thesmiths

Comparaison des images des spectrohéliographes H-alpha et H-beta avec l'image traditionnelle du continuum

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Voilà des images remarquables, quelle finesse dans les détails...

Bravo!

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c'est impressionnant, bravo !

quel filtre est utilisé ? un prisme de herschel ou un filtre ND ?

 

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C'est vraiment impressionnant.

On voit rarement des détails aussi fins avec un SHG.

 

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Remarquable en effet pour un SHG (bon ce n'est plus un Sol'Ex non plus ;))

 

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1 hour ago, Vincent_L said:

what filter is used? Herschel prism or ND filter?

 

I forgot to mention that  I used one of my custom-made chrome-on-quartz slits (see Chrome on fused quartz SHG slits). The typical SHG slits (like from Shelyak or Ovio) are made from soda lime glass and are therefore prone to thermal shock (and breakage). Fused quartz has a much lower coefficient of thermal expansion so can tolerate an intense thermal load. I have put the quartz slit into a focused beam from a 140mm aperture f5.7 refractor (very intense) and the quartz survived. However, under this test, the chrome / chrome oxide layer degraded after a few hours. This layer seems to be damaged by UV radiation (where it absorbs strongly). Therefore, I now use a 2-inch Astronomik L1 UV/IR filter as an ERF (positioned inside the telescope focuser). This seems to be sufficient to avoid any damage, even with a 100mm aperture telescope and no ND filter or Herschel wedge.

 

My impression is many ND photographic filters will slightly degrade imaging. Herschel  wedges are better but create some geometric problems (and good ones are quite expensive). The Astronomik L1 filter has a very wide (and specified) bandpass which allows imaging in Ca-K/H and high throughput in H-alpha. I typically use shorter than 3ms exposure at H-alpha at zero gain.

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1 hour ago, Guillaume BERTRAND said:

I would love to see the same thing in the calcium wavelengths. 

I ran out of time to do Calcium during this imaging session. But since you asked, I include a nice image taken at Ca-H with the same telescope but on a different day. This was taken with the same instrument, but with the aperture masked to 72mm (i.e. f/10). This image was taken 6 August 2022. Since I stack images, I usually take around 20 scans, which takes around 5 minutes. I also spend a lot of time refocusing all three lenses for each wavelength, which also takes quite a bit of time. Therefore, I normally can do only 2 wavelengths during the short period when imaging is good in my location (during the early morning). In the images above, in the mosaic, by the time I did the continuum, the thermal turbulence was quite high.

 

208107900-444416d4-2ace-4550-bc10-4386f1

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il y a une heure, thesmiths a dit :

But since you asked, I include a nice image taken at Ca-H with the same telescope but on a different day

 

This one is really splendid !

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2 hours ago, Pulsar59 said:

Remarquable en effet pour un SHG (bon ce n'est plus un Sol'Ex non plus)

 

Comme il ne s'agit pas d'un Solex, il est peut-être utile de montrer à quoi ressemble l'instrument. J'ai préparé une courte vidéo qui donne une impression : 106mm aperture spectroheliograph of 720mm focal length

 

J'ai eu de bons résultats avec les objectifs Asahi Pentax M42. Mon préféré est le 150mm f4 Super Takumar. J'utilise une paire de ces objectifs avec une caméra ZWO 183MM.

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