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Old 15-02-2019, 08:40 AM
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Coronograph for stars

As a result of last night (unsuccessful) observation of Procyon B with my C11, I was thinking about building of suitable "coronograph"...



Obviously, I will need to place it in the system focal plane, and I wil have to use relay lens to project the image of the blocked star and remained star field onto the image sensor.


The blocking shade should be suspended by thin wire and it should be quite small, 10-20 pixels maybe? That is ~100um, 0.1mm..

Quite a challenge....

Last edited by bojan; 15-02-2019 at 12:43 PM.
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Old 15-02-2019, 09:15 AM
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Originally Posted by bojan View Post
Aa a result of last night (unsuccessful) observation of Procyon B with my C11, I was thinking about building of suitable "coronograph"...



Obviously, I will need to place it in the system focal plane, and I wil have to use relay lens to project the image of the blocked star and remained star field onto the image sensor.


The blocking shade should be suspended by thin wire and it should be quite small, 10-20 pixels maybe? That is ~100um, 0.1mm..

Quite a challenge....
Hi Bojan,

As a quick solution, For a 100 micron wide blocking shade, the wire and the shade could be one in the same thing. Just use a 100 micron wire to block the star (or whatever diam is appropriate).

Most speaker and hookup cable will have individual strands diameter in the 100 to 200 micron range. Some RF/Coax cable shields and Litz wire also use tiny wire. Silicon test lead is also a good source of <100 micron diameter wire strands. The thinnest I've noted were 50 micron diameter strands in a silicone rubber flexible cable that a friend like to use for speaker cable.

The only other solution would be to microdeposit an appropriatelty positioned 100 micron dot on glass in the optical train. Wire suspension of a 100 micron dot, would be extremely difficult since the suspending wires would be difficult to obtain in much thinner than 50microns, let alone finding a suspending a 100micron dot on the wire. Hence my suggestion to simply use a 100micron wire to obscure the star (and unfortunately of course everything else along the wire)

Best
JA
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Old 15-02-2019, 09:19 AM
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... the wire and the shade could be one in the same thing. ...
JA

Quite right, I was also thinking along the same lines...


Even optical fibre may be OK (it is trasparent, but it is also round so it does disperse the light, it should attenuate the star sufficiently (I am using optical fibers for cross hair in finder).


BTW, I have some lenses from webcams, they may be small and short enough for trial... There will be 3D printing again :-)


The first attempt will be visual - I intend to position the optical fiber end in the centre of an eyepiece.

Will report the result asap.

Last edited by bojan; 15-02-2019 at 09:35 AM.
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Old 15-02-2019, 09:51 AM
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This is what I already have in my finder....

Only this time I will use 5mm Ortho eyepiece and only one fiber (from edge to centre of the FOV).
Simulation/raytrace of round fibre in light path of the eyepiece-eye is also attached (light from one source is deflected by fibre, while nearby source enters eyepiece and eye.

I could even try to use this assembly as eyepiece projector, to image Procyon B.


Of course, if component B happens to be located in one of Airy discs, or visibility is poor, this will not help a lot...
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Last edited by bojan; 15-02-2019 at 01:12 PM.
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Old 15-02-2019, 05:07 PM
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that's a cool idea. I like imagining how it popped up in your head.
Do you happen to know at what eccentricity both stars are towards each other in their current stage of 42 years orbit? I mean, was it easier to split them 10 years ago than it is now?

Wiki on Procyon says they're both lightweight suns, A at 1.5 solar masses and B 0.6.
What would it take to measure how much the path of the photons from B is warped by the curvature caused by A? Your crosshair blocking out A's photons must be the valuable first step towards that.
That they're difficult to split right now could indicate that they're in the best orbital position to "see" that effect, if it can be made visible.

This double star may well be too lightweight a test pair. But in theory, with a pair with a heavier dominant A, how would you make that visible with your powerful C11...
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Old 15-02-2019, 05:45 PM
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A larger occulting bar which is rotatable (to suit anticipated elongation angle) could be used.
You just need to block the primary....
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Old 15-02-2019, 06:02 PM
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Have you considered Florent's REDUC program?
http://astrosurf.com/hfosaf/
This works very well on close doubles.
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Old 15-02-2019, 07:43 PM
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Originally Posted by Merlin66 View Post
Have you considered Florent's REDUC program?
http://astrosurf.com/hfosaf/
This works very well on close doubles.
Yep...
Loreal also looks promising for clean-up images.

I only need to detect B component first
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Old 15-02-2019, 08:19 PM
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Placing fiber in such a small barrel (3mm) proved to be very hard task (I am using stereo microscope for such jobs). I kept breaking the fiber with my tweezers... must stop now and take a break, otherwise all my fiber stock will be wasted.

