|
Dear All,
I played around with OSLO to found out what is the optimal
positioning of the Schmidt plate with the classic C14 design (ie.
not relevant to the Edge-HD).
It turned out that if the Schmidt plate is set 400 mm ahead of
its original position, the radius of the field limited by
diffraction is enlarged by 4 (9 arcmin instead of 2.2 arcmin).
This is not as large as the C14 Edge-HD (12.4 arcmin) but not far
away.
Of course, the optical tube becomes much longer (there is no free
meal ...).
The other optical characteristics do not look to be affected
(Strelh ratio on the optical axis, variation of focus with
wavelength).
More information here :
Best regards
Christian Viladrich
|
Of course one also has to support the secondary with spider vanes Charles
Sent via the Samsung Galaxy S8, an AT&T 4G LTE smartphone
toggle quoted message
Show quoted text
-------- Original message -------- From: "viladrich christian christian.viladrich@... [C14_EdgeHD]" <C14_EdgeHD@...> Date: 12/25/17 6:49 AM (GMT-06:00) To: C14_EdgeHD@... Subject: [C14_EdgeHD] Optimization of the positionning of the Schmidt plate in a C14
Dear All,
I played around with OSLO to found out what is the optimal
positioning of the Schmidt plate with the classic C14 design (ie.
not relevant to the Edge-HD).
It turned out that if the Schmidt plate is set 400 mm ahead of
its original position, the radius of the field limited by
diffraction is enlarged by 4 (9 arcmin instead of 2.2 arcmin).
This is not as large as the C14 Edge-HD (12.4 arcmin) but not far
away.
Of course, the optical tube becomes much longer (there is no free
meal ...).
The other optical characteristics do not look to be affected
(Strelh ratio on the optical axis, variation of focus with
wavelength).
More information here :
Best regards
Christian Viladrich
|
Christian, I am rebuilding my C-14 (will send photos) but decided that moving 200 mm forward would be a good tradeoff (also based on Oslo) between length and field of view. the nice thing with 200 mm is that I can (I think) built it without a spider, just a 3d printed holder that will span the gap.
-- benoit
?
Dear All,
I played around with OSLO to found out what is the optimal
positioning of the Schmidt plate with the classic C14 design (ie.
not relevant to the Edge-HD).
It turned out that if the Schmidt plate is set 400 mm ahead of
its original position, the radius of the field limited by
diffraction is enlarged by 4 (9 arcmin instead of 2.2 arcmin).
This is not as large as the C14 Edge-HD (12.4 arcmin) but not far
away.
Of course, the optical tube becomes much longer (there is no free
meal ...).
The other optical characteristics do not look to be affected
(Strelh ratio on the optical axis, variation of focus with
wavelength).
More information here :
Best regards
Christian Viladrich
|
Hi Benoit- have been a fan for years :-)? I certainly don't doubt your ability to build stuff! But supporting a fairly heavy secondary 200mm back will be a challenge to avoid vibration and maintain alignment. What would the diffraction limited field be at that distance? I too considered putting my corrector at the optimal distance - 1400mm- with a carbon fiber tube but decided against it. Is field curvature the only aberration with the corrector at about prime focus? The field curvature of a C14 is about the same as that of a 6"f/8 refractor (1/7th focal length vs 1/3rd). A field flattener for a 6" f/8 refractor should be pretty close it would seem.? I just haven't tried that yet. Charles
|
Sorry- and Christian. Your images are also legendary :-) Charles
|
Hello Charles. I am away from home, so cannot get the right ray tracing... but : I do plan to have a small counterweight to keep the secondary assembly in line... basically on the outside of the corrector. My C14 is now tubeless, having no tube is really a great improvement Imo. no more tube currents at all ! -- benoit On Mon, Dec 25, 2017 at 2:35 PM, drgenovese@... [C14_EdgeHD] < C14_EdgeHD@...> wrote:
Hi Benoit- have been a fan for years :-) I certainly don't doubt your
ability to build stuff! But supporting a fairly heavy secondary 200mm back
will be a challenge to avoid vibration and maintain alignment. What would
the diffraction limited field be at that distance? I too considered putting
my corrector at the optimal distance - 1400mm- with a carbon fiber tube but
decided against it. Is field curvature the only aberration with the
corrector at about prime focus? The field curvature of a C14 is about the
same as that of a 6"f/8 refractor (1/7th focal length vs 1/3rd). A field
flattener for a 6" f/8 refractor should be pretty close it would seem.
