Jump to content

sgl_imaging_challenge_2021_annual.thumb.jpg.3fc34f695a81b16210333189a3162ac7.jpg

vlaiv

Members
  • Posts

    8,283
  • Joined

  • Last visited

  • Days Won

    6

Everything posted by vlaiv

  1. Nova and supernova are two different things. Supernova is exploded star, while nova is transient phenomena that does not destroy the star. It is usually pair of stars orbiting close enough so that smaller (usually dwarf) star stars pulling material from larger neighbor. This material is then heated by rapid rotation and at some point runaway fusion event is triggered - on that material, but not on either of two stars. This process emits bright light that brightens whole star couple of magnitudes. As this is regular nova - I expect that it gives off same amount of Ha radiation as any star with similar temperature - meaning not significant amount. Very nice image by the way.
  2. Yes, aperture controls resolution when the scope is diffraction limited. That is always true if we don't include effects of atmosphere - like when we do planetary imaging at critical sampling rate. Most scopes are diffraction limited on axis - even cheap Chinese mass produced telescopes. However, some astrographs are not diffraction limited. Why is that? Because they are astrographs and it is much more important that they have large corrected field then diffraction limited field and because they will be used in long exposure where seeing can mask effects of diffraction limit on scope. If you are going for wide field of view image that you sample at say 3"/px, is it important for your telescope to have spot diagram that fits inside 1.28" (airy disk diameter of 8" scope), or can you have one that maybe fits inside 2.5" circle. Both will be smaller than single pixel. Such wide field scope needs not be diffraction limited.
  3. This depends on a) What you mean by more detail b) if you assume detail in terms of resolution - then it will depend on respective star FWHM. Telescope with smaller FWHM will produce sharper / more detailed image. If by detail you assume "depth" of image or achieved SNR - then HyperStar will win for given imaging time - it will be faster system as it has more aperture on same resolution If they both sample at the same sampling rate / resolution - then yes, there will be no difference in terms of crops - you can crop the same region and it will have the same size in pixels
  4. It is sort of like that with small difference - optical blur adds up. If you take two otherwise identical scopes - one diffraction limited and other having say bad spherical aberration that makes it not be diffraction limited (spherical greater than 1/4th wave) - and place those on the same mount and under same skies (say side by side setup) - one that is diffraction limited will produce tighter stars - smaller FWHM.
  5. We can't simply equate these two as Dawes limit is an approximation (empirical). What we can do is use well established formulae. 5in telescope has 127mm of aperture and for that optimum sampling rate for planetary case is 0.41"/px. We have very exact solution to this and it is based on: https://en.wikipedia.org/wiki/Spatial_cutoff_frequency combined with Nyquist criteria for sampling of band limited signal. However, this is case where there is no atmospheric influence. For long exposure images - it much more depends on sky conditions, mount tracking and other factors. There is simple formula in that case as well and that is FWHM / 1.6. If your system produces FWHM of 3.9" (like above hyperstar) then you need to sample it at 2.4375"/px. Going in opposite direction - if you sample at 0.9"/px - you better have 1.44" FWHM stars in your image. In my experience - that is not likely in regular seeing that by itself is 1.4" or more (without added optics and mount performance).
  6. First advice would be to purchase telescope from a well known supplier of astronomical gear. Avoid amazon and department stores and such (unless you are very confident in what you are purchasing). Second important point - stocks are quite low at the moment as all C-19 thing has upset worldwide trade and transportation. It is very likely that you'll need to wait a few weeks for your telescope. Orion XT8, Skywatcher 200p dob, Bresser 8" dob - are in essence very similar instruments (all good quality). They have same capability and only difference is in accessories / eyepieces and mechanics of dob mount (all are quite ok). https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-200p-dobsonian.html https://www.firstlightoptics.com/bresser-telescopes/bresser-messier-8-dobsonian-telescope.html https://uk.telescope.com/Telescopes/Dobsonian-Telescopes/Classic-Dobsonians/Orion-SkyQuest-XT8-Classic-Dobsonian-Telescope/pc/1306/c/1316/sc/1352/p/109907.uts?refineByCategoryId=1352 Yes, I have one in my basement - SkyWatcher 200p version, and it is often used (not as often as I'd like but that will hopefully change soon). 