At this thread of cloudy nights, an issue on sensitivity of tri-bahtinov mask has been raised. So, this is a study to improve it.
Modified Version (Ver.2) Tri-Bahtinov Mask Generator
Diffraction gratings colored in the same color makes up a set of Bartinov mask. And the tri-bahrtinov mask is formed by the three colored masks.
Note: All the images below are taken with the same amount of un-collimation. The test star is Vega, OTA is C6, the camera is ASI224 MC, and the mask is made equivalent to F.L.=800mm.
| Description | Diffraction images | Mask patterm | |
| Defocused image without mask Misalignment of optical axis is recognized. |  | ||
| Original Misalignment is seen in the 3 o'clock direction |  |  | |
| Second modified version A misalignment larger than the original is seen in the 6 o'clock direction. The light streak is thick. NOTE: The diffracted light streak of this modified version rotates 90 degrees with respect to the original. |  |  |
Compared with the original Tribatinov mask, the distance between the oblique gratings(purple) and the horizontal gratings(yellow) is widened. It will contribute to increased sensitivity.
And, assuming that the influence of un-collimation is coma, the coma aberration creates aberration due to the image formed by the portion with a different distance from the center of the aperture.(Reference) Therefore, the second modified version made it possible to detect by using zones with different distances from the center of the aperture.
The reason why the light streak became thick was probably because the length of the grating was shortened.
| Description | Diffraction images | Mask patterm | |
| Original The three sets of diffraction images each show equal amount of de-focusing. |  | | |
| Second modified version Larger de-focusing signs are seen. Light streak is thick. |  | |