Ca II I at 8542.1A

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Valery
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Ca II I at 8542.1A

Post by Valery »

Dear spectroheliographs,

Can you, please, pay more attention to improving your results in the Ca-II I at 8542.1A ?

Don't give up, try to reach a full success - when your images will show a rich mixture of
middle chromosphere filaments and low chromosphere - upper photosphere granulation.


Valery


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Re: Ca II I at 8542.1A

Post by thesmiths »

Valery wrote: Fri Aug 05, 2022 6:16 am Can you, please, pay more attention to improving your results in the Ca-II I at 8542.1A ?
Hi Valery, I tried again to image this line with my triplet APO. I was not able to get good focus. The APO I have seems to focus nicely at both H-alpha and Ca-H (and presumably also some place in the green). But I think what that means is the aberrations probably become very large at 854nm. I think that's a bit the issue with this type of lens.

Would a doublet be a better choice? And ideally probably a reflective telescope? I think you said you could do some calculations to see. I'm assuming professional astronomers who look at this wavelength are using some sort of large reflector.


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Re: Ca II I at 8542.1A

Post by Valery »

thesmiths wrote: Fri Aug 05, 2022 7:00 pm
I'm assuming professional astronomers who look at this wavelength are using some sort of large reflector.
Hi Douglas,

You are correct. I believe that a reflective telescope like Cass or RC with 125mm aperture and F/8-F10 willl be OK for such an experiment.


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Re: Ca II I at 8542.1A

Post by thesmiths »

Valery wrote: Sat Aug 06, 2022 5:38 pm You are correct. I believe that a reflective telescope like Cass or RC with 125mm aperture and F/8-F10 willl be OK for such an experiment.
I tried again today with another telescope, this time a 90mm f11 achromat from SkyWatcher, but the focus again was not good that far into the infrared. It looks like you need a reflecting telescope to get very good spatial resolution. I think when Peter Zetner did this, he used a Maksutov.


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Re: Ca II I at 8542.1A

Post by thesmiths »

Valery wrote: Sun Aug 07, 2022 2:49 am You definitely need even a cheaper 150mm Cass as a feeder for Ca-II - I 854nm line. Seeing at 854nm will be remarkably better than at Ca-H and even than at H-a.
In my last attempt at this wavelength, my impression was the problem was not only the optics of the telescope but that of the camera lens and the collimator also. I could see that even the spectral lines were not as sharp as in the visible range.

So my guess is it will be necessary to use something like a solar Newtonian for the primary, in order to reduce the incoming solar radiation somewhat. Above 100mm you definitely need some attenuation. But my guess is that you do not really need a long focal length (something like f6 to f8, similar to the refractor I use now).

But I think the other optics will also need to be replaced by reflecting elements. This is a common feature for broadband spectrometers (see the image below). But this is quite a new endeavour. I will have a think about it but it is not straightforward.

A compact Czerny-Turner spectrometer.
A compact Czerny-Turner spectrometer.
compact Czerny-Turner cavity spectrometer.jpg (38.38 KiB) Viewed 17 times


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