SolarChat!

christian viladrich wrote: ↑Fri Sep 28, 2018 3:19 pm Here is an image taken a while ago with the Lunt Ca K filter:


This is quite a good Ca K filter. I use it with a 150 mm refractor and no ERF with no problem. But don't use it with a larger aperture and no ERF. A friend tested it with a 200 mm and the fiter got damaged ...

TheSkyBurner wrote: ↑Sat Sep 29, 2018 1:57 am Peter has got an apo-triplet. that explains it! Super-apo telescopes are just in a league of their own for all wavelengths. I cant beat that high strehl ratio with out using my 150mm f15....

christian viladrich wrote: ↑Sat Sep 29, 2018 9:11 am Hello Mark,
If I may, I would suggest rephrasing your statement as follows :
"the Strelh ratio at 436 nm (g band for the opticians) is not relevant to the performance of the refractor at 393 nm".
This is because the spherical aberration increases very fast when you go to shorter wavelengths.

Here is an example with the SC :

Because of the refractive index evolution with the wavelength, spherical aberration increases gently with longer wavelengths, and sharply will shorter wavelengthx.

Indeed, the Strehl ratio includes all aberrations of the optics. Accordingly, The Strelh ratio at 393 nm is fully relevant to the performance of the optic at 393 nm. The optics is diffraction limited when the Strelh is greater than 0.8.

Best regards

Valery wrote: ↑Sat Sep 29, 2018 1:43 pm This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

marktownley wrote: ↑Sat Sep 29, 2018 5:28 pm

Valery wrote: ↑Sat Sep 29, 2018 1:43 pm This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

Hi Valery,

Is the c11 one that you selected from a number over time, or this the only one you've had?

Mark

TheSkyBurner wrote: ↑Sat Sep 29, 2018 7:36 pm

Valery wrote: ↑Sat Sep 29, 2018 1:43 pm This image is at 393nm continuum taken with a standard C11 280mm F/10 telescope.

download/file.php?id=34233

The image is quite crisp.

Valery: it is a good image, but it is not entirely "crisp". It is very blurry to my eyes, and it is over processed to bring out the details. Processing is a personal ability, and not a good indication of how well the scope is. It is a factor of lucky imaging.

You would get a better image if the optics were turned in favor of the blue wavelength, your hydrogen alpha image is the proof in the pudding. It is so much sharper, and has pure definition across all the whole-image. Which means the optics on the c11 are definitely made for h-alpha more than calcium. (as they should be, it is a deep space imaging scope)

If you could post the single frame data or a 10 frame raw data animation we can conclude the sharpness with better opinion of the sct optics. http://gifmaker.org/ (just extract 10 frames from the .avi file using avidub and upload them to gifmaker)

Post 10 frames of h-alpha raw, and 10 frames of calcium raw (unedited, unprocessed, screen grabbed straight from the .ser capture.)

Again, the image is great. But, there are definitely better optics out there for this color, like peters. We all work with what we have.


However I would trade the c11 for the apo triplet every day of the week,. (sacrificing the aperture for the strehl)

Valery: if i could give you my 150mm f/15 telescope, i would. You would likely use many times over the c11 and c14. Sometimes more aperture is not always the best choice, but of course; aperture IS king!


Christian your images are going to be very helpful! Thanks for posting.