vlaiv

Out of interest, what are the requirements for your project? What sort of resolution you hope to capture, what sort of FOV / focal lengths are you working with? It might be much more feasible to just use astronomy mono camera as there is no need to debayer anything? Over USB 3.0 it can achieve pretty decent frame rate in high bit depth. Take a look at this camera for example: https://astronomy-imaging-camera.com/product/asi183mm-mono With right sort of laptop (ssd, usb3.0, decent processor and memory) - it will be capable of 3840×2160 at 36.12fps Only drawback is that it is 1" sensor - much smaller than APS-C and full frame - and that needs to be taken into account when choosing matching lens if FOV is important.

What is?

Yes, that is particularly hard one. It can be handled in many different ways and best ones are rarely supported in software. I think that simplest approach is - to leave things as they are and slowly introduce new concepts with software support. For the time being - treat color cameras as equals to mono with respect to resolution.

At expense of SNR and without additional detail captured. However - proper sampling is not meant for looking at the image at 500% - most people don't even bother to look at image at 100% zoom level. Proper sampling ensures one can capture all the detail available when viewing image at 100% zoom level. Ringing artifacts are maybe frowned upon - but they are nature of the beast. Telescope produce ringing artifacts - Airy pattern is ringing artifact around airy disk. Increase magnification - beyond what is resolving power and you'll see ringing artifacts - airy rings. Whenever you have band limited signal - it means that it is composed out of finite number of sine waves with different amplitudes and phases. If you want such signal to go down to 0 and vanish - you need infinite amount of sine waves - eventually mutually cancelling. That is not what telescopes produce and that is not what the sampling is all about. Aperture produces band limited signal, and atmosphere further attenuates high frequencies of that signal. Anyway - there are other interpolation algorithms that deal with ringing - if you really want it to. By the way - here is another example of optimum sampling (As you mentioned that single pixel does not produce accurate circle - it will not as it is not optimally sampling): This is gaussian curve sampled at FWHM / 1.6 - minimum needed for perfect disk (enlarged to 2000% or x20 using nearest neighbor): It has just 9 pixels covering it - 3x3, but that is enough to properly sample it and if I enlarge it to 2000% by using Quintic B-Spline - here is what I get: It has captured underlying function completely. Yet compare number of pixels in that "star" with number of pixels you have in stars that you claim to be heavily under sampled: If I take your "under sampled" image and bin it 3x3 as it seems that you enlarged it to 300% and then enlarge it using some nice resampling - situation does not look that bad ((mind you - this was done on 8bit data that is no longer linear). Stars actually seem tighter and definitively go deeper in that image.

If you are going to enlarge any image to 500% of what it is original size and you don't want to see pixlation - use proper interpolation function. Above is not astronomy related - it works on any image. If I take nice image online - like head of this parrot: And enlarge it to 500% using nearest neighbor - it won't look nice: You'll see all the "pixels", but if I enlarge it with good interpolation technique: Pixels won't be seen anymore and image will be smooth (although without detail as it is now over sampled by x5 due to resizing it to 500%)

I made comment about that earlier - that is simply not true. Ugly blocky discs are artifact of used resampling method and not over under sampling. Here - look at this example. I have slightly under sampled stars here (according to FWHM/1.6): this is original 100% zoom / crop I will now enlarge this image to say 500% using nearest neighbor: uh that's ugly - must be under sampling, or is it? Here is Lanczos resampling to 500% of that same data: Whoa, what is this? Nice stellar discs? "Pixellation" / "Blockiness" is not feature of under sampling. It is feature of resampling method used when you zoom in to such image. Look at one of my first posts in this thread and single pixel. Even single pixel will look like little ball/disk if you use proper resampling method.

Can you now provide the same images at original resolution recorded and not enlarged by you using nearest neighbor resampling?

Beautiful stellar disc is not measure of optimum sampling. Optimum sampling means that you can fully reconstruct underlying function. Can you provide one hugely under sampled image so we can actually see those poor stellar discs vs beautiful stellar discs you now see?

That is very interesting assertion. How do you know you are badly under sampled?

