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'[OT]:: Parabolic off focus focus'
2019\05\10@030031 by RussellMc

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I wish to establish what happens to parallel light entering a parabolic
reflector from off axis angles.
The intention is to work out where the light is focused from a solar
parabolic reflector that is statically pointed as the sun moves away from
the on-axis correct-focus position.
What I wish to investigate is how effectively one or a few vacuum solar
tubes located horizontally in parallel above the dish at right angles to
the main axis will collect energy as the sun moves 'off axis'.
Such tubes will cause shadowing, but blocked light will fall on the upper
sides of the tubes.

- I could easily do some practical experiments and observe focus spot
alterations (and will) but a numerical solution is 'a good idea'.
- I can "easily enough" sit down and work out the geometry (odds are that
it will take a few false starts to get it right but 'not too too hard')
but,
- It seems that others will have considered this before now and there may
be a ready built 'calculator' avaiable somewhere.

Garglabet divulges many many parabola focus pages, but none seem interested
in off axis illumination of a dish designed for on axis focusing.
(There are designs where the illumination axis and focus axis differ - but
these too are always used with illumination along a single intended axis.

Any leads?

I expect that the focus spot will broaden both along the sun-track axis and
also at 90 degrees to it. Broadening along the solar path axis can be
accommodated by a thin longish collector. Broadening in focus "width"
requires additional collector tubes as it gets wider.


Russell
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2019\05\10@030906 by Ross McMillan

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Stack exchange?

On Fri, 10 May 2019, 7:00 PM RussellMc, <spam_OUTapptechnzTakeThisOuTspamgmail.com> wrote:

{Quote hidden}

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2019\05\10@033251 by Mike

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Russell,

Light entering a parabolic reflector at an angle causes a optical
distortion called "coma", since the shape of the focused spot becomes
elongated in the shape of a coma.  Searching for this term might yield a
way to determine the extent for a given reflector size etc.

Regards

Mike

On 10/05/2019 08:00, RussellMc wrote:
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2019\05\10@041925 by AB Pearce - UKRI STFC

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Another option may be to search for details of using a satellite dish off axis to mount multiple LNAs to access multiple satellites.


{Original Message removed}

2019\05\10@051728 by David C Brown

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You will find a lot on this in a radio astronomy textbook.

Also off axis parabolic mirrors are common components of optical systems
where an uninterrupted light path is required
https://wp.optics.arizona.edu/optomech/wp-content/uploads/sites/53/2016/10/521_Tutorial_Newman_Kevin.pdf

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On Fri, 10 May 2019 at 09:21, AB Pearce - UKRI STFC <
alan.b.pearcespamKILLspamstfc.ac.uk> wrote:

> Another option may be to search for details of using a satellite dish off
> axis to mount multiple LNAs to access multiple satellites.
>
>
> {Original Message removed}

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