I just haven't tried that yet. Charles
[Non-text portions of this message have been removed]
|
I eliminated tube currents in mine by first putting two 4" fans on the back and 4 holes in the tube under the corrector. With about a 10 degree temp difference it comes to thermal eq in about 30 minutes. and then the fans can just be turned off and it tracks the temperature drop perfectly. But as the temperature would drop to the dew point (it's never very far away here in Louisiana) the inside of the corrector would dew up because of the tube temperature dropping below ambient. This was virtually completely resolved by wrapping the tube in aluminized bubble wrap (from Lowes) but now I have a carbon fiber tube (pretty good insulator) and the bubble wrap is unnecessary. ? I also cut 2 2" holes in the tube- one just ahead of the rear cell and the second just behind the corrector cell all under the dovetail and glued a small fan in the rear hole half way countersunk in the tube. I planned to put some plastic (or aluminum) along each side of the rail to seal to the tube so as to make a tunnel to circulate air from front to back (the other holes would be covered) but I haven't gotten around to adding the sealing strips and testing it. I like the low profile Celestron rail which keeps the scope as close as possible to the mount. (I also have one that I may add to the top of the tube with another fan).? Charles
On Monday, December 25, 2017 4:51 PM, "Benoit Schillings benoit.schillings@... [C14_EdgeHD]" wrote:
?
Hello Charles. I am away from home, so cannot get the right ray tracing...
but :
I do plan to have a small counterweight to keep the secondary assembly in
line... basically on the outside of the corrector.
My C14 is now tubeless, having no tube is really a great improvement Imo.
no more tube currents at all !
-- benoit
On Mon, Dec 25, 2017 at 2:35 PM, drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
>
>
> Hi Benoit- have been a fan for years :-) I certainly don't doubt your
> ability to build stuff! But supporting a fairly heavy secondary 200mm back
> will be a challenge to avoid vibration and maintain alignment. What would
> the diffraction limited field be at that distance? I too considered putting
> my corrector at the optimal distance - 1400mm- with a carbon fiber tube but
> decided against it. Is field curvature the only aberration with the
> corrector at about prime focus? The field curvature of a C14 is about the
> same as that of a 6"f/8 refractor (1/7th focal length vs 1/3rd). A field
> flattener for a 6" f/8 refractor should be pretty close it would seem.
> I just haven't tried that yet. Charles
>
>
>
[Non-text portions of this message have been removed]
|
I do have 3 fans on the back, but the temperature change in California during the evening is pretty steep... often a change of 40 degrees F. I have typically found that even if I had the fan running for a few hours, some tube currents would still appear when I turn the fans off (Carbon tube).
If the current experiment of tubeless C14 works, I will replace the current Aluminum beams with carbon tubing.
-- benoit
On Mon, Dec 25, 2017 at 6:15 PM, charles genovese drgenovese@... [C14_EdgeHD] <C14_EdgeHD@...> wrote:
?
I eliminated tube currents in mine by first putting two 4" fans on the back and 4 holes in the tube under the corrector. With about a 10 degree temp difference it comes to thermal eq in about 30 minutes. and then the fans can just be turned off and it tracks the temperature drop perfectly. But as the temperature would drop to the dew point (it's never very far away here in Louisiana) the inside of the corrector would dew up because of the tube temperature dropping below ambient. This was virtually completely resolved by wrapping the tube in aluminized bubble wrap (from Lowes) but now I have a carbon fiber tube (pretty good insulator) and the bubble wrap is unnecessary. ? I also cut 2 2" holes in the tube- one just ahead of the rear cell and the second just behind the corrector cell all under the dovetail and glued a small fan in the rear hole half way countersunk in the tube. I planned to put some plastic (or aluminum) along each side of the rail to seal to the tube so as to make a tunnel to circulate air from front to back (the other holes would be covered) but I haven't gotten around to adding the sealing strips and testing it. I like the low profile Celestron rail which keeps the scope as close as possible to the mount. (I also have one that I may add to the top of the tube with another fan).? Charles
?
