As usual, Christian Buil has something to say on this topic http://www.astrosurf.com/buil/lhires_ir/obs_us.htm. He presents a nice mosaic of spectra taken of various classes of stars. (The Sun, of course, is an example of a G-type main-sequence star.)The infrared Ca II triplet, commonly known as the calcium triplet, is a triplet of three ionised calcium spectral lines at the wavelengths of 8498 Å, 8542 Å and 8662 Å. The triplet has a strong emission and is most prominently observed in the absorption of spectral type G, K and M stars.
I used this mosaic in order to identify the correct line. Christian Buil also recommended placing a red filter in front of the camera: this filter, known as an "order filter", is to remove the blue part of the 2nd-order spectrum which would ordinarily overlap the 1st-order infrared spectrum.
We used our 80mm f6 APO refractor setup viewtopic.php?t=36961, which is very flexible and allows quickly changing the diffraction grating. For a first attempt at 854.2 nm, we used a 1200 l/mm grating, which gives lower dispersion but more range. We were able to quickly identify the Calcium triplet region:
The image is extracted from a real video file from our SHG, oriented to match the mosaic above. The middle line is a little narrower than the H-alpha line, and while some structure is visible in the line, there is not nearly as much as in the H-alpha, Ca-K/H or even the H-beta line. Here is an SHG image reconstructed from a scan of the middle Calcium triplet line:
For comparison, below is an image of the H-alpha line taken with the same setup, just before the one above (morning of July 15).
We also took the opportunity to image the H-alpha line in 2nd order, equivalent to the dispersion of the 2400 l/mm grating that we normally use (the light throughput is much lower, however, so the image quality is slightly reduced).
We can also compare the 854.2 nm image to a CaK image taken with a 1200 l/mm grating download/file.php?id=68989 and a CaH image taken with a 2400 l/mm grating download/file.php?id=69613.
I should mention that Peter Zetner has also done work on the Calcium triplet viewtopic.php?f=8&t=29064. He imaged the 849.8 nm line rather than the 854.2 nm line.
My conclusion: while an interesting academic exercise, I do not find the 854.2 nm line as interesting as some others. Qualitatively, the image is intermediate between those from the H-alpha and the Ca-H/K lines and shows features in common with them. It is not particularly difficult to image the 854.2 nm line, but the final result is not as exciting as the more "popular" lines. I will give it another attempt with a higher dispersion grating (1800 l/mm), but I do not expect the image to be significantly different than the result presented here.