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All of that sort of looks ok - except all those settings for PI. Could you possibly upload following for inspection: - two dark subs (choose one randomly from the beginning of the batch and one from the end of the batch) - master dark (this is needed as you say that dark / dark calibration does not remove amp glow completely) - one flat dark - one flat - one light sub I'm going to inspect all of those and see what I can find. I think we should look into individual subs rather than stack to see if they are working as they should prior to moving onto creating masters.

Wrong reason to choose such ota. TS 130 APO is capable of getting you "really close" to your targets - as close as you can go with current cameras and their pixel sizes (in fact - it is likely that you'll be oversampling with about half of current cameras even with that scope). Good reason to go for 8" OTA is to speed up your capture - but in order to do that - you need to set your working resolution. Do you have any idea what working resolution you want to image at? Do you have idea of what your mount and skies are capable of?

Two things need to be checked: 1. what is your offset and what is your calibration method (which calibration frames do you take and how you calibrate)? 2. If you are using APT - are you using any sort of "helpers" / "assistants" - like flats assistant that "automatically" do things for you?

There is significant difference between: Stacking 2s subs to get 1 minute sub and then using 60 of those to get 1h total exposure and using long exposure length and getting again 1h of total exposure. Two approaches would be the same if one had camera with 0 read noise, but since such thing does not exist - we must take into account read noise. In your case - you took 30 x 60 subs and stack those - that is 1800 subs. In normal case, one would use say 2 or 3 minute subs - let's say 2 minute subs - so stack would contain 30 of those. You made a stack containing 1800 "doses" of read noise when you could have done the same with only 30 "doses" of read noise. Remember - each time you read out sub, even short one, it will contain some read noise. On top of that - you are using very long focal length scope and you are sampling at very high sampling rate - you are "zoomed" in much more than your skies / mount / scope support - look at this: That is size of stars when you look at image at 100%. When you look at your image at 100% - you want your stars to be point like - here is example: See the difference? Moral of the story: - Use better software for image capture - try NINA for example. - Use ASCOM driver, capture in 16bit format and not 8bit - Set gain and offset properly - Use calibration frames - Expose for at least 2-3 minutes if not 5 - Learn about binning and sampling rate. Aim for 1.2-1.4" if your sky and mount can support it. - Process images in 32bit format

Hi and welcome to SGL. HEQ5 + 130PDS is very nice starter setup. Most frequently used eyepieces are 1.25" and 2" - larger ones are used when you want larger field of view. Don't get carried away with magnification. For general observing you'll be using magnification in x30-x50 range with some targets requiring a bit more magnification (up to say x100 on small planetary nebulae). It would be good to get yourself familiar with what you'll be able to see to set your expectations right. Here is nice video explaining things: https://www.youtube.com/watch?v=jI7IPPmu76U In fact - you'll find several videos on this subject if you do the search: https://www.youtube.com/results?search_query=telescope+expectation+vs+reality For this reason - FOV calculator that show you image of object can be a bit misleading in what you'll see - as these use photos rather than trying to simulate actual targets. Not sure if I ever observed M51 at such high power with small or even larger scope. This looks nice, doesn't it: But that red circle is larger than your computer screen so M51 would take up half of your screen. that is just too large / magnified. In reality - it will be more like this: Actual / realistic size of object that you'll see (say you are sitting 60cm away from computer screen). That is about it - you'll see two cores and that will be at much lower magnification - like x50 or similar. Maybe, if you are lucky and have excellent night and you are in very dark location and M51 is high up in the sky, you'll be able to see it like this: (hint of bridge and some spiral structure visible) On different end of spectrum are planets - you'll need magnifications up to x200 realistically. In most cases you won't be able to use x200 due to atmosphere. Not sure if you'll benefit from barlow lens at the beginning, since you are mentioning Morpheus eyepieces. Usually barlows work to get extend magnification range of few eyepieces and save money on those. Instead of jumping straight at Morpheus (skip Hyperions - they will be very poor at F/5) - look into getting nice set of BST StarGuiders. You can get like 4-5 of those for price of single Morpheus eyepiece. Nothing wrong with Morpheus eyepieces and if you have the budget - go for them, but I think that you'll appreciate them more once you learn how to observe. Observing is a skill and you learn it by practice. Once you have some experience - then you'll now what sort of eyepieces you like. BST StarGuiders are very nice upgrade from stock eyepieces, and since you'll be using 130PDS - they will form very nice set to get you going. You'll attach any filter to coma corrector, then coma corrector to extension tube, then extension tube to T2-Lens adapter for your camera and camera in the end. It will all look like this: and is inserted into focuser like this: Don't worry about type of matrix on your sensor - there is software support that will deal with getting images from raw format and making astro photography out of it. There are plenty of tutorials both on youtube and here on SGL to show how it is done. Best filter will depend on type of light pollution that you have and target that you are imaging. For emission type nebulae - UHC filter works very good, while for general AP look into LP suppression filters - I used to use IDAS LPS P2 because there was plenty of sodium lights in my home town. If most of LP is in form of LEDs - look into different model like IDAS LPS D4 (or whatever the actual model name is) - or ask here on SGL depending on your budget. 130PDS is different than 130P because it has DS - dual speed focuser that is made for imaging. It is good enough to hold camera and coma corrector (which is actually inserted in focuser). Mirrorless camera is lighter than regular DSLR - so you'll be fine, and yes - you'll need T-ring for your camera model, and you'll also need to calculate proper distance. Cameras have flange focal distance - which means how far away lens must focus to properly focus on sensor itself. See here: https://en.wikipedia.org/wiki/Flange_focal_distance T-ring for your camera has certain optical length that is specified and coma corrector has certain working distance - you must match things to get good image: coma corrector working distance = flange focal distance + T2 optical path length + any needed spacers.

