ODM also determines the contrast of the object against the sky background, presenting this as the "Log Object Contrast," or LOC.
Log Object Contrast: +0.15 Log Threshold Contrast: -0.08 Log Contrast Difference: +0.23 ODM: 55X While for the urban setting,
Log Object Contrast: -1.45 Log Threshold Contrast: -0.82 Log Contrast Difference: -0.63 ODM: Not detectable Not surprisingly, ODM predicts the galaxy will not be visible in the urban environment.
The ratio of image contrast to object contrast
at various angular scales is called the telescope's modulation transfer function, as explained in this department by William Zmek (S&T: July 1993, page 91, and September 1993, page 83).
Evaluating a telescope's contrast performance is just a matter of plotting the ratio of image contrast to object contrast for details in a whole range of angular sizes.
* Image contrast is always less than object contrast, even for a perfect telescope.
Ensuring an object contrasts
well with its background will guarantee it has visual impact.