OIII images taken with the 300 mm on August 5

[christian viladrich]

Hi,

Here are some other belated images taken on August 5 at St Véran.

I kind of like this first one. We can see that the right border of the umbra of these two spots is brighter than the left border. If we remember that the umbra is at altitude a bit lower than the filaments (and the granulation), we can figure out that this effect is explained by a perspective effet.
These spots being close to the solar limb, the bright "head" of the filaments (= the part close to the umbra) is directly visible on the right border of the umbrae. On the opposite, it is hidden on the left border because of its lower altitude:

http://astrosurf.com/viladrich/astro/so ... 0-OIII.jpg

The diversity of size and shape of the granules :

http://astrosurf.com/viladrich/astro/so ... 0-OIII.jpg

Clear skies

Christian

[JochenM]

I kind of like it as well

Out of curiousity, what's the reasoning behind using the OIII filter? The shorter wavelengths will be a lot more sensitive to conditions being right (not like that's an issue by the looks of it, but still), so I'm guessing there must be a specific purpose?

[banjo]

[torsinadoc]

Excellent HR shots. I always appreciate excellent WL images.

[MAURITS]

Great HR WL images Christian, nice to see the detailed convection cells.

[Petrus]

Wonderful images Christian, as always. So many details to look for. Thank you for sharing!

[ffellah]

Superb results Christian.

Franco

[christian viladrich]

Thanks guys !!

Jochen, there are different factors involved in the choice of the filter :
- seeing quality decreases when going to the blue (i.e. it is more difficult to have good image in the blue),
- diffraction decreases in the blue (i.e. resolving power of a reflecting telescope increases),
- contrast of solar features visible on the photosphere increases in the blue.

On top of that, an often overlook factor is atmospheric dispersion. The atmosphere acts like a prism, star images are vertically dispersed a bit like a small spectrum.
Dispersion increases to the blue, and with the width of the filter bandpass.
For example, when the Sun is 30° above the horizon, atmospheric dispersion with the OIII filter (12 nm bandpass) is 0.09 arsec, much lower that the resolving power of the 300 mm Newtonian.
With a typical green filter (100 nm bandpass), atmospheric dispersion would have been 0.6 arsec, which is larger than the resolving power of the 300 mm telescope.

So finally :
- the choice of the color of the filter (blue, green or red) depends on the seeing (and on the telescope aperture),
- the choice of the bandpass depends on the height of the Sun above the horizon. Using 12 nm filter (or lower) solves this last issue neatly.

[arnedanielsen]

Amazing results as always Christian!

Best regards,
Arne

[Sumpy]

Holy smokes these are incredibly detailed!

[marktownley]

Super images there Christian!

[Alun_H]

Fantastic images Christian.

Alun

[cybermayberry]

Holy Smokes they look great

[Carbon60]

Yet again, mind blowing images, Christian. Superb

Stu.

[christian viladrich]

Thanks a lot !

[Montana]

I'm glad you brought up the perspective of the spots, I hadn't thought of that and now I will look for it

Alexandra

[DeepSolar64]

VERY nice high resolution work Christian. I always enjoy your work. Thanks for sharing.

JP