vlaiv

Well, can you specify exact models - both modified and unmodified one? - that way we could have a shot at answering original question - which one would be a better choice for galaxy imaging in general - and for this image in particular

Here is a bit more details. Scope, atmosphere and mount guiding combine to give you resulting FWHM. Each of those three can be approximated with gaussian of certain sigma. There is simple relation between sigma and FWHM of gaussian and that is x2.355 I think, yes - here is exact expression from wiki: In any case - airy disk of the scope can be approximated with gaussian, seeing is often given as FWHM of star profile - again can be viewed as gaussian and guide RMS is sigma of gaussian. Add those three things in quadrature and you'll get resulting FWHM of stars. For example, if you use 8" scope and have 2" FWHM seeing and your mount has 1" RMS guide error total - your resulting FWHM will be 3.14" and corresponding sampling rate should be ~1.96"/px. Same scope and same guiding error in 1.5" FWHM seeing (good seeing), will result in FWHM of 2.85" and sampling of 1.78"/px - so there is some improvement but not very good improvement. This is because 1" RMS is not very good result. Rule of the thumb is that you need to guide at about half of sampling rate that you are aiming for. If you want to work below 2"/px - you need to guide below 1" RMS. For 1.5"/px - you need to guide at 0.6-0.7" RMS. In above calculation 8" + 1.5" seeing and 0.7" RMS guiding results in 2.3" FWHM and 1.44"/px. If you want to go below 1.5"/px - then make sure you can hit 0.5" RMS or less. This is realistically lower limit for Chinese mounts - even tuned and modded ones. You need premium mount to get below 0.5" RMS. In any case - 0.7 reducer, proper binning and if you manage to get your mount to guide below 1" RMS - yes, then 1.5" is quite achievable (even if on particular night seeing does not play ball - and you have 1.8"/px data - you can still happily image at 1.5"/px - difference is not that obvious). As far as I understand - 4.63µm pixel size is for stock ASI294 (both mc and mm) - unlocked version that is bin x2 by default. If you unlock bin 1 mode - then you split original 4.63µm pixel into 2x2 smaller pixels - each of which has ~2.31µm pixel size (I rounded that to 2.3µm).

That is very odd choice of scope to be imaging Markarian's Chain. Are your cameras full frame or APS-C? With APS-C - you'll get only a portion of the chain: but you can always go for the mosaic - you'll probably need 16 panels (4x4) to frame the target nicely. Aim for 1.2-1.4"/px resolution - depending on your camera - that might mean super pixel debayer and possibly subsequent binning.

Drizzle should be (questionably) used when you under sample - to attempt to recover some of the resolution that optical system has that was lost due to too large pixel size. It was developed for Hubble space telescope - which is outside of atmosphere and has F/24 focal ratio - most CCD pixels at the time were too large to properly record what the telescope is capable of resolving. In majority of cases in amateur setups - you don't need the drizzle algorithm and one of the features of drizzle algorithm is that it lowers SNR (signal to noise ratio) as it reduces number of samples that end up stacked for each pixel. If you stack 20 subs - in normal way - you'll end up with 20 values for each pixel which you average. With drizzle - you literally drizzle pixels over larger area and as result each output pixel gets less samples - SNR is not improved as it could be with regular stacking. Opposite thing of under sampling is over sampling - and with small pixels of modern cameras it happens much more often. Here you again loose SNR due to light being spread over more pixels than is needed. With 8" scope and mount like EQ6 under good conditions - you can realistically hope to achieve something like 1.3 - 1.4"/px and not much more than that. With ASI1600 and 8" scope natively, you are working at 0.48"/px - which is much higher resolution than your system can resolve (and atmosphere allows). You can easily see that if you look at your image at 100% zoom level - where each pixel on screen represents one pixel in the image. When you do that, you should still see "pin point" stars. When I do that with your image I get this: This star is by no means pin point. This is in part due to x2 drizzle - where you increased further sampling rate by factor of two making it 0.24"/px. If we observe what that star would look like natively - it will be like this: Ok, looking better - but still not pin point like. This is close to 0.48"/px. Now look what the image looks like at 0.98"/px (or about 1"/px): This is almost ok - but I would say still a bit over sampled. Realistically you have detail for about 1.3"/px and that would look like this: You can also see that spikes are very thin in this image rather than smeared thick lines. In any case - binning will improve your SNR in similar way to using larger pixels - and has similar mechanism like stacking - stacking 4 images improves SNR by factor of 2 (square root of number of stacked subs). Binning 2x2 - does the same as you in fact again average 4 samples - 4 adjacent pixels are averaged to produce one "larger" pixel. As a comparison, here is crop from one of my images that was binned to ~1"/px (also 8" RC and ASI1600). It is Ha image and due to narrowband filter used - it has tighter stars: This is at 100% zoom level. That sort of star sizes you want in your image. If stars are significantly larger - you are over sampling and in doing so - loosing SNR without any benefit of added detail in the image.

