Artificial Star using Christmas tree ornament ?

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Re: Artificial Star using Christmas tree ornament ?

#21

Post by turboscrew »


@konza , don't throw in the towel just yet. It actually may be feasible after all.
And sorry for the misinformation.
- Juha

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Re: Artificial Star using Christmas tree ornament ?

#22

Post by konza »


Thanks SO MUCH to everyone helping to understand this a bit better. My knowledge was/is somewhat cursory. 'Tis great to have such support!
Mickey K.
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Re: Artificial Star using Christmas tree ornament ?

#23

Post by UlteriorModem »


Lady Fraktor wrote: Mon Dec 21, 2020 6:49 pm
UlteriorModem wrote: Mon Dec 21, 2020 3:15 pm I bought an arti star. It's basically a flash light with a cover and tiny pin holes in it.

Found out I could not use it as there was no where in my yard far enough away. I would have to put it about halfway out in my neighbor's yard... that aint gonna work.
If you have figured out the distance you need to star test, shorten that distance for collimating to 70% of the distance and it will work fine.

Lets see. The average star I use to test is a couple of thousand light years away sooo lets see 70% of that is ... well still past my neighbor's yard
Tom

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Re: Artificial Star using Christmas tree ornament ?

#24

Post by Lady Fraktor »


UlteriorModem wrote: Tue Dec 22, 2020 3:38 am Lets see. The average star I use to test is a couple of thousand light years away sooo lets see 70% of that is ... well still past my neighbor's yard
Arse :lol:

USING A ARTIFICIAL STAR FOR COLLIMATION OR STAR TESTING:

For an artificial star, the apparent angular diameter of a pinhole style uniform opening is:
d = 206265(P/D)

Where d is the angular diameter in arc-seconds, and P is the opening size of the pinhole (mm) and D is the distance (mm) to the “star”.

To FULLY test reliably within the resolution of the scope, you need this distance to match the resolving power of the scope. (if you want to evaluate things like aberrations (Spherical, Astigmatism, Coma, etc. – mainly spherical):
While one CAN use many criteria, it is likely best to use Dawes’s limit for the scope to allow the Rayleigh limit (which is slightly larger) to be satisfied. On average, R ~ 115.9/A; where A is the aperture in mm.

So, 115.9/A ~ 205265P/D, which rearranges to:
D = ~ 206265PA/115.9 – so using mm, that means that D ~ 1780PA.
For a 4” (102mm) scope, and a 100um (0.1mm) pinhole for the artificial star:
D = 1780* 0.1*102 = 18156mm, or 18.16m – this is about 55 feet. To use a 50um pinhole, you would be at ~27.5 feet (9m) in this case.

For a general collimation only evaluation, you can safely use 70-80% of this value or even about 20-24 feet if necessary. That is the CLOSEST reliable test distance.

Testing for proper collimation and especially optical quality is only possible if the “pinhole” for the illumination source is very well made – the more ideal to perfect hole, the better the results.
Illuminants can be anything, like LEDs, flashlights, candles and bulbs, just make sure they are pre-diffused to allow uniform illumination of the source.
This is the minimum pinhole distance for diffraction-limited collimation.

Tables 1 and 2 give the distances in more convenient feet and meters for popular apertures in inches and centimetres and pinhole sizes in microns

TABLE 1: https://www.dropbox.com/s/753wqpzvrspwd ... s.jpg?dl=0

TABLE 2: https://www.dropbox.com/s/i4wio333h0zlh ... s.jpg?dl=0
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Re: Artificial Star using Christmas tree ornament ?

#25

Post by Lady Fraktor »


If you just want to check the refractor collimation then use a refractor collimating eyepiece, very simple and takes all of five minutes or less.
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
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Re: Artificial Star using Christmas tree ornament ?

#26

Post by turboscrew »


Hmm, the formuli are pretty similar to what I put there. Making the same mistake as earlier...
If the "pinhole" was 60 mm (Christmas tree ornament diameter) and lens diameter was 102 mm:

D = 206265PA/115.9 = 206265 * 60 * 102 / 115.9 = 10891646 mm = 10.8 km
Last edited by turboscrew on Tue Dec 22, 2020 7:28 pm, edited 1 time in total.
- Juha

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Re: Artificial Star using Christmas tree ornament ?

#27

Post by turboscrew »


Note, that the d in the above is the diameter of the star (Sun, flashlight) image on the ornament, not the diameter of the ornament itself. (That's where I went astray at first.)
The idea is to consider the ball (bearing ball, Christmas tree ornament) as a convex spherical mirror.
I found out that the focal length of a spherical mirror is half of its radius.
The rest is still under study. :-D
- Juha

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Some filters (#80A, ND-96, ND-09, Astronomik UHC)
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Re: Artificial Star using Christmas tree ornament ?

#28

Post by turboscrew »


I think it goes like this (object is Sun, flashlight, ...). It's the image we're using as the artificial star.
Here the focal length if R/2.
ball_mirror1.jpg
Clear for "earthly goods" but a bit fifferent for far away big objects.
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Some filters (#80A, ND-96, ND-09, Astronomik UHC)
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Re: Artificial Star using Christmas tree ornament ?

