Re: test lens for telescope use

On 7/21/05 1:55 AM, in article vpJDe.7936$je2.783387@xxxxxxxxxxxxxxxxxxxxx,
"waz" <wazungy@xxxxxxxxxxxx> wrote:

>
> Hello!
>
> I have a astigmatism developing in my eyes, -0.50 each eye.
> I also use a telescope. I prefer to observe without my glasses on if
> possible but this is getting to be a problem.
>
> I do not have any test lenses to try, so I have to ask...
>
> In theory, would it be possible to mount a test lens (let's say to correct
> for -0.50 cylinder) BETWEEN the telescope eyepiece and the objective and
> have it correct the view for me?? Could this lens be placed somewhere in
> the barrel of the eyepiece?
>
> (I am sure it would work between the eyepiece and the eye).
>
> Would the distance between the test lens and the eyepiece lenses be critical
> or would a centimeter either way be usable?
>
> If this trial lens (-0.50 cyl) would work for one eyepiece of a given focal
> length, would work for several eyepices of different focal lengths?
>
> I was thinking of trying some "quality test lenses" but thought I would ask
> my question here before I looked into where and how to obtain them.
>
> Many thanks for your thoughts on this.
>
> Waz
>
>
What you are asking for is almost available in devices or cameras. In many
models compensation is available for spherical refractive error.

Your approach is fundamentally correct. While not optimum, the lens can be
placed outside and adjacent to the eyepiece. Of course, you will have to
rotate the cylindrical lens or the combination to give best results. You
should be able to get lenses from Edmund Scientific or cozy up to an
optometrist to get ophthalmologic lenses.

Bill

.

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