8" dob is really life time visual instrument. Many people never feel the need to upgrade to something bigger. Just do keep in mind what sort of instrument you are using and what are its strong suits. It is great visual instrument that will show you plenty of stuff - planets, moon, deep sky objects. It is however on undriven mount so you'll have to find objects yourself and track them (not issue for low power views where drift time is in minutes - not ideal for high power views - when you have say 10-15 seconds to observe planet before you have to nudge the scope to recenter it). This can be changed later by adding equatorial platform that will track the sky for limited amount of time (say half an hour or hour before it needs to be reset): https://www.teleskop-express.de/shop/product_info.php/info/p10148_TS-Optics-EQ-Dobsonian-Telescop2-Drive----Platform-for-50--N-S.html It is best used seated - so get good height adjustable chair, and it is heavy and bulky. If you are ok with all of that - then it is perfect beginner and advanced observing scope. AzGti is very nice little mount that can be easily converted to Eq version for wide field astrophotography. That is very good and affordable way to get into astrophotography - but it can only hold lightest / smallest telescopes. I have one of those as well: Here it is converted to EQ mode (very DIY) and ready to snap some images of heavens. It really depends on your budget. I think that AzGti is something that people doing astrophotography should have for wide field applications - but that might not be everyone's interest. It might not be in everyone's budget either - there are cheaper solutions like DIY barn door tracker and similar. Do keep in mind that: - it is of limited use as regular mount - it will hold only small telescopes like 100mm Maksutov or maybe 70-80mm light weight ED/APO refractor, but can work in both Az and EQ mode - it is suited for wide field / low resolution work as AP mount - it needs a bit of DIY to make it work in EQ mode (need to get wedge, counter weight bar and counter weight and flash special firmware - instructions can be found online) - it is mass produced item and some people had issues like roughness in tracking or noise or stiff axis - but that can also be fixed (although warranty is void when opening the mount)
  7. Here is interesting reference: taken from here: https://www.cloudynights.com/articles/cat/articles/the-amazing-hyperstar-a-guide-to-optimize-perf-r3013 We have 3.9" FWHM stars on 14" telescope - ideal pixel size being 7.8µm (2.43"/px).
  8. Noise by itself is not really that important - it is signal to noise ratio that is important. ISO is just multiplier and as such does not impact SNR at all (it does a bit but in different ways). If you multiply ratio of two numbers with same coefficient - well, that ratio does not change 5:1 is the same as 5*2.23 : 1*2.23 (you can simply cancel out 2.23 from ratio). What ISO does for astrophotography is two fold: 1. It affects full well capacity and your ability to record bright stuff like star cores properly. This does not mean you should use low ISO because of this - as there is another better way to deal with that - you just take a few short exposures that you use to replace over exposed parts in long exposure image (just scale data properly before blending). 2. It affects read noise - high ISO means lower read noise. Again - read noise is not something that should overly concern you if you know how to handle it. It is only important as long as it is largest source of noise - but with DSLRs in light polluted areas - it very quickly becomes unimportant. In any case - read noise should be determining factor for your exposure length - you expose until you swamp read noise with other noise source (like thermal or LP noise - both of which grow with time while read noise constant per exposure). All this means that ISO is really not that important - go with some nice middle value and if you want higher ISO - you can expose for shorter and if you want lower ISO - expose for longer so that read noise is swamped by LP noise for example. Simple as that
  9. Have no idea what Tosh means :D, but I have two observations: 1. Hyper star is not diffraction limited system - far from it, it has very large spot diagram - I think that 1.46"/px for hyper star is over sampling. 2. I'm not sure if 5" refractor is able to achieve 1"/px in regular conditions. In the end, I'd like to add that I agree with you on 5" vs 11" hyper star - just try to make planetary image with 11" hyper star and you'll see how easily it can be out resolved by 5" refractor.
  10. Single exposure in lucky imaging is fine balance and in principle - if you can, you should go with longer exposures. On one hand - you want longer single exposure as that improves SNR both for that single frame and for whole stack. Software will more easily recognize good frame from poor one if there is not much noise - it will align it better. Total SNR will let you sharpen more before noise and artifacts become apparent. Problem with longer exposure is something called coherence time. Atmosphere is in motion and most of the blurring we see at telescope is actually motion blur of atmosphere. Point of lucky imaging is to minimize that motion blur among other things. In order to do so - you need to use very short exposures. You need to expose for just enough time for atmosphere to be stable. You'll still have distortion of the image - but that distortion won't turn into heavier blur if you don't let it by freezing it in "an instant" instead of letting it change and create motion blur on top of distortion (it's like blending two or more different distortions on top of each other). Given the above - correct approach would be - expose for short enough time to freeze the seeing (for coherence time for you site and telescope size) but not shorter than that. In answer to your question - yes, you can gain quite a bit if your coherence time is less then 5ms and you expose for shorter period of time, but if your coherence time is longer than 5ms - you gain nothing and actually loose a bit because each sub will have more noise and be harder to stack properly and resulting stack will have lower noise. People with very good observing sites on good nights can even expose for 10ms or even more - but that combination of things is rate. In most cases you need to limit yourself to about 5-6ms for 8" aperture.
