Exit pupil and AFOV

[vlaiv]

Just now, Ags said:

But if we are talking about an airy disk / diffraction pattern, we should stick to trating the photons as waves right?

 

We can use simplification that I gave above - no need to think of photons as waves or anything - we think of waves that produce certain intensity of light - which you can relate to photon count for higher intensities or probability that photon will hit for low intensities (same thing really).

In this context -  photon is a "hit" rather than particle - +1 number in our CCD detector. Everything else that we use is more or less classical wave.

[Ags]

Not so relevant, but I once made a little program to model diffraction patterns using the Huygens-Fresnel principle, high school maths and Java. No Fourier transforms, just brute force programming... as I increase the number of samples the pattern evolves like this:

Edited May 20, 2020 by Ags

[John]

I guess one thing that might have affected this discussion is that the original post was made in the eyepieces section of the forum where discussion usually centers around tools that are used for observing and the practical observing experiences with them.

There seem to be quite a lot of aspects of this particular thread, especially recently, that might be more relevant to the Physics, Space Science and Theories section of the forum perhaps ?

 

 

 

[Stu]

Very true @John. Either way I have no idea what the thread is now trying to achieve now, it seems to be getting ever more abstract!

[andrew s]

2 hours ago, Stu said:

Very true @John. Either way I have no idea what the thread is now trying to achieve now, it seems to be getting ever more abstract!

And what is wrong with abstract may I ask? I have just found an interesting paper that shows experimental results that the eye can detect a single photon . In doing so it turns up the gain  so it is more likely to detect the next few. Which is an excellent strategy given that light follows London Bus statistics (Poisson) which makes "photons" bunch togather.

Regards Andrew 

Harmless fun.

Edited May 20, 2020 by andrew s

[Stu]

3 minutes ago, andrew s said:

And what is wrong with abstract may I ask? I have just found an interesting paper that shows experimental results that the eye can detect a single photon . In doing so it turns up the gain  so it is more likely to detect the next few. Which is an excellent strategy given that light follows London Bus statistics (Poisson) which makes "photons" bunch togather.

Regards Andrew 

Harmless fun.

Nothing at all Andrew, I just find it hard to see how we are now addressing the original question.

[andrew s]

1 minute ago, Stu said:

Nothing at all Andrew, I just find it hard to see how we are now addressing the original question.

That applies to a large number of threads! They are organic and evolve. I normally find a thread is reaching its end when it reduces to a series of jokes. I have tried to kill a number of Takahashi threads this way without any success. 

Regards Andrew 

[Stu]

1 hour ago, andrew s said:

That applies to a large number of threads! They are organic and evolve. I normally find a thread is reaching its end when it reduces to a series of jokes. I have tried to kill a number of Takahashi threads this way without any success. 

Regards Andrew 

Indeed so, although in this case there seemed to be a contentious question about airy disks dimming or otherwise which remains unanswered. I’m actually interested to know what the correct answer is!

[andrew s]

4 minutes ago, Stu said:

Indeed so, although in this case there seemed to be a contentious question about airy disks dimming or otherwise which remains unanswered. I’m actually interested to know what the correct answer is!

For what it is worth my view is that we don't  know for sure. Not withstanding  the lack of clear agreed definitions of what it all means,  I don't  know of any modern experiments on this. Yes even a single photon can be detected certainly 5 to 7 at the limit. However, I am not sure about localising that in the field of view etc. 

Controlled experiments  would be needed to decide for sure.

Regards Andrew 

[miguel87]

For whatever my view is worth too...

I think we could boil it down to the question of whether the airy disc changes size or not.

Because the star is a fixed brightness that doesn't change.

So IF it does get bigger, surely it MUST dim?

IF it doesnt change size then it shouldn't change brightness?

🤷‍♂️

Edited May 20, 2020 by miguel87

[Stu]

26 minutes ago, miguel87 said:

For whatever my view is worth too...

I think we could boil it down to the question of whether the airy disc changes size or not.

