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I guess that you don't cycle filters, but rather take some time to do the Ha, then OIII and in the end SII, not necessarily in that order? Was this a single night? In any case, depending where target is in the sky - slight PA error + guiding can lead to different levels of field rotation. You can have PA error in altitude and/or azimuth - meaning your mount needs to be turned "left/right" to reach true NCP or it needs to be tilted "up/down", or some combination of these. Left/right error differs from Up/Down error in sense that it causes DEC drift in different part of the sky. One is near meridian and other is when the mount is pointing east or west. Depending where you are on "a circle", and depending how big your DEC error in that moment - guiding will cause more or less field rotation (field rotation is created when there is DEC drift and guide system compensates. In fact - I think that it would be there even without guiding, guiding just helps to stay on target). In any case - if you shoot Ha in one part of the sky and SII in other - this can cause one set of subs to have very small field rotation and other to have somewhat bigger.

No, it is due to field rotation because of slightly off polar alignment. It can also be that your subs are all aligned but there is small rotation between channels so one of the channels needed to be aligned to others. Try restacking - but use different reference frame.

What software are you using for stacking and what interpolation algorithms does it offer? Above is artifact related to a small angle rotation when aligning subs and using certain forms of interpolation.

As far as I understand, if there is no some sort of trade agreement between countries - when you purchase from another country, VAT of that country is removed but your local VAT is applied along with any import duty. When people from EU purchase in EU - they don't go thru that. They pay VAT as expressed, regardless of which country they are in and where from (in EU) they are purchasing. However, when I purchase from either EU countries or say UK or any other country, I purchase with VAT removed, but then when item arrives, provided that it is above certain amount (I think it is around 70 euro mark) - I get charged local 20% VAT on it as well as 10% general import duty. There are different tariffs for import duty and businesses get accurate tariff applied, but most people get general import duty unless they explicitly get someone to do the paper work of assigning a proper import tariff. In any case, I believe that VAT will be subtracted, but you are likely to pay local VAT + import duty.

That looks like legit hit, but we can't really tell what the source of it is. If you were inside of the house - it is most likely local in nature, but again, some high energy particles can go thru solid walls with ease.

I often wondered how does it compare against Delite? Delite does not come as 6mm, but in general use, why would one want Radian over a Delite?

Use standard deviation stacking to expose the streaks.

There is this eyepiece planner website (still in beta?). Don't know who built it, but it lists 30ish eyepieces that have exactly 6mm FL - as advertised. Granted, some of them are clones, but I also think that not every eyepiece out there is on the list as well. Below screen shot is just a segment of the list. Website is accessible here: https://eyepieceplanner.com/#/ Just sort by eyepiece focal length and you will find all 6mm eyepieces grouped.

I think that 99.9% of "cosmic" rays that we capture during recording of darks are in fact terrestrial in origin. I once recorded set of darks near wood burning stove that was not clean (it was winter time and it has been fired up day before). I had massive amount of streaks. It appears that ash has heightened levels of radioactivity. Nothing to cause concern otherwise - but shows up in darks readily.

When it says 6mm on the eyepiece - it might not be exactly 6mm When it says something like 52 degrees AFOV - you can be sure it's almost certainly not exactly 52 degrees. Even x2 barlow won't be exactly x2 and will change its magnification between eyepieces. All of these should be considered "class" rather than exact number. 5.5mm, 6mm, 6.5 and even 6.7mm are all in the same "class", and there are quite a few offerings in that range.

They actually use two sets of 1D + temportal information to construct 2D+time, right? Does scattered light "freeze" frequency at the moment of scatter? I'm trying to figure out how chirp plays into all of that - it is probably combined with diffraction to separate different moments, but I'm failing to see how that would be possible if scattered light continued to change in frequency with time.

Yep, that part is evident. There is one more detail, that I might have gotten wrong - it took 8 hours to "analyze" the recording?

You are sort of right with that statement. There is only one exposure as far as readout goes, but clever mechanism allows for single row (1D spatial) signal to be shifted in Y direction by change of electric field to get multiple images spread in time. Not sure how sharp stair stepping can be achieved as it would require very sharp changes in electric field to create fast transition in deflection angle, but I guess it's possible? It does not explain this however: How can such device be used to record 3 dimensions? Two spatial and one temporal?

@Ouroboros Just to be clear on above post: First is shutter speed of sub-pico second and second is having FPS that matches sub-pico second. I have no issues against the first. I just say that second is impossible.

When you say this, does it mean: - you can record event that lasted sub-pico second with this type of camera or you are saying: - you can record event that lasts sub-pico second, every sub-pico second with this type of camera?