If you operate HST and have camera with very large pixels that can't resolve airy disk at said scope (but almost never in conditions amateurs experience). I don't think flats can be used - at least I never heard of it nor can imagine how it could be used, but I don't think you need to waste clear night on that. It can be done with artificial star or maybe some sort of high contrast edge somewhere. First method will be precise, second approximate. With star / artificial star - you simply focus in center and move scope so that star ends up in each corner and measure FWHM - you adjust tilt until FWHM is equal in each corner once you focus star in center and that should be it. With high contrast edge - you do the same - except you rely on your vision to make edge the sharpest in center and equally sharp in each corner. If you think that your focuser is square on the tube and that camera has tilt - there has been recent thread about DIY piece of kit that you can use to square tilt plate on sensor without using telescope. It requires laser and something to rotate camera about its axis. Let me see if I can find that for you

What is your gear that you used for this image? You say you are at 1.65"/px - but this image looks like it is taken at much higher sampling rate. Did you drizzle by any change? Stars in left part of the image (both top and bottom) - are out of focus, that indicates tilt. In your signature, I'm seeing SkyWatcher 150P newtonian - that scope is really not suited for imaging due to focuser. Did you change focuser on it? Did you move primary mirror up the tube? I'm also seeing Nikon D5200 as camera - so you have DSLR and above is Ha image. When shooting Ha with DSLR - you are actually only using every second pixel so resolution is halved and you are effectively imaging at 3.3"/px - which is fine, but you should not be having this large or zoomed in image. My guess is that you drizzled (which is really pointless thing to do in this case).

I probably should not comment on that since I have certain disliking for SCTs that I can't explain. Never used one, but as a design - I don't really like them for some reason.

Ok, this was sort of a nightmare to process. I like calibrated data and really struggled with vignetting and dust shadows on this one. Attempted to make synthetic flats - and it sort of worked, except in two places:

Each telescope design will have different spot diagram over its illuminated and corrected field. For example - Newtonian without coma corrector is next to useless for AP. It suffers from serious coma as soon as you move off axis. If you want to use one without coma corrector (for some reason) - you need to use very slow version - so you'll have extremely long tube with very small field of view. Add coma corrector - and you might get system that is no longer diffraction limited / suffers from too much spherical aberration. In order to avoid that - you need to choose your CC carefully and get good design - like 3 or 4 element one over simpler 2 element designs. This introduces constraints on your imaging train as you need to put gear at certain distance from CC for it to operate the best. Similar thing happens with EdgeHD or other designs that have corrective lens close to focal plane. Other than that - there are differences in F/ratio of telescope. SCTs are usually at F/10, RCs are at F/8 and DKs and Modified DKs are at F/6.8. That means different focal lengths / FOVs for given aperture and different choice of camera (pixel size and/or binning) for optimum sampling rate. Some designs have better baffling of stray light than others - for example Newtonian needs much longer tube than it usually has to properly baffle it. My RC has plenty of knife edge baffles in tube as well as primary and secondary baffles. I'm choosing things purely on technical bases - yes, optical characteristics come first - but mechanical are also important - you'll need to mount that scope and scope needs to be rigid as well. Some designs fare better in this regard.

