Star analyser 100 and 3.8 prism

[Nigella Bryant]

Hi all, I began to use a star analyser 100 a year ago but circumstances meant I've not done much with it. I've just added a 3.8 prism to this. Any help would be great in using this. Thanks for reading.

[robin_astro]

Hi Nigella,

If you use the prism line up the marks on the grating and prism  (You can test the correct alignment by looking through the combination with the zero order on the left and rotating the prism until the zero order and spectrum move as far as possible to the left. )

you can add the prism before or after the grating, fix it in the right orientation using the locking ring or a bit of plumbers ptfe tape wrapped round the thread

By adding the prism the dispersion becomes the combination of diffraction from the grating and refraction from the prism so you need to use a non linear fit for wavelength calibration using several Balmer lines instead of the simple 2 point calibration you can use without the prism

Cheers

Robin

Edited October 4, 2020 by robin_astro

[Nigella Bryant]

Thanks Robin, appreciate this. If I ever get rid of the clouds I'll have a go. I'm using Base Project and a member of the BAA. I want to start serious observations but understand the star analysers aren't up there like the costly slit spectrographs. Still I'm really interested in this aspect of astronomy. 

Edited October 4, 2020 by Nigella Bryant

[andrew s]

1 hour ago, Nigella Bryant said:

Thanks Robin, appreciate this. If I ever get rid of the clouds I'll have a go. I'm using Base Project and a member of the BAA. I want to start serious observations but understand the star analysers aren't up there like the costly slit spectrographs. Still I'm really interested in this aspect of astronomy. 

It's about finding the right project for the spectrograph. There is no best instrument. You can have high resolution with limited spectral range or lower resolution with greater range. The higher the resolution the longer the exposure needed or the brighter target has to be.

I use a SA200 in a home built spectrograph to monitor flares stars with a cadence of 10 to 20s . A flare lasts a matter of a few minutes. Unfortunately,  they don't happen that often so it needs reliably clear skies. So not a UK project.

Regards Andrew 

Edited October 4, 2020 by andrew s