How many megapixels

[derbu]

I have the Cybershot DSC-W7 with 7.2 megapixels. A friend recently told me that after 5 megapixels (roughly) there is no change in the quality of the image since it is just the size that changes.
I bought this camera in order to have as more megapixels as possible. I also read somewhere that with around 11 megapixels or more digital camera quality is going to be the same as old cameras with films.
Which is true?

[bytethis]

G'day derbu. Welcome to Byte

There's several things to consider here.

Firstly, it's not all about megapixels...yes increasing the megapixel count has a direct relevance on image quality and also resulting print quality.

All you have to do is look at the major brands like Nikon and Canon to see that the highest level of digital SLR they have currently is in excess of 13 mp.

What it will come down to, in essence, is the quality and mp count of the sensor, but primarily the optics (lenses) that are between the sensor and the subject, and indeed the sensor size itself. The sensor in a digicam is the same as what would be behind the lens of a film cam, and technically, the bigger the better...put it this way...you don't see any compact film cams using a film size of less than 35mm...

With smaller (compact) cams, to keep them small, there is a compromise on lens and sensor size, thus directly affecting the amount of light, size of image and quality of image landing on the (often) much smaller sensor. This is why you see wide lenses and lots of glass on dslr lenses.

So your friend may be fairly correct that there's no point really buiding a compact or phone cam that has 12mp on it if the lens is only 1/2 inch across. It can't 'see' or record an image the way a film or slr cam can.

Ultimately, for the last 200 years or so, 35mm film has been the standard (not counting medium format cameras which are primarily desgined for professional magazine quality print and billboard type sizes) So dslrs have tried to get close to this size in sensor to provide professional photographers the convenience of digital with the quality of film.

Canon got there with their top of the line 1ds mkII thing which is 16mp - so their cam is known as a 'full frame' camera, which in other words means the sensor is the same size as a 35mm film frame, Nikon has a 13mp which is not quite the same size as film and etc...

Where your friend is incorrect is their reference to there's no change in quality beyond 5mp...in fact Phase One and Hasselblad both have cameras (medium format) which are in excess of 22mp and up to 39mp. Meaning the sensor is huge and approaches the size of medium format film.

In fact, there are reports that suggest that to get the same results and extremely fine detail of professional film you'd need to have a sensor with around 80+mp on it.

With current prices of film equivalent dslrs reaching in excess of AU$13,000 and medium format around AU$30,000 then a 80mp cam would be closer to +$100,000... plus lenses, digital memory and batteries of course...

So it's all relevant...size does matter lol...where your 7mp comes into play, is that it should take great pics and print possibly beyond A3 size...

To further clarify your last point, if you have in excess of say 7mp for your sensor and lens size (in other words non SLR), then no, you'd not really see any appreciable difference as you'd have to increase your sensor and lens size to record the extra detail.

Hope that helps some.

[derbu]

Thanks for the great reply and analysis. The question is the following:
I am nor printing in A3 not even in A4. I am just printing normal photos as with my film camera. Is it the same quality if I sell my 7.2 megapixel and buy a 5.1 megapixel?

[pip22]

For normal 4 x 6-inch prints then, yes, a 5Mp camera will give you as good results as bigger prints from a 7Mp camera, assuming all other important components were of equal quality such as the lens etc. But If I could afford a 7Mp one I would still buy it instead of a 5Mp one (I have just done that in fact) because you never know when you might need those extra pixels to make big enlargements of those really special pictures. A 7Mp camera gives you the option of 'turning it down' to 5Mp if that's all you need for a particular project, but a 5Mp camera cannot be 'turned up' to 7Mp. You shoot everything now at 7Mp even though you think it's too much for small prints --- BUT , you might want to 'crop' an image on your PC to bring the subject closer, but without reducing the overall finished size. Unless you have plenty of pixels in the original, quality will suffer when you crop and resize because you won't be able to maintain the ideal resolution of 250-300 pixels-per-inch for printing. Megapixels aren't everything, it's true, but a higher pixel-count does give you more freedom to resize and crop in photo-editing software without losing quality.