Calibrating Slide

[Harald]

Hi there good people,
I bought a calibrating slide from eBay. It contains several dots in known size. Like 0.15mm dot.
One quick question for you...
If I take an image of the 0.15mm dot and make a print the same size as my camera sensor, I can measure the difference and calculate the magnification?

[Charles Krebs]

If you photograph an object of known size, and you also know the physical size of your camera sensor then it is pretty simple to determine the magnification at which it was recorded.

As an example...
My Canon 50D has a sensor that is 22.3mm wide. Knowing this, I can determine the size of this circle as recorded on the sensor. Suppose your 0.15mm dot measures 3mm on the image sensor. The magnification is 3/0.15 = 20

[Olympusman]

You slide may also have a cross made up of dashes with a posted value of the size between each dash. From this, you can view the cross on your camera's LCD and find out the width in microns of the field of view for each objective. Once you have determined the width of the field of view, you can interpolate the size of an object by holding a ruler up the object on your computer screen and calculating the relative size of the object to the known size of the displayed image width on your computer screen.

Mike

[Harald]

Thanks for the kind explanation both of you...

I have the same sensor size in my EOS 7D.
Made a quick test, and measured the dot to be 6mm on my sensor.
6/0.15=40