Hello Charles. I am away from home, so cannot get the right ray tracing...
but :
I do plan to have a small counterweight to keep the secondary assembly in
line... basically on the outside of the corrector.
My C14 is now tubeless, having no tube is really a great improvement Imo.
no more tube currents at all !
-- benoit
On Mon, Dec 25, 2017 at 2:35 PM, drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
>
>
> Hi Benoit- have been a fan for years :-) I certainly don't doubt your
> ability to build stuff! But supporting a fairly heavy secondary 200mm back
> will be a challenge to avoid vibration and maintain alignment. What would
> the diffraction limited field be at that distance? I too considered putting
> my corrector at the optimal distance - 1400mm- with a carbon fiber tube but
> decided against it. Is field curvature the only aberration with the
> corrector at about prime focus? The field curvature of a C14 is about the
> same as that of a 6"f/8 refractor (1/7th focal length vs 1/3rd). A field
> flattener for a 6" f/8 refractor should be pretty close it would seem.
> I just haven't tried that yet. Charles
>
>
>
[Non-text portions of this message have been removed]
|
Wow 40 degrees- here the total temp variation from 2 PM to 6 AM is rarely more than 20 degrees but much less during the night! Typically only about 6-8 degrees from twilight to midnight and a slower drop after that to the minimum at dawn. I guess due to the high humidity Charles
On Monday, December 25, 2017 8:55 PM, "Benoit Schillings benoit.schillings@... [C14_EdgeHD]" wrote:
?
I do have 3 fans on the back, but the temperature change in California during the evening is pretty steep... often a change of 40 degrees F. I have typically found that even if I had the fan running for a few hours, some tube currents would still appear when I turn the fans off (Carbon tube).
If the current experiment of tubeless C14 works, I will replace the current Aluminum beams with carbon tubing.
-- benoit
On Mon, Dec 25, 2017 at 6:15 PM, charles genovese drgenovese@... [C14_EdgeHD] <C14_EdgeHD@...> wrote:
?
I eliminated tube currents in mine by first putting two 4" fans on the back and 4 holes in the tube under the corrector. With about a 10 degree temp difference it comes to thermal eq in about 30 minutes. and then the fans can just be turned off and it tracks the temperature drop perfectly. But as the temperature would drop to the dew point (it's never very far away here in Louisiana) the inside of the corrector would dew up because of the tube temperature dropping below ambient. This was virtually completely resolved by wrapping the tube in aluminized bubble wrap (from Lowes) but now I have a carbon fiber tube (pretty good insulator) and the bubble wrap is unnecessary. ? I also cut 2 2" holes in the tube- one just ahead of the rear cell and the second just behind the corrector cell all under the dovetail and glued a small fan in the rear hole half way countersunk in the tube. I planned to put some plastic (or aluminum) along each side of the rail to seal to the tube so as to make a tunnel to circulate air from front to back (the other holes would be covered) but I haven't gotten around to adding the sealing strips and testing it. I like the low profile Celestron rail which keeps the scope as close as possible to the mount. (I also have one that I may add to the top of the tube with another fan).? Charles
?
Hello Charles. I am away from home, so cannot get the right ray tracing...
but :
I do plan to have a small counterweight to keep the secondary assembly in
line... basically on the outside of the corrector.
My C14 is now tubeless, having no tube is really a great improvement Imo.
no more tube currents at all !
