Preparing and running your first test

(Let the fun begin!)

 

All righty now, lets have some series fun!  Hopefully you’ve completed the getting started guide which walked you thru the steps needed to tell RTAFT all about your test platform.  At this point your should be sitting with something that looks like this:

 

 

If the main video window is black, then you need to go setup your Foucault platform, preferable somewhere near the null for zone 1 J  The only part of Foucault setup I’ll touch on is, you need to make the image as large as possible on the main display.  HOWEVER, you need to leave a little room on the left and right side of the mirror!  Two reasons for this:

  1. Your platform is probably going to have a little periodic error (well maybe not, but mine sure does!)  Anyway, this periodic error will show its self as the mirror moving about a bit on the screen during the test.  Consequently you need to leave a little wiggle room for this!
  2. Tracking works by finding the edge of the mirror.  If you have ZERO periodic error, you really have no need for tracking.  As I said, my platform has periodic error, so for me tracking was a must have, so leave a little extra wiggle room for this as well

 

Ok, at this point you should hopefully have some type of Focualt image on the screen.  Next thing to do is tell RTAFT all about the mirror your testing.  To do this follow these steps:

  1. Click Mirror Database / Add or Edit mirror profiles.
  2. This will take you to the following screen (which needs some work, but its usable!)
  4. Now enter the following data:
    1. Mirror Name (Note this will also be used for the name of the folders used to save test result data in, so no FUNNY characters! Ya know the ones like “/\:*?<>|” J
    2. Mirror diameter, actually the mirrors clear aperture (diameter minus bevel)
    3. Mirror ROC (2X focal length, but if you needed to be told this, you probably need to shut the computer down and go do some manual Foucault testing!)
    4. Deformation Constant (All intents and purposes, leave this alone as you are probably making a paraboloid, and that’s the default.  However if your doing a sphere/ Hyperbolic, or whatever, enter it here)
    5. Secondary obstruction (If any) 
    6. Number of zones to test (I suggest leaving this at 5 for the time being, but it can be anything from 3 – 13)
    7. Last entry is the Tests ran to date, you can leave this one alone as well J
    8. Finally click OK to save the profile and return the main interface, where things will look a little different J
    9. It’ll look like this:
  5. First thing you’ll notice are new bar graphs at the bottom of the screen. 
  6. Second is you will notice that the main video screen is a little different, there are now tick marks on the horizontal cross hair. 
    1. These are the spots measured for each zone.  The intensity of the image under the tick mark is plotted on the bar graphs on the bottom of the screen.  For instance Zone 1 Left is plotted in Blue, right in red, under the Zone1 bar graph Section.
    2. Also notice the Black text window.  This is the data you would use if you were going to manually enter test info into a program such as TEX.exe or AdMir.exe.  For each zone a column of data for the equivalent paper mask zone holes inner and outer radiuses.  Also you get the center radius, which is used by RTAFT to locate the tick marks for pixel intensity recordings.  Lastly, you get generated perfect zone readings for reference. 
  7. Now, we need to inform RTAFT how BIG the image of the mirror is on the screen.  In the above image, we need to get that BIG purple circle to lay right on the edge of the mirror.  To do this there are two methods:
    1. Manually adjust the cross hair and circle diameter:

                                                              i.      See the slider control to the right of the main video display?  It move the cross hair UP/Down

                                                            ii.      See the slider control directly underneath the main video display? It move the cross hair Right/Left

                                                          iii.      Finally the second slider control underneath the video display adjust the diameter of the purple circle

                                                           iv.      Use these three controls to center the cross hair on the mirror, and get the diameter to lay right on the edge of the mirror

    1. Alternatively, I have written a semi-automated process for getting this setup correctly.

                                                              i.      Fully illuminate the mirror by backing out the knife edge (whole surface of mirror is bright)

                                                            ii.      Click on the center of the mirror with your mouse.

                                                          iii.      Hopefully the code will find the mirror on the screen, center the cross hair and get the diameter pretty close.

