?

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

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

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

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 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

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 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

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]

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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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

On Mon, Dec 25, 2017 at 4:49 AM, viladrich christian christian.viladrich@... [C14_EdgeHD] <C14_EdgeHD@...> wrote:

?

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