-- benoit
On Mon, Dec 25, 2017 at 2:35 PM, drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
>
>
> Hi Benoit- have been a fan for years :-) I certainly don't doubt your
> ability to build stuff! But supporting a fairly heavy secondary 200mm back
> will be a challenge to avoid vibration and maintain alignment. What would
> the diffraction limited field be at that distance? I too considered putting
> my corrector at the optimal distance - 1400mm- with a carbon fiber tube but
> decided against it. Is field curvature the only aberration with the
> corrector at about prime focus? The field curvature of a C14 is about the
> same as that of a 6"f/8 refractor (1/7th focal length vs 1/3rd). A field
> flattener for a 6" f/8 refractor should be pretty close it would seem.
> I just haven't tried that yet. Charles
>
>
>
|
Very interesting. I have found that
moving the plate 200 mm forward increases the diffraction limited
flat field from 2.2 arcmin (nominal design) to 4.1 arcmin (in
green light).
With 200 mm, you will probably still have a good access to the
collimation screws.
Christian
Le 25/12/2017 à 22:04, Benoit Schillings
benoit.schillings@... [C14_EdgeHD] a écrit?:
toggle quoted message
Show quoted text
Christian, I am rebuilding my C-14 (will send
photos) but decided that moving 200 mm forward would be a good
tradeoff (also based on Oslo) between length and field of view.
the nice thing with 200 mm is that I can (I think) built it
without a spider, just a 3d printed holder that will span the
gap.
-- benoit
|
It would be nice to have a look at some
images of your tubeless C14 when your are back home.
Christian
Le 25/12/2017 à 22:51, Benoit Schillings
benoit.schillings@... [C14_EdgeHD] a écrit?:
toggle quoted message
Show quoted text
Hello Charles. I am away from home, so cannot get the right ray tracing...
but :
I do plan to have a small counterweight to keep the secondary assembly in
line... basically on the outside of the corrector.
My C14 is now tubeless, having no tube is really a great improvement Imo.
no more tube currents at all !
-- benoit
On Mon, Dec 25, 2017 at 2:35 PM, drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
Hi Benoit- have been a fan for years :-) I certainly don't doubt your
ability to build stuff! But supporting a fairly heavy secondary 200mm back
will be a challenge to avoid vibration and maintain alignment. What would
the diffraction limited field be at that distance? I too considered putting
my corrector at the optimal distance - 1400mm- with a carbon fiber tube but
decided against it. Is field curvature the only aberration with the
corrector at about prime focus? The field curvature of a C14 is about the
same as that of a 6"f/8 refractor (1/7th focal length vs 1/3rd). A field
flattener for a 6" f/8 refractor should be pretty close it would seem.
I just haven't tried that yet. Charles
------------------------------------
Posted by: Benoit Schillings
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|
Hi Charles,
Can you post some images of your tube ? I only have two 80 mm
holes at the back of the mirror, each of them with a 90 mm fan.
This is much better than nothing, but I can see you push it one
step further.
Thanks !
Le 26/12/2017 à 02:15, charles genovese drgenovese@...
[C14_EdgeHD] a écrit?:
toggle quoted message
Show quoted text
I
eliminated tube currents in mine by first putting two 4" fans
on the back and 4 holes in the tube under the corrector. With
about a 10 degree temp difference it comes to thermal eq in
about 30 minutes. and then the fans can just be turned off and
it tracks the temperature drop perfectly. But as the
temperature would drop to the dew point (it's never very far
away here in Louisiana) the inside of the corrector would dew
up because of the tube temperature dropping below ambient.
This was virtually completely resolved by wrapping the tube in
aluminized bubble wrap (from Lowes) but now I have a carbon
fiber tube (pretty good insulator) and the bubble wrap is
unnecessary. ? I also cut 2 2" holes in the tube- one just
ahead of the rear cell and the second just behind the
corrector cell all unde r the dovetail and glued a small fan
in the rear hole half way countersunk in the tube. I planned
to put some plastic (or aluminum) along each side of the rail
to seal to the tube so as to make a tunnel to circulate air
from front to back (the other holes would be covered) but I
haven't gotten around to adding the sealing strips and testing
it. I like the low profile Celestron rail which keeps the
scope as close as possible to the mount. (I also have one that
I may add to the top of the tube with another fan).?