Very nice image. What this taken with ASI1600? If so, did you drizzle by any chance and why? Instead of drizzle - you should really bin x2 your data.

Are they same model or different one? What scope will you be using? Modification of IR filter in camera is not going to be very beneficial for broad band targets like galaxies - only minor benefit and depending on pixel size and sensitivity and other factors - unmodified might be more suited.

This one looks decent: https://www.firstlightoptics.com/diagonals/william-optics-125-45-degree-erecting-prism.html Baader has similar one. https://www.teleskop-express.de/shop/product_info.php/info/p2672_Baader1-35--Amici-Prism-45--with-24-mm-clear-aperture.html Both of them have larger clear aperture than cheap versions by SW and Astro Essentials (24-25mm vs 19mm) I have no experience with either of them, so can't say much. I do know that SW and other cheap versions are not very high quality (I used to have one that came with the scope - but gave it away).

I remember seeing some very deep images of M106 taken by members here on SGL - and space was "flat" around it - no noticeable nebulosity. Very likely that it is calibration issue or light leak or something like that.

Very complex topic, but here is quick introduction. Given your scope (optics and aperture size), mount and guiding accuracy and seeing conditions - you will achieve certain detail in the image. There is limit to how much detail you have because all of things listed - blur image to some extent and final blur in the image is governed by total blur when you combine all those things. Good measure of that blur is FWHM of stars in the image. You need certain sampling rate - or "/px resolution in order to record all the detail available. If you don't have enough resolution - which means "low" arc seconds per pixel (actual number is high - say 4"/px but we say low resolution) - this is condition called under sampling. Nothing wrong with under sampling (in spite of what you may read) - and it is valid way to get wide field of view in your shot as there is only limited number of pixels on any camera - and you have to have low sampling rate to cover larger parts of the sky in single go (without making a mosaic). If you use too much pixels to record the image - this condition is called over sampling - and it is bad. It is bad because light is spread over more pixels than you need - and each individual pixel gets less light and hence signal to noise ratio suffers - image is more noisy because of that. More noise and no additional detail - well, you get it - poor image. There is also optimum sampling rate that sits in between of these two. That is most "zoomed" in image - while it still makes sense to zoom in (afterwards - higher zoom - just makes image look blurry with no detail). In fact, this optimum resolution can't be precisely determined for long exposure imaging, but can for planetary imaging as for planetary imaging there is hard cut off that happens due to physics of light - there details are lost because of aperture of the scope. In deep sky imaging - this happens sooner because there is also atmosphere and mount / guiding performance, however actual line where it happens is "fuzzy" - there is no clear line. I've done some calculations and set some conditions where it is sensible to draw the line and optimum sampling rate for DSO is at x1.6 (number was just rounded up because of fuzzy nature of this bound) FWHM of the star in arc seconds. This means that if you manage to record stars that are 3" FWHM - you really need 3 / 1.6 = 1.875"/px. Problem of course is that you can't know in advance how good your sky is going to be on particular night and what sort of FWHM you will manage to record. But above approach can tell you if you are in principle over sampling (bad) or you are close to optimum sampling rate (good). It can also give us some rules of thumb in terms of what can be achieved by amateur setups. So breakdown is as follows: 4 or more "/px - very wide field resolutions, any decent mount will do and small scopes / lens will manage that (50-60mm aperture) - average sky conditions 3-4 "/px - wide field resolutions - mount can still be entry level one and scopes in class of 70-80mm - average sky conditions 2-3 "/px - medium to wide resolutions - here we are looking at Eq5 or higher class of mount and 80-100mm of aperture - average sky conditions 1.5 - 2 "/px - this is very good medium / general working resolution. Mounts like HEQ5 and scopes of 120-150mm are needed - better sky conditions 1.2-1.5 " /px is high resolution 150mm + needed, very good mount and guiding (tuned and modded HEQ5 / HEQ6 mounts) - very good sky conditions 1-1.2"/px is very high resolution - I'd say 8" + aperture needed, premium mount needed - exceptional sky needed. higher than 1"/px - don't bother. This does not mean that you can't image with 0.47"/px - it just means that you are wasting resolution - you'll get massive stars when viewed 1:1 or 100% zoom level and things at that scale won't be looking nice. It also means that you are spreading light around too much and that you can achieve better SNR if you change working resolution. There are few ways in which you can change working resolution for a given camera: - change scope for one with shorter focal length - use focal length reducer - use binning - whether hardware (only CCD sensors) or software (any type but in principle only used with CMOS as CCDs have hardware version) to increase effective pixel size In the end 294 will have 2.3µm pixel when it is not binned. With such a small pixels - you'll have a problem finding large scope of suitable focal length (remember - small scopes don't have enough resolving power for high resolution work). Good thing about such small pixels is that you can pick your bin factor after to match actual resolution of the image. With 2000mm FL and 2.3µm pixel size - you'll be 0.24"/px If you bin that x4 you'll be 0.95"/px (which is too high in my view - but close enough to very high resolution limits in above "table"). Bin x5 or x6 and you get more sensible working resolutions. Throw in focal reducer and things get even more interesting as you have more room to play with. In the end - having sensor of 47MP - does not mean much as resolution is governed by sky, scope aperture and mount performance, however having large sensor with small pixels is a good thing as it lets you "dial in" your working resolution better (important thing is to have low read noise as well if you are going to bin in software - but most CMOS sensors have low read noise). Hope this helps

