Eyepiece Focal Length?

"David Neal Minnick" wrote in message
om...
Can someone draw me a word-picture or direct me to a resource showing
just how the focal length of an ep is measured? That is, if one could
cut an ep in half lengthwise showing everything intact, from which
part to which part is the f/l measured?

David Neal Minnick
Lake Elsinore, CA

"The meek shall inherit the gulag."

This website shows calculations for 2-3 element eyepieces:
http://www.astronomyboy.com/eyepieces/ep_calc.html

Regards,
Ed T.

The FL of an eyepiece is not measured from anyplace in particular, unless it is
a single element EP. The EFL is based on the magnification with a particular
objective, not a measurment from somewhere in it. There are formulas for the
EFL of an eyepiece, depending on the design and glass used. The formula for a
2-lens EP is pretty straightforward (using the FL of each single lens and the
distance between them), but adding more elements complicates this. Generally,
the FL printed on an EP is an approximation.
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

The FL of an eyepiece is not measured from anyplace in particular, unless it is
a single element EP. The EFL is based on the magnification with a particular
objective, not a measurment from somewhere in it. There are formulas for the
EFL of an eyepiece, depending on the design and glass used. The formula for a
2-lens EP is pretty straightforward (using the FL of each single lens and the
distance between them), but adding more elements complicates this. Generally,
the FL printed on an EP is an approximation.
Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

"Edward" wrote in message
link.net...


This website shows calculations for 2-3 element eyepieces:
http://www.astronomyboy.com/eyepieces/ep_calc.html

Regards,
Ed T.


Note: If you take your eyepieces apart to measure the distances between the
elements in order to use this calculator, the chance that you will ever get
them back together again correctly is rather small.

"Edward" wrote in message
link.net...


This website shows calculations for 2-3 element eyepieces:
http://www.astronomyboy.com/eyepieces/ep_calc.html

Regards,
Ed T.


Note: If you take your eyepieces apart to measure the distances between the
elements in order to use this calculator, the chance that you will ever get
them back together again correctly is rather small.