wavelength calibration

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Robin Leadbeater

– Calibration – still having problems in getting Demetra to ‘automatically’ recognize the calibration image and to properly assign the right spectral line.  When I use ‘automatic’ I cannot get better than 2.4 RMS, where if I go in an manually set the lines to the image (5852, 6562, 6965, 7067, 7383) my calibration gets a very good .2-.8 RMS. 

Yes these automatic systems tend to either work or fail catastrophically. (I often tell the tale from my other life in paper  technology where we had developed a sensor which used a neural network to measure a property using the NIR spectrum. It was trained on a range of products and worked flawlessly….. until one day it started producing compete nonsense. It turned out the manufacturer of one of the materials used in the paper had made a subtle change in the formulation which he had not told us about !)

I can’t help with Demetra, though at Francois Cochard’s zoom workshop meeting on calibration, I did promise to try it!


(ISIS has an automatic function which works flawlessly for me with my ALPY and LHIRES, though unlke Demetra it does need some manual input to tune it initially and you need to point it to the approximate position of one line, then it can find them all)