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1700 subs stack should be saved as 32bit floating point fits rather than 16bit. You can loose quite a bit of precision as 1700 subs is almost 11 additional bits.

Well, there won't be much visual difference between 90min and 135min. That is only 50% increase in number of frames or about 22.47% increase in SNR. That is on edge of perception. However, it can be seen with a bit of "trickery". Human brain is very good at recognizing patterns - and if you give it two patterns side by side - it will spot similarity and differences rather easily. here is animated git that I made from 90minute and 135minute fits - green channel, linearly stretched and employed "split screen" trick. Right part of the frame does not change - it is 135minute fits. Left side alters between 90 and 135 minute fits. It is obvious that 135minute looks a bit smoother - smaller grain and more uniform than 90 minute data. Even with such a small increase in data - difference can be seen if you know where to look for it. No. Background extraction will remove very uniform component of background signal and leave background noise in place. Here is analogy to help you understand better. Imagine that you have mountain trail full of rocks that you walk on. It's bumpy ride. That is noise. Background level is just difference between that path being on Mount Everest versus your local hill. Bumps in that trail won't change if you lower the mountain level. Last and most important thing is - although size of bumps in the path does not change - their relative size to the mountain does change. Average size of rocks of 10cm on path compared to Mount Everest being 8848 or whatever meters - makes that almost one in 100,000, but if you "wipe" the mountain and leave local hill that is 100meters high - now rocks are 1 in 1000. This makes no difference to the image - it just makes difference to processing parameters - where you put your black point. Depending on that - you'll get relative noise level - same image can appear quite noisy or very smooth - depending on how you process it. Here is 135 minute data in two stretch versions: Same image - different background. One of very important skills to learn in image processing is to push the data only to the point it allows to be pushed. It is SNR that is important. In my view - it is better to keep the noise at bay by sacrificing signal part - maybe you won't be able to show those faint tidal tails nicely or those outer parts of the galaxy will be too dark to your liking - but image will be smooth and with very little noise. Not being able to show faint detail does not mean that you did not push your data enough - it means that you did not spend enough time imaging.

Can you post just couple of linear stacks without stretching them (as fits please as I don't have PI and can't open xifs)? Visual feedback on how much noise there is - depends on stretch level. I think that you used PI automatic stretch - and that one works on basis of noise floor - this is why it stretched each sub so that noise in background is the same. You can see that by size of stars in your animations. there is much more "light halo" around left star then on the right - but they are the same star (you can see this in your animated gifs - just watch any single star and see it "bloat" as total exposure increases). In order to measure noise accurately - take two stacks still linear and select piece of background not containing any signal - no stars, no objects, mostly empty and do stats on each image in that region. Compare pixel standard deviation values between images. If you want to visually asses difference between two images - make sure they are normalized (one with respect to another) - or that they are stacked against same reference frame. Then do "split screen" type image while you still have linear data - prior to any stretch. This is easily done by selecting half of one stack and pasting it in the same place onto another stack. Only when you have such image - do the stretch to show background noise. This way you are guaranteed to have same stretch on both images - as you'll be doing stretch on single image consisting out of two halves of different stacks.

Given your budget - you probably won't be getting what I recommended (as it is too expensive), but here is answer to your question. iPolar is electronic polar scope. It has USB connection and needs to be connected to laptop in order to run windows app to do polar alignment. As far as I know, ASIAIR also has polar alignment feature - but uses main camera on the scope to do that rather than separate electronic polar scope. You don't need both. In fact - I would argue that simplest method is to polar align with regular polar scope and simple phone app that will give you Polaris position. Electronic assisted polar alignment is useful if you can't see Polaris or you are on southern hemisphere. This is something completely different from GOTO feature. GOTO is system that instructs telescope to point to wanted object in the sky. It is part of observation while polar alignment is part of setup of EQ mount. Most mounts that you are likely to get have goto functionality irrespective of ASIAIR - they have it in hand controller. ASIAIR just connects to the mount and uses mount goto feature so you can direct the mount with your tablet / phone rather than using hand controller. ASIAIR is also useful for controlling exposures - looking at focus and frame shots and guiding the mount - it replaces regular laptop in the field and is handy for mobile use - less things to carry around.

Hi and welcome to SGL. I'm inclined to recommend something like this: https://www.firstlightoptics.com/ioptron-mounts/ioptron-cem26-center-balanced-equatorial-goto-mount.html rather than that ES mount. In combination with: https://www.firstlightoptics.com/zwo-accessories/zwo-asiair-pro-wireless-astrophotography-controller.html will give you much better mobile imaging platform that you can control over your phone.

You are quite right about that - but there is a good reason why that is happening. When you image something with your smart phone - you use telescope, eyepiece, telephone camera lens and telephone camera. Combination of eyepiece and telephone camera lens acts as powerful focal reducer. This turns complete system into very fast imaging rig - at a cost of resolution and image definition (most phone images are very blurry and suffer all kinds of aberrations - but we tend not to care because we don't expect perfection from phone camera). When you attach camera directly to telescope at prime focus - telescope becomes massive telephoto lens. It is very different configuration. You can get similarly good or even better images with DSLR type camera if you attach it the way phone is attached: use long focal length eyepiece to get maximum of field of view and match camera lens in FOV to that eyepiece. Say you use 32mm Plossl with 50° AFOV and APS-c sized DSLR - then you need lens that will get 50° FOV on aps-c sized camera - which would be 28mm lens. This combination will act as 28/32 = x0.875 focal reducer. In comparison, focal length of phone camera lens is just few mm because crop factor is something like x7. This means that you can get 4/32 = x0.125 focal reduction - that is massive. However, smartphone lenses actually work as aperture stops. Exit pupils from telescope are often very large - like 4-5mm and aperture on phone lens is often smaller than that - like 2-3mm.

