26 replies to this topic

[robin_astro]

I am surprised that there is enough chromatism in the HD8 at f10 to make it worth while taking two spectra focussed at the blue and red end with the ALPY600.  I have never heard of anyone having to do this. (This would make the instrument response correction very complicated as you would have to also take two spectra of the reference star at exactly the same two focus settings) .

 

With slit spectrographs like the ALPY  the chromatism does not affect the resolution in the spectrum. (This is controlled by the slit and the spectrograph focus)  You just lose some signal in the regions where the focus is not so good.  I would expect if anything, adding a focal reducer will make the situation worse. 

 

Cheers

Robin

[robin_astro]

I have just made a rough calibration of the Pleione spectrum image you posted earlier.

Blue is the raw spectrum, red is the response curve using the Pickles B8v spectrum as a reference and Green is the response corrected spectrum

(The ripples in the response come from the camera response. These will be reduced if you use a flat correction)

 

 

 

The quality is good even with the chromatism so there is no need to take two spectra. Just average the focus across the spectrum and make sure you use the same focus for target and reference.

 

Cheers

Robin