#29

Post by turboscrew »


For artificial stars (distances are not 1"optically" infinite):
1/do + 1/di = 1/f, where do is object distance and di is image distance (in this case behind the mirror).
m = hi/ho = -di/do, where m is magnification, ho is height of the object and hi is height of the image.
distance behind the mirror is considered negative (always the case with convex mirror)

So 10 mm flashlight 10 meters away gives an image on a 100 mm Christmas tree ornament:
f = 25mm, 1/di = 1/25 - 1/10000, di = 25,062
di/do = 0,002506
hi = (di/do) * ho = 0.025 = 25 um

Please correct if I'm wrong.
- Juha

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Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
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Re: Artificial Star using Christmas tree ornament ?

#30

Post by JayTee »


Whoa, way too much math. My anecdotal experimental data says put a chrome ball bearing more than 200 m away and you're good to go.

JT
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Re: Artificial Star using Christmas tree ornament ?

#31

Post by turboscrew »


There are many ways to do collimation, but 'm not trying to find solution to an assumed problem. I just try to answer the original question. :lol:
And I'm learning too in the process.
- Juha

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Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
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OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
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Some filters (#80A, ND-96, ND-09, Astronomik UHC)
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Re: Artificial Star using Christmas tree ornament ?

#32

Post by turboscrew »


JayTee wrote: Sat Dec 26, 2020 1:00 am Whoa, way too much math. My anecdotal experimental data says put a chrome ball bearing more than 200 m away and you're good to go.

JT
BTW, about what size is your bearing ball?
- Juha

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Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
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Re: Artificial Star using Christmas tree ornament ?

#33

Post by JayTee »


turboscrew wrote: Sat Dec 26, 2020 1:21 am BTW, about what size is your bearing ball?
14mm
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
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Re: Artificial Star using Christmas tree ornament ?

#34

Post by SkyHiker »


If you have two 12" scopes then simply put a pinhole lit by a laser at the focal plane of one, and let it face the other. No long distances needed.
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Re: Artificial Star using Christmas tree ornament ?

#35

Post by turboscrew »


SkyHiker wrote: Sun Dec 27, 2020 4:17 pm If you have two 12" scopes then simply put a pinhole lit by a laser at the focal plane of one, and let it face the other. No long distances needed.
In konza's signature it says "Scopes: ES102 apo carbonfiber, Orion 127 mac/cas"
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
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Re: Artificial Star using Christmas tree ornament ?

#36

Post by turboscrew »


I did an experiment with a laser pointer and a Christmas tree ornament, and a funny thing happened: I got two spots - one seems to be the beam hitting the ornament, but close to it is the image of me behind the laser pointer. The laser dot of the image was notably smaller even if the laser beam reflection was smaller than normal too. The image of the laser was like a pinhole pushed to a paper against some harder wood - quite tiny, and the distance between me an the ornament was about 1.4 meters.

This myth is feasible! :smile:
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

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Re: Artificial Star using Christmas tree ornament ?

#37

Post by turboscrew »


Another experiment: A 22 mm flashlight only gave the image (only one bright dot), and that was about 2 mm in size.
The ornament diameter was 60 mm and the distance was the same 1.4 m.
- Juha

Senior Embedded SW Designer
Telescope: OrionOptics XV12, Mount: CEM120, Tri-pier 360 and alternative dobson mount.
Grab 'n go: Omegon AC 102/660 on AZ-3 mount
Eyepieces: 26 mm Omegon SWAN 70°, 15 mm TV Plössl, 12.5 mm Baader Morpheus, 10 mm TV Delos, 6 mm Baader Classic Ortho, 5 mm TV DeLite, 4 mm and 3 mm TV Radians
Cameras: ZWO ASI 294MM Pro, Omegon veLOX 178C
OAG: TS-Optics TSOAG09, ZWO EFW 7 x 36 mm, ZWO filter sets: LRGB and Ha/OIII/SII
Explore Scientific HR 2" coma corrector, Meade x3 1.25" Barlow, TV PowerMate 4x 2"
Some filters (#80A, ND-96, ND-09, Astronomik UHC)
Laptop: Acer Enduro Urban N3 semi-rugged, Windows 11
LAT 61° 28' 10.9" N, Bortle 5

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TSS Photo of the Day

Re: Artificial Star using Christmas tree ornament ?

#38

Post by KenGS »


SkyHiker wrote: Sun Dec 27, 2020 4:17 pm If you have two 12" scopes then simply put a pinhole lit by a laser at the focal plane of one, and let it face the other. No long distances needed.
Great excuse for getting yet another scope!!
--Ken
GSO RC8 CF; Vixen 150mm F5 Newtonian c.1983; Super Polaris mount; DMD-1 controller; DIY Arduino controller; EQ6Pro mount; Synscan 3 controller; Avalon M-UNO; Vixen 60mm F12 refractor guidescope; Meade Lightbridge 12"; ASI1600MM-C; ATIK 420, Tamron 46A 70-210mm, ST80, Imaging Source DBK-21AU04-AS cam, Prostar/Toupcam GPCMOS0120KMB, ZWO ASI120MM-S, Bortle 5 sky.
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