achromats needed for H-alpha light?

I've a Coronado PST which, I assume, has for convenience a regular achromatic objective and eyepeice but would simple single element lenses serve as well for a monochromatic light source like H-alpha?

Nytecam

On Sat, 19 Nov 2005 09:21:36 +0000, nytecam
wrote:

I've a Coronado PST which, I assume, has for convenience a regular
achromatic objective and eyepeice but would simple single element
lenses serve as well for a monochromatic light source like H-alpha?

Simple lenses are not as well corrected for spherical aberration. Day
Star sold a simple lens for use with its solar filters. It was around
f/30 so spherical aberration would be minimal.

On Sat, 19 Nov 2005 09:21:36 +0000, nytecam
wrote:

I've a Coronado PST which, I assume, has for convenience a regular
achromatic objective and eyepeice but would simple single element
lenses serve as well for a monochromatic light source like H-alpha?

If by "simple" you mean uncorrected for chromatic aberration, than yes.
But a single lens with spherical surfaces produces other sorts of
aberration. You could reduce those by producing a single lens with
aspherical surfaces, but that would probably be more expensive than a
two or three element (all spherical) objective.

Consider apochromats- their improved performance is only sometimes
related to reduced color. Chromatic aberration can be reduced to
insignificant levels with a basic achromat for the vast majority of
objects you are likely to observe. Arguably more important than color
correction is the additional freedom to control distortion causing
aberrations through the degree of freedom afforded by an additional
element.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

nytecam wrote:
I've a Coronado PST which, I assume, has for convenience a regular
achromatic objective and eyepeice but would simple single element
lenses serve as well for a monochromatic light source like H-alpha?



No need to assume: Somewhere on line is a description of the desing of
the Coronado H-alpha scopes.

On Sat, 19 Nov 2005 14:27:37 GMT, Chris L Peterson
wrote:

On Sat, 19 Nov 2005 09:21:36 +0000, nytecam
wrote:

I've a Coronado PST which, I assume, has for convenience a regular
achromatic objective and eyepeice but would simple single element
lenses serve as well for a monochromatic light source like H-alpha?

If by "simple" you mean uncorrected for chromatic aberration, than yes.
But a single lens with spherical surfaces produces other sorts of
aberration. You could reduce those by producing a single lens with
aspherical surfaces, but that would probably be more expensive than a
two or three element (all spherical) objective.

Consider apochromats- their improved performance is only sometimes
related to reduced color. Chromatic aberration can be reduced to
insignificant levels with a basic achromat for the vast majority of
objects you are likely to observe. Arguably more important than color
correction is the additional freedom to control distortion causing
aberrations through the degree of freedom afforded by an additional
element.

_______________________________________________ __


I thought the idea of the simple lens in solar scopes was to avoid
extra surfaces, dust, etc?
-Rich
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sat, 19 Nov 2005 16:52:23 -0500, Rich wrote:

I thought the idea of the simple lens in solar scopes was to avoid
extra surfaces, dust, etc?

Not really an issue for a solar telescope intended for viewing or
imaging the solar disk and prominences. Managing scattered light is
critical for coronagraphs, but those aren't amateur instruments. (Does
anybody know of an amateur coronagraph?)

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Sat, 19 Nov 2005 22:15:28 GMT, Chris L Peterson
wrote:

On Sat, 19 Nov 2005 16:52:23 -0500, Rich wrote:

I thought the idea of the simple lens in solar scopes was to avoid
extra surfaces, dust, etc?

Not really an issue for a solar telescope intended for viewing or
imaging the solar disk and prominences. Managing scattered light is
critical for coronagraphs, but those aren't amateur instruments. (Does
anybody know of an amateur coronagraph?)

Didn't Baader Planetarium sell one?
-Rich

Chris L Peterson asked:

(Does anybody know of an amateur coronagraph?)


There's the one featured in S&T some 20 years ago:

Dennis Gallagher. "How to Build a Coronagraph." _Sky
and Telescope_, December 1985, pp. 607-611.

The author was a college student in San Leandro when he wrote that
article. And because San Leandro's mean elevation is about 15 meters
above sea level, he used his coronagraph mostly to look at prominences;
the corona was viewable only when he hauled it to high-altitude sites
(such as the RTMC), of course. Last I heard, Dennis now performs
optical magic for Ball Aerospace, not far from Chris Peterson country.

--
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Mark Gingrich San Leandro, California

Paul Schlyter posted:

Are there even any remaining professional coronagraphs still in
operation? Hasn't the coronagraph been obsoleted by SOHO and
similar spacecrafts?


Yes, there are a number of ground-based coronagraphs still in operation.
The one on Mauna Loa (operated by the High-altitude Solar Observatory
based in Boulder, Colorado), provides some close-in K-corona images in
areas where the space-based units may be blocked by their occulting
disks (1.12 to 2.79 solar radii). The National Solar Observatory on
Sacramento Peak in New Mexico operates a 16 inch coronagraph. Clear
skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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