playing with Ronchi...

Astroman (Andrew Wall) · #1 22-08-2006, 07:42 PM

Hi all,

I have just completed a simple ronchi tester, mainly to help me understand how these things work. I used a program called grating to make the grating and had a LED shining through the transparency which was at the centre of curvature of my 8" f7 mirror. The same grating extended out so I could have my camera there to take a pic of the return beam. This was only a test and so far it is starting to work, but there is alot of blurring of the lines, its quite possible I need to diffuse the LED more make a smaller slit for the light to go through and use a real ronchi screen

Anyway here is one of the first pics from it. The blocks holding the mirror can be seen on the bottom.

Astroman (Andrew Wall) · #2 22-08-2006, 09:56 PM

okay here is another image taken with the light source blocked a little, might end up changing light sources as this one is dying a slow death under battery power

cristian abarca · #3 22-08-2006, 10:10 PM

Hi Andrew I use an LED light on my tester (a green one) and it works fine. The slit on the tester has to be really thin though. From the 2 set of pictures it looks pretty good specially the second one, you can see the lines pretty even.

Regards Cristian

Astroman (Andrew Wall) · #4 22-08-2006, 10:15 PM

Just wondered if the colour of the LED makes much of a difference, might try the green.

Astroman (Andrew Wall) · #5 24-08-2006, 08:31 PM

Here is my latest effort at a ronchigram. Decided to do it in B&W for better contrast...

cristian abarca · #6 24-08-2006, 10:06 PM

I've seen red blue and green LED lights used all to good effect. Your image seems to be quite clear. I tried the green because it was recommended from an ATM website. I'll try and post a picture of a test on my mirror tomorrow night.

Regards Cristian

h0ughy (David) · #7 25-08-2006, 07:39 AM

looks good to me , But then again I don't know that much, better than Matts that is posted in IIS as well, saw that yesterday, yours is 1000% better than his. i think thats why he is getting a replacement scope!

cristian abarca · #8 27-08-2006, 08:11 PM

Hi Andrew here is a picture of my new mirror through green LED and 100 lines per inch grating. The lines are supposed to be bowed as the picture was taken with the mirror on a stand not on the telescope.

Regards Cristian

Astroman (Andrew Wall) · #9 27-08-2006, 09:35 PM

Hi Cristian,

I am enjoying watching your progress with the cassegrain, it looks a great project and something that I wish I had the skills to do also. I made a simple test rig with a green LED, how bright does it have too be? I was using an old scratched up lens as a diffuser, I think it was a little too much as I am not getting a clear image.

cristian abarca · #10 28-08-2006, 10:29 AM

Hi Andrew I don't know much about electronics so I took this down from a website 350mcd,565nm,60m.A@2.8V and tookit to jaycar and Dick smith and they got me something similar. The webpage ishttp://www.stellafane.com/atm/atm_fo...er_plans_3.htm
Regards Cristian

joe_smith · #11 28-08-2006, 03:31 PM

Andrew were can I find the grating program? also what printer did you use to print it out on?

Astroman (Andrew Wall) · #12 28-08-2006, 04:33 PM

http://www.coaa.co.uk/software.htm

The program is called Grating. I used an inkjet Canon MF450, but would be better on a laser printer. I used transparency film that was a year or so old so not sure if that has an effect.

joe_smith · #13 28-08-2006, 04:45 PM

cheers Andrew with give it a go at work