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LhiresIII 600 Ln/mm Grating

PostPosted: Mon Feb 11, 2019 5:43 pm
by James Foster
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.

Re: LhiresIII 600 Ln/mm Grating

PostPosted: Mon Feb 11, 2019 7:36 pm
by Robin Leadbeater
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

Re: LhiresIII 600 Ln/mm Grating

PostPosted: Mon Feb 11, 2019 11:50 pm
by James Foster
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.

Re: LhiresIII 600 Ln/mm Grating

PostPosted: Wed Feb 27, 2019 10:19 pm
by James Foster
Took longer than I thought but I finally calibrated the 600 l/mm grating in its housing unit. I usually avoid adjusting the LihesIII itself and do all the adjustments
on the grating housing to minimize re-calibration btw the gratings. I needed to shimmy the one side because of extreme ccw tilt of the continuum; see image:
Image

The resultant conituum tilt is about 0.2 degrees and smile (from Ne-Ar calibration lines) is about 1.4 degrees. No further adjustment, besides rotating the CCD,
on the LihesIII was needed.

I took a few images centered near H-Alpha and H-Delta. Using the Atik 460ex and this 600 l/mm grating, I get a spectral coverage of just over 1000A and
R=2700 (H-Alpha). I think I can get the majority of the visual spectrum btw 3800-6750A in 3 passes with sufficient overlap to stitch them together; sort of like
a "Super Alphy600." I can recover the rest of the deep-red spectrum, when I use my LISA IR, which I'll shoot just after a visual run. Here are some spectra
I've taken just before going to the SMSW-2 last weekend (Note: NGC 3242 is the planetary nebula "little Jupiter"):

Image
Image
Image
Image
Image
Image
As noted in previous posts, any non-balmer/telluric line(s) identification are speculative.

James