LhiresIII 600 Ln/mm Grating

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LhiresIII 600 Ln/mm Grating

Postby James Foster » Mon Feb 11, 2019 5:43 pm

I just acquired the 600 grating for the LhiresIII and was surprised to find the H-Alpha line
was around 800 on the micrometer; full length of mircometer travel 0-2200.

Does this seem right? On my 2400/1800 gratings, the H-Alpha is closer to 1900. The physical
grating does look much smaller that the 2400/188 l/mm gratings for the LhiresIII.
James R. Foster
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope,
LISA IR/Visual Spectroscope (IR Configured Presently)
Alpy 600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
James Foster
 
Posts: 274
Joined: Sun Jan 24, 2016 7:14 am

Re: LhiresIII 600 Ln/mm Grating

Postby Robin Leadbeater » Mon Feb 11, 2019 7:36 pm

Hi James,

That is ok. The diffraction angle is much smaller with the lower dispersion grating. (In fact you have to watch out that you dont go too far and select the 2nd order by mistake). The higher dispersion gratings have to be longer because the angle is so high that the projected length would be to short to avoid vignetting with a square grating.

This is what the angle of the grating looks like with the 2400 high dispersion grating
http://www.astrosurf.com/thizy/lhires3/ ... uille1.jpg

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
Robin Leadbeater
 
Posts: 1169
Joined: Mon Sep 26, 2011 4:41 pm

Re: LhiresIII 600 Ln/mm Grating

Postby James Foster » Mon Feb 11, 2019 11:50 pm

To: Robin,

Thanks for the helpful reply. RE:" (In fact you have to watch out that you dont go too far and select the 2nd order by mistake)"

I was struggling with finding the Neon calibration lines (referencing Christian's use of the 600 grating here http://www.astrosurf.com/buil/test600/eval_en.htm)
around H-Alpha which I though were near 1900 micro reading......after I took the LhiresIII off the scope, took the CCD off and replaced it with an eyepiece, I think I was looking at 3rd order! The spectrum starting at mirco reading 800 was very bright and colorful in direct sunlight. Will get some spectra tonight before the rains
come back to SoCal.
James R. Foster
Lhires III (2400/1800/600 ln/mm Grat) Spectroscope,
LISA IR/Visual Spectroscope (IR Configured Presently)
Alpy 600 with Guide/Calibration modules and Photometric slit
Star Analyzer 200
James Foster
 
Posts: 274
Joined: Sun Jan 24, 2016 7:14 am


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