Jacarandas & Z6 surfaces

Add another striking colour to the Hex River Valley's palette: Jacaranda trees in full bloom!

 

So what are we trying to achieve with this M4 alignment?  Darragh's encyclopaedic collection of Zemax simulations includes an amazing grid of Z6 (one of the two astigmatism Zernikes) surface plots that shows the effect of M4 tilt & decentre.  The perfect saddle-shaped surface (in the centre of the grid) that indicates no tilt or decentre is what we're after...  The astigmatism curves mentioned in recent posts refer to sets of wavefront measurements that slice through the Z6 surface in the X & Y directions.

Below's a zoomed in version of the central part of the grid.  Note that the vertical scale's exaggerated in the middle plot to show the saddle more clearly.

At the moment we're struggling with erratic wavefront measurements, which result in vicious spikes all over our Z6 saddle...  Naturally this is far from ideal so we've been trying Everything to track down the source of the noise.  One thing that proved marginally useful was wrapping the wavefront camera & its USB cable in aluminium foil to shield it from interference. 

 

Besides, it contributes to the spacey look we're going for ;)

Still adjusting M4!

Sadly not much excitement to report - we're still chugging away on the M4 alignment...  A recurring theme in this project is the thrill that goes with working out how to do something, followed by the slow torture of actually grinding out the process to the required tolerances!

 

Producing those beautiful astigmatism curves raved about in an earlier post is now part of our daily slog & not all the results generate streams of poetry...

Charl's been particularly insensitive to our misery during this phase.  Each time we make our way to/from the clean room we have to walk past him happily beavering away (making visible progress - constantly!) on the new electronics for the calibration system!

 

Cynthia appears to have the right idea: Retirement!!  The hostel staff put on a wonderful surprise farewell tea for her this afternoon (with the help of Linda & Glenda who hauled her up here on false pretences!).  After 44 years of service, it's the end of an era at the SAAO - all the best, Cynthia!

 

1 fierce rodent, great wavefronts & a big bottle!

Ardisha found this little guy in her kitchen & brought him up to SALT before releasing him into the veld.  It's a Spectacled Dormouse, probably the same one that's been known to visit the 1.0-m dome from time to time..   Really cute but Extremely aggro - made the most amazing noises while trapped in the bucket!

Aah... free at last! Now where the hell am I??

 

Meanwhile, back in the clean room we were getting M4 aligned to M5 & along the way obtained our best wavefront to date: RMS = 0.05 waves!

 

By the end of the day we all needed to let off some steam so it was off to Eben's place for one of Ockert's potjiekos dinners (pronounced "poy-kee-kos": a traditional South African stew that's cooked in a cast iron pot over a bed of coals).

As the sun sank, the temperature plummeted & we had to get serious about survival.  Our host to the rescue with a bottle of wine to share between the 10 of us...  While that may sound conservative, the bottle was of course a Jeroboam :)

The little corkscrew that could!

 

Not exactly the sort of weather you'd expect in November in the southern hemisphere - apologies to our visitors from the north!

 

It really helps to be Eben & be absolutely immune to cold...

 

Thanks guys - a great evening had by all :)

What happens in...

Upon returning to the clean room, we found this up on the door! :)

The modifications to the tilt-adjustment mechanism on the M4 mounting ring have been made so the whole lot could be re-installed...

M4 back in the SAC, ready to be aligned - really this time! ;)

Successful trial-alignment of M4

We've decided to make some further modifications to the steering wheel part of the M4 mount, but before taking it down to Cape Town, we spent a full day doing a trial alignment of M4 to M5.

The procedure involved finding the minimum coma position for the pinhole, then moving it off axis in X by +/- 1.5 & 1.0 mm & making wavefront measurements. Plotting the Z6 values (one of the astigmatism Zernikes) as a function of the X-offset allowed us to iteratively adjust M4 in X decentre (aiming to find a symmetrical Z6 minimum). When we could make no further improvements with X decentre, M4 was iteratively tilted in X to minimise the coma again. Next we repeated the whole procedure in the Y direction, obtaining better Z6 vs Y-offset curves & again minimising coma. A final pinhole scan in the X direction yielded the vastly better pink Z6 curve in the image below - the technique works beautifully! :)

Once we got over that excitement, it was time to remove M4 & detach it from the ring that's going home with us tomorrow. Therewith my best M4 photo-op so far!

Without its ring, we had to figure out a new secure way to store M4 - 'n boer maak a plan as they say in Afrikaans. Although in this case the boer's an Irishman, but that's OK... he's one of us Africans now ;)

Off for a week now while the SALT Board Meeting takes place in Cape Town, we'll return on Monday the 9th!

M4's Back!!

We had to tip the SAC over to extract the tube that holds the pinhole stages & light source for the M4/M5 test which needed some modifications. This afforded us a rather unusual view of the new top end...

Mods completed, the new pinhole carrier for the M4/M5 test went in, positioned at the centre of the hole in M5.

James started assembling the removable part of the new M4 mount.

The vanes needed some minor machining so it was off to the workshop with Craig for a quick milling machine tutorial.

Vanes ready - in they go...

Next, M4 itself (wearing a stylish designer cover) could be attached.

The rest of the Formula 1 car must be in this clean room somewhere?!

M4 back (very roughly) where it belongs - much fiddling to be done to get it properly aligned, but great to have a 4 mirror corrector again!

The Faro Arm was used to check the position of M4 by measuring the hole in the top of the cup.

Installing the new mount for M4

The necessary modifications have been made to the new M4 mount so all the gear & players came back up to SALT today to start the installation process.

To ensure the best possible fit, everything had to be drilled in situ - making for quite an eventful evening!

With the mounting blocks in place, the M4 mount's intermediate structure (popularly known as The Pizza) could go back in...

The fancy new vacuum cleaner for the clean room (aka the "Zoem Tjoeb" - pictured below with its ever-attentive handler) was soon to be put to work guzzling up the swarf.

First just spotting to mark where to drill...

Next some protection was taped in place to catch anything the vacuum cleaner might miss.

& so Craig's work-out could begin!

Not the easiest positions to work in - perhaps we should've had the guy with the drill dangling from the ceiling instead?

But with a little help from his friends, it was all over pretty quickly.

All 6 done! Great stuff :)