Digital cameras forum: Confusion over digital camera megapixels

Megapixels are figured up by multiplying the horizontal resolution by the vertical resolution. This will give you the number of pixels in an image. Megapixels are one million pixels.

Sensor size doesn't have as much bearing on the final print, until you go really large and with a lot of megapixels. The larger the sensor, the shallower depth of field and the pixel density on the sensor is usually lower.

What you are able to print with what megapixel is not set in stone, but there are graphs that show what size of print you can make with different megapixels. Here's one for you.

http://www.lesjones.com/2008/07/15/megapixels-vs-print-size/

Now on the flip side, we have had quasi studies done to show that a 5MP and 13MP printed to 16x20 are indiscernible. Here was the article called, "Breaking the Myth of Megapixels".

http://www.nytimes.com/2007/02/08/technology/08pogue.html

Take the info how you like it, but for me, I don't need more than 8MP because I don't crop much at all.

You read my posting right, but the original question had nothing to do with depth of field or high ISO/low noise. You made an argument about something that was never asked. I'd put up a Canon G11 print against many DSLRs at 10MP when printed at A4 size.

I shoot with a 30D and know the advantages of a larger sensor for DOF and high ISO, but that's not what this thread was about. It's about megapixels and print output. And, I did add in the DOF and pixel density of the larger sensors when I wrote it. I've printed 8x10s with my old Canon G2 that matched the quality of my 30D shots printed at 8x10, and that's a 4MP point and shoot compared to a 8MP DSLR. If were talking above A4 size prints then I would say a high MP Medium format camera is the best choice....but do you have $30,000?

Read the original question again and you'll understand my answer.

S

but, I just added the DOF and pixel density as the reason why people choose large sensors, not because of making large prints.

First of all, thank you for explaining that Depth of Field (DOF) is a function of the lens, NOT the size of the sensor. Second, I'm surprised that no one has mentioned that pixel density is directly correlated to light sensitivity. In other words, the more densely packed the pixels are on the chip, the less sensitive it is to light; this is why the sensors with the highest number of pixels are on larger chips - the larger chip reduces pixel density, which improves light sensitivity (especially valuable in low-light situations, where the camera must activate it's on-board gain stage in order to boost the brightness of the image). The problem with gain stages, of course, is that they all have their own characteristic noise signature, which results in a "grainier" picture (but it's not grain as with film, it's noise!). In my experience, for most casual users a 5 - 7 MP pickup is plenty of resolution; I would offer the advice that a camera that is easy to use and has a good lens is a better value than a more expensive camera with more pixels that is either difficult to operate and/or has a mediocre lens. I sold Canon cameras for years, and I think that the price/performance value is among the best you can find. I also think they are one of the most intuitive cameras to use. I still use my Leica for "real" photography, but love my little Digital Elph for point-and-shoot snapshots of friends and family (and the occasional "art" shot when I'm not packing my Leica, 'cause the Canon will fit in my pocket and it's always with me and ready to go - hauling the Leica around like I do the Canon would be impossible!).

The Canon 7D is now being considered the crop sensor high ISO/low noise champion, and it has more megapixels than any other crop sensor in history. It definitely makes a difference in small sensors, but DSLR sensors are able to do pixel binning and sharing information between pixels to get farther.

It's not as simple anymore of more MP will equate to grainy photos. I think we have hit and surpassed the MP limit in compact cameras, and now were seeing some cameras go backwards.

A 6 megapixel camera will take nice photos and you can blow them up to 8X10 with no loss of picture quality. The reson I like the 10 or larger megapixel is that I rare print a photo without croping. If you crop 20% of the photo taken on a 6 megapixel camera and and blow it up to 8X10 you will notice some loss of picture quality. That is why I go for the larger megapixel camera. I am not a professional photographer and do not know about noise and DOP issues that are discussed.

...Just kidding But I have a weird one. I have this old Sony Cyber-shot 3.2MP that's works just incredible. Big downside, it's so old, it can't use today's mega-sized memory sticks. It's stuck with it's old original default size and you can only get about 80, (+/-10), fully high resolution max size/quality shots saved on each stick. And finding those sticks is becomming more difficult. Fortuntely, I have a couple so I can still go crazy when I'm on vacation and every one of them can be blown up to a beautiful 8X10.

It connects to the PC via the old original USB which isn't that fast, takes almost a minute to download a couple dozen pictures. The darn thing had so many negative reviews that I don't think they sold that many. But if you get your hands on a good one, you'll never need anything else!

Helpful info from an enthusiast--or possible expert--who clearly understands the subject AND has communication skills! Unheard of!

How does one find out the sensor size of a given digital camera when shopping??

