far more megapixels on the target than the equivalent
full frame image.
Next, we need to open up the images on the computer and
view at 100% on the screen.The images below are totally
unsharpened crops and have undergone no post processing
in Photoshop (apart from the usual RAW
1Ds mkII full-frame sensor camera - *100% crop, unsharpened
1Dmk III 1.3x sensor camera - *100% crop, unsharpened
Canon 40D 1.6x sensor camera - *100% crop, unsharpened
As the images from the 40D contain more megapixels than
the other two cameras due to the high pixel-density, there
is a problem in comparing apples with apples. I could
have presented you with one large image from the 40D and
two smaller images of identical (smaller) size from the
other two cameras - as you will remember they share the
same pixel density. Unfortunately this makes them rather
difficult to compare, so I upsampled the smaller images
and downsampled the larger image to the same number of
pixels using Photoshop's interpolation tools. This only
required a modest 22% increase and decrease respectively,
so does not distort the results here. I have stared for
ages at the non-interpolated files at maximum size on
my computer screen but can still see no difference.
All other tests conducted throughout this tutorial will
adopt this approach to better enable comparisons to be
TEST 1 CONCLUSIONS
There is absolutely no discernable difference between
any of the three images to my eye. So despite the enormous
handicap in terms of number of pixels, images from the
larger format sensors appear to withstand much harder
cropping than those from the 1.6x crop camera. Clearly
the larger, better spaced pixels on the full frame camera
can punch above their weight ! If the full frame camera
had less pixels than the 16.7 Mp of the 1Ds mk II then
it would struggle harder to keep up with the other cameras
here unless the individual pixels were of even higher
This all came as big surprise to me. I firmly believed
that a crop camera would be more beneficial for telephoto
work - such as photographing small birds than a full frame
camera. I would mistakenly remove my 1Dmk III from my
500mm lens and put on the 40D if I wanted to get a bit
more "pull". It appears from these experiments,
that I would not get any benefit from doing this. To fill
the frame more, it is necessary to either change to a
longer lens, get a bit closer (not always possible) or
add a teleconverter. Doubtless this will change as technology
improves and I expect high-density crop sensors will soon
be able to match the quality of today's full frame sensors.
In turn the megapixel race will also continue on the large
sensors too and these will probably hold massive amounts
of small pixels packed onto the larger surface area.
TEST 1 CONTINUED
The results from test 1 were very surprising. The crop
camera should have a big advantage in this test as in
theory it puts far more pixels on the target area. I therefore
set up another test to challenge my findings. This time
I enlisted the services of my co-operative chimp. Here
he is taking it easy on the garden furniture..
starting image taken with the 1DsII
This and all the test images was taken using the Canon
400mm f5.6 L lens, tripod mounted, using mirror lock-up
and cable release. ISO 200, Aperture fixed at f8, shutter
speed set by camera to around 1/250 sec. Images shot in
RAW and individually matched for white balance etc in
|1Ds mk II 100% crop at original size
40D 100% crop at original size
1Ds mk II 100% crop interpolated to match 40D size
40D 100% crop interpolated to match 1Ds mkII size
CONCLUSIONS FROM THE REPEATED TEST
If you compare the 100% crops at the original size, the
40D has produced a larger image because of the greater
number of the pixels on the area covering the chimp (as
it has a 30% higher pixel density than the 1DsII ). On
paper this should mean that the 40D has a big 30% pixel
advantage and should beat the 1Ds mk II easily if sheer
number of pixels is all that matters.
I find it difficult to compare the images from the two
cameras because of this size difference. In some ways
the 40D image looks a little better than the 1DsII image
- but is it more impressive simply due to it's size alone
- or is there actually more detail present ? If you look
at the fur in the area between the eyes and the brow of
the chimp, I think I can see more detail in the fur on
the smaller 1Dsmk II image. If you compare the nose, I
think there is a tiny bit more detail in the 40D image.
In the last two size-matched images above, I matched them
again (as before in the first experiment) by interpolating
up or down as appropriate to the mid point so both cameras
will be equally disadvantaged. To differentiate them is
really splitting hairs and pixel-peeping at the extreme.
I would be happy to call this a draw again, but if you
put a gun to my head and forced me to say which image
is best, I would have to say that the 40D just has
it. If I had to put a value on it I would say it is about
2% better - whereas the 40D should have a 30% advantage
with all those extra pixels.
So, if you were in the field and you saw a bird that
was a bit small in the frame, should you put down your
1DsII full frame camera and swap to a 40D for extra reach
? I would say not -
although this goes against the theory and also some other
tests that I have seen on other websites. The full frame
camera's individual pixels must make up in quality for
what they lack in quantity (on target not in camera base
megapixels). What would the story be with the 1Dmk III
? From the first experiment with the butterflies, I would
suggest that it can still hold it's own OK.
Finally what about the 5D full frame camera ? It is a
better match to the 40D in base megapixels (see the
table again), but it has a very low pixel density
(50% lower), however it also has a very high per-pixel
quality. I can't answer that question as I don't own a
5D, but I've got a feeling that it might be a very close
call once again.
Things should swing into the full frame 1Ds mkII's favour
when you can get closer to the subject. and put all of
it's 16.7 Megapixels on the subject. To find out if it
does, you will need to read part
two of this tutorial.