The 5% Solution

Started Aug 5, 2014 | Discussions thread
OP Stephen Barrett Contributing Member • Posts: 683
Re: The 5% Solution

Thank you for your thoughtful comments, Don.

In my original post, I mentioned the possibility of cropping, which would make the frame size smaller than the maximum that would fit on a sensor. You have added a lot more detail about the processing of the image from what is collected at the photosites.

I have been dealing only with optics, sensor sizes and and image sizes.
The photo taken with the closeup lens was of an object that was 5.32 mm wide. The optics calculations show that the image of that should be 6.40 mm wide, which is too large to fit onto the normal 1/2.3" sensor, which is only 6.17 mm wide. Any cropping and all of the mechanisms that you mention only make things worse. We should not be able to see an object 5.32 mm wide, and yet we do.

There are two possible reasons that we can see all 5.32 mm of the object. One possibility is that the sensor is bigger than the normal 1/2.3" sensor. So much bigger that Canon's specified crop factor of 5.58 would have to be incorrect, regardless of which of the two definitions they are using.

Another possibility is that the optics magnify less less than the specified focal length predicts. Less magnification means that the whole image could fit onto the normal 1/2.3" sensor. If there is cropping taking place and other edge effects from demosaicing of Bayer arrays etc, that means that the image has to be even less magnified for us to see the whole object. To get less magnification , the focal lengths have to be smaller than specified.

So the possibilities are:

  1. 5% bigger sensor
  2. focal length 5% smaller than specified.
  3. Some combination of 1 and 2 that adds up to 5%.  For example 2% bigger sensor and 3% smaller focal length.

You are probably right that the complicated details that you mention play a part in this, probably changing the 5% to 6% or 7%.

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