On 1/10/19 11:14 PM, Eric Stevens wrote:
On Thu, 10 Jan 2019 10:32:22 -0500, nospam
wrote:

In article , Eric Stevens
wrote:


This illustrates the disadvantage of not using the language with
precision. As I said, all my lenses make use of f/numbers which are a
measure of stops. Your thoughts have jumped the rails and are now
talking about the intervals of Exposure Value of which the camera is
capable. The exposure value may be used to set lens aperture, shutter
speed or ISO. They are not identical to stops.

EV's are equivalent to stops for any purpose related to exposure.

I can change exposure value without changing the stop setting.

you are confusing f/stop with stop.

'stop' is an abreviated way of referring to an obsolete way of
changing lens aperture. It's use as a reference to lens aperture is
now normal.


The British astronomer, John Waterhouse (1806-1879), invented Waterhouse
Stops, metal plates with a hole that could be inserted into a slot in
the lens. Prior to this, lenses were 'stopped down' by unscrewing them
and inserting a metal disc with a hole inside the lens.

I couldn't find why the word "stop" is used, but, based on the fact that
Waterhouse's home (Well Head House in Halifax, Yorkshire) had extensive
gardens and greenhouses with exotic plants, I suspect that the term
might have come from plumbing. The irrigation systems may have had
"stops" to control the water flow to the different plants. This is
entirely a guess- don't bother arguing!


--
Ken Hart