thesmiths

Collection d'images du spectrohéliographe H-alpha

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En ce qui concerne l'instrument, voici quelques photos qui montrent la configuration de l'équipement. Caractéristiques techniques:

 

720mm APO triplet refractor. 106mm aperture for H-alpha and H-beta (usually 72mm for Ca-K). ASI 183MM camera. 13x sidereal rate scan for H-alpha and H-beta (11x scan for Ca-K). 2400 l/mm holographic grating, 50mm x 50mm. 135mm f3.5 collimator and camera lenses. 9 micron wide by 12mm long chrome on fused quartz slit. 2-inch Astronomik L1 UV/IR filter 15cm in front of the slit. HEQ5 Pro mount with EQMod. Software: FireCapture, AS!3, ImPPG, Photoshop Elements.

 

file.php?id=71090

file.php?id=70574

file.php?id=70573

 

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Comment est fixé le SHG sur la lunette ? Par la queue d’aronde ou par le porte oculaire ?

 

Oui, la façon dont il est attaché n'est pas très claire. As you well know, even with the Solex, there is considerable torque at the focuser. This would become worse with anything heavier. Therefore, I decided to change things around so that only the collimator (and slit) is attached to the focuser (in this case, a 135mm f3.5 Asashi Pentax M42 lens). This allows smooth focus at the Feathertouch (shortly I will attach a ZWO electronic focuser to allow remote focus). The other part of the instrument is attached to ADM Vixen-style dovetail extensions. The ADM bars are very rigid and strong (the bottom telescope dovetail is also from ADM so the main axis is essentially like one bar 72cm long). 

 

There is a lighter dovetail bar attached to the end of the long dovetail with a 1/4-20 bolt which forms an angle of around 40 degrees. The angle between the collimator and camera can be adjusted. The grating is attached to an ADM dovetail clamp so it can be moved or swapped (I have one for 2400 l/mm and another for 1800 l/mm). The camera is mounted on an M42 macro bellows (from BPM) and the camera lens is a 135mm f3.5 macro lens. Course focus is via the bellows and fine focus by an M42 Pentax helical focuser in front of the camera. By the way, the  white board behind the camera is a sunshade to reduce solar heating of the camera.

 

I recently added a tilt corrector in front of the slit to achieve better focus across the long (12mm) slit. There is still curvature of the telescope focal plan itself, but focusing is much more complicated if there is also tilt.

 

As I mentioned, this is essentially a Solex design scaled up by about a factor of 1.5. The larger size (and particularly weight) necessitated a change in how the optics is supported. I went through a few iterations before the current version. By the way, the orientation of the grating (and therefore the slit) means that the current arrangement can only scan in DEC. But the orientation is quite precisely oriented and typically shows a misorientation of less than one degree.

 

The cover to block out stray light is made from black foamboard, black cardboard and blackout curtain material (black on the inside, white on the outside), assembled with a hot glue gun. It is very lightweight and slides onto the end of the secondary dovetail. It seems sufficient to block out stray light. In the case of Solex, the box/cover is quite structural and even at its standard size is subject to deformations (especially if it gets too warm). My assessment was a box to structurally support a larger instrument would need to be made of much stronger material (maybe carbon fibre would work), and if it were made of aluminium, it would be too heavy to attach directly to the focuser.

 

file.php?id=72989

file.php?id=72988

file.php?id=70575

file.php?id=72990

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A big thank !!!

 

C'est très intéressant. Pour le moment, je me suis fait un exo-squelette pour ma version de SOl'Ex avec imageur/collimateur de 125 mm :

Solex-Alluxa-1A-Solex-Rug-f125-125-ASI29

 

La rigidité est très bonne, mais comme je vais passer à une version avec collimateur/imageur de 200 mm (pour le test des filtres Ha), il y a ce problème embêtant de la fixation/flexion sur le focuser. Ta méthode est fort intéressante. Faut que je réfléchisse un peu plus.

 

Merci !!

 

 

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Wow, the spatial resolution is really really impressive! Of course the focal length helps but sill...

Just wondering, where did you find such a long (12mm) and narrow (9um) slit?

 

Clear skies!

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Just wondering, where did you find such a long (12mm) and narrow (9um) slit?

 

I ended up designing the slits myself and asking a semiconductor mask making company here in England to manufacturer them. I was quite sure that they would give an improvement over existing slits, which for the most part were designed for other purposes (night-time spectroscopy, laboratory spectroscopy or laser characterisation). The slits from Shelyak are lithographically made but are the same ones conceived for use for night time use. The slits from Thorlabs are made by laser cutting and are not very smooth, leading to imaging defects.

