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Artificial stars.......

whizzbang

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russ.will

russ.will

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I kept looking into artificial stars, but (and this may matter more with long Newts) because collimation shifts with the declination/altitude of the scope, I couldn't see the point of colimating for the horizon which is all an AS can offer.

Russell

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ollypenrice

ollypenrice

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Forget fancy electonic/fibre optic/blah blah blah gadgets. The best artificial star will cost you less than a quid. I visited Danny Cardoen's optical workshop recently and saw mirrors in preparation for sending to professional observatories the world over. This man is a genius. His artificial star is a ballbearing illuminated from just off one side. He stressed that, in any serious optical shop, this is what you will find. Danny has mirrors at Paranal, for heaven's sake, so I'm inclined to believe him and it is also what TeleVue told me to do in order to fix a damaged Genesis. It worked.

Olly

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JamesF

JamesF

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I kept looking into artificial stars, but (and this may matter more with long Newts) because collimation shifts with the declination/altitude of the scope, I couldn't see the point of colimating for the horizon which is all an AS can offer.

Depends where you mount the artificial star?

James

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JamesF

JamesF

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Forget fancy electonic/fibre optic/blah blah blah gadgets. The best artificial star will cost you less than a quid. I visited Danny Cardoen's optical workshop recently and saw mirrors in preparation for sending to professional observatories the world over. This man is a genius. His artificial star is a ballbearing illuminated from just off one side. He stressed that, in any serious optical shop, this is what you will find. Danny has mirrors at Paranal, for heaven's sake, so I'm inclined to believe him and it is also what TeleVue told me to do in order to fix a damaged Genesis. It worked.

In the main I agree.  A ball bearing is a nice simple solution.  Where I have found an artificial star useful is for collimating an SCT or Mak where the light source needs to be quite some distance away.  It's probably still feasible to use a battery-powered LED and ball bearing, but I just decided it was easier to buy one of these: http://www.hubbleoptics.com/artificial-stars.html

James

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ian_bird

ian_bird

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His artificial star is a ballbearing illuminated from just off one side. He stressed that, in any serious optical shop, this is what you will find.

Olly

Hi Olly

What kind of distance from the mirror does it need to be?

Cheers

Ian

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JamesF

JamesF

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Great post Olly. What sort of light source would be best?

I've heard of it being done with a bright torch (a Maglite, perhaps?) or a desk lamp with a foil shield and a 1"-ish aperture cut in it.  I'm told you can even use the Sun if it's in the right sort of position.

James

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whizzbang

whizzbang

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interesting, have heard  about the ball bearing before.......whats the best light source, did televue specify a light source Olly? and what distance? 

keep it coming, i like cheap ....

R

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JamesF

JamesF

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What kind of distance from the mirror does it need to be?

I've read all sorts of figures -- divide the aperture in mm by four for the distance in metres and all sorts of multiples of focal length.  I always assumed "as far away as is reasonably possible, or for an SCT or Mak, further than that".

There's probably some way to work out the distance as the source of the light from the ball bearing or artificial star needs to be (I think) smaller than the smallest thing the telescope can resolve.  I can handle the maths for an artificial star of known aperture, but for a reflection in a sphere I'm a bit lost.  Presumably if the source is too large you can use a smaller ball bearing.

James

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lensman57

lensman57

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Cheers.... How far just out of curiosity? With the new house I can get about 100m away, far enough to work with a RC8" do you think?

A minimum of 25~30 X the FL. So for an 8" F5 the unit needs to be placed at about 30 meters. Another way of emulating a star is to shine a narrow LED beam on to a ball bearing. Never tried these but I just know of the ways to do it.

A.G

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ollypenrice

ollypenrice

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I don't think it matters too much where the light source is. Close enough to the BB to light it up. The whole point is that only the bit of the BB nearest the scope will direct light towards the scope so you get, effectively, a point source.

Olly

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perfrej

perfrej

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I once put a christmas tree silvar glass ball on the quay abut 75 m from my balcony. I used in bright sunlight and it worked a treat. The resulting light source needs to be super small and the distance depends on how small you make it. I also bought two Hubble devices and ripped them apart. The laser cut screen has small enough holes in it so I mounted a 3W super LED behind it. That works good too.

The finest one you can get is the old Carl Zeiss artificial stars. Thet were made by hand with pins by ladies in Jena!

THere is also a new hologram device by Lasermax, or at least they have a patent for it, that is mounted on the scope and looks like an artificial star through the scope...

/per

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lensman57

lensman57

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I once put a christmas tree silvar glass ball on the quay abut 75 m from my balcony. I used in bright sunlight and it worked a treat. The resulting light source needs to be super small and the distance depends on how small you make it. I also bought two Hubble devices and ripped them apart. The laser cut screen has small enough holes in it so I mounted a 3W super LED behind it. That works good too.

The finest one you can get is the old Carl Zeiss artificial stars. Thet were made by hand with pins by ladies in Jena!

THere is also a new hologram device by Lasermax, or at least they have a patent for it, that is mounted on the scope and looks like an artificial star through the scope...

/per

Hi Per,

My reservation about using an artificial star is more to do with the position of the scope , Newtonian that is,  while being checked out or collimated as the scope is at or near horizontal. They should surely be collimated at the roughly same altitude of the intended target not horizontally, I guess with a lens scope it would not make any difference. The hologram device sounds interesting though.

Reagrds,

A.G

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perfrej

perfrej

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Yes, AG, I agree on that one. I modified my 190MN's primary mirror cell so that it would at all model wit hthe 10Micron mounts, and that sort of removed the problem of collimation angle as well ;)

/per

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Jussi_K

Jussi_K

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I bought artificial star for my GSO 12" RC. I mainly used it to make an "very close collimation" With an DSLR Liveview. I used camera screen to collimate main mirror and laptop screen to secondary. This worked very well, the feedback was much faster, than to wait my SBIG 8300 to download the image after every tweak.

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Macavity

Macavity

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If you can't always rely on the sun, use some basic (dreaded skool!) physics.  

No need for "fibre optic exotica", but still fairly hard to drill very small holes? :p

Let 1/f = 1/u + 1/v be your guide? I drew inspiration from:

http://observatory.mvastro.org/library/Star_Test/ArtStar.html

With sundry stuff hanging around, I came up with:

http://stargazerslounge.com/uploads/monthly_08_2013/post-539-0-25390800-1376986947.jpg

It is EASY to set the size of star by interchanging "eyepieces"! But you cannot avoid the need for a

longish baseline - OR you are going to need substantial out-focus, the test might be less valid etc.

It works nominally at 15m lol. But with approx 80mm outfocus on my 8"/F4 Newt. One of these days,

in the wee small hours, I'm going to try the STAR mounted on a tripod, placed a few tens of metres down

the road? Trouble is, my nemesis (stalking!) neighbour would probably report a UFO landing... :D

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