Will my pinhole camera make a good artificial star

[Doc]

I'm thinking about making an artificial star.

I have an pinhole camera shown below. With shutter closed.

With shutter open.

Close up off the pinhole. The aperture of the pinhole is 0.012"

The bottom showing nut for fitting onto a tripod.

Inside the camera. Notice the curved plane this is so all light falls evenly onto the film.

Now my idea is to put an LED behind the pinhole so hopefully an artificial star is produced.

Also within the compartment will be a 9v battery. Or get one of this keyring type LED fobs and position that.

My questions are is this viable, will it work. The maths involved are pretty tricky but how far away would this have to be.

Pinhole = 0.012"

Scope is F4.5

FL= 1829mm

Mirror = 400mm

I'm really struggling at the maths and need help.

[philsail1]

Sorry I can't help you with the maths "Doc," but I must say that you've made a really good job of the "Pin Hole" camera!

I would just go ahead and give it a go! What have you got to lose?

Best wishes,

philsail1

P.S. I think a few people would like to produce "artificial stars" as they are the only ones we are likely to see thesedays! (It could be a kind of "therapy" for those who are suffering from lack of visual skies!).

[ngc2403]

hey some possibly wrong maths but - 196meters?

i don't know why cause with the picostar is was about 20 meters for a 16'' telescope.

with a simple web camera in the back we got images of the colimation, i can post them if you like and tell you how we got on with it?

ally

[mik]

This may be of some use Doc.

http://www.iceinspace.com.au/63-265-0-0-1-0.html

[ngc2403]

after some checking the picostar has a diameter of 50um so 6 times smaller than the hole is yours hence the much longer distance for your scope.

try using a fibre optic cable or getting the hole much smaller. this will bring the distances down.

ally

[Psychobilly]

I use a 62.5um fibre patch lead illumninated by a maplin fibre optic torch kit at about 20m to do my 8" SCT...

(click to enlarge)

Billy...

[Doc]

Cheers guys for all your comments.

196m that was a bit of a shock. Would need a runway or motorway for that one.

I'm going to give it a try anyway.

Then I'll look for a ibre optic set up from Maplins.

[Doc]

I use a 62.5um fibre patch lead illumninated by a maplin fibre optic torch kit at about 20m to do my 8" SCT...

(click to enlarge)

Billy...

Billy whats smaller 50um or 62.5um

[narrowbandpaul]

basicall, the angular width of the pinhole is 0.012"/distance from pinhole (also in inches), multiply this by 206264 to covert to arcsecs. now the human eye has a pupil diameter of around 3mm during daylight conditions...meaning a theoretical resolving power of...46 arcsecs, at 550nm. Now...once the image of the pinhole is magnified, it needs to be less than the resolving power of your eye...fully generalising first, we have

L= x_h * f * D_eye / (1.22*f_eyepeiece*W)

where L is the distance where observed angular size through scope equals resolution of eye, x_h is the pinhole size, f is the focal length of telescope, D_eye=diameter of pupil, f_eyepiece is the focal length of eyepiece, and W is the wavelength...

for your setup, with the values above...with everything in SI units, and assuming a 10mm eyepiece. Note L increases for more magnification

L=250m, if I did the numbers correct

how interesting...

anyway thats the maths as I see it.

I hope this helps, I fear not

Thats the arguement from a diffraction point of view

Paul

[ringz]

Here's some info I've found about artificial stars and pinholes.

The best reference book regarding artificial light sources for star testing/collimation is

Star Testing Astronomical Telescopes by HR Suiter.

In it he states pinhole sizes that can be used with various optical systems.

the following is an extract:-

[tt]

Focal Ratio

Aperture F4 F5 F6 F8 F10 F15

61mm 2.4" 0.07 0.07 0.08 0.11 0.13 0.20

76mm 3" 0.09 0.07 0.08 0.11 0.13 0.20

108mm 4.25" 0.12 0.08 0.08 0.11 0.13 0.20

152mm 6" 0.17 0.11 0.08 0.11 0.13 0.20

203mm 8" 0.23 0.14 0.10 0.11 0.13 0.20

254mm 10" 0.28 0.18 0.13 0.11 0.13 0.20

318mm 12.5" 0.35 0.23 0.16 0.11 0.13 0.20

356mm 14" 0.40 0.25 0.18 0.11 0.13 0.20

406mm 16" 0.45 0.29 0.20 0.11 0.13 0.20

[/tt]

These pin hole sizes are such that they are smaller than the resolution of the telescope.

So for example, my 10" F5 Newtonian would need a pinhole size of 0.18mm or less.

There is another way, in daylight, of producing a light source with the required size (in my case 0.18mm) and that is with a Christmas spherical glass tree ornament.

An ornament of 50mm being lit by the sun produces a light source of 0.17mm.

[tt]

Sphere Size "Pinhole Size"

12.5mm 0.04

25mm 0.08

50mm 0.17

75mm 0.25

100mm 0.33

125mm 0.42

150mm 0.50

[/tt]

If you want to use the globe in the night time you can use a torch placed 1 metre away from the globe and stopped down with a piece of foil with a hole of size 1cm.

I hope this helps out.

--

Martyn

[Kaptain Klevtsov]

I wonder if a red laser (as in collimation tool) pointed at a ball bearing would make a small spot? I reckon it should do, based on the tree ornament idea. How is the range thing worked out though, based on the available focus of the 'scope or what?

Kaptain Klevtsov

[Doc]

Thanks Paul and Martyn.

Well I definetly do not have access to 250 metres of space so I'll forget this for now. Still the maths Paul is very impressive. I tried to follow on a calculator and got a little lost.

Think I should go back to school.

[narrowbandpaul]

i am not sure if the spot has to be a perfect spot...perhaps a small extent to the pinhole would be OK...however try and get as far as possible from the spot as possible, and try it?...you never know

[Psychobilly]

I use a 62.5um fibre patch lead illumninated by a maplin fibre optic torch kit at about 20m to do my 8" SCT...

(click to enlarge)

Billy...

Billy whats smaller 50um or 62.5um

Hmmm is that a trick question :scratch:

50um is 12.5um smaller than 62.5um

[ringz]

Doc,

You only need to set an artificial star a long way away from the telescope when you are star testing. For collimation you can stick a star as close as your scope will focus.

you do have to ignore the ensuing spherical aberration the nearness produces, but it's a small price to pay for convenience 8)

KK,

Using a laser with a ball bearing is something that is done. It produces a very small "pinhole" diameter depending on where you place the laser and the divergence of the beam.

--

Martyn