  11. No, but you can get special bags for storage and transportation like this one: https://www.teleskop-express.de/shop/product_info.php/info/p10107_Geoptik-Transport-Bag--Pack-in-Bag--for-Skywatcher-AZ-EQ6.html It uses polystyrene foam that came with original box and is the right shape to accept it. Alternative is this: https://www.firstlightoptics.com/telescope-bags-cases-storage/oklop-padded-bag-for-sky-watcher-eq6-neq6-az-eq6-mounts.html In any case - those are for mount head only, you'll need to carry counter weights and tripod as well - you can purchase similar bags for those as well. Btw, I don't bother and just carry delicate stuff on the back seat and tripod and weights in car boot without any sort of bag/cover. I think it will be time well spent, and also - you can always ask questions here if you are in doubt about something or just want people's opinions on which is better...
  12. Give it a go, but it is not as user friendly as some other software as it is primarily for scientific image manipulation. Check out Fiji - it is distribution loaded with plugins. In principle - you can perform every step of processing with it, but I tend to finish off things in Gimp as it is much easier. You can however do stacking and everything else in ImageJ and even code your own stuff if you know how to program - it accepts macros and you can also use Java to write plugins.
  13. Best indication is to measure FWHM and average FWHM of stars in the image should be about x1.6 sampling rate (if you measure both in arc seconds per pixel - or simply FWHM should be ~1.6px if you measure both in pixels). However, you can see it fairly easily by naked eye. Just do simple processing of the image and if your stars look like this at 100% zoom level: Then you are hugely over sampled. You want your stars to be as small as possible when image is displayed at 100% zoom level - something like this: or maybe like this: Faintest stars should really be almost point like, and medium and brighter stars - maybe just 5-6 pixels across (if their FWHM is 1.6px then they can't be much larger in diameter when fully stretched). Another way to test if your image is over sampled is to resample it to smaller size and then scale it back up to original size. If it shows same level of detail (just be careful - noise is not detail although our brain perceives noise as sharpness) - then you can use smaller resolution without loss of detail. For example - let's take first example and scale it down. here is small version that I resized to only 25% of original image: When we scale that up back to 100% we get this: Original image is more aesthetically pleasing perhaps due to noise grain size (second one has lost detail in the noise and noise looks blurred) - but data is not lost - every single star / feature and its shape is the same in first and in second version. This means that you don't need to waste pixels to record the data - you can do it with only 1/16th of pixels in this example (25% or 1/4 by width and same by height). Note also that stars look much better in small version of the image - they look pin point-ish and much closer to other two examples that I gave as visual guide of proper sampling rate.
  14. Hi and welcome to SGL I'm not sure where do you get that red cast in upper left corner. I loaded fits into imageJ, did quick debayering, scaled channels, converted to composite image (RGB) and got this: There is a bit of light pollution but otherwise image looks ok. As far as number of stars - well, you mist focus a bit. When you don't focus properly on stars - their light gets spread out and they are less visible. They really need to be pin point in order to show properly. Here is non debayered raw data crop - you can see a lot of stars - but since they are little circles instead of dots - they are rather faint.
  15. Hi and welcome to SGL. Like it has been already pointed out - there is no telescope / setup that will do it all. Astrophotography can get very expensive. It can be done on a budget - but in that case, one should really modify their expectations. These days we have access to vast number of images taken by other people - and it is very easy to think that quality comes as a standard - but it really needs a lot of money, time and talent invested in order to create very good images. On the other hand - decent looking modest images can be taken with very basic equipment - like camera, lens and simple DIY tracking mount (or even tripod without tracking). Before getting into AP I recommend that you spend some time learning about it - maybe get a book or watch different tutorials on you tube - a lot of people document their work in making an astrophotography. If you want do it all scope for visual - there is almost such thing - get 8" F/6 dobsonian telescope. Do be careful - scopes of that size are heavy and bulky. You need to store them, transport and set them up for each use and if scope is too large for you - it can become a chore very fast. In case you still want "do it all" kind of telescope that is smaller in size - thus more manageable and one that will provide you imaging capability as well, then maybe get yourself something like this: https://www.firstlightoptics.com/ts-telescopes/ts-photon-6-f6-advanced-newtonian-telescope-with-metal-tube.html and put it on mount such as this: https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-az-eq5-gt-geq-alt-az-mount.html Rationale being that for visual use, newtonian type telescope is better served by AltAz type mount (EQ mount gets eyepiece / finder / focuser in very strange positions thus must be constantly rotated in tube rings), F/6 6" telescope will do rather well on deep sky objects for visual and will be good planetary scope at F/6. You can easily connect such mount to computer by using dedicated cable and EQMod (ASCOM driver for SkyWatcher mounts). Mount can be converted into EQ mode easily (just adjust for latitude) - and can serve as decent beginner AP platform. There is better / heavier (and more expensive) version of this mount: https://www.firstlightoptics.com/skywatcher-mounts/skywatcher-az-eq6-mount.html but that mount alone is about 20kg of weight. I do urge you to consider size and weight of this equipment as it is important factor.
