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For the calibration lamp image I expose so the strong Ne reference line at 5852A is not quite saturated (30 sec exposure unbinned with my setup) This produces strong enough Ar lines in the blue for ISIS to lock onto while still allowing the strong Ne lines to be used.

Cheers
Robin

I'd be interested to see your profile at 30s. I have been unable to get good Ar lines (that ISIS can detect automatically), despite spending quite some time on focus today. My lamp spectra is quite a mess down the blue end, and resembles nothing like the published profiles in the Shelyak or Buil literature - despite trying a range of exposures from 7s up to 120s (though I can, and have, identified 4200) for calibration purposes. No such luck for 4510 or 4764, and I'm less than certain about 3948.

Attached are short exposure and long exposure examples. It's almost as if I don't have much argon in my neon lamp

Here's a 120s image:

Hi Paul,

I think mine looks much like yours. The Ar lines are much weaker than the strong Ne lines but ISIS finds them ok

I just ran a calibration lamp spectrum through ISIS, effectively producing a calibrated spectrum of the lamp using itself as the calibration reference. ISIS had no problem finding the lines and getting a good fit. See attached zip file with screen shots, the log file and the final calibrated spectrum fits. If you like I can send you the raw lamp spectrum image to try.

Robin

Hi Robin,

Most useful data - thanks! I will try a similar test.

Much appreciate your time.

Cheers,

Paul

Since we are addressing the issue of Alpy calibration, may I jump in with an issue I am having? Perhaps it is related to what Paul is experiencing.

Recently I began having some difficulty with the Calibration Assistant in ISIS that I have not had before. I am using the Alpy600 with the calibration module and Atik314L camera. The resulting calibration has been giving RMS results of 16-20A for some spectra but .2-.5A range in others. Today, one of my spectra gave an RMS of .3 and the next spectrum gave an RMS of 19.

My setup is very much like Robin’s, but use only the neon lamp. And with my settup, I found the pixel size of 6.38 to be optimum.

After many trials of trying to figure out what is causing this, I noticed that the tilt angle I derived on the Calibration tab would change when I pressed the Go button in the assistant. On one spectrum I derived a tilt angle of .07 in the Calibration tab, but when I pressed the Go button in Calibration Assistant, that angle changed to -4.31. On a different spectrum, the tilt angle would not change more than a few hundredths, and the resulting calibration RMS was .19.

Can anyone comment on what would cause the tilt angle to change so drastically on one spectrum but not on another? I believe this major change is causing the very high RMS. I have found that changing the binning size has worked on occasion, but now that does not seem to work. If I can get to the bottom of this drastic automatic tilt change, I think I will have the issue resolved.

Thanks,

Keith Graham

Although of no help to Keith, I'd like to close the loop on the original issue.

I. I replaced my Ne/Ar bulb. This resulted in a great reduction in UV “parasites” and a much cleaner neon image. Clearly there’s a great variety in the relco lamps.

2. I fine tuned the grism alignment with the slit. This made a HUGE difference to the quality of the neon profile and subsequent calibration. Despite the smile algorithm in ISIS, starting with near vertical lines is clearly preferred.

Using 5 lines and a 3rd order poly in ISIS my dispersion RMS is 0.014.

Cheers,

Paul

Paul,

1.
In case of Alpy will its coverage (UV+IR), 5 lines is very few, your RMS will be artifical, will show just a mathematical model's fit within your well chosen wavelength region, only for 5 preferred points.
If you've chosen those 5 lines from the middle, the wavelength-pixel coord function can have a much less complex curve than at the edges.
It is critical to have tons of lines at UV I think, + IR ones, taking care not to overweight one region to fit better making it worse for other regions... Also important not to have this polynom too overdetermined (then it takes up local variabilities due to just overlapping lines) and not too underdetermined (won't follow optical aberrations).
IRAF has a window to check this function visually, lots of things can happen - especially at the 2 edges -, it's a pity ISIS doesn't have this.

This is a much harder problem than everybody could pick his own preferred solution I think, for such a large coverage.
Needs a common way to do it (as there is no perfect solution), otherwise our spectra won't be fully compareable.
I did chose the automatic calibration with ref.star Balmer lines for this reason based on the wiki, assuming one has already put this research effort for an optimum.

I had similar problem with LHires 150/mm which doesn't have such a common way, but "fortunately" LHires has just a short wavelength coverage and assumed to be close to linear.

2. I was also thinking having cal.lines vertical was preferred for a long time. Later I was told have the spectrum line horizontal instead, otherwise loosing resolution. Others opinion needed here, I'm also uncertain.


Clear skies,
Peter

Hello Paul,
My English is not good so i can't read all your messages.

I use a Alpy with a caméra Atik314L+ and this is my result for ~60 secondes exposure :

I will close the loop on my question as well as I have found the issue. My ADUs on the spectra well below 10000,and it appears they should be at around 10000 or higher for ISIS to be able to read it adequately.

Cheers,

Keith