A hair of the SV's EDT?

I think that most of our jobs are fairly safe for years to come...

On what planet is that?

Unemployment in the IT industry has gone
from 1.6% in 1998 to nearly 6% now.

Hello, Jon

Jon Isaacs wrote:


Darren

It's so very funny that you would allow Valery the right to damn the
Stellarvue 102EDT without ever having
seen it but at the same time you bite deep into my shorts for doing a spoof
on one of Valery's posts.
Somethings to consider:

1.This is a technical forum, Valery, at least when the 102EDT was first
addressed, did present the reasons for his thinking.

2. Let us not forget that Valery was right on the money when it came to his
assessment of the SV 102EDT......

3. Your "spoof" had more venom than it did laughing gas.

I often wish Valery was more tactful and stayed away from personal issues, but
the bottomline is that he does know his optics and he is willing the share that
knowledge.

The bottom line for you, in this context. The bottom line for me in this context
is civility. You are civil, I am civil, why not everyone? Is it so difficult? If I
am really really smart, does that mean I don't have to be civil to people? (Be
careful how you answer, because I am really really smart. :-) Not about optics,
though.)



That is why some people allowed him the right to evaluate the SV 102.

jon

Cordially,
Bill Meyers

Hello, Jon

Jon Isaacs wrote:


Darren

It's so very funny that you would allow Valery the right to damn the
Stellarvue 102EDT without ever having
seen it but at the same time you bite deep into my shorts for doing a spoof
on one of Valery's posts.
Somethings to consider:

1.This is a technical forum, Valery, at least when the 102EDT was first
addressed, did present the reasons for his thinking.

2. Let us not forget that Valery was right on the money when it came to his
assessment of the SV 102EDT......

3. Your "spoof" had more venom than it did laughing gas.

I often wish Valery was more tactful and stayed away from personal issues, but
the bottomline is that he does know his optics and he is willing the share that
knowledge.

The bottom line for you, in this context. The bottom line for me in this context
is civility. You are civil, I am civil, why not everyone? Is it so difficult? If I
am really really smart, does that mean I don't have to be civil to people? (Be
careful how you answer, because I am really really smart. :-) Not about optics,
though.)



That is why some people allowed him the right to evaluate the SV 102.

jon

Cordially,
Bill Meyers

"Jackie" wrote in message .net...

I've heard that Chromacors need to be "matched" to an objective (or is it
the focuser? Or the focuser + objective?) in order for them to deliver the
best views. Assuming one has a larger 6" achro refractor and wants to obtain
a Chromacor for it, how does one go about this "fitting", exactly? Do you
need to send the scope or just the focuser to Valery, or do you need to take
specific measurements and e-mail him, or how does this work? I didn't even
think to ask this question of the person whose 6" Chromacorred Celestron I
looked through last summer...

Jackie


Jackie,

All is much more simple, than you think. Here "matching" does mean, that a
Chromacor should be choosed to nullify telescope's own spherical aberration.
All 6" F/8 achromats (if being classically C-F corrected, when blue F and red
C light with 486 and 656nm lengths respectively, have a common focus) and
Synta too, has exactly the same color correction (difference in few %).
Therefore Chromacor works same good on all of them.
However in mass manufacturing, a manufacturer has no possibility to change
the design of an objective for each melt of a glass. This will be expensive
additional procedure. So, all objectives in such mass produced scopes have
variation in spherical aberration correction.
According to my statistic, based on about 80 objectives (reported by their
owners) Synta telescopes, usually have such corrections:

1. Undercorrection in 1/3-1/4 wave - 5%
2. Undercorrection in 1/5-1/6 wave - 50%
3. Undercorrection in 1/8 wave - 20%
4. About null correction - 15%
5. Overcorrection in 1/7-1/8 wave - 10%

During manufacturing of Chromacor we can change one parameter (easy to
control it) and add spherical aberration to it. So, along with color
correction it has also spherical aberration correction power.

For many kinds of observings, spherical aberration correction is very
important - almost same important, as color aberration correction.

And with simple matching procedure we can fix spherical aberration of
a given telescope to a high degree. This will add to image sharpness.
Sometime the difference is quite obvious.

Say, let take a scope with 1/5 spherical aberration. This is acceptable
level for mass produced telescope. If we will use in it two Chromacors
one of type N (no spherical aberration correction) and second of type U1
or O1 (depends of telescope own spherical aberration), then it will be
quite noticeable a difference in image sharpness. Images will be identically
color corrected, but sharpness will be different.

An owner of a scope can easily estimate his scope spherical aberration
correction (there is a simple and reliable enough Ronchi method) and
order a Chromacor with about the same spherical aberration of opposite
mudulus. Say, if a scope has 1/5 wave Undercorrection, then a proper
type of a Chromacor will be Chr-O1 (with 1/6-1/7 wave Overcorrection).
As the result, residual spherical aberration will be about 1/5 - 1/6 = 1/30(!)
wave at best and 1/5 - 1/7 = 1/18(!) in worst case.

Not bad prize for performing simple procedure of a spherical aberration
estimation with Roncho grating (254 lpi, need about 30min to perform a
test with reliable conclution of SA volume).


Of course, if an observer is fully satisfied with image sharpness in his
scope or he is not sure in his ability to estimate his scope SA, he always
can order Chromacor type N and his scope will be fixed for color aberration.


Valery Deryuzhin.

"Jackie" wrote in message .net...

