Phase Contrast Telescope - Part II

[Quarker]

Over a year ago I started a post on a theoretical proposal for a phase contrast telescope (link here https://www.physicsforums.com/threads/why-no-phase-contrast-telescopes.1010127 ). However, the post was based on real experiences that were so different from anything I’ve ever experienced in my many years of observing that I was hesitant to describe them. But since my post went nowhere, I’m going to describe them here just to get them on the record.

So what did I see? On a night with viewing conditions I would call excellent, I was observing M33, a nearby face-on spiral galaxy in Triangulum, with an f9 Newtonian reflector. As usual, most of the galaxy could only be seen with averted vision. But as I lifted my eye from the eyepiece, the HII regions in the middle 20% or so of the eyepiece field came into view, with direct vision. The HII regions were not resolved into stars. Rather, they looked like blobs of abberrated or unfocused light. They even had different levels of brightness. Outside of the central circle, the rest of the galaxy couldn’t be seen. This only lasted for about a second, but the image was unmistakable.

But that’s not the strangest part. Simultaneously with the HII regions coming into view, I felt a strange but not unpleasant sensation in the center of my observing eye. It felt as if the rods and cones in my eye were focusing on the image. When the image went away, so did the physical sensation in my eye. About a year later, the same thing happened while observing M51, a face-on spiral galaxy in Ursa Major.

And that’s it. Try as I might, I haven’t been able to reproduce these two experiences. My previous post was an attempt to explain what I saw. The fact that both times I was lifting my eye up from the eyepiece tells me that there is an area above the eyepiece where the eye has to be placed. This could only be the area called depth of focus, especially since slow telescopes like my f9 have larger depths of focus than most telescopes. I think spherochromaticism, an extra concave lens in my Nagler 13mm eyepiece, and the steep light cone of my f9 telescope are the sources of the phasing which I think occurred, but doing a detailed ray diagram is way beyond my abilities. I’m not a physics student, I’m just reporting my experience because if what I saw was actually phased light, this is a brand new, non-electronic way to view face-on galaxies, a notoriously difficult class of objects to see. Certain nebula may also be the right size to view this way.

Why hasn’t anyone else seen this? Probably because most people with slow enough telescopes, with large enough depths of focus, don’t use them to view dim, face-on galaxies. They are most famous for the excellent planetary images they provide. Also, viewing conditions have to be excellent, since we are talking about light shifts of half a wavelength, any thermal instability will be enough to blur the image. Also, the right eyepiece has to be used. And there may be other factors I haven’t even considered. But 400 years after the invention of the telescope, we are just now finding out that phased images can be viewed if the eye is properly positioned in the right telescope. This has got to be useful information to somebody.

 

[Philip Koeck]

Over a year ago I started a post on a theoretical proposal for a phase contrast telescope (link here https://www.physicsforums.com/threads/why-no-phase-contrast-telescopes.1010127 ). However, the post was based on real experiences that were so different from anything I’ve ever experienced in my many years of observing that I was hesitant to describe them. But since my post went nowhere, I’m going to describe them here just to get them on the record.

I would say, what you saw cannot be phase contrast imaging for a very simple reason.
In phase contrast imaging you make the phase shift of coherent light due to a specimen visible.
This means that the specimen is not the light source. The specimen must be between the detector and the light source.

You, however, are looking at a light source with your telescope.

 

[DaveE]

I don't understand how there can be "phase contrast" spatial information when the light sources aren't coherent. The phase received is random in all respects. I'm not sure what "phase" means in this context.

Coherent light isn't necessary if you are observing another object's effect on the phase of the source i.e. "phase shift". But even if you argue that you are observing illuminated dust in the galaxy, it seems any phase shift would be completely obscured by all of the other stuff in the optical path, like, as you said, the atmosphere.

Also, eyewitness testimony isn't very reliable. With n=2 out of many observations I think it's difficult to make any hypothesis of what you experienced.

 

[Quarker]

I would say, what you saw cannot be phase contrast imaging for a very simple reason.
In phase contrast imaging you make the phase shift of coherent light due to a specimen visible.
This means that the specimen is not the light source. The specimen must be between the detector and the light source.

You, however, are looking at a light source with your telescope.

