Re: Telescope magnification question

"Chris.B" wrote in message
news:8ffa824e-e479-4114-985c-a5444258b11b@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Mar 18, 3:03 am, Mike Williams <nos...@xxxxxxxxxxxxxxxxxx> wrote:

The objective lens in optics is the lens in a telescope or other optical
instrument that receives the first light rays from the object being
observed.

With respect, Mike

While remaining on the correct side of pedantic I'm not sure one can
agree with the above definition without reservation.

For practical purposes:

The objective is usually the largest element in a telescope's optical
system.

In a refractor it is the largest lens at the front of the instrument.

In a reflector it is the large mirror at the bottom of the tube.

In a compound instrument (Schmidt or Maksutov) there is usually a
corrector lens in front of the large mirror.

The large mirror is still the objective. The corrector lens has very
little power and can be treated as a plain piece of glass for
magnification purposes.

For simplicity the focal length is the distance from the objective
where a real image is formed by the objective.

i.e. where an image can be focussed on a piece of paper, photographic
film, sensor or ground glass.

It is also the point where an eyepiece can be focussed to obtain a
magnified image.

Magnification = Focal length of objective / focal length of eyepiece.
(in similar units)

I'm not sure if we are talking about the same things. I'm asking about the
Object Distance and the Image Distance. Are you saying that the distance to
the mirror is the Obect Distance? Sorry for being such a novice.







.

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