First of all - that is very nice image. I appreciate it more since it is the object I don't get to see imaged often and of course - can't be seen visually from where I am. ISO is just conversion factor - so it does not mean anything in terms of SNR - but it does affect read noise. Higher ISO means lower read noise, but just how much - that is something that must be measured. Shorter subs + higher ISO vs Longer subs + lower ISO - is again matter of read noise being dominated by other noise sources and unless we know things like read noise value at different ISO settings and your LP levels - we can't really tell which is better. What I can tell you is that there is another way to deal with over exposed regions - and that is to take several short exposures at the end of the session. You stack those in separate stack and then replace over exposed pixels with scaled pixels from short stack. It is a bit involved to do it by hand - but some don't really bother doing linear blending of data - they process both images and then blend in PhotoShop / Gimp by using layers / layer masks.

I used command line dcraw to convert files to TIFFs, and those were stacked fine by DSS. Try using that DNG converter I linked to - it is supposed to work fine.

I just realized that: 1. version 4.2.6 of Deep Sky Stacker opens .RAF files but it is painfully slow 2. FitsWork can easily convert .RAF files into .fits but 3. Fuji X-T1 uses X-Trans sensor that does not have regular bayer matrix - it has some weird 6x6 matrix: https://en.wikipedia.org/wiki/Fujifilm_X-Trans_sensor Looking to see if dcraw will read and output proper color image - it will.

Really great capture!

@Chris I'd like to have a go at processing those files (maybe even do tutorial myself ), but there seem to be just a small number of them. I looked up RAF file format and it appears that Adobe utility (free) can convert those to .DNG filter format. https://helpx.adobe.com/camera-raw/using/adobe-dng-converter.html Maybe if you upload original RAF files instead - maybe all 40 or how many do you have?

Always use 32bit float point precision for all steps past initial recording in camera. Start from calibration and keep using 32bit precision. Bits of precision that you add with number of stacked subs is equal to log base 2 of number of subs. If you say stack 32 subs - it is increasing needed (fixed point) precision by 5 additional bits - you can see how easily you can go over 16 bits even with 12 bit camera. Not to mention calibration part where you operate with masters created by stack that themselves need to be recorded in higher precision. For me it is very hard to even imagine doing beginners tutorial on processing. I complicate things too much - and that is never good for beginners. I echo above comment - don't do any stretching in DSS itself

Yes, I see. Shame that most reducers have such short back focus of only 50-70mm. I have AP CCDT67 - or rather TS/Chinese clone of that reducer - CCD47, but unfortunately that one has only 85mm of back focus. I was hoping to use it with my F/10 4" achromat to get somewhat wider fields - but it simply won't come to focus when trying with 2" diagonal. Must try it with 1.25" diagonal, although I'm sure that same FOV can be had with 2" eyepiece without reducer. Reducers are nice way to extend scope collection - much like barlows. Should we count these as well into our total refractor count?

Can you actually use that reducer for visual? I've searched quite extensively for focal reducer that can be used for visual - to maximize FOV in slower refractor - and there is only one that has sufficient back focus - Astro-Physics 27TVPH which has 118mm working distance - and that is just about right for 2" diagonal + any adapters needed. There was rather interesting thread not long ago - about expensive scopes, so worth checking out if you are keen to get answer if there is reason for Tak being so expensive In any case - if you want ED refractor that is portable in 4" class and don't want to spend silly money - then yes, it's going to be compromise. Question is - what are you willing to compromise. A bit of aperture and go for 80mm scope instead (there is crazy deal at Svbony for 80mm F/7 with FPL51 glass - think of it as ST80 with much better color correction and retracting dew shield and decent focuser)? A bit of color correction and go for faster yet lighter and shorter scope? Portability? in that case - go for 4" F/7 version that actually comes in two flavors - cheaper + some residual color or more expensive but virtually color free. Then there is F/9 version - it has excellent color correction, but mechanical side and portability suffer. For portability maybe look into this scope: https://www.teleskop-express.de/shop/product_info.php/info/p13519_TS-Optics-ED-Apo-96-mm-f-6-with-2-5-Inchl-RAP-Focuser---ED-Objective-from-Japan.html It is 460mm long for transport and only 3Kg. Adding some sort of crazy reducer will make it very fast for EEVA as well (with Long Perng x0.6 it will turn into F/3.6 system that is pretty good match for cameras like 533 or 183 or two new ones that you found interesting 485/482).

