Hubble Artificial Star......its the bong !!!

[Highburymark]

Regarding primitive home made collimation (of SCTs), this is what I posted on another SGL thread today:

 

Just out of interest, last year I did a very simple collimating test at home to see if it worked. After doing a normal star test, which showed my SCT needed slight adjustment, I got some aluminium foil, and stretched it over a hard surface, then made the smallest pinprick possible. I then used this to make an artificial star, and from a distance of about 30ft, it showed exactly the same result as the star test - only brighter. Collimating the scope inside with a non moving target was easy, and when I subsequently did another star test outside, the scope was spot on. The key is to make the smallest hole possible in the foil - which must be flush against the hard surface. I am sure that this process will not work for everyone, and may not be as precise as other techniques, but it is certainly an easy and cheap way to check basic collimating.

[N3ptune]

On 2016-01-21 at 12:39, kirkster501 said:

Since my post three years ago I have revised my opinion on these downwards, regrettably.  The hole which shines the light through and performs the role of the "star" is too big and gives inconsistant results I have found when using it to collimate 8" and above reflectors.  This was even when the scope was 40m away.

I am interested in a device like the Hubble, but maybe I will build one myself instead. I have a Skywatcher 200p reflector which is 203 mm x 1000 mm. I would like to know if it's going to work. 

Given the size of my telescope, does a tiny needle hole is going to be ok? I have the possibility to put the artificial star at 140 meters or even 340 meters away.

Thanks

[kirkster501]

On 2/17/2016 at 22:21, N3ptune said:

I am interested in a device like the Hubble, but maybe I will build one myself instead. I have a Skywatcher 200p reflector which is 203 mm x 1000 mm. I would like to know if it's going to work. 

Given the size of my telescope, does a tiny needle hole is going to be ok? I have the possibility to put the artificial star at 140 meters or even 340 meters away.

Thanks

Yes, only a tiny hole is all that is needed.  Think about it, the angular diameter of a star is infinitesimal.  140m and even better 340m gives you more leeway if the hole is a bit bigger.

[N3ptune]

Ok if it can be done, Iam going to try and make the smallest dot I can. (:

Thanks Kirkster

 

[cs1cjc]

The Hubble has 5 pin holes of 50/100/150/200/250 microns ( 0.05, 0.1, ... mm) of which I find the 0.1 and 0.15mm to be most useful for small scopes, so you would be aiming for something about that size. 

Do note that to minimise aberration, you want to have the artificial star at least 20 focal lengths away from the telescope under test, the further the better and this needs to be *much* further for some designs. Accordingly you want a bright light behind the pinhole, though nowadays an LED torch can work (which is all the Hubble is, really.