I read a lot of theories and discussions on this topic, I decided to experience this issue empirically. I found a binary star, not too bright, not too dark, which, using my telescope and camera, would initially show too low sampling frequency (undersample).
The equipment used is: Telescope 320/1500, Camera ASI290mm-C pixel 2.9µ
Double star: HIP 72153
Parameters of the studied pair of stars:
Sep Mag1 Mag2 Delta Spectr Const Ra Dec Name
0.5 7.75 8.66 0.91 F6V Boo 14:45:29.74 +42:22:56.4 HIP 72153
The biggest challenge was to obtain imaging using a focal length of 1500mm. The image was recorded on 2 pixels, 1x2 size. Below is the result of stacking 200 frames from 10,000. For stacking such demanding imaging I used the old reliable program, Registax 5.
Imaging parameters: 320/1500 / 2.9µ - HIP 72153 - 0.5 ''
A pair of stars arranged on the camera pixels horizontally - vertically - diagonal, stack of 200 best frames from 10,000.
I also present short fragments of AVI - HOR - VER - DIA
As you can see, for my set: Telescope 305/1500 + 2.9µ pixel camera (ASI290MM-C) native focal length (1500mm) does not guarantee capture possible information. Two stars with a separation of 0.5 "are glued into a dash of 2x1 pixels. As we will see soon, this does not have to be the case, because you can get a 3x1 pixel detail, light pixel - dark pixel - light pixel. For this purpose a focal length of 2000mm is necessary, which can be obtained using a Barlow lens with a 1.3x parameter.
Imaging parameters: 320/2000 / 2.9µ - HIP 72153 - 0.5 ''
The distance between the centers of the stars is 1 pixel, so you can see that we have obtained information that due to too low sampling resolution was lost in the previous sample.
A higher Barlow lens (2.25x) provides us with imaging with an even higher sampling frequency, the gap between stars is 2 pixels.
Imaging parameters: 320/3375 / 2.9µ - HIP 72153 - 0.5 ''
The Barlow lens with an even greater multiplicity (2.7x) makes the break even clearer, but no new information is revealed.
Imaging parameters: 320/4000 / 2.9µ - HIP 72153 - 0.5 ''
In this experiment, the first three steps are the most interesting.
In conclusion, it is still difficult to determine where undersampling and oversampling meet, but it is obvious that in my set, in order not to lose data clearly, I have to use a minimum focal length of 2000mm.
Table / summary for 320/1500 optics + 2,9µ pixel, for different resolution criteria, and for different wavelengths of light.
By the way…
An interesting phenomenon is the rainbow drawn by the rings of Airy's disk.
Observation based on the example of a star: HIP 72153 - 0.5 ''
The effect is due to the fact that different wavelengths of light generate rings of different sizes.
Imaging was done with SLOAN filters, because they provide us with a greater difference in the wavelength range than those with RGB filters.
All images represent 800% of the native data.
Edited by GA-HAMAL, 12 September 2019 - 02:47 PM.