astrogazing_dove
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Reged: 07/19/12
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Hubble 5-starArtificial Stars test 8 " Dob ?
#5340245 - 07/28/12 03:19 PM
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Would I be able to start test my 8 " Odyssey with a Hubble 5-star Artificial Stars ? how far would I have to place this to do a star test ? Have someone on this forum tried this unit before for star testing ?
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tomharri
sage
Reged: 09/19/08
Loc: Arizona
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: astrogazing_dove]
#5340285 - 07/28/12 03:52 PM
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The hubble flashlight is great. I tape over 4 of the lights so only 1 shows. You can adjust in the comfort of your house if you have a long distance. I can leave open the door to the garage and have about 75', and the light shows up good in the dark garage.
For a reflector you just make the doughnut concentric, maybe need an extension tube so you can examine on both sides of focus.
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BSJ
scholastic sledgehammer
Reged: 12/22/08
Loc: Grand Isle, VT
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: astrogazing_dove]
#5342911 - 07/30/12 07:39 AM
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You have to be able to reach focus. Whatever the minimum distance that is, is the closest you can be.
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howard929
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Reged: 01/02/11
Loc: Low End of High Ground
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: astrogazing_dove]
#5343136 - 07/30/12 10:38 AM
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According to the Hubble web site the artificial star comes with no instructions. Question #4 in a short Q&A (midway down the page) states the equation for determining the distance.
OTH, Suiter's book has a table page 91 that should be useful. For your scope (8" f/4.5) it shows a min distance of 32 times the focal length (oops) but he cautions that doubling or even tripling that number is advisable.
HTH
Howard
Edited by howard929 (07/30/12 11:21 AM)
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: howard929]
#5343207 - 07/30/12 11:25 AM
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Quote:
According to the Hubble web site the artificial star comes with no instructions. Question #4 in a short Q&A (midway down the page) states the equation for determining the distance.
OTH, Suiter's book has a table page 91 that should be useful. For your scope (8" f/4.5) it shows a min distance of 32 times the focal length (oops) but he cautions that doubling or even tripling that number is advisable.
HTH
Howard
Howard:
Artificial stars are useful for star testing but I have found real stars are better. One issue with star testing with an artificial star is that the scope is horizontal, if there is any shift in collimation with altitude, the test will not be accurate.
Jon
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Fuzzyguy
sage
Reged: 12/21/11
Loc: Colorado/Kansas
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: howard929]
#5343232 - 07/30/12 11:39 AM
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I've never used an artificial star for collimation. When I changed my scopes over to Bob's Knobs, I pointed the scope at a reflection of the sun off of a power line insulator about 200 yards away to get a coarse collimation. When I went out that night collimation wasn't perfect, so I fine tuned it using a real star. A couple of weeks later, I had a great seeing, so at the end of my viewing session when I was sure my scope had reached equilibrium, I did touch it up a bit using the diffraction rings of an in-focus star at very high magnification.
To expand on the OP's questions, could you accomplish everything above just using an artificial star? Do you still need to finish it off using a real star?
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Fuzzyguy
sage
Reged: 12/21/11
Loc: Colorado/Kansas
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: Fuzzyguy]
#5343233 - 07/30/12 11:41 AM
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Sorry, I guess Jon answered my question before I got it posted! 
Thanks Jon!
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howard929
Member
Reged: 01/02/11
Loc: Low End of High Ground
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: Jon Isaacs]
#5343252 - 07/30/12 11:50 AM
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Yep Jon, Agreed.
Though interested in at one point, my conclusion is it's just more accurate for a lot of reasons to star test with a star.
All IMHO and I guess YMMV.
Howard
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: Fuzzyguy]
#5343288 - 07/30/12 12:08 PM
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Sorry, I guess Jon answered my question before I got it posted!
Thanks Jon!
I am not sure what question I answered but...
The star test is good for checking the collimation but collimating a Newtonian really needs to be done with tools. This is because there are several adjustments necessary including the tilt of the primary, the tilt of the secondary, the rotation of the secondary. The the star test does not tell you the cause of the miscollimation.
Jon
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howard929
Member
Reged: 01/02/11
Loc: Low End of High Ground
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Re: Hubble 5-starArtificial Stars test 8 " Dob ?
[Re: Jon Isaacs]
#5343497 - 07/30/12 02:08 PM
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Jon,
My overall conclusion from reading Suiter's book was between collimation issues and main mirror figure, a star test holds more value with determining the condition of the primary mirrors figure.
Howard
Edited by howard929 (07/30/12 02:09 PM)
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