Using the ALPY200

[Robin Leadbeater]

I thought I would start a thread for people using the Shelyak version of the ALPY 200. I have been using my version for 10 years now. You can see some information about it on my website
http://www.threehillsobservatory.co.uk/ ... opy_20.htm
and I talk about it in this workshop
https://www.youtube.com/watch?v=0L6LLn9HjUY&ab

J'ai pensé créer un fil de discussion pour les personnes utilisant la version Shelyak de l'ALPY 200. J'utilise ma version depuis 10 ans maintenant. Vous pouvez voir quelques informations à ce sujet sur mon site Web
http://www.threehillsobservatory.co.uk/ ... opy_20.htm
et j'en parle dans cet atelier
https://www.youtube.com/watch?v=0L6LLn9HjUY&ab

Cheers
Robin

[Robin Leadbeater]

If you are using ISIS with the ALPY200, it is important to crop the images to remove the large areas of black where there is no spectrum. If you do not do this ISIS calculates the average of the flat and gets a very low value. When it then tries to scale the images it produces very high values in the black areas and very low values where the spectrum is. This severely limits the dynamic range in the spectrum, particularly for faint objects.

This is an example of the area I crop. You can crop at the image acquisition stage but I prefer to acquire full fame images and then crop using ISIS "tools", "image processing 3", "crop a directory" as it reduces the risk of cropping incorrectly and losing an important observation.

flat_ATK428_alpy200_2bin_20240108_crop_area.jpg (31.16 KiB) Viewed 690 times

[Robin Leadbeater]

When measuring very faint objects it is important to accurately subtract the sky background which can be much brighter than the target. If using ISIS, a good check is to look at the sky subtracted image of the spectrum that ISIS produces and turn up the brightness. The sky background in the region directly above and below the spectrum should be just noise with no features in it. (If there are any features these will also appear in the target spectrum so adjust the geometric corrections and/or sky binning zones to minimise them)

ALPY200_skysub.png (170.7 KiB) Viewed 688 times

(Do not worry about what appears to be the very high level of noise in the blue region. This is because the flat correction artificially increases the gain in this region where the flat lamp signal is low. Provided you average enough flats (I use 30) The flat does not significantly contribute to the noise above ~3800A in the final reduced spectrum)

It is also a good idea with faint targets to use a narrow spectrum binning zone and use the "optimal binning" function in the ISIS "General" tab to minimise sky and camera noise

[James Foster]

To: Robin,

Thanks for the helpful hints at successfully using the Alpy in 200 mode. Hope to configure mine after the winter clouds go away and do some test with my Alpy600 on the CDK at F/4.5.

James

[Bernard Heathcote]

An excellent initiative Robin.

After 26 of spectroscopy (from a Rainbow Optics grating, through, S100, Lhires3, eShel, LowSpec and UVEX) I've finally come around to the Alpy 200 and 600. For a variety of reasons, which I won't bore you with, I need to mainly move away from 'bright' higher res spectroscopy to the faint low res stuff, with the hope that it will revive my spectroscopy interest in my dotage.

Bernard

[Tom Love]

Hi Bernard,

I have both an Alpy600 and a Lhires, and I have to say that the Alpy has seen more use in the last couple of years. Especially in the winter months, when Southern novae are easier to observe. Classifying and monitoring transients is quite a satisfying activity, though it has its own challenges.

We haven't had an Aus/NZ spectro catch up for a bit - I will organise one soon.

[Bernard Heathcote]

Hi Tom,

Thanks for your interesting comment. While I have an excellent dark-skies observatory I no longer use it as I only get to visit the site one night at the weekends, with no guarantee of a clear sky, and my city skies are very limited due to a neighbour's tall trees and buildings. My current thinking, and hope, is that there are many times more faint than bright targets in those limited shies, which my new Alpy 600/200 should reveal.

I've just finished 3D printing the necessary adapters for my Calibrex and Guidex units (designed for use with the 3D UVEX) for use with the Alpy (saving a ton of money) so I should be good to go in the next few days.

Cheers,
Bernard