3 ms·

How does it see the stars? Even modern CMOS image sensors cannot see the stars during the day.

by porphyra 3y ago

bhhaskin 3y ago
Likely not much of an issue at the altitude the SR-71 flys at
jpm_sd 3y ago
Probably by flying above most of the atmosphere.
- porphyra 3y ago
  That makes sense. What kind of sensor does it use to track the stars though? Stars are very dim.
  - geon 3y ago
    Stars don’t move a lot, so exposure time can be high.
  - numpad0 3y ago
    Simplest implementation of star trackers I've seen is the Canopus sensor[1] used in old spin stabilized satellites: the "tracker" is just a light intensity sensor and a computer on a spinning spacecraft. I don't know if that has to do with this implement or not, but a star tracker in general could be that simple. 1: http://petermasek.50megs.com/starplot.jpg http://petermasek.50megs.com/starplot.jpg
- stevenwoo 3y ago
  The navigator verified their position with the device while they were still on the ground.
txnf 3y ago
With a big enough aperture and low enough f-number you can definitely see the stars during daylight even from the ground
gmiller123456 3y ago
Modern, and even old, sensors absolutely can see stars during the day. It's really a question of magnification. When you magnify the image, the pixels a star falls on don't change much, but the background gets darker because the background is spread over more pixels. I was talking to a grad student who was having an issue getting descent flat frames (images of a uniform field, used to account for dust and optical train effects). I asked why she didn't just take a picture of the sky in the daytime like most amateurs do, and she said she always ends up with stars in the image doing it that way. They tried finding the least populated part of the sky, but still always picked up stars.
- photoGrant 3y ago
  Put a lens cap on! Then shoot.
  - gmiller123456 3y ago
    That is for taking "dark frames". "Flat frames" need light going through the optics so that things like dust and vengetting can be detected. This link explains them in more detail: https://www.highpointscientific.com/astronomy-hub/post/astro-photography-guides/understanding-calibration-frames https://www.highpointscientific.com/astronomy-hub/post/astro...
    - photoGrant 3y ago
      You're right! I read too quick. Instead, you want one of these! https://support.phaseone.com/knowledgebase/article/KA-01239/en-us https://support.phaseone.com/knowledgebase/article/KA-01239/...
- porphyra 3y ago
  That's a very cool anecdote. What did she end up doing? I guess you'll need something like an integrating sphere? https://en.wikipedia.org/wiki/Integrating_sphere https://en.wikipedia.org/wiki/Integrating_sphere Photography reviews often measure vignetting by putting a piece of tissue paper on the lens lol.

How does it see the stars? Even modern CMOS image sensors cannot see the stars during the day.

bhhaskin 3y ago

Likely not much of an issue at the altitude the SR-71 flys at

jpm_sd 3y ago

Probably by flying above most of the atmosphere.

porphyra 3y ago
That makes sense. What kind of sensor does it use to track the stars though? Stars are very dim.
- geon 3y ago
  Stars don’t move a lot, so exposure time can be high.
- numpad0 3y ago
  Simplest implementation of star trackers I've seen is the Canopus sensor[1] used in old spin stabilized satellites: the "tracker" is just a light intensity sensor and a computer on a spinning spacecraft. I don't know if that has to do with this implement or not, but a star tracker in general could be that simple. 1: http://petermasek.50megs.com/starplot.jpg http://petermasek.50megs.com/starplot.jpg
stevenwoo 3y ago
The navigator verified their position with the device while they were still on the ground.

txnf 3y ago

With a big enough aperture and low enough f-number you can definitely see the stars during daylight even from the ground

gmiller123456 3y ago

Modern, and even old, sensors absolutely can see stars during the day. It's really a question of magnification. When you magnify the image, the pixels a star falls on don't change much, but the background gets darker because the background is spread over more pixels. I was talking to a grad student who was having an issue getting descent flat frames (images of a uniform field, used to account for dust and optical train effects). I asked why she didn't just take a picture of the sky in the daytime like most amateurs do, and she said she always ends up with stars in the image doing it that way. They tried finding the least populated part of the sky, but still always picked up stars.

photoGrant 3y ago
Put a lens cap on! Then shoot.
- gmiller123456 3y ago
  That is for taking "dark frames". "Flat frames" need light going through the optics so that things like dust and vengetting can be detected. This link explains them in more detail: https://www.highpointscientific.com/astronomy-hub/post/astro-photography-guides/understanding-calibration-frames https://www.highpointscientific.com/astronomy-hub/post/astro...
  - photoGrant 3y ago
    You're right! I read too quick. Instead, you want one of these! https://support.phaseone.com/knowledgebase/article/KA-01239/en-us https://support.phaseone.com/knowledgebase/article/KA-01239/...
porphyra 3y ago
That's a very cool anecdote. What did she end up doing? I guess you'll need something like an integrating sphere? https://en.wikipedia.org/wiki/Integrating_sphere https://en.wikipedia.org/wiki/Integrating_sphere Photography reviews often measure vignetting by putting a piece of tissue paper on the lens lol.