I'll probably leave FWHM/1.6 = sampling rate bit for tomorrow as I'm a bit tired now, but I wanted to show how much different results can one get depending on method used. Let's say I'm a beginner with a limited budget and I wanted to get into astrophotograhy. I've seen people use say 70mm F/6 refractor and AziGti mount and modern CMOS camera like ASI183. I live where good seeing is not that uncommon. What will existing tool say about this combination: It tells me that I'm mostly in the "Green" that I'm slightly under sampled at 1.15"/px and that this reduces influence of guiding errors and improves my SNR. Let's now calculate things in a new model. First the mount - from AzGTI we can expect 1.5" total RMS guide error on average (it has 0.625"/ step stepper resolution - 2073600 total steps for 360*60*60 = 1296000 arc seconds per revolution) Let's take both 1" and 2" seeing and see what will difference be between them 1" FWHM = 1 / 2.355 = ~0.42463" sigma 2" FWHM = 2 / 2.355 = ~0.85" sigma And finally let's calculate corresponding sigma for 72mm aperture (at 550nm wavelength - mid spectrum is fine approximation). 0.42 * 0.55µm / 72000µm (we convert all to micrometers) = ~0.0000032 radians and that is 0.0000032 * 180 / pi * 60 * 60 arc seconds or ~0.662" sigma Total sigma will be: sqrt( 1.5 * 15 + 0.42463*0.42463 + 0.662*0.662) = sqrt(2.25 + 0.1803106369 + 0.438244) = 1.693681 sigma = 1.693681 * 2.355 FWHM = ~4" FWHM (for 1" seeing) sqrt( 1.5 * 15 + 0.85*0.85 + 0.662*0.662) = sqrt(2.25+0.7225+0.438244) = ~1.84682 sigma = 1.84682 * 2.355 FWHM = ~4.35" FWHM (for 2" seeing) 4" FWHM requires sampling of 2.5"/px 4.35" FWHM requires sampling of 2.72"/px With 1.15" we will be more than double over sampling in reality! Even if we bin our data x2 - we will still be over sampled with 2.3"/px in 1"-2" FWHM seeing.

Sure - I don't think actual interface needs to change - it will remain the same - except results and recommendations.

Now for a bit of mathematical stuff. Part 1. How to calculate expected FWHM depending on seeing FWHM, mount guide RMS and telescope aperture? We will assume diffraction limited telescope and will assume all three component are Gaussian shape (we will use Gaussian approximation to Airy pattern). Step 1 - convert all to RMS / sigma - mount guide RMS stays the same - it is already sigma / standard deviation - seeing FWHM is divided with 2.355 to get corresponding sigma (that is relationship between FWHM and sigma for Gaussian curve) https://en.wikipedia.org/wiki/Full_width_at_half_maximum - for telescope airy disk we use 0.42 * lambda / diameter as sigma - instead of expression for airy disk radius that is 1.22 * lambda / diameter. This expression is in radians - need to be converted to arc seconds. for reference check this for example: https://www.researchgate.net/publication/304247659_Realisation_of_a_Digitally_Scanned_Laser_Light_Sheet_Fluorescent_Microscope_with_Determination_of_the_System_Resolution 1.22 / 2.9 = 0.42 Step 2: Once we have all three sigma figures - we take square root of sum of their squares to be resulting sigma. (convolution of a gaussian by gaussian is a gaussian and their sigmas related like that again see this: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.583.3007&rep=rep1&type=pdf ) Once we have final sigma - we divide it with 2.355 and get final FWHM expected in the image.

Here is what I would recommend to be changed: 1. replace seeing with expected star FWHM calculation based on mount, seeing and telescope aperture (assuming diffraction limited optics) 2. given expected star FWHM - use FWHM / 1.6 as optimum sampling frequency. (I can expand on both above points). If telescope focal length + pixel size is below optimum frequency give warning and offer binning that will place it above optimum sampling frequency. If not - say that it is ok, under sampling is not bad and that there is potential for a bit more detail if not under sampling - maybe categorize it as wide field setup - but don't put negative note to it. So under sampling - ok, over sampling BAD - but can be corrected with binning the data.

