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You don't need to do that - that part is very well known. You won't get any information if you perform that task on your plain text, at least not any sort of particularly important information Check out https://en.wikipedia.org/wiki/RSA_(cryptosystem)#Encryption Cypher text is just message encoded as integer raised to some power (depending on public key), module some other number (again part of public key).

Sure that attacker can take any plain text and encrypt it. There is no mystery in how encryption part works - that is not the strength of RSA algorithm. If you have public key - you also have private key as well. Attacker does not even have to bother seeing what happens during encryption - they already have private key in their hands, all they need to do is to compute it. It is far easier just to compute private key from public then it would be to somehow "decipher" encryption stats with plaintext and public keys. Strength of RSA algorithm lies in the fact that it is very computationally expensive to find private key from public key. It is fast to generate both public and private keys from base prime numbers but it is very very difficult to go in reverse direction from public key to base prime number in order to derive private key part. Here is an example. If I say - what is 11 x 17 - you should be able to do it in your head in no time - 11 x 10 + 11 x 7 = 110 + 77 = 187, but if I asked you - what two numbers you have to multiply to get 187, how much time would it take to figure out it is 11 and 17 and how would you go about it? That is the strength of RSA - some mathematical procedures are far far easier to do in "forward" direction than it is in "reverse". That will be true until we find efficient factoring algorithm that can do it in less time. Problem is much much greater in general and is one that you can easily win $1,000,000.00 if you solve it It is one of millennial prizes - so called "P vs NP" We still don't know or have proof if P=NP or P!=NP. P and NP stand for "polynomial time" and NP stands for "nondeterministic polynomial" time. Two terms are used to denote complexity of a problem (or algorithm as a solution). P means that complexity is polynomial in nature - and can be thought of - for input of size N, output is calculate in time that is equal to P(N) - or polynomial of N. That polynomial can be as simple as 2X or can be more complex as X^5+4*X^2, but in both cases if you double the amount of input data - it would take in first case x4 more time to solve it and in second case something like ~x40 more time to solve it. Both are within reach of either waiting some time or using more machines in parallel or simply waiting for computers to become stronger - and it will be solved. NP class of problems have "stronger" complexity where complexity is not polynomial but rather exponential for example (don't nondeterministic polynomial part confuse you - it is conceptual machine that does calculations - that is where term comes from). If we increase input size - time to calculate output is increased much much more than it would be in P case. This is why say 2048 bit RSA key is significantly stronger than 1024 bit key. We just doubled amount of input data - but time to factor that large number increased much much more. Back to P vs NP - we still don't know following: if problem has solution that is NP in nature (algorithm has nondeterministic polynomial complexity) - is there solution to the same problem that is P in the nature, and that holds always (P=NP case) or if problem is NP then there certainly is no P solution to it (P!=NP). One who solves this and provides proof can win one million dollars prize (https://en.wikipedia.org/wiki/Millennium_Prize_Problems)

That is the thing with RSA type encryption - that is not how it works. What you are describing is symmetrical cypher. With RSA type encryption we have asymmetrical mapping. Simplest explanation would be as follows - imagine you have function that says a mod b = output value (reminder or modulo function) if you have output value of say 5 and you know that b is 10 - then you can't tell if a is 5 or 15 or 25 or 35 and so on ... In fact - if you look at RSA encoding function - it uses modulo:

It is rather confusing thing. I always have to stop and think deeply about it and even then I'm not certain that I've got it right. It depends on refraction indices of glass and air. There is law of refaction that says n1 * sin a1 = n2 * sin a2 When we rearrange this we get n1 / n2 = sin a2 / sin a1. So relation of angles is inverse to relation of refraction indices. Air has n1 = ~1 and glass is "thicker" and has higher refraction index - so angle in glass must be closer to normal (smaller angle). It shows in above diagram - angle in air is larger than angle in glass - and that is similar to what barlow does and it pushes focal plane further away (unlike reducer that brings it inward because it does the opposite).

There you go - answer provided by Olly. Here is handy diagram - in converging beam - filter pushes focus point further out so yes - for example it will be 56mm instead of 55mm so adding spacer is required.

