Artificial Starfield - Would this work

[Mav359]

Hi Guys

I have a C9.25 with a Hyperstar @F2.3. Apparently according to the calculation on the Hubble Optics website their Artificial star (which i have ordered) @ 6.5m would be good enough to collimate the scope. The problem with the Hyperstar is you need to collimate against an entire frame to account for any tilt on the CCD so in my head i'm thinking this based on Hubble Optics Artificial Star.....

If i took a piece of A3 sized 3mm hardboard & used a 0.2mm drill bit to drill multiple holes over the sheet, then placed it over my Flat Field panel like a mask and then mounted the whole thing 10m away, would i have a usable star field to work from?

Thoughts please

[Peter Drew]

Sounds worth a try. 

[russellhq]

Plate metal might give nicer stars. You can pick up plates of aluminium quite cheap from ebay. Definitely worth a try though.

[Psychobilly]

Another option would be to use fibre optic patch leads fitted into a sheet of plastic... use an LED or Bulb as a light source... Much smaller "stars" then...

Peter...

[Mav359]

mmmmm plate ally is a good idea might give that a go, cheers Russell

Fibre and all those bits might be a Mark II version i think, starting as above i can keep it cheap.

Cheers Guys

[Psychobilly]

Really small pinholes can be made in aluminium foil placed in a stack of paper or card...

Peter...

[Mav359]

Right lets see what this does, i've ordered an A3 sheet of Aluminium or as the Americans would say Aluminium & a set of Micro Carbide Drill Bits

I'll put it all together and report back

[perfrej]

The holes need to be round with smooth edges, and I think you may need the smaller of the holes (at least I did). In fact, I bought two of the Hubble things and took the template out of one of them. Said template now sits in front of a 3W lensed LED so that it can be used in daylight

/per

[Mav359]

The drill bit set starts with 0.1mm, 0.2mm & upto 1mm so if that aint small enough then it wont work at all

[Mav359]

The holes need to be round with smooth edges, and I think you may need the smaller of the holes (at least I did). In fact, I bought two of the Hubble things and took the template out of one of them. Said template now sits in front of a 3W lensed LED so that it can be used in daylight

/per

Any pictures of the LED setup?

[Psychobilly]

The very small carbide drills tend to be very brittle and will need very high speeds to cut efficiently... they are normally used for drilling pcb laminates and will typically run at 30,000 rpm or higher...

Peter...

[Mav359]

I ordered a Dremel with the flexi tool to make it easier to work (I needed this for something else) that apparently according to the desc runs up to  32000rpm, & the ally is only 1mm thick. Again if you believe the desc the drill bits should cut through ally so we'll have to wait and see what happens.

I'm no worse off if it don't work but if it does i should be able to spend as much time as i like indoors getting the collimation perfect

[Psychobilly]

Have fun

Badly typed on my Galaxay S4 in Tapatalk4

[perfrej]

The mask on the Hubble thing is very, very thin and obviously laser or water drilled. I already had a home-made artificial star so I just cut off a quarter of the Hubble mask and taped on top of my previous hole in the box. It works.

I am not sure how it would work with a 1mm thick plate, though. Actually, the going method for artificial stars is more along the lines of kitchen aluminium foil and a pin-hole (made with a pin). You should start there. And the LED needs to be really close or you get a star that is extremely sensitive to angle.

Picture coming up...

/per

[perfrej]

[Mav359]

Heres what im thinking i can do

Im going to build an A3 box, it will only be 1cm deep & will have a hardboard base. In that i am going to lay multiple strips of LED lighting and essential flood the box with light. There is an 1mm A3 ally sheet on top with multiple 0.1mm holes drilled in it. The LED's will sit no more then 0.6mm from the ally sheet and i will put a battery pack on the back to power it, a LED dimmer switch so i can lower the brightness and a tripod mounting bracket so i can attach it to a tripod in a fixed position and distance.

@Per - If the Ally sheet is too thick then i'll try the foild over the top of the frame, i like the idea of the metal sheet because its a more solid structure and can be reused often if needed.

Thoughts

[perfrej]

You will find that point sources are aimed using a design such as your contemplated. I had 4mm of spacing between the foil and the LED initially and it was very difficult to aim the "beam" properly. With multiple LEDs, all at some distance from the holes, you are going to have a spray of rays coming out in multiple directions, none of which are going to coincide at your scope (well, one or two then).

I promise, the beams are very narrow since the holes are small. The only way to make it more wide angle is to have the LED right up behind the hole.

What you need is a very bright and perfectly even light source. 500W or so, perhaps?

/per

[Mav359]

So if i reduce the gap to the back of the ally to nothing and line the LED's up with the holes do you think that would that help?

[perfrej]

I think you need one LED behind each hole in order to assure that all rays make it. The Hubble has a very short distance between the LEDs and the screen, and you have to turn the thing to the max intensity (moves the screen over the LEDs), i.e. get a LED right behind the hole.

/per

[Mav359]

Does this make a difference.....

I wont be de-focused on this like you would for collimation normally, i can use the hubble optics star for that, this will focused in on so that i can check for tilt on the CCD or Hyperstar

[Mav359]

I can get the distance down to less then 1mm

[russellhq]

Could you use Led's like these to get closer to the holes?

http://m.ebay.co.uk/itm/271078701124

[Mav359]

That was already the plan, i've already build most of it

http://stargazerslounge.com/topic/207556-artificial-starfield-build/

[RogerTheDodger]

I was thinking of making a starfield with small ball-bearings glued to a sheet of ply with the light source behind the telescope. I know people have done that with a single ball bearing.