There is interesting fact - with say 120mm refractor - you have more scopes in one. You also have 100mm and 80mm refractor. They are however equally long and weigh about the same and need same class mount.

Difference suggests that you are doing something wrong and it offsets by 90° as 52°+32° is pretty close to 90°. Remaining few degrees could be because mount is not level. Do you point to Polaris like this: Or like this: First one is correct, second one will make altitude dial show (90° - latitude) so close to ~38° if you are at 52°

Choosing optimum sub length is balancing act. On one side - you have incentive to get as long subs as possible, as stack of smaller number of longer subs has edge over large number of shorter subs - if they add up to same total time. On the other side - here are things that make / let you use shorter subs: - mount tracking - it is better to have shorter subs with round stars than longer subs with little streaks - light pollution - different between long and short subs is only in read noise of your camera, or rather what is relation of read noise to other noise sources. If you are in light polluted area - LP noise quickly becomes dominating noise source and swamps read noise - when this happens - there is not much benefit in going with longer subs (there is still benefit but that benefit is very small and often not perceived by humans in the image) - chance of ruined sub. Wind gusts? Cable snag? Passing airplanes / traffic / neighbors turning lights on/off, earthquakes? All of these favor shorter subs as it is better to loose 1 minute of imaging rather than 10 minutes of imaging in case something goes wrong. There are some things that go in favor of long subs - like amount of data storage and processing capability. Do notice that some algorithms actually prefer having larger data set to work with - and that favors shorter subs. All of this can be a bit daunting to take into account - and for that reason look into taking 30s-60s to start with - and test if your tracker is capable of good tracking at those times.

I think that best you can hope are nuances. Measure FWHM of a star in final stack and you might notice that APP produces somewhat tighter stars. Difference might be small enough not to be seen by eye, only measured. Similarly if you select what appears to be uniform patch of signal and measure standard deviation on it (thus estimating noise) - you might find that APP one is slightly lower in noise than DSS - again - this is most likely in domain of measurement and probably not something that you'll notice readily in images. Is that worth the money paid? Well - that depends, but I think that APP has some features that DSS does not have (like automatic mosaic stitching) - and that is probably where your money is spend.

Well what are you expecting compared to DSS? DSS is very good stacker - and there are only a few things that I object to it - otherwise it works just fine. Given one set of data - there is only so much choice of stacking algorithm can do - in most cases, result of stacking will be more alike than different between different stacking algorithms - if all used properly. Don't blame stacking software for color management - that is sort of your responsibility and if you don't properly color manage - you'll get "color nonsense" in any scenario.

That is quite possible. Stellarium simply uses catalogs of celestial bodies and if that catalog lists particular item at certain distance - that is what you'll get. For some bodies it is not easy to determine actual distance, and there might be corrections for previous surveys. For example - if you try to measure distance to certain Ha region with associated cluster - you'll use distance to stars in that cluster. Maybe parallax measurements for those stars has been off in previous survey and newest survey gives different values. Interestingly Fish Head nebula (part of Heart nebula) is listed to be 5545 Ly I'd go by wiki in this case, but you can also go to Simbad and look at more recent surveys like Gaia2 - for some of the stars in cluster to determine their parallax and hence distance.

6200 or 2600? It's starting to get confusing with all those numbers In any case, I'd say - go with lowest number you can maintain in your conditions. Do remember that each camera has deltaT and you'll only achieve in best conditions - ambient - deltaT. If you do your darks indoors where you have say 25°C and you have only 35°C deltaT - then I would go for -5°C as my target temperature. This is because I like to round things to nearest 5° and in all likelihood 25°C - 35°C = -10°C will be hard to maintain as it is right at the edge of what cooling can do - so next 5°C step is used at -5°C. Keep in mind that you'll probably need to have set of summer and winter darks, and if you want to only use one set - go with summer darks as you won't be able to achieve lower temperatures in summer than in winter - but it will be easy doing other way around. Also - take into account ambient for shooting of calibration frames - if you can shoot in colder environment (basement or observatory) - then adjust above to suit you. There is no "preferred" temperature setting - lower is better - just make sure it works for you with respect to being able to achieve and hold that temperature for both imaging session and calibration frames.