Charles
?
Hello Charles. I am away from home, so
cannot get the right ray tracing...
but :
I do plan to have a small counterweight to
keep the secondary assembly in
line... basically on the outside of the
corrector.
My C14 is now tubeless, having no tube is
really a great improvement Imo.
no more tube currents at all !
-- benoit
On Mon, Dec 25, 2017 at 2:35 PM,
drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
>
>
> Hi Benoit- have been a fan for years
:-) I certainly don't doubt your
> ability to build stuff! But supporting
a fairly heavy secondary 200mm back
> will be a challenge to avoid vibration
and maintain alignment. What would
> the diffraction limited field be at
that distance? I too considered putting
> my corrector at the optimal distance -
1400mm- with a carbon fiber tube but
> decided against it. Is field curvature
the only aberration with the
> corrector at about prime focus? The
field curvature of a C14 is about the
> same as that of a 6"f/8 refractor
(1/7th focal length vs 1/3rd). A field
> flattener for a 6" f/8 refractor should
be pretty close it would seem.
> I just haven't tried that yet. Charles
>
>
>
[Non-text portions of this message have been
removed]
|
Christian - how do coma and field curvature change as the corrector is moved forward.? Charles
On Tuesday, December 26, 2017 11:36 PM, charles genovese wrote:
The first 2 images show the rear cell with holes drilled under the fan - much easier than cutting a big hole- and the inside wiring. The picture of the side of the tube with the fan is under the dovetail rail which will be eventually modified with stick on side pieces (and small pieces at the front and back) to make the rail into a conduit to circulate air. (there is also a hole in the tube just below the corrector cell). There are also 4 1" holes in the tube just below the corrector to exhaust air from the fans from the rear cell. When not in use the holes are simply covered with blue painter's tape. when air is just being "circulated the rear fans and 4 holes are covered. Otherwise they are uncovered and the inside of the scope comes to thermal EQ with the surrounding air Charles
On Tuesday, December 26, 2017 4:32 AM, "viladrich christian christian.viladrich@... [C14_EdgeHD]" wrote:
?
Hi Charles,
Can you post some images of your tube ? I only have two 80 mm
holes at the back of the mirror, each of them with a 90 mm fan.
This is much better than nothing, but I can see you push it one
step further.
Thanks !
Le 26/12/2017 à 02:15, charles genovese drgenovese@...
[C14_EdgeHD] a écrit?:
I
eliminated tube currents in mine by first putting two 4" fans
on the back and 4 holes in the tube under the corrector. With
about a 10 degree temp difference it comes to thermal eq in
about 30 minutes. and then the fans can just be turned off and
it tracks the temperature drop perfectly. But as the
temperature would drop to the dew point (it's never very far
away here in Louisiana) the inside of the corrector would dew
up because of the tube temperature dropping below ambient.
This was virtually completely resolved by wrapping the tube in
aluminized bubble wrap (from Lowes) but now I have a carbon
fiber tube (pretty good insulator) and the bubble wrap is
unnecessary. ? I also cut 2 2" holes in the tube- one just
ahead of the rear cell and the second just behind the
corrector cell all unde r the dovetail and glued a small fan
in the rear hole half way countersunk in the tube. I planned
to put some plastic (or aluminum) along each side of the rail
to seal to the tube so as to make a tunnel to circulate air
from front to back (the other holes would be covered) but I
haven't gotten around to adding the sealing strips and testing
it. I like the low profile Celestron rail which keeps the
scope as close as possible to the mount. (I also have one that
I may add to the top of the tube with another fan).?
Charles
?
Hello Charles. I am away from home, so
cannot get the right ray tracing...
but :
I do plan to have a small counterweight to
keep the secondary assembly in
line... basically on the outside of the
corrector.
My C14 is now tubeless, having no tube is
really a great improvement Imo.
no more tube currents at all !