Let me just contrast that with following argument (to be honest, I've look at streak camera and saw this: and did not bother to read the rest). So you want to capture light scatter from light propagating in some medium and you capture frames in succession and two frames next to each other are say 1 millimeter apart in sample that scatters). This simply means that whatever travels at speed of light can cross 1 mm between two frames. We have scientific sensor. It does not need to be large - let's make it rather small - say 3x2mm in size with handful of pixels. First frame is read out of those pixels and signal is sent out. That signal can travel at most 1mm before next signal - next frame needs to travel down the same line. We can't have any sort of multiplexing for readout in that case as we would need to put signals from many pixels at the same time in one wire - but we can't have that as whole mm is taken up by one pixel. This means that we would need to have wire for each pixel. Even if you do that - no recording device can record this information unless there is whole thing per pixel as at some point you need to do some multiplexing. I don't want to even start on issues like interference with such high clock speeds and multiple wires coming from pixels and ultimately - some part of system needs to move slower than speed of light. We have electrons in potential well of pixels and we have electrons in electronic device that records the signal. Those don't travel at the speed of light. In that context - streak camera with "sweep circuit" would need sweep to move faster than the speed of light in order to sweep necessary surface in needed amount of time (remember - we are dealing with changes that occur when light moves 1mm or less - how is sweep circuit going to move more than 1mm in time that it takes speed to move 1mm?).

On the page you linked: So it's a bit like instead of capturing lightning as it progresses you capture this: and the then do what exactly to get the actual motion? You make things up ... Not science in my book ....

Ok, here it is again I just again opened link and title is: 10 Trillion FPS and two guys stand there and talk about actually recording at 10 trillion FPS. How many pixels, at which bit depth? Someone care to calculate data throughput of that needed? Someone care to calculate speed of readout in electronics and how high clock rates do you need to have in order to do that? Then proceed to add the fact that electronics also works on EM field like light and that it takes time for electronic impulses to travel certain distance. With very clock speeds (like in Gigahertz range already) - you have issue with length of your wires. Want to go to terahertz speeds - how are you going to sync left and right side of your microchip when there is not enough time for signal to travel that distance?

My first impression was that it is fake. I did not do the exact math, and to be honest, I just skipped thru the video to see what it is all about, but when they started talking about incredible amount of FPS - my gut feeling was to think along the lines: - in order to record smooth image at certain FPS - you need to have enough photons - if you capture that much photons in such short amount of time - it means that total flux must be extraordinary. - That much photons with photon energy at certain level - equals enormous amount of energy. Gut feeling "calculation" pointed out that it's just too much energy in light to be feasible / real.

If I recall correctly, a prominent lens maker once said that any properly designed and well executed negative doublet does not introduce visible aberrations in the image. Not sure if there is need for "Ortho" barlow if above is true ...

We really don't need to. We have enough understanding and have good working theory of color and light that we can be certain we can process even astronomical images realistically. That does not mean that we should do that and in most cases we need to "augment" them to show detail which would otherwise not be visible if we matched processing to what our eyes would see. We can however be selective in the way we apply that augmentation - for example we can simply elect to represent image as it would be if light was brighter than it is - either by having brighter sources, or sources being closer to us. All of that is not mandatory for making of nice image, but it is there should one like to utilize such an approach.

Most professional astronomers do data reduction in such way. If you go to any server and download data - you'll get nicely calibrated and reduced data with complete workflow of how it's done - so that you know what sort of data you are using. So that is first stage - use well known and deterministic algorithms up to point where you have linear stack ready for processing. Next stage is automated as well in some cases - we just don't think about it. Every time you take your phone or your digital camera and do following: 1. Set auto 2. Shoot image 3. Download jpeg and/ or send image to printer That is what happens - predetermined, exact sequence of processing steps is taken to produce uniform looking image. Not only uniform looking - but also "correct" image. You will 100% agree that image that you are looking that is taken by digital camera is what you are seeing with your eyes.

I think that days of hand figuring are long gone. It is all done by machines and I don't think that quality of figure is related to time anymore. It can be related to what particular machine can achieve, but I'm certain that it takes same amount of time (so huge part of cost of making item - except for the cost of material) to do different quality lenses.

For me, there is clear distinction between the two. In case of stacking images - there is precisely defined mathematical workflow that has been proven to be correct. In second case - it's much like giving someone a list of numbers and asking them to guess which number comes next. Sure, it is educated guess (AI has to be trained) - but it is still a guess and as such - not 100% right all the time. When solving a mathematical equation, you don't say - here, this is solution, but I'm 87% confident it is the right one , If you apply correctly mathematical principles - you can be 100% sure you have the right solution. Since I consider astronomical imaging to be more than producing pretty pictures - even if that one step above is just to "document" what is out there (rather than doing additional measurements and analysis) - I value the workflow that does not utilize guesswork.

I would not otherwise post this in dedicated threads regarding said scope, but I think I can post it here because of they way thread topic was phrased. Is it too good to be true? Well - consider this: You can't really purchase 80mm F/7.5 achromat for less than say 250 euro - but I managed to purchase said lens for 35 euro of AliExpress. I won't go into detail of how much other components cost - except to say that I'm confident that my DIY scope based on this lens will be less than 100 euro. Rest is just labor costs and profit margins. If someone decides to cut down their profit margin from say 100% to 60% - what you get is a bargain scope