Perhaps I should try with larger eyepiece (10mm FL) and use Barlow if higher magnification is needed.
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Old 15-02-2019, 10:11 PM
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How do you know where to place the fibre so it is in focus?

Best

Markus
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Old 16-02-2019, 04:56 AM
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How do you know where to place the fibre so it is in focus?

Best

Markus
The round mask inside the eyepiece is in focus of the eyepiece... if fiber is placed on the mask, by focusing the telescope, fiber will also be placed into the focal plane of the telescope.
Ideally, it should be movable (in my finder, I can move both fiber and eyepiece in relation to objective lens).
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Old 16-02-2019, 05:05 AM
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Originally Posted by silv View Post
that's a cool idea. I like imagining how it popped up in your head.
Do you happen to know at what eccentricity both stars are towards each other in their current stage of 42 years orbit? I mean, was it easier to split them 10 years ago than it is now?

Wiki on Procyon says they're both lightweight suns, A at 1.5 solar masses and B 0.6.
What would it take to measure how much the path of the photons from B is warped by the curvature caused by A? Your crosshair blocking out A's photons must be the valuable first step towards that.
That they're difficult to split right now could indicate that they're in the best orbital position to "see" that effect, if it can be made visible.

This double star may well be too lightweight a test pair. But in theory, with a pair with a heavier dominant A, how would you make that visible with your powerful C11...

I think Procyon system is not the best "laboratory" to look for this kind of effects, components are widely spaced and never aligned...
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Old 16-02-2019, 10:21 AM
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maybe also worth trying a square aperture over the front of the scope as an apodiser? - rotate the aperture so that the object falls into one of the corners in the diffraction pattern.
https://www.photonics.com/Articles/S..._Planets/a8748
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Old 16-02-2019, 01:59 PM
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maybe also worth trying a square aperture over the front of the scope as an apodiser? - rotate the aperture so that the object falls into one of the corners in the diffraction pattern.
https://www.photonics.com/Articles/S..._Planets/a8748
Never heard of apodization before. That sent me off on a little journey to Wikipedia. Fascinating!

Markus
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Old 16-02-2019, 02:23 PM
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Never heard of apodization before. That sent me off on a little journey to Wikipedia. Fascinating!

Markus
yes, I guess that a square aperture is not strictly an apodis(z)er, since it does not suppress the Airy pattern in all directions, but it does modify it in a way that could be useful in this application. Might even be worth Bojan's time to look at a simple graded mask (http://www.astronomyhints.com/apodize.html), but a square aperture might help as a first step.
Cheers Ray

Last edited by Shiraz; 16-02-2019 at 02:47 PM.
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Old 16-02-2019, 03:23 PM
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yes, I guess that a square aperture is not strictly an apodis(z)er, since it does not suppress the Airy pattern in all directions, but it does modify it in a way that could be useful in this application. Might even be worth Bojan's time to look at a simple graded mask (http://www.astronomyhints.com/apodize.html), but a square aperture might help as a first step.
Cheers Ray
I take it that since the airy disk requires point sources, this little trick wouldn't tease out any more detail in planetary observations?

[Edit; I just read that it does! Interesting. I'll have to give it a try!]

Best

Markus

Last edited by Stonius; 16-02-2019 at 03:52 PM.
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Old 16-02-2019, 03:52 PM
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I take it that since the airy disk requires point sources, this little trick wouldn't tease out any more detail in planetary observations?

Best

Markus
The square aperture could help Bojan get in close to a bright star by redirecting the diffraction pattern in such a way that he may be able to place the low brightness star in a niche where there isn't much unwanted bright star energy.

A graded apodizing mask may apparently also help in close to a bright star by actually reducing the total amount of diffracted energy (at the expense of a broader central point) - and it will improve planetary contrast if used with a biggish scope. However, looks like a simple graded mask may not help all that much with a large central obstruction - the square aperture should be useful though.

From https://www.telescope-optics.net/apodizing_mask.htm

"The two main opposing effects of this type of pupil apodizing are:
(1) improved contrast transfer for larger details, but decreased for those close to the limit of resolution, and
(2) impaired limiting stellar resolution, but improved resolution of unequal doubles with much fainter companion in the area of the first bright rings of the brighter principal star.

Bojan, a square aperture will redirect the diffraction into a strong cross shape - if that pattern could be aligned to lie behind your crosshairs you may have a neat solution.

Cheers Ray

Last edited by Shiraz; 18-02-2019 at 08:48 AM.
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Old 18-02-2019, 02:27 PM
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Hmmm intersting.

I will try asap.
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