You do know how to throw a curve ball. Thought you were die hard CCD man Can't combine HEQ5 and Samyang 135 - to each their own - Samy is with AzGTI and HEQ5 has nice telescope sitting on it

It can be more than that - it can be valuable resource as is envisioned - it just needs few corrections and different interpretations of results. For someone that wants easy advice to match two pieces of equipment - like scope and camera - it can do wonders. Imagine you come and say - I want this scope and that camera, is it good combination? And it says - yes, it is good combination given average seeing but only if you bin your data in such and such way and you have mount that is capable of such and such performance. I'd add couple more things like illuminated and corrected field versus sensor size. I'm sure that most people with experience do this "manually" when choosing potential combination - why not offer it as a tool that does the same view few clicks

I'm sure of it. If I come too strong in some of my comments about this - that is just because I feel strongly about this topic. Given that the FLO is rightfully seen as very credible and trustworthy by so many people that do business with FLO - you can see how sensitive / high impact this can be.

In any case, let's start at the beginning - I'll make series of short posts - outlining what is flawed and then we can think of the way to make it better. This one will address errors on theoretical side. I'll try to cite sources for further verification on claims that I make. This is not entirely false, but here is what I would use instead: "Star point actually depends on several variables - seeing conditions, telescope aperture and hence airy disk / spot diagram and mount tracking performance. These all add up together to produce PSF in final image." Even if telescope is high optical quality - it does not mean that it will be diffraction limited. That is often not the case - even with top line products if field flatteners / coma correctors are used. There are always tradeoffs - and if we correct for serious aberrations across the field - we can introduce minor aberrations even on axis. This should be taken into account - if we assume diffraction limited performance of the telescope - it should be noted that it is "best case" scenario and that actual PSF in the image might be larger. Star won't be appear blocky or angular if it is under sampled. This is myth and is consequence of interpolation / resampling algorithm used. To demonstrate this effect - I'll use single pixel - representing very under sampled star. I'll upsample it considerably using different resampling methods: this is single pixel - enlarged x20 so it can be clearly seen. First one is enlarged using Nearest Neighbor interpolation method. Second is enlarged using Linear interpolation, third one using Cubic interpolation and so on. There are many interpolation algorithms used. All produce different result. We often think of pixel being that first image - like a little square - but it is not. Mathematically, pixel is dimensionless point - it is just value at coordinate. As such, when we reconstruct image from it (or collection of them) - we need to do interpolation of some sorts - choice of this interpolation will give different resulting images. One will create "blocky" looking pixel, but others will produce "diamond" shape, or circular shape - or even shapes that start to resemble airy pattern (and for the same reason as airy pattern is created). Moral of this part: - undersampling is not bad and will not lead to blocky stars if we handle our data properly - over sampling look as nice as properly sampled images when scaled up using one of these advanced interpolation algorithms - Over sampling does not reduce field of view. Focal length and size of sensor do that. Over sampling is much more sinister than this - it is very bad because it costs us signal to noise ratio - or in another words - it slows down our setup. Forget F/ratio and all that. Take F/4 setup and make it over sample and it will be sloooow. There are several things wrong with this. First, Nyquist theorem is proven mathematical theorem so there is really no doubt about what it says or is it correct or not. It states following: For band limited signal, if we want to capture / reconstruct completely and faithfully (exact match) - we need to (point) sample it at frequency that is at least twice the highest frequency component of the signal. FWHM should not be equated with highest frequency component of band limited signal. Saying that 2-4" FWHM requires 1-2"/px sampling is wrong as FWHM does not represent highest frequency component of the signal. FWHM of 4" with sampling of 2"/px - does not mean that star will either fall on single pixel nor on 2x2 pixels. Here is 1D Gaussian profile with plotted FWHM. I added "pixels" in two different rows / offsets - one representing centered pixel on star and other representing star centered between two pixels. You can clearly see that star profile will cover 6 or more pixels in either case as it extends considerably beyond FWHM "belt". Not sure what 1/3 of analog signal means - but if it refers to using 1/3 of period of maximum frequency as sampling period (using 3x max frequency as sampling frequency) - that is over sampling, using x2 is enough. We have seen that stars won't become squares because of under sampling. Correct sampling is done at x2 max frequency. Problem is - determining that frequency and understanding Fourier transform of signal of the image produced by telescope in presence of both guiding errors and atmospheric seeing.

