Know Your Gear: Digital Sensor Limitations

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"Urban Tunnel" by D. Travis North

Your sensor’s dynamic range cannot handle large difference in light. (Photo credit: D. Travis North

Of all the camera technology that has helped to push the limits of modern photography, none is more inspiring than the digital sensor.  Ten years ago, digital sensors capable of producing good quality photos weren’t even commonplace on the consumer market.  Yet today, even our phones seem to rival the best digital cameras of that era.  Compared to all other camera technology, the digital sensor is still an infant.  As with all infantile technologies, the digital sensor has its own limitations.

This is not a film vs. digital discussion.  I do not want to consider film in any aspect of this article except where its precedent has set certain standards (such as the standard 35mm frame size).  What I do want to consider is how the digital sensor impacts your photo quality:

  • Dynamic Range – Camera technology is incredible, but the best sensors out there still cannot come close to the dynamic range of the human eye.  This means the relative difference between the bright spots and the areas in shadow will appear exaggerated in the photo.  This is why exposure is so important – there is a small viable range for your subject to look good.  You can use this to your advantage as well by hiding things in the shadows or the bright spots.  But it can also be a disadvantage if you want to capture more of the range in a photo.  Take note of the example photo shown herein.  This is not a Photoshop trick, this is the direct result of metering for an area in shadow.  A human eye would easily be able to see all of the color and surfaces in this shot.  The sensor, however, is not able to take in all of that information.
  • Cropped Sensors – Sensors come in different sizes.  A full frame sensor is about the same size as 35mm film but are often costly and available only in larger pro bodies.  Mainstream cameras have cropped sensors, so named because they crop out much of the image circle.  This is referred to as the crop factor. You should research and memorize your crop factor.  Cropped sensors affect your photos in the following ways:
    • Focal Length Multiplier – Since more of the image circle is (for lack of a better term) wasted, the resulting image has the effect of being taken at a longer focal length.  Note that it doesn’t actually zoom further, it just crops out a portion of the angle of view.  The relationship is known as the focal length multiplier and it’s a simple as multiplying your sensor’s crop factor by the focal length.  My sensor has a 1.5 crop factor, which means my 50mm lens acts like a 75mm lens.
    • Lens Options – There are lenses designed specific to cropped sensors and lenses specifically designed for full-framed sensors.  Very often, they cannot be interchangeable.  Even if the lens supports both sensors, it does not come without its own limitations such as vignetting, distortion and decreased sharpness.  In short, your sensor will limit what lenses are available to you.
    • Depth of Field – A full framed sensor will have a much shallower depth of field as compared to a cropped sensor.  For that reason, a full framed sensor may be more ideal for portrait work while a cropped sensor may be more desirable for landscape and other deep depth-of-field work.
    • Pixel Size – What’s the difference between a 12 megapixel full-sized sensor and a 12 megapixel cropped sensor?  The size of the pixels.  The advantage of larger pixels is an improved signal-to-noise ratio and an increased dynamic range.
  • Pixel Depth – The megapixel battle seems to have subsided now that the cameras are all above 10 megapixel.  In all honesty, most of you will not need anything greater than that.  But if you’re printing large format posters, the pixel depth is going to limit how clear your photo will print at such sizes.  As a general rule of thumb, you can print up to a 9”x12” print effectively with 10 megapixels (unprocessed, there are ways to make a print look good at twice that size with only 10 megapixel).  Note that on-screen viewing is much less of a concern with respect to pixel depth.
  • Noise – The new battle among manufacturers is noise with respect to ISO.  In film, the grain sizes was the major factor – the faster the film, the larger the grain and the result was clearly more grainy.  In digital, however, we can change this on the fly by altering the ISO setting of the sensor.  There are a number of contributing factors to noise in a digital photo such as sensor heat build-up and hot pixels and so on.  This is exaggerated with long exposure as well.  Bottom line, there will be a point that your camera’s sensor will look too grainy and un-sharp as a result of a high ISO.  Cameras are improving and that threshold is getting much higher, but it is still a limitation.  You’ll need to be aware of these limitations if you’re shooting in poorly lit areas.

Of course there are other potential limitations that are specific to different formats and configurations.  Please feel free to point these specific limitations, or any other limitations that I might have missed, in the comments below.

 

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About Author

D. Travis North is a professional Landscape Architect, a Freelance Photographer and founder of Shutter Photo. Ever since he picked up his first SLR, his father's Nikon N2000, he's been hooked on photography. Travis likes to photograph urban environments, architectural details and has a new-found interest in close-up photography. His work can be found at D. Travis North Photography. Follow Travis on twitter: @dtnorth.

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