crop factor vs megapixels

I'm sure there is a formula for this, or an easy way to figure it out. Camera A has X mp and a crop factor of Y. Camera B has W mp and a crop factor of Z. How do you compare the images from each? Example, the 5D vs 20D/30D, the 1.6x crop cameras win over the same image from the 5D (since the one from the 5D would cover less mp.) Sorry if I am not making my quesiton clear enough. I'm thinking about the new 40D and 1Ds3, of course (and how to compare them to other bodies.)

Compare X*(Y^2) to W*(Z^2). Whichever is bigger wins the pixel density "beauty contest". The numbers you'll get are the approximate number of pixels/MP of a full frame sensor of the same density.

The only way to really compare images is to make prints and place them side by side.

If competent photographers, image processors and printers make both prints there is surprisingly little difference.

Mathematics doesn't really show what the eye will see.

gasrocks wrote in post #3768128
How do you compare the images from each?

I think you will need to be a tad more specific in your question before you get any real help!

Is it worth the extra $1000.00 bucks for a ff sensor?????????

Billyj571 wrote in post #3780353
Is it worth the extra $1000.00 bucks for a ff sensor?????????

To some, yes - to others, no. It's just choices- as we used to say "different strokes for different folks"

I just got the hang of this too.

Here is the easiest way. figure the pixels per sensor mm (max pixel length/max sensor length in mm). The higher the number the more pixels 'on target' you get. Of course the crammed pixels may give up quality to noise, etc.

So here you go in order (pixels per mm)

Lowest pixels on target
121 - 5D (example 4368/36=121)
122 - 1D MK IIN
135 - 1D MK III
138 - 1Ds MK II
155 - 20D/30D
156 --1DS MK III
175 - XTI and 40D
highest pixels on target

Beyond the math, photography is recording light. The more light you record, the better images you can make.

The 30D and the 1DsMkIII have similar pixel density. For the sake of argument let's assume that they will give you similar noise characteristics at a given ISO. But if you take a the 21mp image and downsize it to 8.2mp you will dramatically reduce the noise and still have the resolution of a 30D.

Larger format means recording more light to create better images. It's true whether you do it with bigger photocells, or more photocells, or some combination thereof.

Then there is the 'technology' behind the pixels so for instance the 40D's pixels should be far superior to the XTI's pixels and a lot less noise.

Curtis N wrote in post #3781036
Beyond the math, photography is recording light. The more light you record, the better images you can make.

The 30D and the 1DsMkIII have similar pixel density. For the sake of argument let's assume that they will give you similar noise characteristics at a given ISO. But if you take a the 21mp image and downsize it to 8.2mp you will dramatically reduce the noise and still have the resolution of a 30D.

Larger format means recording more light to create better images. It's true whether you do it with bigger photocells, or more photocells, or some combination thereof.

morehtml wrote in post #3781028
Lowest pixels on target
95 - D30
121 - 5D (example 4368/36=121)
122 - 1D MK IIN
135 - 1D MK III
135 - Rebel/300
138 - 1Ds MK II
155 - 20D/30D
156 --1DS MK III
175 - XTI and 40D
569 - S5 ....

And to jsut confuse you even more, I added a few. Clearly shows that pixels per MM though is a metric, it does not tell the whole story.

gjl711 wrote in post #3781150
And to jsut confuse you even more, I added a few. Clearly shows that pixels per MM though is a metric, it does not tell the whole story.

Well in Canon's new line MK III, 1DS MK III and 40 D the technology behind the sensor is similar so the 40D would put more pixels on a small target (A bird for example) than the others at a cost of possibly more ISO noise.

gjl711 wrote in post #3781150
And to jsut confuse you even more, I added a few. Clearly shows that pixels per MM though is a metric, it does not tell the whole story.

The venerable 1D was only 87/mm So many people still love that camera - those buckets captured lots of photons!

Pixels per duck is the accepted measure on POTN, I believe.

Visualisations like this one (which I need to update to include the newest models) show that the 400D gives you more PPD than any other DSLR in Canon's range.