-- benoit
On Mon, Dec 25, 2017 at 2:35 PM,
drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
>
>
> Hi Benoit- have been a fan for years
:-) I certainly don't doubt your
> ability to build stuff! But supporting
a fairly heavy secondary 200mm back
> will be a challenge to avoid vibration
and maintain alignment. What would
> the diffraction limited field be at
that distance? I too considered putting
> my corrector at the optimal distance -
1400mm- with a carbon fiber tube but
> decided against it. Is field curvature
the only aberration with the
> corrector at about prime focus? The
field curvature of a C14 is about the
> same as that of a 6"f/8 refractor
(1/7th focal length vs 1/3rd). A field
> flattener for a 6" f/8 refractor should
be pretty close it would seem.
> I just haven't tried that yet. Charles
>
>
>
[Non-text portions of this message have been
removed]
|
Hi Charles,
The coma is much lower with the plate moved forward by 400 mm.
Here are the spot diagrams over a 0.25° field and the classic
design. We can see a nice coma:
And with the plate moved forward by 400 mm:
The field curvature is about the same.
Best regards
Christian
Le 27/12/2017 à 05:39, charles genovese drgenovese@...
[C14_EdgeHD] a écrit?:
toggle quoted message
Show quoted text
Christian - how
do coma and field curvature change as the corrector is moved
forward.?
Charles
On Tuesday,
December 26, 2017 11:36 PM, charles genovese
wrote:
The first 2 images show the rear
cell with holes drilled under the fan -
much easier than cutting a big hole- and
the inside wiring. The picture of the side
of the tube with the fan is under the
dovetail rail which will be eventually
modified with stick on side pieces (and
small pieces at the front and back) to
make the rail into a conduit to circulate
air. (there is also a hole in the tube
just below the corrector cell). There are
also 4 1" holes in the tube just below the
corrector to exhaust air from the fans
from the rear cell. When not in use the
holes are simply covered with blue
painter's tape. when air is just being
"circulated the rear fans and 4 holes are
covered. Otherwise they are uncovered and
the inside of the scope comes to thermal
EQ with the surrounding air
Charles
?
Hi
Charles,
Can you post some images
of your tube ? I only have
two 80 mm holes at the
back of the mirror, each
of them with a 90 mm fan.
This is much better than
nothing, but I can see you
push it one step further.
Thanks !
Le 26/12/2017 à 02:15,
charles genovese drgenovese@...
[C14_EdgeHD] a écrit?:
I eliminated
tube currents in mine
by first putting two
4" fans on the back
and 4 holes in the
tube under the
corrector. With about
a 10 degree temp
difference it comes to
thermal eq in about 30
minutes. and then the
fans can just be
turned off and it
tracks the temperature
drop perfectly. But as
the temperature would
drop to the dew point
(it's never very far
away here in
Louisiana) the inside
of the corrector would
dew up because of the
tube temperature
dropping below
ambient. This was
virtually completely
resolved by wrapping
the tube in aluminized
bubble wrap (from
Lowes) but now I have
a carbon fiber tube
(pretty good
insulator) and the
bubble wrap is
unnecessary. ? I also
cut 2 2" holes in the
tube- one just ahead
of the rear cell and
the second just behind
the corrector cell all
unde r the dovetail
and glued a small fan
in the rear hole half
way countersunk in the
tube. I planned to put
some plastic (or
aluminum) along each
side of the rail to
seal to the tube so as
to make a tunnel to
circulate air from
front to back (the
other holes would be
covered) but I haven't
gotten around to
adding the sealing
strips and testing it.
I like the low profile
Celestron rail which
keeps the scope as
close as possible to
the mount. (I also
have one that I may
add to the top of the
tube with another
fan).?
Charles
?
Hello
Charles. I am
away from
home, so
cannot get the
right ray
tracing...
but :
I do plan to
have a small
counterweight
to keep the
secondary
assembly in
line...
basically on
the outside of
the corrector.
