I have, as always a dumb question. Does the Star Analyser 100 grating modify your field of view?
It was my intention to take spectra of the star V1357 Cyg (yes, the one that is part of a binary system with the very famous X-1 black hole). The star, for my 80 mm apo triplet refractor, is kind of faint (for spectroscopy purposes), since it is now shining at a magnitude very close to 9. So I decided to print me a chart of the star considering the field of view of my camera (ASI120MM-S) and refractor (80 mm / 480 mm, f/6) combo in astronomy.tools. The calculator there gave me a FOV of 0.57 deg x 0.43 deg, so I made a chart with a 0.43 deg width.
I am always bragging of my capacity to identify asterisms that give me a hint where the variable star is in the FOV of my camera compared to what I see in the chart. But yesterday was another story: could not find any resemblance of what I had on the screen and what the chart was showing me.
Important note here: I made some slews before with the above mentioned rig and the SA 100 during the star alignment and polar alignment of my mount, in which I had no trouble in getting the target in the FOV.
I noticed though, or I believe I noticed, that the FOV in my screen was much smaller than on the chart. Is this true then? Does the SA modify (a.k.a. shrink) your FOV? I must say that the star and it's spectrum fit very tight in my SharpCap display.
So, I leave this here. Maybe someone can clarify or rectify this claim.
The short answer is no. The field of view is unchanged ie the zero orders will be in the same place with and without the grating.
(If you are using a focal reducer there might be a very small field of view change due the glass giving a small change in optical path length and if you are using a wedge prism this will shift the position of the zero orders to the left if the spectrum is running from left to right but the plate scale will remain the same)
You can even plate solve images taken through the Star Analyser using eg astrometry.net which will use the zero orders ignoring the spectra.
Looking at the field on
If your field of view calculation is correct, I reckon if you put eta Cyg at the bottom right in your field your target should be on the left edge half way up the field, exactly where you need it to run the spectrum across the image. (The lower of a close vertical pair of stars, the other being V1674 Cyg)
I followed your advise and I am trying now to capture the spectrum of V1357 Cyg. I am using NINA and for plate solving in this software I have configured Astrometry.net as main plate solving tool. It takes some time to plate solve (no more than 2 min, really nothing to complain about), but it does it very nicely. This opens the door to a lot of us that were not aware of this feature in NINA to capture spectra of more difficult objetcs.
Thanks so much, Robin. I really appreciate your help.
Clear and dark skies!
Thanks so much for the clarification. I keep on forgetting that much of the stars in my chart are not visible in my screen since they are too faint for my rig. Have to only look at the bightest stars on the field (eg. 7 and 8 magnitude).