Actually no. That is probably mistake on my part. I just assumed that some of staff members are reading topics on here and that they would pick up on that chatter. I'm also not familiar with level of communication between moderators and staff at FLO - I also assumed that if any of moderators picked up on that - they would let you know. Since no change was happening, I decided to start this thread (and mention FLO - so it would get the attention and we could all participate in this).

Is it ok if I do it here? I already posted several times what I find to be substandard / wrong, but I would like it to be open to a discussion so people can have their input on the matter?

APO scopes can be really expensive, but you can also find the middle ground - something not completely color free but as good ST102 on deep sky object and much better on planets than ST102. One such scope is this: https://www.altairastro.com/starwave-ascent-102ed-f7-refractor-telescope-geared-focuser-468-p.asp This comes as OTA alone and you'll have to purchase other accessories for it. Again, it will sit well on AZ4 type mount. It is the same aperture but a bit slower at F/7 (while still being small in size). This is good because eyepieces will work better on slower scope. This scope will show much better image at high magnifications, although it will still be some purple fringing on highest magnifications and on brightest targets (like Vega and Venus for example - possible a bit purple fringing on Jupiter as well - but image will be miles better than ST102 on these targets). If you want to have "universal" type instrument that will do it all - then I'm afraid it is newtonian reflector. Only drawback is the size / bulk and need for collimation. Something like 6" F/5 newtonian will have plenty of light grasp to show you DSOs, short enough focal length to be able to show wide field views but also, with addition of barlow capable of nice high power views. No color issues with it. Alternative to having one scope is to purchase two scopes. With two low cost scopes you can have almost the same performance as single apo - for less money. ST102 together with Mak102 is such combination. ST102 excels at low power wide field observing, while Mak102 is high power specialist for lunar and planetary viewing. For example - this package (although, someone will need to confirm it is good mount + scope combination: https://www.firstlightoptics.com/startravel/sky-watcher-starquest-102r-f49-achromatic-refractor-telescope.html and https://www.firstlightoptics.com/maksutov/skywatcher-skymax-102-ota.html I like that StarQuest mount as it can work as both AZ mount and EQ mount. It is lightweight mount however, and I'm not sure if it will be stable enough. Az4 or Az5 are going to be much more stable mounts (and heavier). To get the idea of what sort of views are possible with Mak102 (I have that scope as well) - here is the moon taken with that scope:

Ok, if everything is mechanically sound - you need to tune your backlash for both axis. Here is short video on how it's done: https://www.youtube.com/watch?v=_s8941MvYXg You can also search for other resources that show this procedure on EQ5 - it is fairly easy but always sort of fiddly business as you need to make sure that slack is minimal and there is no binding all the way around the revolution. Often, because of precision of manufacturing - there will be one part of the turn that is "tighter" and make sure that it is not binding. Do it on both axis.

Yes and things like this as well: It further says that 2.2"/px with 80mm leads to "significant undersampling" Or this part from "theory explanation": and so on ...

I had said scope and recommendation to use it on AZ4 or AZ5 versus AZ3 is good one. Those two are simply better mounts for number of reasons. ST102 is not scope for general astronomy. It is telescope for deep sky observation / wide field primarily. View of planets will be very poor as it is fast achromat with serious chromatic aberration and some spherical aberration (spherochromatism). Lunar views should also be restricted to low power / full disc viewing. Here is lunar image taken with said scope: you can see yellow fringing even at this low power.

As others have already mentioned - yes, moving to a dedicated camera usually brings significant improvements for DSLR users. Cooling and set point temperature really helps as well as absence of different filters present on DSLR (like anti alias filters and UV/IR cut filters with slope that seriously hamper Ha performance).

One of the features of wide field setup is under sampling - but that should really not bother you that much. If you say go for 4° field of view with say 4000is pixels - then it must lead to 4 * 60 * 60 = 14400 covered by 4000is pixels - or 3.6"/px. That might be under sampling - but in context of FOV is perfectly fine (and high pixel count image for that matter). You should not worry about "square" stars - that is just a myth and never happens, even when under sampling. Under sampling in itself is not as bad as over sampling. With under sampling you possibly don't record the finest detail available but have no other ill effects. With over sampling you don't record detail as none is available and suffer SNR loss over regular sampling. That is why over sampling is bad - you loose SNR over nothing.