alex_stars

Thanks for the additional input @vlaiv I will continue to think about fractional binning and how to best implement it. Now I don't want to high-jack this thread further and let you guys focus on the astronomy.tools

the page "5" was just a stupid joke from me on how we progress in the discussion.

That clearly depends on your fractional binning approach, wouldn't you say? We did not discuss what "weights" the neighbouring cells should get, say what fractional binning we attempt. why do you shift the image by 0.5 px. were we not trying to fractionally bin the image?

Again the purpose of my post was not to demonstrate anybody being right or wrong, I wanted to point out that quantifiable results such as the ones with resolutions charts is the way to go to discuss matters. Be scientific is the motto. I think most of us do know that. So page "5", we are getting there.

Sorry @vlaiv I was not asking for your elaboration on how you would do fractional binning and if "you" are fond of it, I was asking for experiments with quantifiable results so that we can discuss what strategy would be best to work with. Nevertheless thanks for always putting in the work to answer with great detail 👍 Either way, I think it is still clear that "one" wants a sensor with the smallest pixels possible, else one does not even get the chance to experiment with binning, fractional or integer wise.

Also an interesting idea. So we need resolution charts to actually quantify what happens test ideas. Thus we can make progress.

Just to give an example of a possible experiment, I found a very interesting post over at the other forum: https://www.cloudynights.com/topic/526385-planetary-camera-rant-11-micron-pixels/?p=7067915 and I shamelessly copy the images here for a summary (😀 reference above) So the setup of "Vanguard" is as such: and just as a teaser some results at F/8.35 We can actually see how well the 1.66 µm images do. Just imagine you only own the 3.75 µm camera, all is lost for the really good seeing nights 😢.

so where do you publish your experimental results? just for clarification I was NOT asking if somebody is using binning to process their astronomical images. I was referring to @Martin Meredith original post: The keyword would be "fractional" here. So we are not talking about binning 2x2, 3x3 or even 4x4, but fractional, so values like 1.7x1.7 and such. Here is an example of what is meant: Say you have a CMOS camera with 2.9 µm pixels and you worked out that that you actually want to have 4.8 µm pixels (given your telescope's specs) to achieve critical sampling. If you "just" bin the usual way, you could get effective 5.8 µm pixels if you bin 2x2, or 8.7 µm pixels if you bin 3x3 But that is not what you want, you want 4.8 µm pixels. With fractional binning you can get that exactly by binning 1.65x1.65, which would lead to effective pixels of 4.78 µm (rounded) That is what we talk about, so again, do you experiment with fractional binning @vlaiv? If so, which software to you use and where do you publish results? It would be really interesting to see those, because as @Martin Meredith points out, experiments would be very interesting and are needed.

Glad to read this. I think solid experiments on binning of small pixel CMOS cameras would be great. Is anybody doing those?

True, and we so often tend to forget. Do we know if anybody did some simulations on the subject we discuss?

Hi @bluesilver I owned a Skymax 180 for two planetary observing seasons and in the end sold it and got a 125 mm APO instead for planetary observations. Reading that you already own a 150 triplet APO I sincerely recommend that one instead of the MAK. Here is a short summary why: When observing planets, we really want contrast, I think we agree on this. The 180 Skymax has less contrast than a 125 mm APO, so you 150 APO has already more contrast (you can read a very long discussion on why this is here on the forum https://stargazerslounge.com/topic/371424-mtf-of-a-telescope/ I even submitted some measurements of my Skymax). I found the Skymax 180 to be a good scope, but cooling times (of several hours if you are unlucky) and the mechanics of its main-mirror focus (mirror shift and or flip) are clearly a disadvantage compared to an APO. So I would recommend getting some good EPs for your 150 APO and enjoy sharp, high contrast views of the planet. With a 4 mm planetary EP you are already up to 265x, That should be great for Saturn. Talking of observing planets with an APO, @John managed to observe Triton with his 130 mm APO https://stargazerslounge.com/topic/383630-jupiter-the-oval-ba-and-others/?do=findComment&comment=4143988, so there is really no limit to observing planets with a decent sized APO. Hope this helps.

Given all other observing conditions equal (light pollution and such) isn't this the telltale sign for the refractor having a lot more contrast than the SCT, due to its design. I'd argue it is 👍

Fantastic, we agree to agree. I think it will be a wonderful tool! Looking forward to see the new setup. Thanks for your input from my side @vlaiv always a pleasure to have a good discussion on matters.