I don't think that these have special name as a cluster of galaxies - but that is edge of Virgo super cluster. Close by there is M94 / Canes I Group (https://en.wikipedia.org/wiki/M94_Group) but I don't think that is it - that one is outside of your image - in upper direction. Probably just outskirts of Virgo super cluster.

I have both 1.25" and 2" GSO 99% dielectric diagonal - and both are quite fine - though I don't have much to compare them against except cheap 91% Skywatcher diagonal - one that comes with scopes as accessory.

Yep, not doing dark calibration means messed up flat calibration. Calibration is not about noise removal - it is about signal removal. You don't remove signal - well, odd things happen. Flats correct vignetting that is result of light obstruction - it only affects light coming in from the front of the telescope. If your image contains both light signal and dark signal - flats try to correct both, but since dark signal is not affected by obstruction as it is not coming from the front of the scope - you are correcting thing that is not messed up - and you end up messing it up - if you understand what I mean. In math terms - it is a bit like this: Pure light case: light * 0.7 / 0.7 = light (light that has been reduced to 70% of its original value - gets divided with 70% flat and you end up with original 100% light) Now imagine you have following scenario: (light * 0.7 + dark) / 0.7 = light + dark / 0.7 since you did not remove dark - it ended up in final image - but "corrected" for vignetting that it does not have - so it get corrected "to the other side" - and that is again vignetting.

There is an easy way to check that. Take your linear stack and measure FWHM (you can do it in say AstroImageJ with CTRL-click, or is it Shift-click on a star - does quick FWHM measurement). There is simple relation between good sampling rate and FWHM in arc seconds which is x1.6 - sampling rate x1.6 needs to be FWHM. It you measure your stars to be less than 1.6" FWHM then it makes sense to go below 1"/px.

Indeed - it shows rotation well. Spikes change orientation. You could be right - I think that polar alignment can also cause this. Not sure which was dominant cause here.

I'm not sure about smaller pixels though. In my view image is still over sampled. What is your original pixel scale - somewhere around 0.5"/px? I'd say that your image has resolution of about 1"/px - which is still exceptional, and data goes really deep. I imaged bubble at 0.5"/px as well - but did not leave it like that, opted to bin x2 for 1"/px, however, mine has slightly less resolution compared to your image and your goes much deeper. I did it with 8" RC scope and Heq5. Here is a quick comparison of the two at 1"/px (btw - notice very similar SHO processing) Your obviously goes much deeper - just look at detail in nebulosity and it does have slightly higher resolution. It might not be apparent straight away - but look at spikes on that bright star - they are slimmer in your image - which means that star jumped around less and has smaller FWHM. To some extent, this can be seen in the stars as well - yours look tighter - more pin point. In any case - this shows that no detail is lost when imaging at 1"/px really, so I don't think that pixel size played a part - but again, I might be mistaken there.

