What do we mean by "sharp" and "resolution"?

A common misconception is that "high resolution" is an image that looks sharp despite it being wide field image of a deep sky object.

The image above was taken with a Canon G3X, at 24mm.

The central section highlighted to show the zoomed in (FL 600mm ) region, with the same lens below.

The image above looks sharp. But is it highly resolved?

How much detail can be seen on the horizon within the highlighted box?

The above image was captured with the same sensor and objective but with the focal length of the system increased considerably.

An optical zoom of 25x can indeed show details that are otherwise invisible.

BUT.....what happens when we image the same scene with a much larger objective and larger but albeit similar sensor??

The above image was taken just a few seconds later with a Canon 500mm F4.0 lens and 5D MarkIV

Use your mouse to roll-over the image below to compare the two imaging systems, under more controlled conditions

(both tripod mounted, with data captured within a few minutes of each)

All images and text copyright Peter J Ward 2017