So to summarize what I would like to contribute to this discussion. Let me start of with a quote from Wikipedia () https://en.wikipedia.org/wiki/Strehl_ratio#Usage on the Strehl ratio: We often only think of the Strehl ratio as a measure describing the perfectness of our telescope. However it is really noteworthy that it is also often used to assess the astronomical seeing conditions on site at a given time. We as amateur astronomers don't do that too often. But the point is There is an every changing atmosphere between our telescopes and the "stars" and we really don't get around that so easily. So even though we can discuss theoretical limits of resolution and based on these optimal pixel sizes and even taking it that far that we discuss "over-sampling" and "under-sampling" with respect to these theoretical limits, it is not really useful for the practical application we aim for. In the end we can get a camera with the theoretically perfectly fitting pixel size, but out in the night, depending on the seeing conditions you are already "over-sampling", depending on what the seeing is doing. To summarize, I really like the images from this page (http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/diflim.html) So we see the light intensity curves for resolving two distant light sources for the different options of "properly resolved", "Rayleigh Criterion" and "Unresolved" on top and below how the Airy discs look like. In the end I guess we strive for the left most case. Now we can ask ourselves how does this look like on a image chip: and we see the diffraction case and the Rayleigh case in this image. To the left the "simulations" on how these look like on the chip and to the right how they theoretically should look like. The point is all of this is assuming no atmosphere with seeing, it is just the basic theoretical physics limits. And the atmosphere is gonna make it worse.... as we know. So in the end I would advocate to get the camera with the best quantum efficiency, the smallest pixels possible and the lowest readout noise. Why? Well then you are technically ready for all kind of conditions, even the best seeing nights. If you end up effectively over-sampling your images (due to seeing conditions on that night) you can "postprocess" the images with binning and what not (see our phone company colleagues for another application) and hopefully recover more details than anticipated (as we see in good lucky-imaging cases). Ideally we want an imaging system which can adapt its effective pixel size to the task at hand: large effective pixels to collect most photons on faint targets for the benefit of good signal to noise ratios small effective pixels to resolve the finest possible details (whatever the atmosphere allows on that night (location and time)) If I am not mistaken, binning allows us that. Even though unfortunately with CMOS sensors only in post-processing. So if we would have that phone chip with the 1.4 µm pixel size, we could choose effect pixel sizes of 1.4, 2.8, 4.2, 5.6 µm with different binning strategies. If you got the 5.6 µm pixel size camera in the first place, you can't go to higher resolutions when needed or better put "possible", due to your local seeing conditions.

That is exactly my point @vlaiv. Maybe I was not clear enough in my comment on this. And BTW thank you for summarizing the definitions, I think indeed this is very useful for everybody reading along. So we can discuss theoretical details all day, but we have to bring it back to the practicality of observing and imaging in astronomy. I find the discussion on the Strehl ratio of the optical system in a laboratory setting (i.e. optical bench) rather beside the point as we never, really never (!) get to use the full potential of our possibly perfect telescopes (and how perfect they are is also not point of the discussion). We can NOT forget that there is an atmosphere between us and the targets we want to observe (imaging and visual observations), we always have at least the following setup in our optical train (and I know you and everybody else knows that): Distant object we want to observe (from Moon to far away galaxies, etc) The Earths atmosphere at our location and time Our telescope, perfect as it may be... Our sensor (human eye or CMOS camera....) We spend way too much time talking about #3 and possibly #4 and so often forget about #2. It's like owning a super powered sports car and discuss the intricate details of its engine and never getting the chance to blast along the possible 300 km/h with it. Its in the garage and it was INDEED expensive, but you hardly can release its potential.

Yes I know the definition of diffraction limited and Strehl ratio (https://www.telescope-optics.net/Strehl.htm). My point was that we get telescopes sold the be with high Strehl ratios, but I find pseudo certificates like this one: somewhat likes a sales pitch, not really a credible lab report. Don't get me wrong, I really enjoy TS APOs, owning myself one. Nevertheless the question arises how well do you know the actual Strehl ratio of your instruments??

Yes in fact I do. You actually missed the important point in the paper: So here is what our colleagues argue: Their camera technically operates on 1.4 µm and has 41.5 Mpix, which in the above example produces a 38 Mpix image with 1.4 µm pixels after readout. They do not claim that the actual 1.4 µm sensor is oversampling as such. And BTW your math is correct. Taking the 1.4 µm and with 500 nm light wave length (lambda) we get an x = 1.22 * lambda * f = 1.22 5e-7 * 2.4 = 1.4639e-6 or 1.46 µm. And you are right, we should have 1/2 of this However they compare their results to a normal 5 Mpix camera with 3.8 µm pixels and argue that in comparison to such a camera their camera is oversampling 3.8/1.4 = 2.71 so more than two. Another argument they make is that in their optical system (camera phones), the optics are normally not bandwidth limited (and I think they mean diffraction limited?) So the final argument boils down to this: A normal camera utilizing the non diffraction limited optics of f2.4 would have 3.8 µm. That's their baseline. Only a diffraction limited optical system could sample at double the Nyquist "resolution", but who own such a system From their baseline, the "normal" camera with f2.4 and 3.8 µm pixels, they make a resolution jump down to 1.4 µm, which is a factor 2.71 smaller, so from the baseline of 3.8 µm, oversampling. They implicitly assume that the 3.8 µm pixel, 5Mpix camera is the optimal setup for the non diffraction limited optics they have. I think we CAN learn from this paper as we all probably don't own diffraction limited telescopes. Or do you @vlaiv? So we should maybe switch the perspective and not ask what is the diffraction limited "theoretical" resolution limit of our optics (according to the specs on the box), but as what is a useful sampling resolution for the optics we own and the "seeing" conditions of the night at hand. When seen from that angle, oversampling is a good thing and actually what one wants, because then you are ready for the really good nights, seldom as they are. Q.E.D ps. and now please excuse me, I have to leave and look through my scope.

