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Ha imaging without a PST

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Daniel Defourneau is doing some excellent work with his spectrohelioscope. By setting the wavelength to any suitable line, you can scan image the Sun. CaK, Fe, H etc etc.

This one was done in Ha.......


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A spectrohelioscope - or at least Daniel's electronic version is made up from:

A refractor of long focal length which images the Sun onto a long entrance slit - the image is usually >6mm diameter and the slit as narrow as possible, say 20 micron.

The light behind the slit is then collimated by another telescope, the collimated beam hitting a large (50mm sq or better) 2400 l/mm reflective grating.

The spectrum produced is then imaged again by a telescope and the final image recorded on a webcam or similar.


So, the grating and imaging telescope are set so that the Ha line is visible in the image and the Sun allowed to scan across the slit.....no drive reqiured. As the Sun moves across the entrance slit any variations in the intensity of the Ha line is recorded.

At the end, you have an AVI file which has an image of the Ha line across the whole of the surface of the Sun.

Daniels smart software then cuts the Ha line out of each frame and stacks them next to each other thereby building up a complete image of the whole solar disk in the Ha light. Neat!

You can do the same in any wavelength....

La plupart des amateurs ont commencé par acheter une lunette courte et transportable avec une focale de 300 à 400 mm

(Translated into English)


Edited by Merlin66
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Holy heck Ken, it is white-mans magic, and I am intrigued.

Couple of questions (apart from sourcing the plank that is, LOL).

The two scopes I can see and understand. The slit ditto, which is put in the focuser of the "collimating" scope, correct? Focus with the collimating scope focuser I can understand as well. How does one adjust the slit to "original 60mm scope" though, by sliding this scope fore and aft?

What is the "grating" please, where/how much?



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Yes, the original scope must be "adjusted" to bring the front of the slit into focus.

The gratings are blazed reflective diffraction gratings - Optometrics are the best/ cheapest.

Welcome to Optometrics

Any other questions, I'd be pleased to assist.

With a couple of old cheap refractors this system works out far cheaper than even a PST! You can image in Cak, Ha, Hb in fact ANY wavelength you like!

Over the years Daniel has continued to improve the system and is beginning to get resolutions similar to the small PST/ Lunts.

BTW No ERF etc required!!

( there's a section on it in "Astronomical Spectroscopy for Amateurs", p124)

Edited by Merlin66
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Cheers Ken.

So, how would you know the original scope has the grating in focus, where is that displayed or shown? And furthering that, to adjust the original scope, presumably you slide it back and forth, or do you mount it on a focusing stage?

Looked, albeit briefly, at Optometrics site. What sort of cost are we talking, roughly?


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  • 2 weeks later...

Now that 90% of us are bamboozled by all that, and are still amazed by the image produced. Whos' going to be the first SGL'er to construct one, or make a production line.

I'd love one, but, WAY above my head.

Fantastic thread. Once I've passed my Quantum Physics course, need enroll first :BangHead: I'll look into it. ..... all puns intended


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I've have all the necessary hardware (even the wooden plank!) to build a spectrohelioscope lying around for the past couple of years, but what between building Spectra-L200 Kits and moving countries, just haven't got round to it.

Certainly a very worthwhile project and the necessary software is under constant development.....

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