2" 90° Apparent Field Eyepieces Announced

"Chris1011" wrote in message
...
Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass

What a load of crap! All ED my foot. If ED glass was ever used in
eyepieces
they would have narrow fields with very poor off-axis corrections.

The "all ED" got me too. But the total correction across the whole field is
kind of funny.

Maybe they are using that depleted uranium glass!

;-)

Clear Skies

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/
And the Lunar Picture of the Day http://www.lpod.org/
************************************

Roland Christen

"Chris1011" wrote in message
...
Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass

What a load of crap! All ED my foot. If ED glass was ever used in
eyepieces
they would have narrow fields with very poor off-axis corrections.

The "all ED" got me too. But the total correction across the whole field is
kind of funny.

Maybe they are using that depleted uranium glass!

;-)

Clear Skies

Chuck Taylor
Do you observe the moon?
Try http://groups.yahoo.com/group/lunar-observing/
And the Lunar Picture of the Day http://www.lpod.org/
************************************

Roland Christen

"Chris1011" wrote in message
...
Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass

What a load of crap! All ED my foot. If ED glass was ever used in
eyepieces
they would have narrow fields with very poor off-axis corrections.

Roland Christen

The information was relayed wrong. I talked to Bill. These
eyepieces will use Lanthanum, not ED glass. As to the rest,
we'll have to wait and see.

Thanks, Tom Davis

"Chris1011" wrote in message
...
Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass

What a load of crap! All ED my foot. If ED glass was ever used in
eyepieces
they would have narrow fields with very poor off-axis corrections.

Roland Christen

The information was relayed wrong. I talked to Bill. These
eyepieces will use Lanthanum, not ED glass. As to the rest,
we'll have to wait and see.

Thanks, Tom Davis

Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass

What a load of crap! All ED my foot. If ED glass was ever used in eyepieces
they would have narrow fields with very poor off-axis corrections.

Roland Christen

(Shneor Sherman) wrote in message . com...
(Jon Isaacs) wrote in message ...
My experience with Burgess has been excellent value for the money. But
I do wonder about the optical characteristics of this eyepiece.

Clear skies,
Shneor Sherman

Probably best to take the wait and see attitude if something isn't currently
yet available. Burgess Optical has been somewhat optimistic in the past about
delivery dates...

Jon

Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass,"broadband multicoatings on all air-to-glass surfaces", and
pinpoint stars to the edge down to f/3.5. Availability is at least 60
days out.

The part about pinpoint stars to the edge of a 90° apparent field 29mm
eyepiece sounds very attractive. Maybe some of our eyepiece design
mavens can tell us why this is either impossible or comes at the price
of field curvature, loss of contrast or some other desirable optical
characteristic. Or not.

So, all you have to wonder about a
-distortion
-lateral colour
Like most widefields.
-Rich

-Rich

(Shneor Sherman) wrote in message . com...
(Jon Isaacs) wrote in message ...
My experience with Burgess has been excellent value for the money. But
I do wonder about the optical characteristics of this eyepiece.

Clear skies,
Shneor Sherman

Probably best to take the wait and see attitude if something isn't currently
yet available. Burgess Optical has been somewhat optimistic in the past about
delivery dates...

Jon

Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass,"broadband multicoatings on all air-to-glass surfaces", and
pinpoint stars to the edge down to f/3.5. Availability is at least 60
days out.

The part about pinpoint stars to the edge of a 90° apparent field 29mm
eyepiece sounds very attractive. Maybe some of our eyepiece design
mavens can tell us why this is either impossible or comes at the price
of field curvature, loss of contrast or some other desirable optical
characteristic. Or not.

So, all you have to wonder about a
-distortion
-lateral colour
Like most widefields.
-Rich

-Rich

(Shneor Sherman) wrote in message . com...
(Jon Isaacs) wrote in message ...
My experience with Burgess has been excellent value for the money. But
I do wonder about the optical characteristics of this eyepiece.

Clear skies,
Shneor Sherman

Probably best to take the wait and see attitude if something isn't currently
yet available. Burgess Optical has been somewhat optimistic in the past about
delivery dates...

Jon

Here's some more info from Bill Burgess: It's a 7-element design, all
ED glass,"broadband multicoatings on all air-to-glass surfaces", and
pinpoint stars to the edge down to f/3.5. Availability is at least 60
days out.

The part about pinpoint stars to the edge of a 90° apparent field 29mm
eyepiece sounds very attractive. Maybe some of our eyepiece design
mavens can tell us why this is either impossible or comes at the price
of field curvature, loss of contrast or some other desirable optical
characteristic. Or not.

Clear skies,
Shneor Sherman


Don Dilworth demonstrated that its possible to build a 90deg. eyepiece
with extraordinary performance. See U.S. Patent 4,720,183. The
designs published in this patent are among the highest performance
eyepieces I've ever seen. Much better than even the published Nagler
designs. No ED or high-index lanthanum type glasses are needed. The
only drawback is size. A 29mm focal length would have some elements
as large as 4" in diameter. Below is the patent prescription for a
15.9mm Dilworth:

Surf Radius Thickness Glass Diameter
OBJ Infinity Infinity 0
STO Infinity 16.367 3.984463
2 -46.13459 1.294 1.805180,25.430 34
3 59.64817 12.152 1.638540,55.420 39
4 -25.6419 0.4099999 39
5 104.509 14.0534 1.620410,60.320 60
6 -57.40218 24.826 60
7 50.58608 12.4375 1.620410,60.320 62
8 4353.534 0.4099999 62
9 23.4904 10.75047 1.620410,60.320 45.2
10 26.7368 11.6589 40
11 -83.8454 3.57986 1.620040,36.370 40
12 23.38768 14.06033 32
13 33.9786 5.868849 1.846660,23.830 33
14 221.1201 4.122499 33
15 -46.2614 3.39373 1.539960,59.710 33
16 56.31179 -27.43597 33
IMA Infinity 28.58338




Brian
www.caldwellphotographic.com

Don Dilworth demonstrated that its possible to build a 90deg. eyepiece
with extraordinary performance.

I had the pleasure of looking through one of his eyepieces about 20 years ago
at Stellafane. The view was incredible with no kidneybeaning in the daytime
views. The images was sharp to the edge, unlike any other eyepiece design I
have ever seen. There is a drawback to this design, however, and that is the
extraordinary number of air-glass surfaces since most of the elements are not
cemented to their neighbors. Even if fully multi-coated, there will be some
fair amount of light loss through this system.

Roland Christen

(Chris1011) wrote in message ...
Don Dilworth demonstrated that its possible to build a 90deg. eyepiece
with extraordinary performance.

I had the pleasure of looking through one of his eyepieces about 20 years ago
at Stellafane. The view was incredible with no kidneybeaning in the daytime
views. The images was sharp to the edge, unlike any other eyepiece design I
have ever seen. There is a drawback to this design, however, and that is the
extraordinary number of air-glass surfaces since most of the elements are not
cemented to their neighbors. Even if fully multi-coated, there will be some
fair amount of light loss through this system.

Roland Christen

Hi Roland:
I've been interested in this eyepiece for years, but have never seen
Don's prototype. True, there are 14 air-glass interfaces, but really
good coatings should allow an overall transmission in excess of 90%.
I'm curious, do you remember seeing any obvious artifacts due to
scatter or ghosting? I think a small transmission loss might be a
fair price to pay for the extraordinary views such an eyepiece would
offer.

Brian
www.caldwellphotographic.com