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 ;)