I bought myself a Camera Angle Adjuster (CAA) from Agena Astro, in order to allow me to use a SA200 diffraction grating in a filter wheel. The CAA allows me to adjust the angle of the camera very quickly in order to get the spectrum horizontal and in place, without the trouble of doing this the old way…
However, now I am preparing to take my rig to a remote place that has much better weather and more clear nights than those I have here, in Mexico City. The idea is to automate as much as possible my photometry, but also my spectroscopy, which seems more challenging. I am facing now two options:
To take my rig as it is with the CAA, and try to fix it very tight so it does not move (in order to avoid any “service tickets” to the personnel of the remote observatory to adjust the CAA in the future), or…
Buy myself and expensive rotator and instead of placing it after the filter wheel, put it right in between the camera (ASI533MM-Pro) and the filter wheel, which will give me the advantage to adjust the angle of my sensor in respect of the grating remotely anytime.
This last option is ideal, but I have not heard of someone who has put this into practice. On the other hand, I see it is kind of messy to insert the rotator between the camera and the filter wheel. I was trying to figure out the adapters I would need (while taking care that my back focus is correct - 55 mm), but to be very honest I got confused very quickly, especially because I did not find appropriate adapters, e.g. a M42x0.75 (F) to M54x0.75 (F) to connect the rotator to the filter wheel.
So if anyone has already figured this out and done this already, I will really, really appreciate your help here.
Is there room for a slide-in type filter tray in your optical path?
You could draw up something that works for you and send it to one of the online machine shops. Maybe you have a friend with a 3D metal printer?
The filter wheel could be rotated to an open slot so that the camera sees the inserted SA100.
The SA100 could be mounted in something like this:
Though the problem with this solution, although is very good when you are present, it is not so reliable when it is going to be used in a remote location IMHO. This solution is similar to the CAA I have now. Is someone by mistake moves the angle slightly that would be it: I would need to ask someone at the remote site to reposition it, and unfortunately this has a cost.
That is why I was looking for an electronic rotator, but according to what I have found out so far, it cannot be placed between the camera and the filter wheel.
MKS Newport makes a stepper motor optical rotator. It could be run from an Arduino. The Arduino could be another networked device in the remote observatory. You may not have to write your own ASCOM driver.
Enrique,
In my experience KISS -keep it simple!
You already have the grating mounted into the filter wheel and the filter wheel rigidly connected to the camera (?) If that’s the case, then verify the alignment of the grating and put a small dab of loctite on the threads. This should ensure that the angle of the grating remains unchanged indefinitely.
Ken
You are overthinking it (and potentially overspending) your way out of a simple issue.
Do as Ken says, it is a simple task to align the grating in the filter wheel, and hold it in place. No need for rotators etc.
I tied that. I got close, but closer means taking the camera and FW apart, getting new flats, for every tweak. An endless task that never quite does the trick and is easy to overshoot. I suspect that is the best that can be done with limited effort and that meets the criteria for today. I believe you can rotate a bit in the image software. I have yet to submit a single spectra for inspection so I don’t know what is good enough. Many years on an optical table says do it in real time with 100 pitch screws and instrumentation. Kind of like focusing with the V pattern of FWHM. Turns out, it is still easy to miss the mark there.
After thinking about it, Ken is probably right about making things to complicated.
Keeping it simple will probably produce more spectra over time.
Can you really count on things not moving over the years and temperature extremes?
I initially though you were suggesting to perform high throughput, low resolution spectroscopy by running acquisition with the SA at different angles.
I am thinking about a similar system since a few years, the advantage of this would be that it shouldould be a pretty simple way to disantangle le first order signal of interest for each star from the 0th/2nd order of surrounding sky/stars.
I would say even with just a few acquisition, the spectrum quality for the center of the field of view would be much better than for a single acquisition, with a bit of (custom) inverse problem solving.
Anyway, I don’t think that was the main point of your post, good luck with setting up your remote setup !
On the topic you are responding to, I also positioned the grating in the holder once for all.
I am very interested in the content of your reply. Can you give me some references or an algorithm for the spectrum inversion at different angles? I would like to try and write a Python script to read images and angles and derive the spectrum…
I agree, that is why I am going to stick with the CAA solution I already have. This camera angle adjuster allows me to adjust the angle of the camera sensor in respect of the grating. I only need to thight it very hard, once the spectrum is at the right of the zero order star and nice and horizontal, so that no one moves it by mistake. You should try this solution. It will avoid you for doing the awful process of uninstalling the camera, unscrew the filter wheel drawer, adjust the grating, fix the grating, close the filter wheel, install the camera, make a trial shot, and if the spectrum is still not horizontal repeat this process for… I do not want to know for how many times more.
So, yes, CAA is the way to go. Replacing it with an automatic rotator is not feasible now.
Thanks for your comment.
Is not so simple as you think. Have you tried it yourself? I am keeping things very simple, as Ken says, so that is why I am keeping my manual rotator which saves me so much time. As I said to Ken, you should try it yourself as well.
Cheers!
Enrique Boeneker (BETB)
The CAA I have is simple. I will stick with that, and avoids me to go to the overwhelming process that you well described. Also no need to introduce artifacts by rotating the spectra with the software. I was looking for a more automated and remote solution, but is evident that it is not handy (yet).
Thanks for your comment.
Cheers!
Enrique Boeneker (BETB)
Not really, @dolguldur. Just the way to adjust the angle remotely by the use of an electronic rotator… but nevermind, it is a solution that is not really available for the moment. The CAA I have will do the trick for the moment.
Thanks for your comment.
Cheers!
Enrique Boeneker (BETB)
Already checked this. No, I think this is too overboard. As you can see from the replies of others, even a commercial astronomical rotator from Pegasus or Prima Luce is too much. I believe that this will do someday but not for the moment. I am going to keep my CAA solution, which is simple and you do not need to use Loctite or tape, and hours of adjusting the grating position.
Thanks for your advise!
Cheers,
Enrique Boeneker (BETB)
@Stu_Todd I do not understand your comment “But it’s your money Enrique”, since the CAA did cost me only 54 US, nothing to break the bank really. Now, I have a question for you: what did you try a way back, a manual rotator or an electronic one, like from Pegasus or Prima Luce?
