andrew s

Your obviously young and your eyes still accomodate well, unlike mine. It takes a few minutes each morning before I can read the paper on my tablet. Regards Andrew

The most likely cause is cone error, remember that from my first reply? If the telescope tube is not parallel to the dec axis if you align on one side it will be off on the other. The traditional cure is to shim one end of the telescope to make it parallel, sound simple but is a painful trial and error process. See what Google turns up. I have done it in the past but it was a long long time ago. Regards Andrew

Put your ccd there and you would! Just because it's not the image your after does not stop it being an image. Looking in the mirror I wonder why it's my dad looking back at me rather than the young handsome youth I know I am. Regards Andrew PS I know what you mean only playing!

I thought the only felting Taks need was adding your initials in gold leaf. Regards Andrew

Just draw a large X in felt tip on you primary then you will have a real visible image at the exit pupil.🥴 If you were working in the IR your primary would produce an IR image at the exit pupil. Regards Andrew

Assuming you are seeing limited, both will have the same effective resolution. The larger aperture will for the same magnification of extended objects give a brighter image allowing you to see fainter detail. There is a reason astronomer seek larger telescopes. Regards Andrew

That's fine. We have different philosophical positions. Now that's different some quantum states are observable some are not. What fun. I will freely admit that my knowledge is limited and given that leading scientists can't agree on these things I don't feel too bad about it. I have tried to purge the worst of my understanding of pop science views but that still leaves a vast area for discussion. Regards Andrew

@vlaiv that's the problem of confusing how you do the calculation and the physical reality. The path integral method is a way of doing the calculation. It is based on an expansion of the full QED equations. It leads you down the path of thinking virtual particles are travelling all possible routes to interfering at the end to give to a real particle (photon) to detect. Virtual particles don't exist they are calculation tools just as the terms in an expansion of sin(x) are. Personally I don think wave functions are real . No one has ever observed one to the best of my knowledge. Yes, it's remarkable it gives the right answer but that is true of Lagrange multipliers, Taylor expansions and the like. Regards Andrew PS I should have said the physical reality is that over time the probabilities predicted by QED correlate well with the results of experiment. But not individual events, they remain random.

@vlaivI know its very difficult to get the right balance of concepts in these discussions. For me the real thing is the EM field. It interacts with the "particles and compound particles" of the other quantum fields e.g. atoms. If you start with one excitation of the EM field at a time, as in the slit experiment, then all you can do is calculate the probability of a detection at one point or another. When you see a detection you instantly know the probability of detection elsewhere is zero. However this is an information update local to the observer. To talk about a EM spherical wave spreading out from a point source you need a very large number of excitations/photons and then you can use the classical Maxwell equations to good effect. I know Mott did a famous paper on how particles localise along a track in QM. I will look it up. You may well have the better approach in explaining it than I. Regards Andrew

@vlaiv nice explanation. Just two points I might have put differently. I don't think you need to use a quantum wave function you can use the classical EM field but with discrete additions of energy ( creation, adding a photo and absorption, annihilation of a photon). There are no instantaneous changes to the whole EM field in QED as far as I know. QED is comparable with special relativity. (Keeping away from entanglement for now.) Regards Andrew

Bingo. Regards Andrew

Love the peg. Regards Andrew

Yes the eye brain is a very clever and complex system. @vlaiv has given some great references. However, it is not infallible, it seek patterns where none exists, it fills in were data is missing. (My tinnitus is a good example where it is filling in for the loss of high frequency hearing. Ear brain in this case.) Expectations can reliably condition what is and is not observed. Regards Andrew

In GR gravity is the bending of space time. Light just follows the straightest possible path through the curved space time. The straightest path is called a geodesic, and anything in freefall follows them e.g. planets in orbit round their suns. It's best not to think of photons in this context, good old fashioned wave theory is best in this context. Regards Andrew

@jetstream just as with a telescope the gravitational lens collects and focuses the light to give a brighter image albeit with considerable distortions. Regards Andrew

A bit like the last reply. Strong gravity acts like a badly made lens. Look at an object through the bottom of a wine glass. You can see significant distortions which shift as you move it. Similarly as the gravitating objects move or as our perspective changes the image shifts and the distortions vary. Regards Andrew PS the effects are due to physics not the effects alcohol!

Clearly, gravity distorts our image of objects. Just look at the images of Einstein rings, crosses and other shapes. It can also enhances the apparent luminosity of the object. We see the object as it was when the light was emitted not as it is now . Indeed as the light from different elements of an Einstein cross (or ring etc.) travel different paths they were emitted at different times. This allows us to see some events, live, more than once. Regards Andrew

Mike I am glad @vlaiv managed to explain things better than I could. I thought the following might be helpful. a) show vlaiv's diagram above and in b) I have blanked out all but the bit shown in you Blue diagarm posted above (but missing the eye). In c) I have shown how the eyepiece forms an image of the objective at the exit pupil (note the rays are an inverted mirror image but at a steeper angle due to the angular magnification) with d) showing the same thing for a double headed arrow. Regards Andrew

Oh no! A 3/2 diet. Regards Andrew

Probably a matter of taste but the experimental setup is pretty magical to me. I agree the image reconstruction is quite "basic". Regards Andrew

Try some screw lock. Regards

I want my Saturday and Sunday back. You just stole two days of my life. No wonder time is vanishing. Regards Andrew

It is also in the Astrophysical Journal paper linked in the link you gave. So yes it is true. Regards Andrew

Thanks for the link @Macavity a very interesting paper. I scanned the arxiv paper and it is a fascinating read. Not too technical. Given the need to illuminate the target fully with entangled photons it's not applicable to Astronomy just yet, pity. Regards Andrew

Unfortunately it is! Regards Andrew