I've heard that Chromacors need to be "matched" to an objective (or is it
the focuser? Or the focuser + objective?) in order for them to deliver the
best views. Assuming one has a larger 6" achro refractor and wants to obtain
a Chromacor for it, how does one go about this "fitting", exactly? Do you
need to send the scope or just the focuser to Valery, or do you need to take
specific measurements and e-mail him, or how does this work? I didn't even
think to ask this question of the person whose 6" Chromacorred Celestron I
looked through last summer...

Jackie


Jackie,

All is much more simple, than you think. Here "matching" does mean, that a
Chromacor should be choosed to nullify telescope's own spherical aberration.
All 6" F/8 achromats (if being classically C-F corrected, when blue F and red
C light with 486 and 656nm lengths respectively, have a common focus) and
Synta too, has exactly the same color correction (difference in few %).
Therefore Chromacor works same good on all of them.
However in mass manufacturing, a manufacturer has no possibility to change
the design of an objective for each melt of a glass. This will be expensive
additional procedure. So, all objectives in such mass produced scopes have
variation in spherical aberration correction.
According to my statistic, based on about 80 objectives (reported by their
owners) Synta telescopes, usually have such corrections:

1. Undercorrection in 1/3-1/4 wave - 5%
2. Undercorrection in 1/5-1/6 wave - 50%
3. Undercorrection in 1/8 wave - 20%
4. About null correction - 15%
5. Overcorrection in 1/7-1/8 wave - 10%

During manufacturing of Chromacor we can change one parameter (easy to
control it) and add spherical aberration to it. So, along with color
correction it has also spherical aberration correction power.

For many kinds of observings, spherical aberration correction is very
important - almost same important, as color aberration correction.

And with simple matching procedure we can fix spherical aberration of
a given telescope to a high degree. This will add to image sharpness.
Sometime the difference is quite obvious.

Say, let take a scope with 1/5 spherical aberration. This is acceptable
level for mass produced telescope. If we will use in it two Chromacors
one of type N (no spherical aberration correction) and second of type U1
or O1 (depends of telescope own spherical aberration), then it will be
quite noticeable a difference in image sharpness. Images will be identically
color corrected, but sharpness will be different.

An owner of a scope can easily estimate his scope spherical aberration
correction (there is a simple and reliable enough Ronchi method) and
order a Chromacor with about the same spherical aberration of opposite
mudulus. Say, if a scope has 1/5 wave Undercorrection, then a proper
type of a Chromacor will be Chr-O1 (with 1/6-1/7 wave Overcorrection).
As the result, residual spherical aberration will be about 1/5 - 1/6 = 1/30(!)
wave at best and 1/5 - 1/7 = 1/18(!) in worst case.

Not bad prize for performing simple procedure of a spherical aberration
estimation with Roncho grating (254 lpi, need about 30min to perform a
test with reliable conclution of SA volume).


Of course, if an observer is fully satisfied with image sharpness in his
scope or he is not sure in his ability to estimate his scope SA, he always
can order Chromacor type N and his scope will be fixed for color aberration.


Valery Deryuzhin.

(Dave) wrote in message . com...
(ValeryD) wrote in message om...
Hi all!


http://www.cloudynights.com/reviews4/apm-achro.htm


No any exaggeration, clear and simple. And the price is $300 instead of
$1500 (only a focuser is better in the SV's EDT).

Markus, my congratulations!


V.D.

Nor does it have an ED element.

David


I don't know about ED element in Markus' scope. The statement is clear
-
achromat.
In the SV's EDT the usefullness of it's ED element (if it here at all)
is
same as BK-7. ;-)


2 Patriot.

Hey, you, do you know where SV sourced these EDT objectives?
I China. In Taiwan at best. Same with all other SV's objectives.
Even their new (expected soon) flagships SV4 and SV6 will use RUSSIAN
objectives.

Give Vic a call and advice him to develop american industry insted of
cinese one by placing orders for objectives in domestic companies. ;-)
Interesting if he will listen to you. ;-)


V.D.

(Dave) wrote in message . com...
(ValeryD) wrote in message om...
Hi all!


http://www.cloudynights.com/reviews4/apm-achro.htm


No any exaggeration, clear and simple. And the price is $300 instead of
$1500 (only a focuser is better in the SV's EDT).

Markus, my congratulations!


V.D.

Nor does it have an ED element.

David


I don't know about ED element in Markus' scope. The statement is clear
-
achromat.
In the SV's EDT the usefullness of it's ED element (if it here at all)
is
same as BK-7. ;-)


2 Patriot.

Hey, you, do you know where SV sourced these EDT objectives?
I China. In Taiwan at best. Same with all other SV's objectives.
Even their new (expected soon) flagships SV4 and SV6 will use RUSSIAN
objectives.

Give Vic a call and advice him to develop american industry insted of
cinese one by placing orders for objectives in domestic companies. ;-)
Interesting if he will listen to you. ;-)


V.D.

(Dave) wrote in message . com...
(ValeryD) wrote in message om...


Sorry.

I did mean, that Vic sourced objectives for his scopes _in China_.

Also all mounts and acessories.


V.D.

(Dave) wrote in message . com...
(ValeryD) wrote in message om...


Sorry.

I did mean, that Vic sourced objectives for his scopes _in China_.

Also all mounts and acessories.


V.D.

Cover2Cover wrote in message ...
Hi all!


And the price for an entire ED
scope is less than the Chromacor add on thingamajig.

DR

No Doctor, that's just an incredibly expensive replacement finder for
a 6" f/8 + Chromacor near-APO. Nobody would bother to put a Chromacor
on a finder. Would they?

Chris.B