 

First of all, the choice of fused quartz. All lithographic slits are, as far as I know, made on soda lime glass. This material is cheap and easy to handle but has poor thermal characteristics. Fused quartz has a much lower coefficient of thermal expansion (about 1/20 of soda lime glass). Therefore, it is much less likely to crack under exposure to focused sunlight. In fact, I have exposed the slits with a large aperture, low focal ratio refractor (140mm, 800mm) with no light attenuation and the fused quartz did not crack (although the chrome layer suffered some damage after a long time).

 

12mm was about the longest I could imagine using for a full disk scan. I could probably have gone smaller than 9 micron (maybe 7 or 8) but since 10 micron seems to be successful, I decided it was safer not to do too much smaller. Here is what the substrate look like as it comes from the manufacturer. The standard in the semiconductor industry is 5-inch squares. It was cut into 15mm squares, from which 49 pieces can be extracted.

 

file.php?id=68314

 

Here is an image I took with a 40x metallurgical microscope using transmitted light and a 25A red filter. The slit is very straight and essentially without defects (only dust).

 

file.php?id=68315

 

The chrome structure I chose (actually, I didn't really choose, since there were not many options available) is the following:

 

chrome-on-fused-quartz-3.jpg.f2a74372efbb5d2e0262d749f843da30.jpg

 

The chrome layer is actually quite thin -- I think because the lithographic etching will be finer if the metal layer is not too think. The standard in the semiconductor industry is to put dark antireflection oxide layers on each side of the chrome, which also increases the optical density. The slits therefore look black on both sides and therefore absorb quite a bit of solar radiation. They can actually get quite warm so I decided to mount them on copper disks using Torr Seal epoxy (high temperature, high thermal conductivity). I normally use 1-inch copper disks which fit nicely into Thorlabs 1-inch lens tubes (I have also mounted them on 40mm copper disks which fit into M42 type of adapters).

 

1534.jpg.7c0264689be523672e9308283d4ba96d.jpg

1535.jpg.19a740469c2e70ad38779990a3c512e1.jpg

 

The chrome layer is on the side away from the copper disk. The sunlight is designed to fall on the side with the hole in the copper disk (which acts like a mask). The light passes through the fused quartz (which is 2.3mm thick) and focuses on the chrome layer on the other side. 

 

Up to 100mm aperture, I can use the slits with only a 2-inch Astronomik L1 UV/IR cut filter placed 15cm in front of the filter to act like a bit of an ERF. The copper disk and Thorlabs lens tube act as a heat sink. For larger than 100m aperture, I would probably use some additional energy attenuation (e.g. a Herschel wedge or 2-inch wide-band H-alpha filter instead of the UV/IR filter cut filter). I think being able to use very high light intensity improves imaging because it allows short exposure times with very low camera gain. In H-alpha, I typically use zero gain and an exposure time of 2.5ms (at 720mm focal length). This allows an imaging speed of around 300 fps, which in turn allows relatively fast sidereal rate scan.

 

file.php?id=68330

 

I recently decided to standardise on a very short 1-inch Thorlabs lens tube (see attachment). This short tube can be easily screwed into another 1-inch threaded adapter so I can replace the slit quickly and easily (in case of damage, contamination, etc).

 

SM1L03-AutoCADPDF.pdf

 

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Thanks a bunch for the detailed explanations, that's very interesting!

The slit you made definitely fills the gap between the short yet without-defect Shelyak slit and the longer mechanical ones with all their advantages and problems. Having built and tried the Sol'Ex, I now want to go further in spectral resolution, and for this  I'm planning to build a new SHG (closer to the design used by P. Zetner: https://www.pbase.com/p_zetner/shg_2014), and such a longer slit would definitely help, relaxing the constraint on the focal length of the telescope. Would you be ok to share the name of the company that made the slit? We can take this offline if you prefer.

 

Cheers,

 

Simon

 

 

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 I'm planning to build a new SHG, closer to the design used by P. Zetner

 

I'm in contact with Peter Zetner quite regularly and I believe his newest design is described here: A New Spectroheliograph. He recently ordered two slits from me, as have a few others. I don't think he's had time to use them yet though. My 5-inch quartz substrate had 49 pieces, and I have only used about 20 of them so far. Send me a private message here or there is an email address at our GitHub, where you can also find our version of the SHG reconstruction software: Solar disk reconstruction from SHG video files

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Hello TheSmiths,

thanks for sharing your SHG design.

Maxime

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