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Does sensor size matter? YES!
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Does sensor size matter? YES!

Full Frame? Micro Four Thirds? APS? Here's a guide to how sensor size affects image quality.

The size of a camera’s sensor can directly affect image quality, especially when you’re shooting above ISO 100. Here’s what you should know when you’re shopping for a new digital camera

 


 

This scenario has repeated itself numerous times over the last couple of years. “Last year for the holidays, I got this 12MP camera that fits in my pocket,” a friend would say. “And I thought that because it has so many megapixels, the images would be amazing. But I’ve been disappointed with it. Why are my pictures coming out so bad?”

Usually, I discover that the 12MP pocket camera has a sensor that is roughly the size of a pinkie nail, and that’s the source of the problem.

Destroying the resolution myth

There are three factors that work together determine image quality: Resolution, sensor size, and ISO. (Some cameras may have built-in noise reduction firmware, which can modify grain, but that’s usually at the price of some image sharpness.) The problem comes when we want it all: We demand ultra-sharp images in pocket-sized cameras and expect that the higher the resolution, the better our chances are for sharp, clear pictures.

But the opposite is true.

Here’s what happens when your camera has a really tiny sensor with a high pixel count:

1.    The individual pixels have to be made smaller. A sensor is made up of many tiny receptors, called pixels, which record light. The larger these sensors are, the more sensitive to light they are, and that benefits image quality. A “pixel pitch” of 6-8 microns is very good. But a typical compact camera’s pixel pitch is going to be less than 2 microns. In some cases, much less.
2.    Deviated septums. On a larger sensor, each pixel is separated by a septum to prevent light from falling off from one pixel to its neighbor. Smaller sensors lack these septums and as a result, light spills across sensors, causing a kind of internal flare and reducing overall image contrast.
3.    Making a lot of noise. To make up for the small pixel size, camera makers boost the gain in trying to capture a usable image, but this results in what we call digital noise, on photos especially in low light or shadowy areas. The graininess gets worse as ISO is increased.

So, class, what have we learned here? Small sensors in small cameras are bad for image quality, especially at high ISO, no matter what the camera’s resolution is.

Geeking out and pixel peeping

In fact, according to independent tests, it has been determined that the ideal sensor resolution for low-noise 8x10 prints using a compact digital cameras is only 6 megapixels, and that overall image quality deteriorates when using more than that!

But it’s not so straightforward. To accommodate larger sensors, you need a larger camera, and many people like having little cameras that they can slip into their pockets. What to do?

Compromise, but know what each compromise brings. Let’s break down the different sensor sizes and what each means in terms of image quality and camera size.

I’ve put together a chart that might help you to better visualize and decide. Recommendations are based on cameras with 10MP resolution, which is average for compact cameras these days.


Format

Sensor size

Pixel Pitch (10MP)

Camera description

Max. ISO*

1/2.5”

5.76x4.29mm

<1 micron

Camera Phone

None

1/1.8”

7.18x3.2mm

1.4 microns

Pocket camera, internal zoom

100

1/1.7”

7.6x5.7mm

1.7 microns

Compact camera, zoom

100-200

Four Thirds

17.3x13mm

4.8 microns

Interchangeable lens DSLR or compact

320-800

APS-C

22.2x14.8-23.6x15.7mm

5.7 microns

Consumer/Hobyist DSLR

400-800

APS-H

28.7x19mm

6.3 microns

Prosumer DSLR

800-1200

Full Frame

36x24mm

8.4 microns

Pro DSLR or Rangefinder

1000-3200


*Max. ISO is the highest ISO setting that I recommend using, based on typical signal-noise ratio and dynamic range sensitivity as tested by DxOMark. I provide a range for most sensors because the pixel count affects this number.

Still confused? Here’s a more visual comparison of different sensor sizes that breaks it down even further, courtesy of Wikipedia (note actual sensor sizes are smaller than they may appear on screen).


 

Lower-resolution cameras will be able to produce usable images at slightly higher ISOs. Higher-resolution cameras may not deliver usable pictures even at the recommended Max. ISO.

On the other hand, with the exception of camera phones (which generally will always produce poor quality images), if you stick to your compact camera’s minimum ISO, you should be able to get excellent results and prints you should be very happy with.

Price, compact cameras, and image quality

No matter how much a compact digital camera costs, the laws of physics still apply, and image quality won’t change with the price unless the camera has an oversized sensor, which is very rare. (The Sigma DP1 and DP2, with their APS-sized sensors, are notable exceptions.) Generally, the cost of a compact

Moving Down The  Digital Camera Food Chain

Let’s break it down. Here’s the digital camera image food chain, as I see it:

Camera Phones: Photographically speaking, they’re bottom feeders, marginally OK for online photo sharing on Facebook and other social networking sites if shooting in bright daylight. Don’t use them in low light or if you plan to make prints. (They’re great for texting and making phone calls, though!)

 

 

 

 

Pocket digicams (lens zooms internally): Better than cell phones, capable of producing very nice 4x6-inch prints at lowest ISO setting, and super-convenient. But don’t expect much beyond snapshot quality at ISO 200, and by ISO 400, you can look forward to a grainy mess.

 

 

 

 
Compact digicams (external zoom lens, too big for shirt pocket): Can produce 8x10 or even 11x14 images with decent quality at lowest ISO, but don’t go beyond 4x6 inch prints when shooting at ISO 400 or higher.

 

 

 

 

Four Thirds System (DSLRs and interchangeable-lens compacts): A vast improvement over compacts. You should be able to get stunning 8x10s at ISO 100 and 200, passable  prints at ISO 400. Apply noise reduction at ISO 400-800, don’t bother with higher speeds except in emergencies.

 

 

 

Consumer DSLRs: Should deliver excellent print quality even at ISO 400, although you’ll see a bit of grain at ISO 800. At ISO 1600 you should be able to produce decent smaller prints, although some newer prosumer-level cameras have improved to the point where, even at 1600-2000, you’ll get publishable images.

 

 

 

 

Pro DSLRs: The Big Fish. Full-frame sensors will deliver outstanding image quality at almost all speeds, including ISO 1600. While older models may crap out at ISO 3200, newer caneras can deliver publishable (if noticeably grainy) shots at ISO 6400 and even at ISO 12,800! Of course, you pay a premium in size, weight, and cost to get to this level of quality.

 

Most compact cameras only capture JPEG image files and automatically apply some form of noise reduction, but this often means the overall image is softened to make the noise seem less apparent. This firmware fix is constantly being refined; some cameras will selectively reduce noise in the darker areas of high-speed pictures while leaving the highlights (where grain is generally less noticeable) alone.

Recent advances in sensor design are expected to improve high-ISO performance, although right now only a handful of pro-level cameras, such as the Nikon D3s, Canon EOS-1 Mark IV, and Canon 7D, have produced truly high-quality high-ISO results; cameras with smaller sensors are still using older technology.

So now you know what to expect, no matter what camera you buy. Check out our guides to the best budget compacts, fashion compacts, system compacts, starter DSLRs and mid-range DSLRs. I hope these articles and the knowledge you got reading this one will you make a more informed buying decision!

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