I’m not sure what you mean by specimen.

 

[berkeman]

I’m not sure what you mean by specimen.

Like the thing you look at in a phase contrast microscope...

https://en.wikipedia.org/wiki/Phase-contrast_microscopy

 

[Quarker]

I don't understand how there can be "phase contrast" spatial information when the light sources aren't coherent. The phase received is random in all respects. I'm not sure what "phase" means in this context.

Coherent light isn't necessary if you are observing another object's effect on the phase of the source i.e. "phase shift". But even if you argue that you are observing illuminated dust in the galaxy, it seems any phase shift would be completely obscured by all of the other stuff in the optical path, like, as you said, the atmosphere.

Also, eyewitness testimony isn't very reliable. With n=2 out of many observations I think it's difficult to make any hypothesis of what you experienced.

The phasing would occur within the optical system of the telescope. In no way am I claiming to resolve details in distant galaxies, other than the outlines of the HII regions.

 

[Quarker]

Like the thing you look at in a phase contrast microscope...

https://en.wikipedia.org/wiki/Phase-contrast_microscopy
View attachment 324021

This is nothing like a phase contrast microscope.

 

[Philip Koeck]

I’m not sure what you mean by specimen.

You can also call it object or transparency.
See the post by @berkeman.

 

[Quarker]

You can also call it object or transparency.
See the post by @berkeman.

I think the phasing occurs in the eyepiece. Not all light from the primary reaches the eye. Some of the light is disbursed, but a small percent of the light can be shifted a half wavelength.

 

[DaveE]

The phasing would occur within the optical system of the telescope.

I think you are referring to something else, that the rest of us don't call "phase contrast". Whatever the salient features you are amplifying are they have to be from the object under observation. That is the source of the information you care about. The telescope/microscope is an information processing tool.

This is nothing like a phase contrast microscope.

Then you're going to have to describe it in some detail to get any useful comments here. Otherwise were only left with "I saw something a couple of times, did you see it too? What was it?"

Sorry I haven't read your previous link, it feels like too much work right now.

But 400 years after the invention of the telescope, we are just now finding out that phased images can be viewed if the eye is properly positioned in the right telescope.

Really? "Just now"? The people that built the Hubble, Keck, and James Web telescopes really know a lot about optical system design. They did those things with careful analysis and years of prior study in that field.

BTW, my favorite textbook to really understand this sort of thing is "Goodman - Fourier Optics"; but it does require some math background.

 

[Drakkith]

I think the phasing occurs in the eyepiece. Not all light from the primary reaches the eye. Some of the light is disbursed, but a small percent of the light can be shifted a half wavelength.

Not only is a telescope and eyepiece simply not set up to do the sort of phase contrast necessary to generate such an image, you wouldn't notice the addition of this small percentage of light anyways. A decent quality telescope and eyepiece with clean optics is going to get at least 80-90% of the light to your eye. Even assuming 5-10% of the light is somehow phase-shifted in such a way as to only reach your eye when it is shifted to a certain position, it wouldn't produce the effect you described. There just isn't enough leftover light.

The HII regions were not resolved into stars. Rather, they looked like blobs of abberrated or unfocused light. They even had different levels of brightness.

Are you certain you weren't seeing a reflection of a nearby light source off the back element of the eyepiece?

But that’s not the strangest part. Simultaneously with the HII regions coming into view, I felt a strange but not unpleasant sensation in the center of my observing eye. It felt as if the rods and cones in my eye were focusing on the image. When the image went away, so did the physical sensation in my eye.

I don't know what you were observing, but light shouldn't do this.

Why hasn’t anyone else seen this? Probably because most people with slow enough telescopes, with large enough depths of focus, don’t use them to view dim, face-on galaxies.

Unlikely. Plenty of people have SCT's with focal ratios of F/10 or higher. These were (and still are) extremely popular for decades for both visual observation and amateur astrophotography.

As I think I said in your previous post on this topic:
1. Telescopes just don't work the way you think they do when it comes to phase contrast.
2. Almost all of the light is already reaching your eye, so even the addition of a small amount of otherwise-lost-light via phase shift is nearly imperceptible.