You do understand that this sounds like a proper challenge for a pixel peeper like myself? Such large FOVs start to suffer geometric distortion and stitching software needs to account for this by transforming from 2d into spherical coordinates - stitching in spherical coordinates and then again transforming back to 2d using one of projection techniques. Depending on projection technique used - angles might not be preserved - angular magnification distortion. This leads to "split hair" diffraction spikes in stars. Did I get it, did I get it?

This is really sharp and detail is very good. I must notice that not only sky but 10" and CEM60 are components needed to capture such high resolution detail.

A bit more - 60 arc seconds per arc minute and 60 arc minutes per one degree.

Deep sky objects or DSOs how they are popularly abbreviated, are all the things that you can image that are beyond solar system. If you use just camera and lens and simple star tracker - you will still be shooting DSOs. Don't let the name fool you - like these are sort of special objects that you need very expensive equipment to image. There is basic distinction between solar system objects and DSOs in the way they are imaged. Most interesting solar system objects - planets and the Moon (and even Sun) - are imaged with so called lucky imaging technique. It requires special camera that shoots very fast sequence of frames (like hundreds of FPSs) and those images are stacked and processed in particular way. Exposures are extremely short - in milliseconds. You don't need very good mount to be able to do that as tracking only needs to keep object in field of view. On the other hand - DSO imaging requires longer exposures (anything longer than few seconds is considered longer exposure but in practice we are talking minutes rather than seconds), and here mount is very important. If you want to do this kind of photography - next thing to choose is your working resolution. You can go for wide field shots that capture constellations and large diffuse nebulae - that means camera + lens or very small telescope. Working resolutions are above 4"/px and mount tracking is not essential. Star trackers enable you to do this. Focal lengths are in 50-200mm range Next step up is small telescope range. Here we are talking about 200-400mm FL range (although technically more in 4"-2"/px range). Mount becomes much more important here. Larger nebulae and galaxies fall in this category. Again, step up is medium resolution and here we are talking about 2" - 1.5"/px. Mount is very important here. This is general working resolution - most things can be imaged at this resolution but some objects will be small. Above 1.5"/px - we are talking about high resolution imaging and mount is the most important thing here. Sky quality is another important thing. You need stable atmosphere to image at say 1.2"/px This is just small overview of things to get you started - it would be best if you tell us your goals and aspirations so we can give you proper advice.

Hi and welcome to SGL. What mount will you be using and what are your intended targets. In case you are looking to start with astrophotograpy - then first think of the mount that is suitable - scope comes almost last.

I don't have much as I wasn't able to use it for quite some time (and that will hopefully change in summer / autumn this year) - but here are some examples: Most of these are just luminance (or UHC filter) as I did not manage to capture the color as well. I did on NGC7331 - but with another camera and scope (80mm apo + ASI178mcc):

For cared item in a good shape - I'd say that starting point is about %70 of current retail price (one that people can actually get item at - no good if item is out of stock and can't be purchased - but also pay attention that prices might be inflated due to shortage - and many people would rather wait for things to settle down).

I think that it will be excellent in that role. According to Celestron - it is well corrected scope across large field. Put x0.7 reducer designed for EdgeHD scopes and you'll have nice 1400mm of focal length with 8" scope. Pair it with larger sensor - up to APS-C size and aim for about 1.2-1.4"/px (bin if needed - either in hardware with CCD sensor or in software with CMOS) and you'll get very potent imaging system. I have something very similar - RC8" with 1600mm of focal length and ASI1600 and I'm happy with that setup. EdgeHD8 should have similar performance. Consider guiding with OAG.

I would say it is equally suited for both types of targets. If used mindfully and within its limits - it will give you great results on both. What do you want to use it for?

Maybe went a bit overboard with denoising? How about doing it selectively? Here is easy trick that I'm sure can be replicated in CS2. Make copy of base layer and do denoising on that copy. Add layer mask to that denoised layer - consisting of inverted mono version of denoised layer. Do levels "anti-stretch" on mask (opposite of when you want to bring out faint stuff - instead - make dark parts of image stand out - as this is negative). Blend to taste