Why "crop factor" is so pervasive

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I was reading through this thread a couple of times as the title indicated that I would get an answer as to how crop factor is related to the size of the picture I'm dealing with.
As it was swayed towards more scientific details, the crop factor has been lost in the discussion at least for the average but curious person like me.
Here is how I see it and wan to be elightened if I see it wrong.
I compare Canon 1D Mark IV against Canon 5D Mark III as I have the first one and plan to buy the second.
I almost strictly shoot birds. I almost always crop the image.
It is important that the remaining pixels will result a presentable image.
Mark IV has a sensor size of 518.9 square mm and has a pixel count of 16.2 megapixels on that sensor.
Mark III has a 864 suare mm sensor and has a 22.2 megapixel count on that size of sensor.
Therefore cropping the image to be comparable to that of Mark IV the pixel count of the Mark III sensor will be 518.9/864*22.2=13.3
So the full frame picture will represent a 13.3 megapixel image compared to the 16.2 megapixel of the 1.3 crop image.
With other words you will have a 13.3 megapixel image on the Canon 5D Mark III in Canon 1D Mark IV terms.
You will have a better quality and less noise image but smaller pixel density.
I would like to be corrected in simple terms if possible.
Thank you.
 
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Karl,
If you are cropping your 1DIV images, sensor size has nothing to do with any of this. The differences you would see are due entirely pixel pitch or pixel density.

Roger
 
"Karl,
If you are cropping your 1DIV images, sensor size has nothing to do with any of this. The differences you would see are due entirely pixel pitch or pixel density.

Roger "​



Thanks Roger.
Just strictly focusing on image size so I can compare apples to apples and disregard the pixel density and pitch.
Is the math correct in my post?
Will the FF image appear as if it was shot with a 1.3 crop at 13.3 megapixel in terms of image size?
As if the FF was equivalent with a 1.3 crop camera having only 13.3 megapixels?
 
"Will the FF image appear as if it was shot with a 1.3 crop at 13.3 megapixel in terms of image size?"
Allow me to try to re-phrase the question, is it the same questions as yours?
- We print both images at 5x7 inches. Disregarding print resolution, PPI (or DPI). That is, we print both at whatever PPI/DPI prints full frame, just filling, the 7 inches. Will the subject bird that measures 4 inches on the 1D print also measure 4 inches on the 5D print?
Tom
 
I , too, am lost in the details here.
I just got the Nikon D800, which gives you 4 different crop modes.
Am I correct to assume that the crops are just in camera, in other words, other than the file size, should I
just take FX or full frame images and just crop them myself?
Am I going to get the same quality cropping after the fact than just taking the image in DX or 1.2 crop mode?
If that is the case, why aren't all camera's full frame?
 
"If that is the case, why aren't all camera's full frame?"
Taking this literally ( but applies FF, DX, APC) why ? - size, weight, and cost. Of both the body and lens. I would like a DSLR half the size body, about 1/4 sensor, of a current FF - with same IQ. Then I could afford in terms of both weight and cost to fly to African safari with all the kit I want.
Tom
 
Last edited:
dankearl said:
I just got the Nikon D800, which gives you 4 different crop modes.
Am I going to get the same quality cropping after the fact than just taking the image in DX or 1.2 crop mode?
If that is the case, why aren't all camera's full frame?
Click to expand...

Yes, cropping to the DX or 1.2 fov in camera or cropping after the fact are equivalent.

There are cropped sensors for production cost considerations.

Cheers,

-Michael-
 
Karl Egressy said:
I was reading through this thread a couple of times as the title indicated that I would get an answer as to how crop factor is related to the size of the picture I'm dealing with.
As it was swayed towards more scientific details, the crop factor has been lost in the discussion at least for the average but curious person like me.
Here is how I see it and wan to be elightened if I see it wrong.
I compare Canon 1D Mark IV against Canon 5D Mark III as I have the first one and plan to buy the second.
I almost strictly shoot birds. I almost always crop the image.
It is important that the remaining pixels will result a presentable image.
Mark IV has a sensor size of 518.9 square mm and has a pixel count of 16.2 megapixels on that sensor.
Mark III has a 864 suare mm sensor and has a 22.2 megapixel count on that size of sensor.
Therefore cropping the image to be comparable to that of Mark IV the pixel count of the Mark III sensor will be 518.9/864*22.2=13.3
So the full frame picture will represent a 13.3 megapixel image compared to the 16.2 megapixel of the 1.3 crop image.
With other words you will have a 13.3 megapixel image on the Canon 5D Mark III in Canon 1D Mark IV terms.
You will have a better quality and less noise image but smaller pixel density.
I would like to be corrected in simple terms if possible.
Thank you.
Click to expand...

Hi Karl- The title of the original post related to the oft-quoted, pervasive myth that crop factor affects reach and didn't specifically promise to address the issue of how crop factor relates to size of picture. Also, I am not entirely sure what you mean by "size of picture"- a printed image, the size of the file on disk?

Your calculations and logic appear to be correct. If you cut a 5DIII sensor down to the size of a 1DIV sensor you would get a roughly 13mp sensor. By the same token if you cut a D3s sensor down to the size of a 7D sensor you are left with a 5mp camera (actually 4.6). Given all the beautiful images and prints made from a D3s it only goes to show that 5mp cameras do a great job (Roger makes this point about an enlargement from a 3mp camera if I remember).

"You will have a better quality and less noise image but smaller pixel density". - I'm not entirely sure about the first two parts of your conclusion here, but agreed you would have less pixels on the subject with the 5DIII compared to the 1DIV.
 
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