Short Barlows

Greetings...

In the book, Astronomy Hacks, they state that the longer barlows are
superior to the new generation of shorties. I have several barlows that
I've bought from various sources and I can't see much difference in any of
them. In fact, the barlow I like best is the shortest---the Orion shorty
plus. I like the convenience of the shortness.

So, is there a real reason a longer barlow would be superior? I understand
the light cone stuff but frankly I don't see more or less CA with longer or
shorter barlows...

Doink

"Doink" wrote in message ...
Greetings...

In the book, Astronomy Hacks, they state that the longer barlows are
superior to the new generation of shorties. I have several barlows that
I've bought from various sources and I can't see much difference in any of
them. In fact, the barlow I like best is the shortest---the Orion shorty
plus. I like the convenience of the shortness.

So, is there a real reason a longer barlow would be superior? I understand
the light cone stuff but frankly I don't see more or less CA with longer or
shorter barlows...

Well, Doink, you have yourself hit on the reason. The shorter the
virtual focal length the greater the potential chromatic and other
abberations for a given barlow design. This assumes identical designs
and executions of the designs. One must compare apples to apples.
That said, if the execution of the design is such that your eyes don't
perceive a difference then then the convenience of the shorty will
trump theory.
--

Hilton Evans
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Doink wrote:
Greetings...

In the book, Astronomy Hacks, they state that the longer barlows are
superior to the new generation of shorties. I have several barlows that
I've bought from various sources and I can't see much difference in any of
them. In fact, the barlow I like best is the shortest---the Orion shorty
plus. I like the convenience of the shortness.

In 'theory' that's probably the case. In practice...there's little
difference in short and long barlows, and the shorties are, yes,
usually a lot more convenient to use.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
and _The Urban Astronomer's Guide_

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