That reminds me of something: https://stargazerslounge.com/topic/371424-mtf-of-a-telescope/ Wasn't that an 11 page discussion on MTFs with the same result. We concluded that we agree to disagree. Well we are still on page "3" here so plenty of room left for fun.

@vlaiv, your scepticism against anything except your own opinion is fascinating as ever. I agree with @Martin Meredith, how do you know whether this paper I posted is peer-reviewed or not? Also in my field of work there are reviewers for conference proceedings and often cooperate researchers contribute, with the same level of scientific quality as academics. I served quite a few times as chief-editor for scientific conference proceedings and always relied on peer-review to ensure high-quality contributions. BTW our colleagues from the phone company were invited by the session chairs to contribute, which is normally a sign of a high standing in the respective field (see proceedings here). One of those session chairs was Shigetoshi Sugawa, a well respected professor and expert on CMOS sensors, with an h-index of 45 and over 8700 citations. Here is his IEEE profile just in case you are curious. I think it is fair to say that those people have "some clue" of what they are talking about, wouldn't you agree? But reading your posts above you obviously don't 😒 So before you jump the gun and judge others to be "not scientific" maybe you would be so kind as to share your scientific credibility with us? Yes? No? Maybe start with your last peer-reviewed contribution on image sensor technology? Else your above comment is just trolling and not amusing at all!

Maybe as a "scientific" addition to the discussion, here is a paper (publication) from an IISW (International Image Sensor Society) workshop (2013) that has analysed the relation between low light performance (that's what we are after) and pixel size in oversampling situations. Here the abstract (summary) of the paper: and the paper can be found here: https://www.imagesensors.org/Past Workshops/2013 Workshop/2013 Papers/13-1_071-Alakarhu.pdf should anyone want to follow the math. I love the result that "there is a significant amount of spatial information" (our star images) "above Niquist frequency of the camera system that can be captures with oversampling". That should be useful for our application I'd say.

Sorry for being late to the party. I was about to post the same approach to the discussion. Fully agree with Martin 👍 From a practical point of view, don't we just want to get the camera with the smallest pixels, the best SNR (low read noise) and the best quantum efficiency we can afford. The we don't run in the problem of undersampling and if we feel that we oversample, binning comes to the rescue.

Hi Dominic, it obviously depends on your budget. I agree with @cajen2 watch out on the Plössls for short eye relief (probably around 5 mm, depending on focal length). This is very uncomfortable for most beginners. Especially if you observe with glasses, that will not work. The BST Starguider are good and then there is no limit on the upper side. I personally do a lot of planetary observing and use Vixen SLVs but they are more costly and have a narrow field of view. As a good rule of thumb you need a spacing between EP focal length of about 1.6x, so if you stick to the BST starguider world you could get these EPs and the BST Starguider Barlow 25 mm (26x) and with the Barlow its a 12.5 mm (52x) 15 mm (44x) and with the Barlow its a 7.5 mm (88x) I'd start there, with 88x you already gonna have fun on Jupiter. If you feel the need for higher magnifications you can add the 8 mm (82x) which obviously is as 4 mm in the Barlow (165x) and then approaching the x180 theoretical limit. However the Barlow is about the price of an EP, so you could also just get another EP instead and skip switching the Barlow in and out. Another option, just to confusion matters more, would be to get a decent Zoom EP and start exploring what magnifications you like (and if you like Zoom EPs more than fixed length). A really good one is the Hyperflex (7.2 mm - 21.5 mm). I personally started out with a decent Zoom EP, learned (and probably still learn) the magnifications I like for my targets. Then I figured out I don't want to zoom around all the time and ended up with fixed focal length EPs. However that is personal preference and one should try that out oneself. Hope this helps. Great scope BTW. CS Alex

Thanks everybody so far for the great answers. For me, I think I should experiment more on the lower magnification side (60x 120x) to see where my low magnification limit lies for the planets. Good to know, will definitely try that. I guess this is in line with the idea that we actually don't want our eyes to dark adapt when we observe planets. Does anybody know more about that?

Dear fellow stargazers, I have been pondering a basic question. When we observe Jupiter (or planets in general), towards which magnifications should we generally aim: As low as possible to still resolve the features we want to see (GRS, BA Oval, etc.)? As high as possible to see the features we look for as large as possible in our eyepiece? Often we instinctively aim for option 2 as we want large views, dreaming of images we saw on the net (e.g. HST). However, with increased magnification we also magnify "seeing" conditions and thereby ruin our view. Also the exit pupil goes down (some, like me, have issues with floaters) and we loose sensitivity to contrast and colour. All these arguments would favour option 1. At least these are the arguments one reads in the forums. So I was wondering what your options/experiences are? Looking forward to your comments. CS, Alex

Hi all, if you land here and wonder when to observe the Oval BA, I just made a new thread with transit times: https://stargazerslounge.com/topic/389474-jupiter-oval-ba-and-grs-central-meridian-transit-times-2022/ Clear skies, Alex