Because the star is a fixed brightness that doesn't change.

So IF it does get bigger, surely it MUST dim?

IF it doesnt change size then it shouldn't change brightness?

🤷‍♂️

Yep, at least we can agree on the question! 👍👍

[Don Pensack]

44 minutes ago, miguel87 said:

For whatever my view is worth too...

I think we could boil it down to the question of whether the airy disc changes size or not.

Because the star is a fixed brightness that doesn't change.

So IF it does get bigger, surely it MUST dim?

IF it doesnt change size then it shouldn't change brightness?

🤷‍♂️

Surely if it changes size by magnification, it must lower in terms of unit area brightness, though not in overall brightness.

The sky is equivalently dimmed by magnification, but an interesting thought just occurred to me:

The enlarged, and now dimmer per unit area, star is still 100% within the field of the higher magnification eyepiece.

The enlarged, and now dimmer per unit area, sky is no longer 100% within the field.  Some of it has moved outside the field, and so its total light is no longer there.

So it not only dims per unit area, but also dims overall.

We might say the total integrated magnitude of the star has not changed, but the total integrated magnitude of the sky in the field has changed to a dimmer magnitude.

That would mean the total amount of light entering the eye from the field has gone down (and we know it has), but the total amount of light from any individual star has not.

Could this be why we see fainter stars at higher power?

[Mr Spock]

The airy disk is a finite size and actual brightness. Both are constants, depending on aperture used. If you magnify the airy disk so it becomes extended, then it's surface brightness will reduce but not its actual brightness.

It would be interesting if someone could verify this through observation. 

[andrew s]

5 minutes ago, Mr Spock said:

The airy disk is a finite size and actual brightness. Both are constants, depending on aperture used. If you magnify the airy disk so it becomes extended, then it's surface brightness will reduce but not its actual brightness.

It would be interesting if someone could verify this through observation. 

I would agree theoretically with this and similar above provided the Airy is resolved by the detector.  If the detector is a eye/brain then I don't  know. One key question would the intensity of the star. I.e is it easily seen or near the limit of observability. 

Regards Andrew 

[markse68]

Would you see it as the same brightness though? Does a higher intensity small dot on the retina register the same as a bit bigger dot with the same light spread out?

[andrew s]

1 minute ago, markse68 said:

Would you see it as the same brightness though? Does a higher intensity small dot on the retina register the same as a bit bigger dot with the same light spread out?

That I suspect is what we don't know.

Regards Andrew 

[markse68]

And of course a very small thing that doubles in size is still very small- you’re never going to magnify till the airy disk is the size of Jupiter in the fov

[John]

2 hours ago, markse68 said:

And of course a very small thing that doubles in size is still very small- you’re never going to magnify till the airy disk is the size of Jupiter in the fov

If you use a smaller aperture scope, you get a larger airy disk.

 

[vlaiv]

2 hours ago, markse68 said:

And of course a very small thing that doubles in size is still very small- you’re never going to magnify till the airy disk is the size of Jupiter in the fov

Jupiter at what magnification and what time of the year? .

It could almost be possible with a small scope. Jupiter is about 45" in size and for 80mm scope airy disk diameter is 3.21" - difference being around x14.

That can "easily" be accomplished with set of eyepieces - take 32mm Gso plossl and 2mm Vixen HR planetary - difference being x16.

80mm scope + 2mm Vixen HR will make Airy disk larger than same scope and 32mm GSO Plossl on Jupiter.

 

[markse68]

Yea but why would you 🤦‍♂️😂

[John]

6 minutes ago, markse68 said:

Yea but why would you 🤦‍♂️😂

Beats me !!!

But I thought this thread had gone into realms beyond practical usage so I thought I'd throw it in

[Louis D]

16 hours ago, John said:

Beats me !!!

But I thought this thread had gone into realms beyond practical usage so I thought I'd throw it in

Yeah, this thread has gone a bit off the rails: