Let's Photograph Comet 46P Wirtanen

On Mon, 31 Dec 2018 09:26:42 -0700, Chris L Peterson
wrote:
Don't you see the beauty in performing that division?

Nope. It discards useful information. It's like characterizing a
aperture
telescope by focal ratio, and not providing the focal length and
aperture.

If all telescopes always had the same focal length it would be
practical to do that. Then the aperture could easily be calculated
from the focal ratio and the implicit focal length. Now, this is not
the case of course, but in the case of visual acuity tests the
Snellen chart is always at the same standard distance.

A patient with 6/6 vision and one with 3/3 vision may have
significantly different visual acuity; if you normalize them to 1.0,
you lose that distinction.

Did you ever see any visual acuity report giving the result 3/3? (is
that in feet or meters btw?)

The standard procedure for that would be to still use the standard
distance but to insert correction lenses in front of the patient's
eye. The strength of that lens must then of course be given in the
report.

In the rare case that the visual acuity test actually is performed at
a distance of 3, this is easily handled by adding a note to the
report. E.g. "acuity 1.0 at distance 3". If the "at distance" note is
absent, the standard distance will be implied.

Btw, how do American eye doctors give the strength of corrective
lenses, or of any lenses? In metric diopters like in Europe? Or do
they have their own diopter scale based on feet instead of meters? Or
do they just give the focal length in feet?