Spectroscopy and Python menu items

Not sure where to post this, but I’ve found that the latest V.10 has two items that are not discussed in the Help files. The Spectroscopy menu isn’t in the Help and under Files, we have an Execute Python Script item that is also not in the Help system. Are these items discussed elsewhere?

they’re actually not as the help file needs an update. There is still a lot of work to be done but we prioritized give you the most functions possible.

As for spectrography, a few season customers are @AgnihotriVK , @vorakuldip and professor @keving can be of immense help.
A remarkable astronomer is Olivier Thizy which I will invite to this forum as well.

hello friends

Will be happy to see the bill’s python script, though more use to windows based spectroscopy software (RSpec/BASS/ISIS/SpectroCalc2) and fitting in magicplotpro (java) and originpro.
In prism, spectrum intensities can be dragged in prism.


Hello Vikrant,
I misstated my comment. I had meant that the Execute Python Script menu item is there, but also has no documentation in the Help system. I am curious if it is just an Open/Select item type window or a Debug window. I’m not sure how Python scripts would be debugged in the Prism environment.


Hello Hamra,
Thanks for the prompt reply. A feature without documentation won’t get much use. New Features might be a good topic area in the forum. Posting initial documentation on a feature before the Help system is updated would give people some quick lookup for a new item.

The Spectroscopy item that got my attention is the ‘Slit Guiding Parameters Settings’ item. Slit Guiding is a problem area for capturing spectra, so I would be eager to see the approach.

I looked at the Slit Guiding Parameters menu item again, it doesn’t do anything even tho it isn’t greyed out. It may require another window or some other set up.

this is the closest to a tutorial I have. This is a video made by @Cavadore a couple of years ago. It might be helpful to turn close captioning on and the translation setting from the gear menu. Here is the video: https://www.youtube.com/watch?v=iiuLnjkhB5k

Hello Hamra,
Thank you, that is helpful though hard to follow at times. I can see I have lots to learn about Prism.


Slit guiding paramters can be controlled from the guiding panel that pops up when you start guiding. Its an option under the ‘Advanced’ tab. I have experimented with slit guiding and found it is not as good as using the ‘fixed point’ guiding option (also under ‘advanced’). Just set the point to be where your star is on the slit, by reading the coordinates in your guide camera view. I think this method was created for fibre transmission to an echelle spectroscope but it works for me with a simple slit arrangement. Here are some pointers.

The exact position can be changed dynamically during guiding so you dont need to obsess about getting it right first time. Change the contrast of the guide image, and blow it up with the zoom tool a few times so you can inspect the slit closely. The adjustment allows sub-pixel accuracy as well!

Use RA and DEC ‘aggression’ settings which are lower than normal. I use around 0.2 for both. Too high and the star oscillates back and forth across teh slit rather than being ‘coaxed’ into it.

For high res spectra, your star is pretty bright so you need small exposures (1-2s) but lower than this and you run teh risk of ‘chasing the seeing’. Set the barycentre radius (basic tab of guiding panel) to be large enough to see the whole star (Typically around 14 for me)

For low res you star might be much fainter. The barycentre can be smaller. I have ever used exposure times as long as the maximum allowed (11s?) to ensure something is visible around the slit.

In my instruments, I can see reflection artefacts of the star next to it if they are bright. If the barycentre is too big, this can contaminate the centroid calculation. if your guiding is struggling with this (just look at the image visually) then you can fool the calculation (as it were) it by pushing the target point a little.

Hope this helps


1 Like

thanks Kevin,
That’s helpful. I need to get busy trying these approaches.


Kevin where/how do you dynamically change the exact point. I watched the video posted by Cavadore and he did it on the Tracking Inspector screen on the 6th tab which now is called Sharplock, but the Sharplock screen doesn’t look like it allows changing position.
Thanks, Al

Hi there

When you select ‘fixed point’ guiding (from the guiding ‘advanced’ tab) , the 6th tab of the Tracking inspector should be ‘Set point’. Here you can change your setpoint dynamically (be sure to ‘Apply’ changes). The scale of change in the small ‘thumbwheel’ boxes is determined by the selection on teh righ (±0.1, ±1, ±3)


1 Like

Thanks Keving. The tab does show while actively guiding. I was looking for it before guiding and the tab doesn’t show… I tried your recommendations setting aggressiveness to .2 and centroid to 14. It improved guiding, but I stillhave the target drift off the cross hair and motion too large error message . Seem like once off the point the guider never pulls the star back to the point without my intervention.

At the risk of stating things you probably already know…
Have you calibrated your guiding OK?
Its best to calibrate guiding at points near the equator (DEC <35deg or so) although if Prism reports calibration was OK, I guess it is…
You need to have the focal length of the system correctly set in the camera setup panel so guiding can interpret what happens correctly - be sure to include the effects of any focal reducers. Its easy to get wrong!

Guiding should be able to accomodate errors of 3-4 pixels… have you set your maximum movement too small?

The centroid of 14 works well with bright stars (mag < 6). If you are recording from fainter stars the barycnetre radius can be reduced.
Use the histogram to get a sense of where the bulk of the star’s image disk is.

Good luck!