3 ms·

(can't reply below) If you had a localised shutter covering pattern X for 6 seconds, could you compensate for that by covering the inverse pattern of X for 6 se

by 0-_-0 6y ago

(can't reply below) If you had a localised shutter covering pattern X for 6 seconds, could you compensate for that by covering the inverse pattern of X for 6 seconds to get the same exposure for all pixels? So if you covered 3 satellite streaks of 6 seconds each using non-verlapping patterns (A,B,C) you could compensate for that by ending your exposure with covering the inverse of A+B+C for 6 seconds, adding only 6 seconds to your total exposure time and get uniform exposure.

welterde 6y ago
If the conditions are quite stable that might work (or if one can live with limited accuracy), but conditions tend to change over time (moon position, thin clouds and of course the seeing - how much the atmosphere distorts the image) so nothing is as straightforward as one might hope for. In space that approach would work quite well indeed, but then you wouldn't need it in the first place.. Edit: Even if one still has to mask the streak in the data in the end, it might still be useful to do, since it will protect the rest of the image from any excess blooming.
- 0-_-0 6y ago
  How much does the bloom extend in the image fom the streak? Can you measure it in arcminutes or is it optics dependent? Is the bloom present if you cover up the satellite exactly? (Is it caused by the sensor, or would diffraction around a shutter cause it as well?) I think you could mitigate the problems with conditions changing if (instead of blocking out the streak in the image with some per-area shutter) you tracked the satellite in the image with a horizontal (or vertical) shutter stripe which has the right width to cover the entire satellite. This would make the data lost really minor, and changing conditions wouldn't be a problem, and the exposure would be even. Does that make sense?
  - welterde 6y ago
    If no light falls onto the detector then there is no blooming. And of course there will be diffraction from the shutter edges as well, so engineering it will be quite a challenge (one can take hints from coronographs). If the satellites does end up on the sensor then the dimension of the streak depends on the optics, how bright it is, the used detector, plate scale, etc. (if you are extremely unlucky you might have internal reflections too and they might end up who knows where on the detector - optics is hard).
klyrs 6y ago
Herein lies the problem. Your proposed solutions are ever more complicated as you begin to grasp the magnitude of the issue. Implementing this idea, and I'm not saying that it's good enough, would require modifications to pretty much every major telescope in the world. And there's no economy of scale because most of them are custom builds. Who's gonna pay for that?
- 0-_-0 6y ago
  That is only necessary in a small fraction of cases. You can just ignore the part with the streak or lower the shutter when you're using existing equipment.

by 0-_-0 6y ago

welterde 6y ago

If the conditions are quite stable that might work (or if one can live with limited accuracy), but conditions tend to change over time (moon position, thin clouds and of course the seeing - how much the atmosphere distorts the image) so nothing is as straightforward as one might hope for. In space that approach would work quite well indeed, but then you wouldn't need it in the first place.. Edit: Even if one still has to mask the streak in the data in the end, it might still be useful to do, since it will protect the rest of the image from any excess blooming.

0-_-0 6y ago
How much does the bloom extend in the image fom the streak? Can you measure it in arcminutes or is it optics dependent? Is the bloom present if you cover up the satellite exactly? (Is it caused by the sensor, or would diffraction around a shutter cause it as well?) I think you could mitigate the problems with conditions changing if (instead of blocking out the streak in the image with some per-area shutter) you tracked the satellite in the image with a horizontal (or vertical) shutter stripe which has the right width to cover the entire satellite. This would make the data lost really minor, and changing conditions wouldn't be a problem, and the exposure would be even. Does that make sense?
- welterde 6y ago
  If no light falls onto the detector then there is no blooming. And of course there will be diffraction from the shutter edges as well, so engineering it will be quite a challenge (one can take hints from coronographs). If the satellites does end up on the sensor then the dimension of the streak depends on the optics, how bright it is, the used detector, plate scale, etc. (if you are extremely unlucky you might have internal reflections too and they might end up who knows where on the detector - optics is hard).

klyrs 6y ago

Herein lies the problem. Your proposed solutions are ever more complicated as you begin to grasp the magnitude of the issue. Implementing this idea, and I'm not saying that it's good enough, would require modifications to pretty much every major telescope in the world. And there's no economy of scale because most of them are custom builds. Who's gonna pay for that?

0-_-0 6y ago
That is only necessary in a small fraction of cases. You can just ignore the part with the streak or lower the shutter when you're using existing equipment.