Filter for viewing faculae?

Use this section to discuss "standard" Baader/Coronado/ Lunt SolarView/ Daystar, etc… filters, cameras and scopes. No mods, just questions/ answers and reviews.
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LostInSpace
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Filter for viewing faculae?

Post by LostInSpace »

Picked up a copy of Jamey L. Jenkins book. Observing the Sun, A Pocket Field Guide. In the chapter "Identifying Solar Features he notes "using the Baader AstroSolar filter coupled with a light green(Wratten #56) or light blue (Wratten #80B)" to enhance the contrast. Any reason for one over the other?

Anyone know of a USA source for a blinking paddle? The paddles, handles with 1.25" filter holder inserts that you can hold the filter to the eyepiece for allowing a quick view. My luck I'll drop, smudge, scratch, misplace a handheld filter. Plus I'm a tool junky :P .

OT: in the book. Fig 2.1 image credited to Alexander Hart, one of our Moderators? Only up to page 28, but from a newbie's perspective. A must read.


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Re: Filter for viewing faculae?

Post by Dennis »

The filters only let through those green or blue wavelengths, otherwise you will have all wavelengths on the camera, including IR. Since different wavelengths dont come to focus in the same spot a certain blur is the result of not using filters.
Blue, green or red is selected dependent on seeing and resolution goals. The shorter the wavelengths, the more resolution you will get, but for the cost of better seeing thats needed.


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Re: Filter for viewing faculae?

Post by Bob Yoesle »

Theoretically the Baader Continuum would be a good choice, and would be less affected by poor atmospheric seeing than a bluer wavelength. I have found it gives very good results:
Cotinuum filter.jpg
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Bob Yoesle


The better optical performance is theoretically due to the fact that most telescope optics are best corrected for spherochromatic aberration at the e line of 546 nm, and that the F line at 486 nm and the g line at 436 nm are generally the least well corrected:
doublet_achromats.png
doublet_achromats.png (90.84 KiB) Viewed 1106 times
EDs diagrams.png
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sct8 10.png
sct8 10.png (10.63 KiB) Viewed 1110 times
telescope-optics.net

NOTE: the horizontal scale varies in mm. The best correction is when the individual line is straighter and less curved (and why a long achro may be superior to a short APO for narrow-band use). The best corrected systems are the Tak TOA series and the well-designed Petzvals.


Perhaps most importantly, daytime seeing often occurs in the early morning and later afternoon, and atmospheric dispersion can negatively impact the views or imaging, and using a monochromatic filter will greatly reduce fine-scale blurring from the low altitude angles:

Atmospheric dispersion.jpg
Atmospheric dispersion.jpg (147.75 KiB) Viewed 1110 times

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Re: Filter for viewing faculae?

Post by christian viladrich »

The contrast of faculae increases when you go to the blue end of the visible spectrum.
This is related to the difference of temperature between the faculae and their surrounding, and to the profile of the black body spectrum.

So, if you observe with a camera, we will see more and more focalae (and not only on the solar limb), when you go from red filter, then to green filter, then to blue filter, then to near-UV filter.

If you observe visually, there is a sweet spot depending on eye sensitivity to contrast and color. For me (using a 150 mm refractor), I preder a G-band filter (430 nm) for faculae observation. But others might prefer a green filter.

And explained by Bob, the filter choice also impact sensitivity to seeing condition, and optical performance of the telescope depending on wavelength.


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Re: Filter for viewing faculae?

Post by Montana »

This thread may be of interest, although it was imaging not visual.
viewtopic.php?t=40811

Alexandra


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