Thanks for the print size chart. Does this apply to projection on a wall/screen with a data projector?

Most people get caught up in the pixel wars pretty much started and continued on by the marketing folks at Canon and Sony. For the most part, for most people taking nothing more than snapshots of the family a camera with two or three megapixels work just fine. That's right, three megapixels. DON'T FORGET MEMORY! My guess the person that used their photo's in a PowerPoint presentation with their 5 MP camera, took the photos at a greatly reduced image size, and probably with a lot of compression!

Memory is really CHEAP today, so buy a large card(s), and use the very best quality (lowest compression)and all the pixels your camera has. If you're HD television is a 720P set, it may have less than 1 million pixels, and as such, can't display the full quality of your photos!

Key things to look for -
Glass - If you have a bad lens, not much else matters!
Sensor size - SLR or look for one of the new compact cameras now shipping with an APS - C or larger sensor if you can afford to do so.
Lots of Memory - with Highest and Largest size your camera will take ( especially important if you're not sure what you're going to do with the image.
Think before you shoot! - Fill the viewfinder with your subject - Cropping = Lower Resolution / Quality!

Kalel33 wrote: "Sensor size doesn't have as much bearing on the final print, until you go really large and with a lot of megapixels. The larger the sensor, the shallower depth of field and the pixel density on the sensor is usually lower."

I just want to clarify that you're not writing about sensor size as measured in megapixels. You're writing about sensor size as measured in inches/millimeters/whatever. Though there is a relationship between physical size and megapixel size, that's not exactly what the original question was about. But, to further explain, the loss of depth of field when using a physically larger sensor (in inches, not megapixels) is because of the multiplication factor of lenses to accommodate for the different sensor size. If you want to take the same picture with two different size sensors, one a "full size", one requiring a 1.6x multiplication factor, then you'll need to use a longer focal length lens on the larger sensor. This longer lens is what causes the loss of depth of field.

Also, regarding larger megapixel sensors having more noise: It would be a mistake to try to compare camera noise levels based on their sensor size. There are a number of other factors that contribute to this. If camera noise is critical to the purchaser, better to compare test data directly and not try to use sensor size as a proxy it.

Finally: What most point and shoot snapshooters need to know about sensor size is bigger can be better--to a point. This is because most point and shoot snapshooters are terrible photographers. The single, biggest improvement that most can make to their work is to get closer. Since most have poor habits and shoot from too far away, better to have a too larger sensor, then to use cropping on the computer to make up for poor technique on the site (and, please be aware that a photo of an object taken with a telephoto (which is essentially what one does when they digitally crop in the camera [never do this!!!] or on the computer), and a photo of the same object taken by stepping closer to it are two entirely different pictures. Understanding this most basic fact of photography is one of a number of things that differentiates competent amateurs/professionals from the typical snapshooter.

--mark d.
http://www.summitpost.org/user_page.php?user_id=26307

Yes, if you multiply the horizontal x vertical number of pixels you get the megapixel number. How do you do the math in reverse? How do you get the horizontal x vertical number of pixels from say an 8 megapixel measurement?

The number of MP absolutely does not affect Depth of field!. Depth of field is controlled by the size of an image element, and F-Stop.

In addition, the depth of field is tied in closely with a phenomenon known as circles of confusion. Which is aptly named, but can be simplified by knowing that an image is critically sharp at only one focus point. And as teh image goes further or closer to the camera, it will go out of focus, and what would have been a point, is now a circle, which gets larger as the image moves away from the critical focus point.

The F Stop will tend to make these circles of confusion smaller ass the lens is stepped down, continuing to decrease in size. When the diffraction limit of the lens is reached, the image will start to display a general unsharpness. This usually happens around 1 f-stop from maximum, but varies by lens.

Megapixels do start to have less effect as they increase.

(I'm going to try this without math, or at least just simple math.

While a 2 megapixel image is a big increase over a 1 MP image, If we have say a 10 MP image versus a 12 MP image, there will hardly be any increase in quality at all.

If we're looking at 300 dpi images, that 12 MP image is only going to be around a 1/4 inch or so bigger - the exact number depends on the aspect ratio of the sensor.

The megapixel quote is the total number of pixels the camera's sensor has. Compact cameras have very small sensors while digital SLR's have much larger sensors. In most cases, the larger the individual pixel, the lower the noise in the resultant image will be. Noise becomes more apparent when you blow up images

A 10 megapixel compact camera (with a very small sensor) can have a poorer resulting image than a 6 megapixel digital SLR with a much larger sensor, especially in low light.

You have to read the reviews carefully to get a camera that meets your needs.