Orion's 80mm ED. Surprising!

Well, I'm surprised at this scope. It's airy disc image
and colour correction appear to be better than my former
TV-85 and just shy of the quality of my Tak FS-78. I'm
amazed that they've been able to produce such a decent
product for $500.

I think a lot of folks have been surprised by the ED-80...

Jon

I'm with you, it's definitely a great refractor for the price.

On axis focused well, I would have a hard time identifying color at all off
the moon at high powers. The crayford focuser is *much* better than the
crappy r&p focusers they put on the rest of their scopes. I did have to
file down the flatspot on the focuser tube in order to handle naglers
though. I think this is a common problem, that the flat part of the tube
for the crayford is not flat, it's a hole.

Mike.

"rander3127" wrote in message
...
Well, I'm surprised at this scope. It's airy disc image
and colour correction appear to be better than my former
TV-85 and just shy of the quality of my Tak FS-78. I'm
amazed that they've been able to produce such a decent
product for $500.

"rander3127" wrote in message
...
Well, I'm surprised at this scope. It's airy disc image
and colour correction appear to be better than my former
TV-85 and just shy of the quality of my Tak FS-78. I'm
amazed that they've been able to produce such a decent
product for $500.

Hi,

You did the same observation as many users.
Indeed, using ED lens FLP-53 this is the cheapest "semiapo-like" than I
know.
Many advanced amateurs and myself have bought it sometimes ago.
We are impatient to see a larger model, as this one become to date.

I review it, in French at
http://www.astrosurf.com/lombry/rapp...-portable2.htm
there is also a translation module of my site (or use altavista or similar
tools)

This ST-80 gives a better image and cripser than the first generation of
Megrez but remains an apochromat; chromatic aberration stay visible at 200x
or so, and it cannot fight against a true apochromat like Stowaway" 92
f/4.9, Borg 76 ED, Brandon 80 f/5.6, William Optics Megrez 80 APO, Pentax 75
EDHF, TMB 80 mm f/7.5 and other Tak FS 78.
Of course price have to be taken into account.

But If I have to suggest a good scope for a novice that 'd be this ST-80ED.
However its diameter limits is capabilities to observe DSO. But it works
also fine in imaging
see http://www.astrosurf.com/lombry/imag...nsit-venus.htm 2/3d of
page with insert using a Canon Powershot S30

Thierry

"Thierry" - wrote in message ...

Indeed, using ED lens FLP-53 this is the cheapest "semiapo-like" than I
know.

I think you need to clarify your definition of "semi-apo".
FPL53 is capable of full apochromatic correction even as a doublet
(paired with
BK7 variant) as partial dispersion is so similar that residual
secondary sepctrum can be pushed well into 1/20,000+ (an APO by all
definitions).
Semi APOs have residual spectrum in 1/4000-1/10000 range (C to f),
some 2 to 5 times better than achromat. Anything above that is an APO.

This ST-80 gives a better image and cripser than the first generation of
Megrez but remains an apochromat; chromatic aberration stay visible at 200x
or so, and it cannot fight against a true apochromat like Stowaway" 92
f/4.9, Borg 76 ED, Brandon 80 f/5.6, William Optics Megrez 80 APO, Pentax 75
EDHF, TMB 80 mm f/7.5 and other Tak FS 78.

Most of the scopes listed are triplets and as such unfair to compare
with a doublet. But doublets like Borg and Tak 78 CAN be compared, and
I do not think they are better in any way (chromatic correction wise)
than ED80. In fact Borg will be inferior as it is faster (f/6.6),
while Tak could be marginally better, depending on what they have used
to pair with fluorite.
You will need to provide longitudinal aberration measurements to
convince anyone otherwise.

Bratislav

On Tue, 12 Oct 2004 15:47:52 +0200, "Thierry" - wrote:


"rander3127" wrote in message
.. .
Well, I'm surprised at this scope. It's airy disc image
and colour correction appear to be better than my former
TV-85 and just shy of the quality of my Tak FS-78. I'm
amazed that they've been able to produce such a decent
product for $500.

Hi,

You did the same observation as many users.
Indeed, using ED lens FLP-53 this is the cheapest "semiapo-like" than I
know.
Many advanced amateurs and myself have bought it sometimes ago.
We are impatient to see a larger model, as this one become to date.

They (Orion) have a 100mm f9 out now using the same material. $999.
Pretty inexpensive!

On 12 Oct 2004 16:49:36 -0700, (Bratislav)
wrote:

"Thierry" - wrote in message ...

Indeed, using ED lens FLP-53 this is the cheapest "semiapo-like" than I
know.

I think you need to clarify your definition of "semi-apo".
FPL53 is capable of full apochromatic correction even as a doublet
(paired with
BK7 variant) as partial dispersion is so similar that residual
secondary sepctrum can be pushed well into 1/20,000+ (an APO by all
definitions).
Semi APOs have residual spectrum in 1/4000-1/10000 range (C to f),
some 2 to 5 times better than achromat. Anything above that is an APO.

This ST-80 gives a better image and cripser than the first generation of
Megrez but remains an apochromat; chromatic aberration stay visible at 200x
or so, and it cannot fight against a true apochromat like Stowaway" 92
f/4.9, Borg 76 ED, Brandon 80 f/5.6, William Optics Megrez 80 APO, Pentax 75
EDHF, TMB 80 mm f/7.5 and other Tak FS 78.

Most of the scopes listed are triplets and as such unfair to compare
with a doublet. But doublets like Borg and Tak 78 CAN be compared, and
I do not think they are better in any way (chromatic correction wise)
than ED80. In fact Borg will be inferior as it is faster (f/6.6),
while Tak could be marginally better, depending on what they have used
to pair with fluorite.
You will need to provide longitudinal aberration measurements to
convince anyone otherwise.

Bratislav

The Tak's i've owned seemed to correct for colour fringing well
enough, but compared to some triplets (AP for eg) they display
an overall colour cast that looks yellowish.
Because they use fluorite, do the Taks correct to 1/16,000?
I think I remember that from one source.

How radical are colour correction differences caused by differences in
glass melts? This would explain some of what I've seen in same design
but different scope tubes.

For high end ED glass from different melts they will all be very close to the
catalog numbers when it comes to partial dispersion, which is the primary
determinant of color correction. You can take any FPL53 from any melt and pair
it with any one corrected set of mates, and the color correction will be
identical. The mates will vary in index and dispersion (but not partial
dispersion) from one batch to the next, but this will not affect the color
correction, just the point of null may shift toward red or blue. You would then
simply change one of the radii to bring it to the same color correction again.
If the actual lenses are not adjusted for these changes in index, then the
correction curves will vary from overcorrection to undercorrection in blue or
red.

Roland Christen