 

[Quarker]

Not only is a telescope and eyepiece simply not set up to do the sort of phase contrast necessary to generate such an image, you wouldn't notice the addition of this small percentage of light anyways. A decent quality telescope and eyepiece with clean optics is going to get at least 80-90% of the light to your eye. Even assuming 5-10% of the light is somehow phase-shifted in such a way as to only reach your eye when it is shifted to a certain position, it wouldn't produce the effect you described. There just isn't enough leftover light.Are you certain you weren't seeing a reflection of a nearby light source off the back element of the eyepiece?I don't know what you were observing, but light shouldn't do this.Unlikely. Plenty of people have SCT's with focal ratios of F/10 or higher. These were (and still are) extremely popular for decades for both visual observation and amateur astrophotography.

As I think I said in your previous post on this topic:
1. Telescopes just don't work the way you think they do when it comes to phase contrast.
2. Almost all of the light is already reaching your eye, so even the addition of a small amount of otherwise-lost-light via phase shift is nearly imperceptible.

Apparently, it doesn’t take a lot of phased light to create the effect I described. Which means that small telescopes may be sufficient to view face-on galaxies, as opposed to large, heavy and expensive telescopes. The SCT’s you refer to don’t have large enough depths of focus to see this effect,. They may be f10, but the primaries are actually quite fast.

 

[Philip Koeck]

Apparently, it doesn’t take a lot of phased light to create the effect I described.

What is phased light?

Assuming you mean light that has been phase shifted half a wavelength, as you mention somewhere, how would this increase the visibility of the galaxy you are looking at?

Maybe you could describe the mechanism qualitatively.

 

[DaveE]

This sort of word salad isn't going to lead to anything useful from us. A well defined hypothesis communicated clearly (maybe a diagram?) is the next step.

 

[Quarker]

What is phased light?

Assuming you mean light that has been phase shifted half a wavelength, as you mention somewhere, how would this increase the visibility of the galaxy you are looking at?

Maybe you could describe the mechanism qualitatively.

I think that by shifting identical wavelengths of light from the galaxy source exactly one half of a wavelength, the eye perceives that light as having twice the amplitude. It’s just constructive interference. But what does increasing the amplitude look like? In this situation, it looks like blobs of light conforming to the positions and outlines of the star forming regions of face on galaxies. The physiological response I described, involving the rods and cones in the eye, is apparently required for the phased image to be seen. There are many questions, of course. What part of the eye has to be positioned in the depth of focus, the eye lens or the macula? What percentage of light from the image has to be phased for the eye to perceive it? How deep does the depth of focus have to be? I know my 8” f9 Newtonian meets these requirements., so I think my problem is not being able to keep my eye properly positioned. I’ve never seen a finely detailed ray diagram of a telescopes depth of focus, but judging from my experience, even in an f9 telescope they are quite small.

 

[Philip Koeck]

I think that by shifting identical wavelengths of light from the galaxy source exactly one half of a wavelength, the eye perceives that light as having twice the amplitude.

Actually the amplitude would be decreased if some of the light is phase shifted by half a wavelength with respect to the rest.

 

[DaveE]

I think that by shifting identical wavelengths of light from the galaxy source exactly one half of a wavelength, the eye perceives that light as having twice the amplitude. It’s just constructive interference.

Nope.

1) You would need monochromatic light. It's is rare that a process shifts many different wavelengths λ each by λ/2.
2) Constructive interference occurs for a full wavelength shift, not half. Half would be destructive.
3) IF you had monochromatic light, you can double the intensity of two rays with constructive interference. But that would only compensate for the fact that you divided the incident light by two when you split the rays. So dividing the ray into two paths, one of which is delayed by λ and recombining them is pointless in this context.

If you want to really pursue this hypothesis you're going to have to study some introductory optics re. interference and such.

 

[Quarker]

Actually the amplitude would be decreased if some of the light is phase shifted by half a wavelength with respect to the rest.

Good point. The shift would have to be a full wavelength.

 

[Philip Koeck]

Good point. The shift would have to be a full wavelength.

If all the light comes from the same source and the shift is one wavelength then it'll be exactly the same as without a shift.
You can't get more light out of a single source by interference.
See point 3 in post 17 by @DaveE .

