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Old Jul 10, 2003, 8:46 PM   #1
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Default The law of diminishing returns.

I read a post by someone a few days ago that said that 3mp is the most bang for your buck because the pixel length and width don't increase that much when you get to 4mp. I decided to do the math, and boy, was he right!

I originally did the calculations from a Canon S45, A70 and a Fuji A201, but found that they were inaccurate due to the S45 being a 3.87mp, not a 4.0, the A70 being 3.2, and the Fuji A 201 to be a 1.92mp.

So I used the pure sizes of 4mp, 3mp and 2mp instead. I ended up doing the math on Exel (If anyone wants a copy, just e-mail me). What I found was that the law of diminishing returns is a strong factor that everone should consider when purchasing a digital camera.

But wait, a 3mp is 50% more pixels than a 2mp right? Isn't this all simple math? Well it's not all that simple. The key number everyone should know is PPI. This means "Pixels Per Inch." It is the only number you should be worried about when printing your photos. And guess what? A 3mp camera has 22.5% more PPI than a 2mp camera, NOT 50%! Take that one step further. A 4mp camera only has 15.5% more PPI than a 3mp camera!

Now here is why this is something that everyone should consider. I think most people will agree that the average camera is running about $100 a megapixel, maybe a little less. What I am getting at is that you may pay 50-150$ more to go up from a 3mp to a 4mp, yet only get 15.5% more PPI! That's an increase in cost of about 30% for only half the increase in PPI.

There are some nice advantages to this though. If you were trying to decide between the Canon A60 and A70 for example (2mp vs 3.2mp), the is a good price advantage to the A70. The a A70 is 20% more $ than the A60, yet the A70 has 26.5% more PPI than the A 60.

In conclusion, I believe that in advancing from a 2mp camera to a 3mp camera gives you far more print quailty for the money than advancing from a 3mp camera to a 4mp camera.

Dan O.
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Old Jul 10, 2003, 9:29 PM   #2
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Funny hting is, i knew all of that without doing the maths. Great to see the nyumbers htough, thanks a million. I personally think 3MPO is the best value on the market unless you want to print big, big prints over 8x10 ... certainly 5x7 and below the 3mp is the best value.
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Old Jul 11, 2003, 1:33 AM   #3
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Well, that may be true, but percentages don't factor in necessity. If I for some reason need or want to crop an image and still get great 8x10s, a 3 megapixel will not get the job done. Therefore the money wasted is 100% of the purchase price of the 3mp camera, because for cropping 8x10s or larger prints, 3mp is pretty much worthless. Also, it is unfair to compare some cameras based solely on mp. The 4mp camera may be 100 more, but it may give more manual control, have a better lense, produce clearer sharper images, etc.
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Old Jul 11, 2003, 6:44 AM   #4
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&lt;<If I for some reason need or want to crop an image and still get great 8x10s, a 3 megapixel will not get the job done.>>

Depends on how much you need to crop. A pure 3mp image is 2000x1500 pixels. Already there is a 125 pixel crop in length inherent in creating an 8x10. Further more, most people will agree that a 150ppi image yeilds a good quality image. at 1500 pixels one gets 188ppi. This means you can crop down to 1200 pixels and still retain a good image quality. In my opinion, 300 pixels off the width and 500 pixels off the length is a good size crop, without the loss in quality.

You may say that buying a camera according to mp is inaccurate, and I agree fully. I also belive that resolution should be one of the last things one should consider if they only make 4x6's and 5x7's.

My point was that a 3mp camera is the most bang for your buck. When doing any scientific study it is neccessary to eliminate all variables, and optics and features are all variables.

Further more, one can not deny that the primary cost factor in most cameras is the resolution. Why else does Canon create two completely idendical cameras with different resolutions? The answer is they wanted one to cost $100 less.

Just my $.02
Dan O.
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Old Jul 11, 2003, 8:14 AM   #5
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Exactly ..... other features and the lens aree things you never mentioned, so they are not part of this discussion. Fact is, consumers are obsessed with megapixels because it is an easy variable to compare ... and the camera makers know that.
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Old Jul 11, 2003, 12:18 PM   #6
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Yeah, part of my point is that I would never buy a 4mp camera because it is 4mp. Rather, buy a less expensive 3mp camera with more features.

I really think that the 3.2mp Canon A70 is optimial. I just bought one at about 6:00 this morning. It's not really 3.2mp though. Rather, it's 3.15mp. The same thing applies to most of the 4mp cameras out there. The Canon S45 is only 3.87mp! I guess people love to round up. There really isn't that much difference between the two. The S45 is built a little better. It rotates the veiw of the image, and it takes time lapse photos. It uses the Type 2 compact flash card and displays the histogram. There are a few more things, but most of them are minor. The key thing that keeps it about $150-200 more than the A70 is the "4mp." The A70 even has advantages over the S45! These include a faster shutter speed (1/2000 vs 1/1500), VGA video, and the non-proprietary AA batteries. Yet the S45 is $150-200 more.

In my opinion, if you have decided on the S45 over the A70 because of resolution I would say you made an unwise decision. The difference in PPI is only 13.5% between the two. If you really felt that you had to have those extra features of the S45, then I would say go for it. Just don't buy it because it's 4mp.
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