Moon in the moorning with FC100DL

[Fedele]

"Luna alla Fluorite di Calcio"
27.10.2021 ore 07:50, Matera (Ita)
Takahashi FC100DL, ASI 178 MM @ f/9 ( under sampling)
AsiStudio, AstroSurface
VixenSXD2

Edited October 27, 2021 by Fedele

[vlaiv]

48 minutes ago, Fedele said:

Takahashi FC100DL, ASI 178 MM @ f/9 ( oversampling)

Actually no - it is quite close to optimum sampling rate for ASI178.

ASI178mm has 2.4µm pixel size and at 510nm, optimum F/ratio for that pixel size is F/9.4, while mid spectrum at 550nm, optimum is F/8.7

[Fedele]

5 minutes ago, vlaiv said:

Actually no - it is quite close to optimum sampling rate for ASI178.

ASI178mm has 2.4µm pixel size and at 510nm, optimum F/ratio for that pixel size is F/9.4, while mid spectrum at 550nm, optimum is F/8.7

error to write

under sampling

[Fedele]

6 minutes ago, vlaiv said:

Actually no - it is quite close to optimum sampling rate for ASI178.

ASI178mm has 2.4µm pixel size and at 510nm, optimum F/ratio for that pixel size is F/9.4, while mid spectrum at 550nm, optimum is F/8.7

F/9 ??  wau so is perfect. 

i know another value  for best FL

[Fedele]

immages are not the TIFF original, but jpeg saved from my FB page

[vlaiv]

7 minutes ago, Fedele said:

F/9 ??  wau so is perfect. 

i know another value  for best FL

Yes, there is simple formula:

found here:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

You need to sample at twice cutoff frequency, so actual expression for F/ratio is:

F/ratio = 2 / f * lambda = 2 * pixel size / lambda (as pixel size is wavelength or 1/frequency).

If we take in above case

F/ratio = 2 * 2.4µm / 0.51µm = ~9.412 = F/9.4 (0.51µm = 510nm)

You can also use other wavelength values for light. ~500 is good for broad band imaging (in theory 400nm is shortest wavelength that you'll capture, but short wavelengths are more prone to seeing effects and it is better to go with 500-510 for calculation), but if you shoot thru Ha filter for example - you would put 0.656µm or 656nm as lambda / wavelength of light.

[Fedele]