No, that is Ganymede for added realism

It does not quite work like that. What spider supports actually do is alter PSF of a telescope. PSF is short for point spread function and you can deduce how it behaves from its name (with a bit of imagination and help of math ). It describes how light "spreads" from each point. Stars are single points of light so star image is good representation of PSF itself. Extended objects behave differently - like they are composed out of vast number of tiny points placed next to each other, and each of those points is affected by same PSF as above star is. However, this process differs from waves in that it won't be susceptible to interference - but rather it is simple addition. Where spikes from multiple points cross - there won't be cancellation on phase (like you get with interference) - but always overlap / addition. For several points this is what happens: In each place spikes overlap - you get just a tad brighter spot. It took some searching online to find suitable image - but look at this crop: Now - we need to "extrapolate" the effect on entire planet - where each little bit of planet's image is single "star" and has its own spikes that overlap. That reduces contrast on the features just a tiny bit and leaves one "gigantic" cross that looks like this: which is really just "tightly" packed pattern like this: If I find suitable image and adjust exposure - we should be able to see it in the images as well. Let me try. This is probably the best example that I could find - not sure if this is imaging attempt or phone at the eyepiece - but it shows the effect:

Most people imaging with newtonians don't in fact have curved spiders. We see spikes in deep sky images because of vast difference in brightness between stars producing them and objects that we try to image so we stretch our data a lot. Planets are on the other hand much much brighter and don't have nearly as much dynamic range as DSO images. Spider effect will be there - but won't be visible in images, so you don't have to worry about that.

I'm not sure that answers my question though. My original question was this. I do respect the amount of expertise you have with 3d printing and above is genuine question. We often (at least I do because I lack any training as mechanical engineer) confuse different terms like strength and toughness. ABS and PETG are tougher but less strong than PLA. They are also more elastic. That is, at least, what I figured from looking at videos like these: https://www.youtube.com/watch?v=ycGDR752fT0 I'm inclined not to overly trust sources like that because to me it looks like it has been generated by AI rather than human that knows what they are talking about. Take for example this part: When was the last time that you've seen same information in two consecutive sentences just phrased differently when reading the genuine article written by a human (without emphasis on something important - ie - "let's reiterate that once more ...").

My guess is that you'll create different spikes depending where star sits in the field of view (it might be hardly noticeable and won't detract from the image). Thick spider will present very thin profile when the star is at optical axis - but as soon as you star moving away from optical axis - it will "widen" in its profile. Difference between thick and thin spider is in level of dispersion. If you've noticed, spikes tend to have rainbow effect on them in RGB images. This is because these are actually little diffraction gratings (spider support I mean) and diffraction grating will diffract light at different angle depending on wavelength. Width of spider support creates different type of grating - which results in different diffraction. I think that narrow spider supports tend to spread rainbow more than thick ones.

When you say stronger, what exactly do you mean in this context? ABS/PETG is more flexible so it will flex more easily under load - which is bad for holding camera Those also have higher impact strength - but I don't see it being important in this application. They are however somewhat weaker in load bearing applications (not too much and I would not dismiss them on account of that) - and have nicer failure mode that might be of some importance for this use case - but again, if properly designed I don't see mount failing under weight. This is something that I consider a lot lately, and to be honest, I've been surprised by results people get when testing different material ability to bear weight. For example - this guy does very interesting (maybe not very scientific) tests: https://www.youtube.com/watch?v=E3WRBp-T42o I've seen numerous videos where he is able to hold his own weight with 3d printed M8 bolt In above video - M8 bolts printed in horizontal orientation fail at about 180-200Kg of load. I would trust such bolts to hold 20Kg for short periods of time (PLA is susceptible to creep, so might not be a good idea to put it under such load permanently). Or how about car park / stop in 3d printed version? https://www.youtube.com/watch?v=JSWtzMzZp9w

Well, wiki does say:

I think it has more to do with water vapor being heavier then the air. There is gradient of relative humidity and air near the ground is moist the most. Dew first forms on grass, and that is organic material and will cool slowly, but it is closest to the ground and there is the least wind to stir things up. If your case is placed on some low table or similar - it is going to dew up sooner than the scope that is higher on the mount.

Another way to handle would be to not handle them at all. Sure, in single exposure - you would get broader diffraction spikes, but with sigma clip stacking of multiple exposures - same thing would happen that happens with satellite airplane trails in the images - what is there in one sub but not the rest would be discarded as invalid signal so one would actually loose long diffraction spikes and perhaps only keep their "stems" as those won't rotate much after alignment. They will probably "merge" into halo what would otherwise form from curved spiders.

