DSLR Cameras – Megapixel vs Sensor Size

3 min

CCD SensorIn the DSLR camera marketplace you’re always hearing the terms megapixel and sensor size.  Whether you’re looking at Canon, Sony, Pentax or Nikon – the marketing numbers are always used.  In this video, I want to break down exactly what those numbers mean and allow you to get a better understanding of what it is you’re buying.

Nikon has now come out with a camera that has a sensor on board that currently no manufacturer has surpassed in the same category.  The Nikon D800 boasts a 36 megapixel full frame sensor, which their marketing material states, has 36.3 effective megapixels. 


For years now it’s been a battle of the megapixel – who could cram more pixels into a smaller camera.  Smart phones today come out with as many megapixels as DSLR cameras had just a short while ago.  And these added megapixels have just added to the confusion.


People began to think that their smartphones or small compact cameras should be able to give the same kind of resolution that much more expensive DSLR cameras could.


I’m here to tell you that megapixels are not the #1 determining factor, to consider, when it comes to camera resolution quality – instead you should be looking at the camera’s sensor size.


Sensors fall into one of two categories: CCD or CMOS.  The CCD sensor is slightly smaller and is what you will find in most compact cameras and many DSLR’s as well.  The CMOS, which is in the Nikon D800, is larger and therefore has more surface area to capture light.


A cameras sensor is where the ‘rubber meets the road’ (to mix my metaphors) or rather where the light carrying the image signal is deposited.  Think of the camera sensor as a bucket catching rain.  Obviously the bigger the bucket – the more rain the bucket can catch.  It works exactly the same way when it comes to the light traveling through your camera lens.


Nikon_D800_CameraThe Nikon D800 has an impressive 36mm by 24mm sensor.  In camera terminology this is known as a full frame sensor.  It is given this full frame designation because it is approximately the same size as 35mm film that was used in film SLR cameras many years ago.


Many of the competing DSLR cameras on the market have a cropped sensor or aka APSC sensor, which is typically 23mm x 15mm – quite a bit smaller.


The D800 not only has a full frame sensor, but Nikon states that it has over 36 million pixels on that sensor.  I want to clarify exactly what this pixel term means.


Camera manufactures often throw out misleading terms like the number of pixels on their camera sensor.  In actual fact a pixel is at the viewing end of an image, or what you look at when you view a monitor.  The sensor’s catching surface is actually made up of numerous photosites.


This is where the light information coming thru the camera lens ends up being received. The photosites are broken up into groups, of red, green and blue. 


An 8 megapixel camera would actually receive light on 2 million blue photosites, 2 million red photosites and 4 million green photosites.  Collectively they would produce an 8 million pixel image to be viewed on a monitor.


So when you hear the term pixel you should really be thinking photosite.


I know it’s a bit confusing.


If you have a smaller point-and-shoot type camera with its smaller image sensor, each photosite would, in turn, be much smaller than the photosites on a larger DSLR camera with the same number of megapixels.


Another thing to consider is that there is a limit to the resolution you can receive on your DSLR sensor, and that limit is set by the aperture opening on your lens.  An f-stop of 1.8 is going to allow more light to be captured by your cameras’ photosites than, say, an f-stop of f4 or f5.6. (Remember the smaller the number the larger the aperture opening).


Allowing more light into the camera will also give you a higher signal-to-noise ratio or, put another way, more information spread out over the photosites.


Allow me to share something with you that will help emphasis my point.


A photographer friend of mine shared this story, regarding of the power this new Nikon D800 sensor. He was snapping off shots of the kids playing off in the distance outdoors.  He paused to share some of the shots with his wife.  She commented that she hadn’t noticed that there was a helicopter in the background.  My friend then zoomed in on the image he had taken – only to realize what they thought was a helicopter in the background was actually a bee flying by.


Now that’s a sensor that gives a LOT of resolution.


I hope I’ve helped to clarify the sensor size issue a bit – as I said earlier size does matter.  But it is important to realize that these things are never completely black and white.  When you’re doing a DSLR camera comparison, there are multiple variables like length of lens, aperture opening and number of photosites which will all have an impact on the final quality of your picture or video.


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Rick Davis


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