Artificial stars

[kerrylewis]

Does anyone have experience of using these? Perhaps for an SCT?

It seems to me that it would be an advantage to do this during the day rather then losing observing time. The units supplied by British retailers seem to be quite expensive but this one: http://www.hubbleoptics.com/artificial-stars.html seems quite reasonable even with postage from the USA.

One problem I might have is placing it at sufficient distance. Given the configuration of my house and garden I would find it difficult to achieve 20 or 30 metres. Is this really critical for basic collimating?

Lastly- has anyone successfully made their own?

Kerry

[Moonshane]

hi Kerry

I bought this same unit and distance was also my problem. I sold it in the end as I was not using it and it was just sitting in my case. I am not sure how critical distance is but I think the requirement increases with aperture too?

[cgarry]

I considered one, but like you I would struggle to locate it far enough away to focus it.  My other concern was that collimating while the scope is horizontal will not be very accurate for when the scope is pointing at the sky, certainly for larger scopes.  I don't believe they are very difficult to make, though it is not something I have done myself.

If money is no object, there are other approaches:

http://www.firstlightoptics.com/hotech-collimation-tools/hotech-advanced-ct-laser-collimator.html

I think I shall carry on using normal stars for now.

Cheers,

Chris

[anthony]

I have seen one of the versions in your link in the flesh so to speak and it was very good.

The issue is whether or not you can get enough distance to get the accuracy in collimating. 20-30m might be enough to get collimating close enough so that you are in the right area for proper collimating on a real star.

I know people have tried with mirrors to increase the distance. I have not read this link yet (but am about to). At a glance it looks interesting.

http://www.cloudynights.com/item.php?item_id=2879

[kerrylewis]

Interesting comments. I hadn't seen the gizmo from FLO before - looks fascinating - but the price! Anybody got one? Don't be afraid to admit it!

I quoted 20-30 m as what seems to be recommended as a minimum. I cannot achieve that but when the rain stops I will measure my maximum distance.

The 'smoke and mirrors' option looks interesting too at a glance. I don't have a spare concave mirror though. I wonder if a shaving mirror would be good enough!

[ollypenrice]

There is a very easy way to make a good artificial star for peanuts. I got the idea from TeleVue themselves but it is also 'out there.' You just take a small steel ballbearing and glue it to some mat black card. Set it vertically and aim a good quality beam at it. A decent cycle headlamp will do the job. Put the light in front and a little to one side so you can observe the illuminated BB with your scope. Only light reflected from the part of the BB nearest the scope reaches the objective so you have a lovely point source.

I used this indoors in a warehouse with a 4 inch refractor. (Indeed this was a warehouse belonging to an enterprise called Captain Condom, though other types of warehouse will do fine!!!) I found I had totally credible diff circles at only about 5 metres, though longer would be better. I took a well collimated Nikon Birder along as a control test to confirm that the method worked. I've also used it outside at greater distances but I don't believe that 30 metres is really necessary. I'm told you can do it just with sunlight but I haven't tried.

There's an even cheaper method, which I've seen Ralf Ottow use here. (Be aware that Ralf can collimate a Newt almost perfectly without any EP, crosshair, or gadget of any kind. He's a professional optical engineer and could probably make a half way decent mirror out of baking foil...)  He aimed the scope at the forests in front of our house and scanned around till he found a tiny gap in the trees which was letting some sunlight through. This was his point source. He even confirmed that my Dob's original secondary wasn't flat. He Set it up on the windowsill pointing at one of these tree gaps and then observed the gap via my secondary from his scope inside the house. His scope suddenly became astigmatic due, of course, to my bad primary.

The ballbearing trick, though, is great.

Olly

[kerrylewis]

Thanks Olly.

I am certainly going to have a go at the 'ball bearing trick'. Seems to solve the distance problem too! You say a 'small' ball bearing  - what size did you use?

Thanks again for the very helpful reply.

I won't ask about the warehouse name! 

Kerry 

[faulksy]

this sounds very good im going to try this as well

[kirkster501]

Good idea Olly. I have heard this method before but not tried it.  I also have the Hubble artificial star and even located 30 metres away it is still not far enough.  On your own property its hard to get much further than that.

[ollypenrice]

Thanks Olly.

I am certainly going to have a go at the 'ball bearing trick'. Seems to solve the distance problem too! You say a 'small' ball bearing  - what size did you use?

Thanks again for the very helpful reply.

I won't ask about the warehouse name! 

Kerry 

Oh, just a small BB. I can't remember the size and doubt that it's critical, but it might have been 1/8 inch. Knowing me it was probably a cycle wheel BB.

Don't talk to me about Captain Condom! I was a pal of Chris, the owner, (known to all as 'the Captain') and he once had me as a Spanish translator on a sales trip to Majorca. We had to go through check in with a condom vending machine as hand luggage. The banter with the airline staff was great. Then once I had my car stolen and he kindly lent me his van. I was a teacher and gained heroic status amongst the kids when I turned up for work in it...

Olly