To: 
From: Chuck Dethloff 
Reply-To: Chuck Dethloff 


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Hi John,

At 07:48 PM 7/17/2003 -0700, John Sherman wrote:
>But I have heard that the Paracorr sacrifices a bit of sharpness in
>the center of the field to sharpen up the edge. I have also heard that
>Naglers and most other wide-field eyepieces also sacrifice a bit of contrast
>and sharpness in the center of the field to sharpen up the edge of the
>field. For these reasons I have heard from experienced planet observers
>that it is best to remove the Paracorr and the Nagler when doing high-power
>work.

I usually leave my Paracorr in when doing planetary viewing because it
increases the size of the sweet spot. That is less important of course on a
tracking telescope mount. I do agree that the Paracorr may sacrifice a
small amount of center sharpness, but I think that amount of difference is
really quite minimal. IMHO

When one compares sharpness through different eyepiece combinations it is
important that the final magnifications be almost identical to get helpful
feedback. Removing the Paracorr from the scope decreases the magnification
slightly which would also provide in practice a sharper image with the same
eyepiece.

>I'd suggest a Plossl or an Erfle.

Those are good choices for eyepieces. I have found the Tele Vue Radians to
be excellent for contrast and sharpness.

Chuck Dethloff

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Hi John,
At 07:48 PM 7/17/2003 -0700, John Sherman wrote:
But I have heard that the Paracorr
sacrifices a bit of sharpness in the center of the field to
sharpen up the edge. I have also heard that
Naglers and most other wide-field eyepieces also sacrifice a bit of
contrast
and sharpness in the center of the field to sharpen up the edge of the
field. For these reasons I have heard from experienced planet observers
that it is best to remove the Paracorr and the Nagler when doing high-power
work. 
I usually leave my Paracorr in when doing planetary viewing because it
increases the size of the sweet spot. That is less important of course on a
tracking telescope mount. I do agree that the Paracorr may sacrifice a
small amount of center sharpness, but I think that amount of difference is
really quite minimal. IMHO When one compares sharpness
through different eyepiece combinations it is important that the final
magnifications be almost identical to get helpful feedback. Removing the
Paracorr from the scope decreases the magnification slightly which would
also provide in practice a sharper image with the same eyepiece.

I'd suggest a Plossl
or an Erfle.  Those are good
choices for eyepieces. I have found the Tele Vue Radians to be excellent
for contrast and sharpness.  Chuck Dethloff


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