andrew s

The attached describes AO for ESO covering ~2 arc minutes (albeit in the IR). It includes an image of Jupiter with 90 milli -arcsecond resolution. AO and Jupiter Regards Andrew

Sorry it was intended as humour, ligh relief. No offense was intended to anyone. The emoji was ment to signal humour. Regards Andrew

I think you misunderstood. It does sense the error on the pixels of the Shack Hartmann sensor. It then corrects via deforming the optics. Regards Andrew

Somewhat more seriously, I have been looking at the recent literature on the effect of the atmosphere on astronomy. They split the issue into two, seeing and scintillation. Seeing is caused by a tilt in the wavefront shifting the object in the focal plane. While scintillation is caused by curvature in the wavefront focusing and refocusing the light. Correcting tilt is simpler than correcting curvature. The latter might sting a bit on the eyeballs (see previous post). Regards Andrew

I am working on a Shack Hartman wave front sensor coupled to a deformable contact lens to allow visual observers to benefit form adaptive optics. This will finally put the refractor v reflector issue to bed. Aperture will win. Regards Andrew PS crowdfunding post to follow. 👹

Not advisable. The pass bands don't match and the UV is heavily attenuated by the atmosphere. K for a bright Venus but difficult for most stars. Better to use a non photometric V filter. Regards Andrew

While following the broad outline of your discussion I have not reviewed the details. However, the recent comments on sampling reminded me that formally the MTF only applies to "shift invariant systems" and as I am sure you both know CCD detectors are not shift invariant as the result depends on where the image fall even with Nyquist sampling. Regards Andrew

I wonder if the Event Horizon Telescope collaboration used the same software. Regards Andrew

I think we are all respectful of each others position. It's hard to add all the linguistic nuances in an online debate especially while defending our own views. Regards Andrew

I did not assume a squeezed function the obstructed psf is the subtraction of two PSFs. It is the subtraction which causes difference I am trying to defend. I will try to do a full argument and present it. I will avoid the transforms you use at it is the assumptions in those (when applied to an obstructed aperture) I am challenging. This may take some time with various commitments. Regards Andrew

You don't have to read it if your not interested. As long as it is within the rules why not allow it to develop? Regards Andrew

Looking after grandchild will respond later. Regards Andrew

See the diagram I posted and link. I think you have to accept that it is narrower and has the first zero is inside that of the unobstructed aperture? Narrower means that if normalised the obstructed central peak is inside that of the unobstructed one. I want to know if you accept this before taking the next step. Regards Andrew

The image is form here http://www.eso.org/sci/meetings/2015/EriceSchool2015/Schreibermapping_PSF.pdf It show the first zero is inside that of the unobstructed one so if normalised must have a" narrower" psf . Regards Andrew

We are repeating the debate we had before. May I try a different approach. The principle of superposition lets us model an obstructed circular aperture by taking the psf of the unobstructed aperture and subtracting that of the obstruction. This I contend leads to a narrower pdf than the unobstructed one. Do you agree with this? If you accept the psf is narrower, do you accept it must have higher frequency components and if not why not? (The reason I question the obstructed is that the maths employed has the cutoff built in from analysing the unobstructed case without proof that that is ok. I can't find the maths to provide the justification. ) Can you answer the questions I pose to allow me to understand your position better. Regards Andrew

I don't disagree with this. It is when it is assumed this hold for an obstructed aperture without proof. I looked but could not find a justification either way. Regards Andrew PS to elaborate slightly. If the obstructed psf is narrower than the unobstructed it must contain higher frequencies by a simple application of the Fourier transform theorem.

@vlaiv we have discussed this before but the so called theoretical cutoff is not in my view always valid. The psf of an obstructed aperture is thinner than that of an unobstructed aperture but with more energy in the first ring. However, the narrow pdf can't be correctly represented on the mtf if you constrain it to zero at the cutoff of the unobstructed aperture. I just note this as our long discussion before did not lead to a conclusion. Regards Andrew

I don't know but Thorlabs sell general ones for £3k+ . I have asked for a quote and will report back if I get an answer. Regards Andrew

It's easy to be misunderstood or missread even in the best of circumstances and especially if English is not your first language. I remember my first trip to Germany on business where the works manager asked "Why are you here" . To English sensitivity it seemed abrupt but was down to a limited vocabulary. In fact he could not have been more helpful. I now try not to assume intent or infer motivation. SGL is a good place for discussion Regards Andrew

I am all for enjoying our hobby anyway you want to. We are all different and get our kicks in different ways. I would love to have a Shackscope40x40 to monitor seeing and test telescopes rather than a high end Takahashi refractor for visual but that's just me. You I suspect would might differ on that.😉 Regards Andrew

To me, on my tablet, the right image has much higher contrast than the left and slightly more detail. A subjective opinion. Regards Andrew

Just imagine what you could see with the 12".😏 More seriously, it highlights the for need objective measurement to compare telescopes. Maybe FLO can set up a measurement service with a Shackscope40x40. Regards Andrew

We will have to club together to buy one of these Shack-Hartman wave front sensor to remove any subjective bias in real world tests! 🤩 Regards Andrew

Sounds like rigging the comparison to me. Regards Andrew

Yes, similar but "old" observations comment on linear v "point" features and visibility differences between l on d and d on l linear features. I felt it would complete the set. Clearly, it's up to you. You have already made a significant contribution so don't feel obliged to do it. Regards Andrew