 

[Quarker]

If all the light comes from the same source and the shift is one wavelength then it'll be exactly the same as without a shift.
You can't get more light out of a single source by interference.
See point 3 in post 17 by @DaveE .

Possibly. My explanation as to the cause of the phasing could be wrong. I started this thread so that other amateur astronomers could look for the same effect. If someone else has a better explanation for this effect, I won’t be offended. I just want to see it again.

 

[Drakkith]

Apparently, it doesn’t take a lot of phased light to create the effect I described.

You are incorrect. It would take quite a lot of light to create the effect you described.

I think that by shifting identical wavelengths of light from the galaxy source exactly one half of a wavelength, the eye perceives that light as having twice the amplitude.

Again, you are incorrect. We've already discussed this in your previous thread, along with plenty about how phase contrast works and why it wouldn't apply in your case. Did you ignore everything that was said in that thread?

The physiological response I described, involving the rods and cones in the eye, is apparently required for the phased image to be seen.

Except that this doesn't make any sense. The behavior and response of the human eye is extremely well understood and nothing about it fits in with what you are describing.

Id' bet money that you simply observed some sort of reflection off the back of the eyepiece (or perhaps your eyeglasses if you wear them) or highly oblique stray light that has entered the scope and made it to your eye. Think about it. You're seeing out of focus light that appears to come from only part of the image. It's MUCH brighter than what should be possible given how much light from your observing target is already transmitted to the eye. It has only appears a couple of times and is hard to keep in view. This just screams 'stray light' to me.

It is FAR more likely to be some mundane effect like this vs some unknown phase contrast effect that hasn't been documented before, doesn't work like phase contrast microscopy, and doesn't even appear to follow the laws of physics.

 

[hutchphd]

I think your explanation (it is hard to know what that is) also must assume that your telescope is operating at its diffraction limit to see any improvement. This is how one checks the figure of the mirror.

 

[Quarker]

You are incorrect. It would take quite a lot of light to create the effect you described.

Again, you are incorrect. We've already discussed this in your previous thread, along with plenty about how phase contrast works and why it wouldn't apply in your case. Did you ignore everything that was said in that thread?

Except that this doesn't make any sense. The behavior and response of the human eye is extremely well understood and nothing about it fits in with what you are describing.

Id' bet money that you simply observed some sort of reflection off the back of the eyepiece (or perhaps your eyeglasses if you wear them) or highly oblique stray light that has entered the scope and made it to your eye. Think about it. You're seeing out of focus light that appears to come from only part of the image. It's MUCH brighter than what should be possible given how much light from your observing target is already transmitted to the eye. It has only appears a couple of times and is hard to keep in view. This just screams 'stray light' to me.

It is FAR more likely to be some mundane effect like this vs some unknown phase contrast effect that hasn't been documented before, doesn't work like phase contrast microscopy, and doesn't even appear to follow the laws of physics.

What I saw was not a reflection. Reflections don’t look like face-on galaxies.

 

[Drakkith]

What I saw was not a reflection. Reflections don’t look like face-on galaxies.

But they kind of look like this:

But as I lifted my eye from the eyepiece, the HII regions in the middle 20% or so of the eyepiece field came into view, with direct vision. The HII regions were not resolved into stars. Rather, they looked like blobs of abberrated or unfocused light. They even had different levels of brightness. Outside of the central circle, the rest of the galaxy couldn’t be seen.

Blobs of unfocused light? The rest of the image disappearing from view? Sounds like you moved your eye out of the light cone coming through the telescope and eyepiece and moved it into a light cone from a reflection.

I'm not saying I'm right. I'm just saying that this is a far more likely explanation than phase contrast is.

 

[Quarker]

But they kind of look like this:

Blobs of unfocused light? The rest of the image disappearing from view? Sounds like you moved your eye out of the light cone coming through the telescope and eyepiece and moved it into a light cone from a reflection.

I'm not saying I'm right. I'm just saying that this is a far more likely explanation than phase contrast is.

Unlikely. I’ve been observing for 50 years. I know what galaxies look like in telescopes from small to large. And the physiological response I described was distinct and unmistakable. The chance that I may have stumbled on something new is a real possibility, especially since slow telescopes like mine are extremely rare.

 

[russ_watters]

Thread closed pending moderation.