Two things happen to make dew shield work. First is temperature. As has been pointed out above - something needs to cool down below dew point in order for dew to start forming on it. Piece of glass facing up towards the sky can get colder than the ambient temperature under some conditions. This is because of ways heat transfers from body to body. One of these ways is heat radiation. Sky is very cold - it is about 2.7K if I'm not mistaken that is about -270C. Two things that are next to each other are trying to reach equilibrium as far as radiation heat transfer is concerned - first object is giving off heat that hits the second and second is giving off heat that hits the first. Problem is - sky is much much colder than glass and that makes glass cool. You can see this effect on cars in the winter. Ice will form mostly on the front windshield and on back - but not so much on side windows (depends where car is parked) - this is because front wind shield is facing towards the sky and side windows often face other objects like other cars and buildings. Dew shield - well shields objective lens from cold of the sky - by restricting how much of it is exposed to the sky - it shields from broader exposure to the sky. Second effect of dew shield is that it lowers humidity of the air. If things get cold enough for dew to start forming - that dew is water from the air and relative humidity drops in vicinity of formed dew. Dew shield traps pocket of air that has lower relative humidity than the surrounding air because it already deposited dew on outside of the dew shield and rest of your gear. If there is little wind - that drier air will stay around the lens for longer. Stronger winds will blow it away and increase chance of dew forming.

As far as I can see - stars now do look better but not quite yet there - so we know that at least part of it has to do with guide performance and stacking parameters. Some subs are probably too distorted and if you manually (or automatically) remove those - things should improve somewhat. Red channel now looks normal, but there is some distortion in green and blue. It would be worth first checking what sort of image you'll get without that filter (to see if it's causing problems) and further investigating optics itself by taking some out of focus images of bright star (small defocus so that there are still rings visible).

I don't think it is tilt, but I do believe it is some sort of collimation issue - maybe decentered lens or something like that. Here we have two stars in R, G and B channel - and they have different size and shape. I can't be sure how much of it is down to stacking (we need simple average stack to check that) and how much is down to optics. This pattern repeats over the whole image and is not prominent in one corner so I don't think it is tilt issue. Fact that colors are affected differently suggests that something is going on with lens. There might be some spherochromatism or something like that. This flaring that is most obvious in red is also very interesting. It looks like some sort of obstruction is present, but I have no idea what it might be. First thing that I would recommend would be loosing the filter and trying to image simple star field to see if this would repeat. Well, actually - first thing to do is to stack using regular average stacking to see if there will be any difference to this stack, and second - loosing filter. Third thing to do would be to image star in/out of focus to check collimation and perform sort of star test in general.

I don't think it is possible without knowing parameters of the lens - like focal length. We could perhaps make some assumptions based on shape of the lens, and say that left one is achromatic pair - telescope lens and that second is focal reducer and then ray diagram might look like this: (black lines are at 0 degrees and red lines are at slight angle and focus at some distance from center of sensor / optical axis).

Yep, that would be great. Do you know how to do it manually? Just calibrate, align and use simplest integration method - average without any weighing of subs or pixel rejection

@oymd Could you restack your data but using simple average method without fancy things like rejection and such? I think that strange effect might be caused by guiding issues and strange stacking settings. Also, if you can - post fits of stack, xisf is PixInsight only format

How do people figure it is a tilt? 1. Pinched optics will make all the stars equally affected. Some are and some are not affected. 2. To be able to diagnose tilt - we need whole image. This is zoom x2 of the center of the field - showing very small section of the center. Note position of the sliders in the vertical and horizontal direction on that screen shot - they are somewhere around the middle. Title is pointing that there is zoom involved - 2:1, so we are basically looking at very small central part of the frame. No way to tell the tilt from that. 3. Effect seems to be present only on some stars. Stars have different brightness in IR / UV part of spectrum depending on their temperature, some will have larger "purple" halo and some won't. Next to Filter / No filter part of the title and knowing what stars look like on fast achromat (which is very similar to what stars look like on a refractor that is not using UV/IR cut filter) - my money is on that until we get further info (if for example UV/IR cut filter was indeed used).

Yes, still linear sub would be great to examine. What sort of filter was this shot with? Was any filter used at all? I've seen strange stars like this when no filter is placed on refracting optics. It is usually due to out of focus IR/UV light.

Hi and welcome to SGL. No issues with magnets attached to OTA - at least not from their magnetic nature. Goto does not have internal compass and works by means of encoders or stepper motors counting steps from initial position. Magnets won't affect light or mirror in any way.

Maybe this: https://play.google.com/store/apps/details?id=com.celestron.skybox&hl=en&gl=US As far as I can tell - it uses smart phone to plate solve. All you need is way to mount phone next to main ota. Simple 1.25" diagonal can be used to point smartphone camera lens in the same direction as OTA Alternative would be maybe to use RPI or some other cheaper single board computer (RPIs are in low supply at the moment, so perhaps Orange Pi or Banana Pi? Lookup Armbian for supported models and hassle free install) and Indigo (there is IndigoSky - pre made RPI images, but as far as I can tell, install on any linux system is easy). That combination has web app control that you can access with browser on your mobile phone to direct the scope once you setup everything. It will however need all the things that you listed - guide scope and some sort of guide camera to act as main / plate solve camera.

I really like the design.