Wed, 12/20/2023 - 07:02
I am beginning to use a Dados spectrograph for my spectroscopy.
I would like to know if someone using a slit spectrograph normally uses plate solving to identify and center the target on the slit. So far I have been unable to plate solve images with the guiding module using an ASI174 MM (5.86 micron pixels in a 11.7x7.1 mm array). The scope I am using is a 130 mm F 910 mm refcractor so with a sensor of that kind I should cover about 51'x32' with a pixel scale of about 1.6 arcsec though part of the FOV shows clearly aberrations. ASTAP seems unable to plate solve images. I may be wrong somewhere. Any idea on what I can do to plate sove images through the guiding module?
Thank you very much
Gianluca
I am using a LISA…
Hello.
I am using a LISA spectroscope with a f/8.5 RC telescope and a ASI 432 camera as guider, giving me 0.62 arcsec per pixel and 16x11 arc min images.In fact, due to aberrations and some shadows at the top and right, the usable field of view is somewhat smaller so a ASI174 mini may do the same job.
I am using PlateSolve3 and it seems to work fine. I could not make ASTAP to work so far, but at forums seems to be the favorite choice. Astronomy.net online also works fine, but is too slow.
A couple of days ago i was able to build a telescope pointing model of 200 points with the guider camera using expositions between 30 and sixty seconds. And last night, using Voyager software, i was able to place the star on the slit fully automatically with Precision Pointing.
Most probably when far of the Milky Way i will have more difficulties plate solving, but i am very happy with the results so far.
David Cejudo.
Observatorio, El gallinero (El berrueco, Madrid).
is the guiding…
Hello David,
is the guiding module affecting in some ways the focal length of the scope? ASTAP returns me a message saying to check the focal lenght and the camera parameters. All the input parameters are correct but I wonder whether the effective focal lenght at the calibration module may be affacted by the optics of the spectrograph.
Gianluca
It dawned upon me that I had to use the slit viewer in front of the ASI174MM to see the slits and to focus stars. Is the slit viewer capable of altering the focal length of the scope at the guiding module?
With the LISA the…
Hello.
With the LISA the plate scale is not affected. The slit is placed on the focal plane of the telescope and then reflected towards the guuider in a 1:1 amplification.
That means that wether you place an imaging camera chip in the focal plane or a slit, the plate sacale is the same at the guider and at the imaging camera.
Yes it is quite possible that the plate scale in the guider image is different from the plate scale at prime focus as the guider will have additional optics to bring the image formed at the focal plane where the mirror slit is to focus.
Robin
In fact I see from the manual (I don't have a DADOS) I see you can actually zoom the guider image to alter the magnification (plate scale)
3.4.3 Zooming the slit view in and out
The lens inside the slit viewer can be adjusted in order to magnify the image size of the 3 slits on the detector of the Webcam
…
Thank you very much Robin.
Actually I solved the issue by using Plate Solve 3 instead of ASTAP. It seems that the magnifying effect of the slit viewer did not impair PS3.
Gianluca
However I have asked Baader to let me know which multiplying factor I may use to take the slit viewer into account, just in case.
As a follow up Baader has responded. They say that the magnification at the guiding module will depend on the mechanical position of the slit viewer assembly with respect to the slit plate as well as on the backfocus of the guiding camera. It is not possible to give a precise factor to calculate the focal length at the guiding camera and the only way is to make guess depending on the estimate of the slit-plate apparent dimensions with respect to the height of the guiding camera. That will not help much in my opinion.
The good news is that Plate Solve 3 manages to solve images without applying any correcting factor that in my case it might be close to 1. Just for other people who may have experienced a similar problem.