My C14 is now
tubeless,
having no tube
is really a
great
improvement
Imo.
no more tube
currents at
all !
-- benoit
On Mon, Dec
25, 2017 at
2:35 PM, drgenovese@... [C14_EdgeHD] <
C14_EdgeHD@...> wrote:
>
>
> Hi
Benoit- have
been a fan for
years :-) I
certainly
don't doubt
your
> ability
to build
stuff! But
supporting a
fairly heavy
secondary
200mm back
> will be a
challenge to
avoid
vibration and
maintain
alignment.
What would
> the
diffraction
limited field
be at that
distance? I
too considered
putting
> my
corrector at
the optimal
distance -
1400mm- with a
carbon fiber
tube but
> decided
against it. Is
field
curvature the
only
aberration
with the
> corrector
at about prime
focus? The
field
curvature of a
C14 is about
the
> same as
that of a
6"f/8
refractor
(1/7th focal
length vs
1/3rd). A
field
> flattener
for a 6" f/8
refractor
should be
pretty close
it would seem.
> I just
haven't tried
that yet.
Charles
>
>
>
[Non-text
portions of
this message
have been
removed]
|
The spot diagrams show that the on-axis spot is much smaller for?the normal plate distance than the extended placement.? So this trick would be destructive for narrow FOV such as planetary.? As for wide FOV, there are correctors that achieve similar spot sizes without moving the plate (re Starizona reducer/corrector).
However, if one were to re-formulate and make a?concentric?corrector then you could have the best of both.? Of course it is unlikely that anyone will do so...
Stan
|
Hello Stan
As a matter of fact, the spot diagrams are a bit deceptive. On the
optical axis, the Strelh ratio are about the same with / without
moving the plate.
I would say that the main benefit of the modification is for high
resolution narrow field imaging (eg. lunar imaging).
Christian
?
Le 28/12/2017 à 16:36, stan_ccd@... [C14_EdgeHD] a écrit?:
toggle quoted message
Show quoted text
The spot diagrams show that the on-axis spot is much smaller
for?the normal plate distance than the extended placement.? So
this trick would be destructive for narrow FOV such as planetary.?
As for wide FOV, there are correctors that achieve similar spot
sizes without moving the plate (re Starizona reducer/corrector).
However, if one were to re-formulate and make a?concentric?corrector then you could have the
best of both.? Of course it is unlikely that anyone will do
so...
Stan
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I would agree with Christian.
The ultimate on-axis spot diagram can always be reached by the combination of wavelength and back-focus... sphero-chromatism is really the limiting factor in SCT's
--
?
Hello Stan
As a matter of fact, the spot diagrams are a bit deceptive. On the
optical axis, the Strelh ratio are about the same with / without
moving the plate.
I would say that the main benefit of the modification is for high
resolution narrow field imaging (eg. lunar imaging).
Christian
?
Le 28/12/2017 à 16:36, stan_ccd@... [C14_EdgeHD] a écrit?:
The spot diagrams show that the on-axis spot is much smaller
for?the normal plate distance than the extended placement.? So
this trick would be destructive for narrow FOV such as planetary.?
As for wide FOV, there are correctors that achieve similar spot
sizes without moving the plate (re Starizona reducer/corrector).
However, if one were to re-formulate and make a?concentric?corrector then you could have the
best of both.? Of course it is unlikely that anyone will do
so...
Stan
|
Maybe.? But it seems "common sense" that moving the corrector forward should cause over-correction.? The spot diagram clearly shows that effect on-axis but it is presumably a non-diffraction monochromatic geometrical ray trace.? ?
The geometrical difference might be overwhelmed by diffraction and obscured by chromo but it is still there.? And spider diffractions that result from extending the plate do not help either.??See if you can convince Christopher Go to modify his C14! <g>
In regards to wider FOV a good question is: do you get a better limiting PSF (on and off axis) via plate-distance modification or via lens corrections?? Is Edge-HD inferior to classical SCT on-axis?? What about off-axis compared to this modification?
Stan
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