Pre-Review: Paul Rini 30mm EP (65° AFOV)

(Rod Mollise) wrote in message ...

Healthwise, Paul is doing a lot better I stopped over to see him about
3 months ago, and he is the one doing the eyepieces etc. Have known
Paul for a number of years, never met or new he had a son. Clear
skies, Bob Midiri

HI Bob:

Next time you see him, remind him how much many of us have enjoyed his
eyepieces over the years, and how glad we are to see him back in the game.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Will do Rod, Paul is a special guy, we are lucky to have someone that
devoted to amateur astronomers, a great asset to us all!! Bob Midiri

(Tony Flanders) wrote in message ...
(Shneor Sherman) wrote in message . com...

But the Rini is a 1.25" eyepiece, not a 2".

Something does not add up -- or should I say multiply. The field
stop of a 30mm EP with a 65-degree AFOV needs to be slightly under
1.5 inches. It is physically impossible to do that in a 1.25-inch
barrel.

- Tony Flanders

Hi Tony,
The field lens does not have to reside within the 1.25" barrel (which
in this case by my measurement has an internal diameter of 29.5mm,
with no other field stop). I have seen 1.25" eyepieces advertised with
a 34mm clear aperture field lens - located beyond the 1.25" barrel. No
guarantees they will come to focus in all scopes, though.

But the actual numbes given are from Paul Rini.

Clear skies,
Shneor Sherman

Clear skies,
Shneor Sherman

Shneor Sherman wrote:
The field lens does not have to reside within the 1.25" barrel (which
in this case by my measurement has an internal diameter of 29.5mm,
with no other field stop). I have seen 1.25" eyepieces advertised with
a 34mm clear aperture field lens - located beyond the 1.25" barrel. No
guarantees they will come to focus in all scopes, though.

A 30 mm eyepiece with (about) a 30 mm field stop has an apparent FOV in
the 57 degree neighborhood. It can only be 65 degrees if the rest of
the eyepiece is designed to yield significant pincushion distortion
(that is, "stretching" the field at its periphery to make the apparent
FOV larger, but at the expense of making grid squares look like pillows).

Moreover, there's the matter of severe vignetting, which seems basically
unavoidable. To give a 65 degree apparent FOV without distortion, one
would need a field stop in the 35 mm neighborhood, which is about 6 mm
more than one can ordinarily get in a 1-1/4-inch barrel. One could set
the field stop back from the barrel, but in an f/10 scope, it would have
to be about 30 mm behind the barrel just to get zero illumination at the
edge of field. In an f/5 scope, it would only need to be set 15 mm back,
but that still seems rather ungainly.

It gets worse. Most people will not put up with zero illumination at the
edge of field, but will accept, say, 50 percent illumination there. But
the "setback" required to do that doesn't scale with focal ratio, but
with focal *length*. In a scope with a 1000 mm focal length, the field
stop would have to be set back around, oh, maybe 180 mm. If it's the
common 2000 mm, it would be double that, or about 360 mm. No eyepiece
is going to set the field stop back *that* far.

A 65 degree FOV could come from moderate distortion plus a bit of round
up error, but I'm just speculating.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

Lawrence Sayre wrote in message ...

I'll second that! I've only ever owned his 2" 38mm Modified Plossl, but
I enjoyed using it a great deal, and it was a great value for the $$$.
Optically superior to the 30mm Wide Scan II and the 30mm 1rpd, for (as I
recall) $46.

Lawrence Sayre

Hi:

I've got the 38, too...wonderful for the money, and, as you say not
equaled by the low-priced competition yet.

Peace,
Rod

(Shneor Sherman) wrote in message om...

The field lens does not have to reside within the 1.25" barrel ...
I have seen 1.25" eyepieces advertised with a 34mm clear aperture
field lens - located beyond the 1.25" barrel.

Yes, I suppose you can do that, and it will even work (sort of) if
the scope is fast enough -- just as you can use a secondary that's
smaller than the field stop of your eyepiece on a fast Newt.
But it's bound to vignette like crazy!

- Tony Flanders

(Tony Flanders) wrote in message m...
(Shneor Sherman) wrote in message om...

The field lens does not have to reside within the 1.25" barrel ...
I have seen 1.25" eyepieces advertised with a 34mm clear aperture
field lens - located beyond the 1.25" barrel.

Yes, I suppose you can do that, and it will even work (sort of) if
the scope is fast enough -- just as you can use a secondary that's
smaller than the field stop of your eyepiece on a fast Newt.
But it's bound to vignette like crazy!

- Tony Flanders

I'll post results when I finally get to use in in my binoviewer with my 22" f/4.
Looks like that will be September 11, depending on the weather, of course.
Clear skies,
Shneor Sherman

Lawrence Sayre wrote in message ...
Rod Mollise wrote:
Healthwise, Paul is doing a lot better I stopped over to see him about
3 months ago, and he is the one doing the eyepieces etc. Have known
Paul for a number of years, never met or new he had a son. Clear
skies, Bob Midiri


HI Bob:

Next time you see him, remind him how much many of us have enjoyed his
eyepieces over the years, and how glad we are to see him back in the game.

Peace,
Rod Mollise


I'll second that! I've only ever owned his 2" 38mm Modified Plossl, but
I enjoyed using it a great deal, and it was a great value for the $$$.
Optically superior to the 30mm Wide Scan II and the 30mm 1rpd, for (as I
recall) $46.

Lawrence Sayre

I had one of these - great eyepiece - but I donated it to the amateur
astronomers in Alexandra, South Island, New Zealand, who had no 2"
eyepieces for their 21" monster.
Clear skies,
Shneor Sherman

(Sky-High) wrote in message om...
(Shneor Sherman) wrote in message . com...
I've been looking for the widest true field I could find in a 1.25"
eyepiece for my binoviewer, and I noticed that Paul is advertising a
new series of eyepieces at astronomy-mall.com.
Clear skies,
Shneor Sherman

Where on the astronomy-mall website do you see the Rini ad for his new ep's?

Thanks,

-sh

In the classifieds.
Clear skies,
Shneor Sherman

(Tony Flanders) wrote in message m...
(Shneor Sherman) wrote in message om...

The field lens does not have to reside within the 1.25" barrel ...
I have seen 1.25" eyepieces advertised with a 34mm clear aperture
field lens - located beyond the 1.25" barrel.

Yes, I suppose you can do that, and it will even work (sort of) if
the scope is fast enough -- just as you can use a secondary that's
smaller than the field stop of your eyepiece on a fast Newt.
But it's bound to vignette like crazy!

- Tony Flanders

Hi Tony,
Paul informs me that he has reduced thr AFOV spec to 60 degrees.
Clear skies,
Shneor Sherman

A big advantage of the 38 Rini is that it can be used as a finder
eyepiece, and owing to the great eye relief, I can keep my glasses on
when it use it. Since I can't see the stars naked eye without glasses,
the ability to look at the sky naked eye with glasses, and then look in
the Rini with glasses, is very convenient for me. But to study an
object I have found, I use a 31 Nagler plus Paracorr, which gives much
better images. Also the 38 Rini that I have is not threaded for filters.
Ciao,
Bill Meyers