                                                           iv.      If the diameter is off a bit (Usually to small?) turn on tracking (this keeps one side of the circle in place) and manually tweak the mirror diameter for best fit (Btw, a little error here doesn’t really effect things too much)

  1. Hopefully your display should look like this now:
  3. While we’re here lets talk about this display
    1. At the top in yellow is the mirror profile being used for this test (Hint, make sure when testing several different mirror’s you select the right profile! BTDT!)
    2. Also at the top is the current test being ran
    3. Big purple circle defines the mirrors’ outer edge
    4. Little blue circle defines the diameter of the secondary obstruction (if any)
    5. Short little tick marks on the horizontal cross hair define the spots were measuring pixel intensity at (IE center of each zone, with zone 1 closest to mirror center)
    6. At the bottom is the Knife edge longitudal travel reading (when you move closer to mirror the number decreases, move away from mirror the number increases!)
    7. One side note, this mirror is pretty ugly IMHO, but its my  test mirror so no complaining! J
    8. OH, one last thing, see the big red spot on the bottom of the mirror, that where the laser alignment system hits the mirror surface. I leave it on during a test as it helps to keep my camera from trying to auto-adjust the image gain (brightness).  The spot fools the camera into keeping a constant shutter speed. 
  4. OK, were getting closer to the magic moment, but first lets talk about the light source intensity:
    1. We want our light source bright enough, so that are bar graphs go all the way to the top when the mirror is fully illuminated (actually if its greater than 200, it will be fine)
    2. Secondly we don’t want the light source so bright that it actually saturates all the pixels!
    3. So, with the mirror fully illuminated, adjust the light source so its bright enough to get above 200,  with maybe a few bar graphs hitting 255.
    4. Once this is done, you should no longer need to adjust the light source intensity for this F ratio mirror.  YMMV of course!
  5. One more thing, remember when we setup the “Shades of Gray” options?  I mentioned we might need to revisit that page depending on some camera noise tests.  Well its time to check this out now. So here’s what to do.
    1. Cut the knife-edge in so the entire mirror is dark.
    2. Look at the bar graph readings
    3. Are they < 10 or so?

                                                              i.      If they are, cool!  You can move onto other things now

                                                            ii.      If they are higher than 10, this indicates you have a pretty good bit of noise floor in your camera system. 

                                                          iii.      If the bar graphs are bouncing all over the place, find the “Frame average slider” and move it to the right to get a frame average of 30 (this means each bar graph will be the result of 30 frames of data averaged together.)  Re-check the noise.

                                                           iv.      If the noise is still higher than 10, record the noise reading, then go back to Platform Settings / Platform and Foucault settings / Zone intensity tab.  Add the amount of noise for your system to each of the two sliders in the dialog box, then click OK.

                                                             v.      BTW, if your noise is higher than 30 or so, try and figure out WHY!  Maybe your test room is to bright or something.  Probably their isn’t much you can do about it, but its worth looking into!

  1. Well Damn, I think were ready to run your first Automated test!
  2. Turn on Tracking (not absolutely necessary, but shouldn’t hurt)
  3. Click the big green “Do the Magic” button (BTW, that is an attempt at humor! J)
  4. Fun stuff starts NOW!
    1. Watch zone 1, depending on where your knife is you should see the following happen:

                                                              i.      If knife on LEFT, the red bar graph should head to the “Shades of Gray” range between 30 & 60

                                                            ii.      If knife on RIGHT, the blue bar graph should head to the “Shades of Gray” range between 30 & 60

                                                          iii.      The opposite bar graph should will do the following

1.      If its brighter than the reference “Shades of Gray” bar graph, the computer will move towards the mirror until it is dimmer than the reference bar graph

2.      Slowly you should see the two bar graphs start to approach being equal

3.      When the two bar graphs are equal the code will call this the Zone Null. 

                                                           iv.      If this is the first zone on the first pass, the computer will reset knife travel to 0

1.      All other zone nulls will be reference this first null

2.      You will see a change in the black text window

3.      Zone 1 Pass 1 will be zero

4.      All other zones readings will remain zeroed until they have been found, where the actually reading will then be placed.

                                                             v.      If all goes well, the computer will move on to Zones 2 – 5, recording null position as it goes.

                                                           vi.      At the end of zone 5, it will re-wind the platform and start the second pass

                                                         vii.      After all 4 passes are complete:

1.       The code will save the data

2.      If auto-launch Figure45 or Sixtests option were selected, the code will Launch each app in series.  With Figure45, you’ll have to take control and select the last test ran (usually the highest numbered test) On Sixtests, the code will launch the app, have Sixtests open the data file, and instantly send you to the mirror surface profile screen, without ever having to touch the keyboard ;)

  1. That’s it, if all went well, you have completed your first Automated Foucault Test, Congrats!

 

That’s it for this page, More will be coming in the future! 

 

Take Care,

James Lerch

jlerch@tampabay.rr.com