18 eyes are better than one. JWST sends back first infocus picture and its breathtaking

[Master Disaster]

31 minutes ago, CarlBar said:

 

It's the equivalent of holding the camera from a spy satellite up in your hand and taking a selfie with it in terms of difference in distance sale.

I'm not even sure that's enough scale differential tbh.

[CarlBar]

5 minutes ago, Master Disaster said:

I'm not even sure that's enough scale differential tbh.

 

Assuming 30cm selfie distance, it works out to about 2,000km, Spy satellites operate at a variety of altitudes so it's acurratte to some, but yeah i had trouble finding a good analogy in regular camerawork.

[Master Disaster]

Just now, CarlBar said:

 

Assuming 30cm selfie distance, it works out to about 2,000km, Spy satellites operate at a variety of altitudes so it's acurratte to some, but yeah i had trouble finding a good analogy in regular camerawork.

Lets just agree that its a freaking insane distance

[CarlBar]

Amen.

[tikker]

  

5 hours ago, Moonzy said:

1) is the center of the image always gonna be that bright? Does it function by slightly offset your target to the side to get a photo of it?

Or is just too sensitive for the star used for calibration and the thing they wanna film is actually much much dimmer?

No. The star it was centred on is super bright for the instrument. It's so bright that its light bleeds out across a large area. They did actually want this star though and it was for calibration, as you say. The fact that you can see other stuff in the field of view is a testament to how sensitive the instrument is.

5 hours ago, Moonzy said:

2) why is only some of the spots affected by artifacts from the hexagon shaped mirror while others aren't affected?

If you mean the diffraction spikes, then that basically scales with compactness of the source you look at (and also brightness to some extent). This pattern is called the point spread function and is the telescope's 'response' to a point source, i.e. an infinitely compact source. In practise stars are close to point sources hence you see these spikes much more on stars and not really on fluffy galaxies. The other random hexagons might be some form of what we call 'ghosting', residual alignment errors or something else; I don't have the deets and the main point of this image was firstly focussing.

3 hours ago, coreygibson said:

Looking at the lines coming out from the star it looks like they are using a bahtinov mask. Not sure though. they could be doing it the old fashioned way and adjust the focus back and forth until the star gets the smallest size in the camera.

Not literally a bahtinov mask here, but the idea is the same. If everything is perfectly focussed and you are diffraction limited then the image of a star should become the expected point spread function. The pattern tells you how well focussed the telescope is and, well, it's pretty well focussed as seen from these beautfiul diffraction spikes. They adjusted each mirror segment until each one was properly in focus to achieve this.

[porina]

5 hours ago, Moonzy said:

1) is the center of the image always gonna be that bright? Does it function by slightly offset your target to the side to get a photo of it?

Or is just too sensitive for the star used for calibration and the thing they wanna film is actually much much dimmer?

They could vary the exposure. I'd guess this was also to demonstrate the detecting and resolving power of background stuff.

 

5 hours ago, Moonzy said:

2) why is only some of the spots affected by artifacts from the hexagon shaped mirror while others aren't affected?

Relative brightness. It would always be there, but for a dim object it would be faint enough not to be visible.

 

3 hours ago, coreygibson said:

Looking at the lines coming out from the star it looks like they are using a bahtinov mask. Not sure though. they could be doing it the old fashioned way and adjust the focus back and forth until the star gets the smallest size in the camera.

Just where would they fit the mask? For a one time job?

 

Looking at the image there's hints of two phenomenon going on. The hexagonal diffraction spikes will be from the mirrors not being a single perfect shape. There will be those tiny discontinuities between mirrors contributing to that. You can also see what appears to be a + shape diffraction spike too, but you only see half of it since it overlaps with the other spikes. Don't know if that is due to other optical related parts or could be related to sensor. Looking at the scope design I think it could be one of the arms holding the secondary mirror in place. Two of the arms looks like they're aligned with the mirror pattern, but the 3rd isn't.

 

Edit: if it is that arm, it is not a + shape, just a single line. I'm perhaps too used to seeing traditional + shaped spikes I jumped to that conclusion.

[Master Disaster]

1 hour ago, tikker said:

  

No. The star it was centred on is super bright for the instrument. It's so bright that its light bleeds out across a large area. They did actually want this star though and it was for calibration, as you say. The fact that you can see other stuff in the field of view is a testament to how sensitive the instrument is.

Not just in the FoV though, you can clearly make out objects almost touching the main focal object and as you say, considering how sensitive the sensor is and how much light it was getting from that star its pretty damn incredible.

1 hour ago, tikker said:

If you mean the diffraction spikes, then that basically scales with compactness of the source you look at (and also brightness to some extent). This pattern is called the point spread function and is the telescope's 'response' to a point source, i.e. an infinitely compact source. In practise stars are close to point sources hence you see these spikes much more on stars and not really on fluffy galaxies. The other random hexagons might be some form of what we call 'ghosting', residual alignment errors or something else; I don't have the deets and the main point of this image was firstly focussing.

Not literally a bahtinov mask here, but the idea is the same. If everything is perfectly focussed and you are diffraction limited then the image of a star should become the expected point spread function. The pattern tells you how well focussed the telescope is and, well, it's pretty well focussed as seen from these beautfiul diffraction spikes. They adjusted each mirror segment until each one was properly in focus to achieve this.

I guess from the thoroughness of your posts and the apparent expertise you have in this field that you do something related to space as a job?

[tikker]

1 hour ago, Master Disaster said:

Not just in the FoV though, you can clearly make out objects almost touching the main focal object and as you say, considering how sensitive the sensor is and how much light it was getting from that star its pretty damn incredible.

I'm really impressed with how clean it looks with such a bright object nearby. Not quite sure what I was expecting besides awesome images, but it still blows my mind how well it performs.

1 hour ago, Master Disaster said:

I guess from the thoroughness of your posts and the apparent expertise you have in this field that you do something related to space as a job?

Yep, I'm an astronomer. I mainly work in radio astronomy at metre-scale wavelengths to study active galactic nuclei though, but lots of similarities remain and the excitement about JWST spreads wide