Digital megapixels vs DSLR lenses

[Skippy2525]

I recently received a SX730 HS Powershot hand held digital camera from my family.  I've been "playing with it" and am impressed with how close I can zoom in to a subject that's across our yard or the field next door.  According to the information on the camera, it has a 20.3 megapixel lens. 

I know that DSLR lenses have mm and f stop ratings.  Does anyone know if you can compare a 20.3 megapixel lens to a DSLR lens?  If so, how would you calculate that?

Thanks!

[Waddizzle · Accepted solution]

First, and foremost, lenses do not have a megapixel specification.  Image sensors are rated in megapixels.  Also, the number of megapixels is not as important as the size and type of the individual pixel sites.  

The bigger the pixel, the more light it can absorb, which directly translates into more detail and contrast.  The size of the image sensor is one of the primary differences between your camera and a DSLR.  

Another significant difference is the lens itself.  Because of the smaller size of the image sensor, the range of DOF, depth of field, you get will naturally be quite deep.  So, the lens does not need as wide of range of aperture values, which also makes the lens less expensive to manufacture.  DOF is what makes for a blurry background in a portrait shot.

[Waddizzle · Accepted solution]

First, and foremost, lenses do not have a megapixel specification.  Image sensors are rated in megapixels.  Also, the number of megapixels is not as important as the size and type of the individual pixel sites.  

The bigger the pixel, the more light it can absorb, which directly translates into more detail and contrast.  The size of the image sensor is one of the primary differences between your camera and a DSLR.  

Another significant difference is the lens itself.  Because of the smaller size of the image sensor, the range of DOF, depth of field, you get will naturally be quite deep.  So, the lens does not need as wide of range of aperture values, which also makes the lens less expensive to manufacture.  DOF is what makes for a blurry background in a portrait shot.

[kvbarkley · Accepted solution]

Your lens is a 40X with a Full Frame equivalent of  24 mm to 960mm. (Be careful, it also has a digital zoom which simply crops to a smaller area on the sensor.

960 is a really long telephoto and you would be hard pressed to get an equivalent on an APS-C or Full Frame DSLR.

That being said, your sensor is *tiny* you are cramming 20 MPixels into a very tiny area. A DSLR will have a much larger sensor with better noise and low light performance.

[Skippy2525]

Thank you both for your information.  I appreciate you taking the time to reply.  What you've said makes perfect sense and satisfied my curiosity. 

Again, thank you!

[amfoto1]

Previous responses are correct.

Cameras like yours use a very small sensor so that their lens "acts like" something much more powerful.

The ACTUAL focal lengths and aperture of your camera's zoom lens are 4.3mm - 172 mm,  f/3.3-6.9 (this may be marked on the lens somewhere).

Because this type of camera use a variety of different size sensor, manufacturers usually market them using "35mm/full frame digital equivalent focal lengths", to be able to compare one camera to another (and to DSLRs or others).

Your camera uses a pretty tiny, so-called 1/2.3" sensor which gives EQUIVALENT focal length of "24mm-960mm".

There's some slight variation among 1/2.3" sensors, but the dimensions of it are about 6.4mm x 4.8mm, giving about 30.7 square mm total area. A camera with 20 million pixels and this size sensor has roughly 650,000 individual pixel sites per square mm.

In comparison, a Canon "APS-C/crop sensor" DSLR uses a sensor with actual dimensions of 22.3mm x 14.9mm, giving 332 square mm. As a result a 20MP DSLR using this sensor (such as a 7D Mark II or 70D) has about 60,000 individual pixel sites per square mm.

Or, a Canon "full frame" DSLR uses a sensor with actual dimensions of 36mm x 24mm, to have an area of 864 square mm and the same 20MP camera (i.e., the original Canon 6D) has roughly 23,000 individual pixel sites per square mm.

So you can see, the APS-C/crop camera's sensor is approx 3X "more crowded" than the full frame camera's.... And in comparison your camera's 1/2.3" sensor is about 10X more crowded than the APS-C... or it's almost 30X more crowded than the full frame camera's.

Because camera's individual pixel sites have to be much smaller and much more closely packed into that small sensor,  they aren't as good gathering light, are more prone to heat gain and are more likely to produce cross talk between adjacent sites. All these factors effect image quality.... significantly limiting the high ISO (sensitivity) settings possible before image "noise" becomes a problem and effecting how much fine detail is captures. Of course, the trade off is that that lens acts much more powerfully on your camera, than it would on either of the DSLRs with their larger sensors. To have similar "reach" as your camera, they need to use much, much bigger and heavier, and far more expensive super telephotos.

Although it has a selectable ISO range from 100 to 3200,  I would guess you will find images from your camera much over ISO 400 or 800 have a lot of noise. In comparison, the original Canon 6D was commonly called the "low light king" in its day, with an ISO range settable from 50 to 102400, and I know folks used them as high as 12800 and even 25600 with acceptable results. This simply means that a 6D user can keep shooting in much lower light conditions than you're able to. However, to enjoy the same telephoto power that you have in your 10 oz. camera, the 6D user would need to lug around approx. 10 lb. camera, lens and teleconverter that cost upwards of $10,000 (plus a sturdy tripod to sit it all on)!

It's actually quite amazing what's possible these days. Digital cameras have come a long, long way in a relatively short time and are doing things that were unheard of just a few years ago. The lenses developed for use on them are equally impressive. It has some limitations, but the capabilities of a compact, lightweight, pocketable camera like the SX730 are actually pretty incredible. Have fun with it!

***********

Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & ZENFOLIO 

[Waddizzle]

“So you can see, the APS-C/crop camera's sensor is approx 3X "more crowded" than the full frame camera's.... And in comparison your camera's 1/2.3" sensor is about 10X more crowded than the APS-C... or it's almost 30X more crowded than the full frame camera's.

Because camera's individual pixel sites have to be much smaller and much more closely packed into that small sensor,  they aren't as good gathering light, are more prone to heat gain and are more likely to produce cross talk between adjacent sites. All these factors effect image quality.... significantly limiting the high ISO (sensitivity) settings possible before image "noise" becomes a problem and effecting how much fine detail is captures. "

I am going to have beg to differ.  Closely packed photo sites is a good thing.

A good analogy of an image sensor is cupcake tin.  But, imagine a cupcake tin with millions of cups arranged on a very small cupcake pan. Light falling onto the image sensor can be compared to rainfall.  How intense the rain is, and how long it rains, will determine how much rain will be collected in each cup.

How much rain collected in each cup can be measured just like the weatherman measures rainfall.  Let’s say one quarter inche of rain fell.  The small 1/2.3” sensor and a full frame sensor will both collect one quarter inch of rain fall.  The full frame sensor will collect a greater volume of rain because it is a larger size, [a larger diameter].  This greater volume of light that the larger sensor collects directly translates into more detail and dynamic range.

But, a real cupcake tin has space between the cups.  An image sensor has space between its’ photo sites.  When rain falls on the cupcake tin between the cups, that rain goes to waste, and the same happens to an image sensor.  Light that falls between photo sites is lost, which means less detail.

Being able to pack photo sites more closely together means less loss of light, which means more details in the image.  So, being able to pack large photo sites closely together is a GOOD thing, a very good thing.