  16. With Jupiter, you are limited by planetary rotation speed. Capture time depends on resolution you are working with (larger scopes mean less time). Video can be derotated but that is special type of processing. I'd say limit video length to about 4-5 minutes with 8" scope if you are using AutoStakkert!3 (it can handle a bit of rotation without issues - otherwise, 2-3 minutes on 8" scope). Try to get at least 20000 frames captured (say you capture at 100fps - that would be 200s or just over 3 minutes - but greater FPS is better of course, with 5ms exposure you can capture up to 200fps if your camera and computer can handle it).
  17. Binning is procedure where you take certain number of adjacent pixels and create one "large" pixel in their place. Imagine you take every 2x2 pixels and sum / average their value and produce a single value in their place. This does two things: - it reduces pixel count of the image. If you start with say 5200px x 3600px image for example and bin x2, you'll end up with 2600px x 1800px image instead. - it improves SNR. It's a bit like stacking, stacking also averages pixel values - but does it on pixels in successive images. Binning averages adjacent pixels on single image - but SNR improvement is the same. If you end up over sampling your image, it is handy way to increase SNR without loosing detail. If image is over sampled in the first place - then you won't be loosing anything except pixel count. Over sampled means that you are using "too much zoom" for image sharpness - or more precisely, you are using too much pixels to capture what can be captured. I don't particularly like such techniques in images. I don't like to even sharpen image. If you get the sampling rate right - you'll match star size to pixels and there won't be a need to do any star reduction - stars will be small. I don't like B masks either. Have two of them but they just gather dust. My preferred way of focusing is just by looking at the stars - I tweak the focus until stars are tightest. That might not be as practical with DSLR (I use computer and dedicated camera so it is easier to see stars on computer screen) - but why not give it a go using DSLR screen in live mode zoomed in? In any case - that is something that you can try and maybe you'll find it easier and more precise than B-mask (if not, you can always revert back to B-mask, I'm sure that with practice one can be mastered as well).
  18. Gimp and ImageJ In gimp I first loaded tiff and separated channels into mono images and saved them as fits format. Then I loaded them into ImageJ where I did very small crop to remove stacking artifacts. Then I binned data x4 - as it was grossly over sampled to start with. That recovers much quite a bit of SNR. Next step was background / gradient removal for each of channels (custom plugin for ImageJ that I wrote) and then I just made sure min / max values for each channel were the same (it's like normalizing to 0-1 range except I don't have to do that as Gimp will automatically do that when importing data - I just needed to make sure that color will be preserved and each channel image has same min and max value). I then loaded images into Gimp, did RGB compose and three step levels stretch and a bit of wavelet denoising. Exported image as png I think that you missed focus by quite a bit in that image. Stars are huge and in fact - in blue channel stars are doughnuts rather than stars: For that reason I needed to bin x6 and to sharpen things up on top of that in order to try to get decent looking stars. In any case, here is the result:
  19. Pacman data is actually quite nice if handled properly:
  20. Hope you don't mind, I took liberty to process a bit more your image: I applied a bit more sharpening, RGB align, white balance and I resampled image to size that is appropriate to captured detail (it looks less blurry that way).
  21. If you mean EQ mod, then this one: Planets and stars / DSOs are tracked with "star" icon. The Moon is tracked with second one (lunar rate) Third one is solar rate for Sun.
  22. That is most likely artifact from display interpolation. If image was scaled, capture application probably used some sort of interpolation algorithm to do the scaling. Some interpolation algorithms don't deal particularly good with lone pixels that have big variation with respect to surroundings. Say you have hot pixel (that goes away with cooling) - then it will have value much larger than surrounding pixels. Look what happens with a single hot pixel when image size is reduced by 50% using bicubic interpolation:
  23. Do you have your scope on EQ mount? Your signature says that you have Heq5 pro mount. Make sure your mount is properly polar aligned and setup and it should track your target without much issues.
  24. Just to add - tracking needs not be ideal and planet can and even should have slight drift across the FOV in movie - that will naturally dither recording.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.