Jupiter is best observed when it is close to opposition. This year that will be second half of August (opposition is on Aug 19th if I'm not mistaken). At that time you'll be able to view Jupiter due south at midnight at highest position in the sky. In the meantime - it is visible during different time of night - currently it rises around 2:25am your local time. You can see details on this website: https://www.timeanddate.com/astronomy/night/usa/peoria

Don't be discouraged - even in this time of year it is worth going out and trying your best to see brightest objects. Observing is a skill - and you need practice. Just don't get discouraged if you can't find all objects now as conditions are not the best. This will only last for few months - in second half of August - you'll again start having full darkness. I made that reference about the sea - because I'm used to Mediterranean sea at summer time. There is a lot of heat and lot of water vapor in the air - which makes for poor transparency. You are quite a bit northern and you might not get temperatures of 30°C+ during the day and night in order to have those conditions. Wind also helps to clear water vapor from the air.

Don't worry - most cities are too large to be able to find a person. Saying that you are from particular city is not much of info (at least I think so - I'm from Novi Sad in Serbia - it says so in my info). Just don't give exact coordinates or similar. You are actually at Bortle 6 - SQM around 19 (a bit less) - that is well - less bad (I wanted to say good - but obviously it's far from ideal). I think that most of your issues will come from being very low on sea level and the fact that sea is close - you have much better chance of observing in winter than in summer. Also, since you are in Latvia - be careful about darkness - you are further north and in summer you won't have complete night. Yep, that is a problem - you don't have full darkness any more: https://www.timeanddate.com/sun/latvia/ventspils It gets dark only until and of April and starts again - mid August.

M81/M82 is another relatively easy pair to find. In your 25mm eyepiece you should see them both. I usually don't exactly know where to find them - I just point telescope in general direction and scan the skies for a bit - they are usually very easy to see.

What city is that? If you are in Riga - then yes, LP is pretty bad in city center. If you are just a bit away from center - then you should still be able to see at least a few objects. Click on light pollution map and look at SQM number. I managed above objects from ~SQM 18.5 - so anything higher than that should be fine - but anything lower is rather bad. As far as I see - most other cities in Latvia are not nearly as bad.

I've seen plenty of objects from red zone (bortle 7) with 100mm telescope, and quite a few with smaller aperture like 60mm. First thing is to know what to expect - most are just faint smudges - very faint, barely showing against the skyglow. Next thing is to optimize your chance of seeing anything at all by: - shielding yourself from any direct light sources. If you have to - put a blanket over your head to cover yourself. Really. - get dark adapted as much as you can - wait until late at night. Most people go to sleep at some point and turn of their lights. There is less cars in the streets around 1-2am for example. - look for objects that are near zenith and in direction where sky is the darkest. Depending on your position to city center - you might have darker side - use that and look for objects in that area. My "dark zone" is due south and a bit to the west. Close to zenith there is the least air to look thru and that makes things easier to see - use applications to plan your observing. - make sure that you are looking at the right place. Yes, really - it helps if you are actually looking at object rather than just empty patch of sky with stars in it. Learn to star hop and find objects. - observe on transparent nights with no moon. Moon makes sky brighter - so avoid it. Make sure there is no haze in the air or no thin high altitude clouds. Use this forecast service: https://atmosphere.copernicus.eu/charts/cams/aerosol-forecasts?facets=undefined&time=2021051100,3,2021051103&projection=classical_europe&layer_name=composition_aod550 It shows how much aerosol / pollution is there in the sky. Make sure your city is in blue/gray range rather than yellow or red at your observation time. This is not something that you can influence - but check it out to be mentally prepared. If transparency is poor - you might have no luck trying for harder targets. In the end - use very easy targets to get you started. Globular clusters - bigger ones are nice targets and so are some larger and stronger nebulae like M42 for example. M31 - you can't miss it is very strong - but you'll probably just see core smudge and no detail (I only once managed dust lanes from city with 8" telescope). Recently someone posted this and I think it is good idea to use it. Use very easy and easy column to start with. Use Stellarium application to see where objects are at the time of your observation and to limit yourself to ones high in the sky. Tonight around 2am - there should be at least 5-6 nice globulars on display - M13 and M92 high in the sky, M3 and M5, M10 and M12. M57 is also very nice target - however it is very small and for that reason you can miss it. Use higher magnification to spot it.

Hi and welcome to SGL. Depends on how "little" serious you want to get 1000$ won't get you far in astrophotography I'm afraid. At least not one with telescopes. You could get very nice star tracker and very small telescope. Something like Star Adventurer mount or iOptron offering and pair that with nice telephoto lens that you have or maybe 60-70mm ED doublet. That would be within budget. Mount is super important in astrophotography - go to is nice bonus - it can get you close to target but not necessary. I purchased my mount without go to functionality and connected it to a computer to get go to functionality and much more. However mount needs to have motors to track the sky and it has to be EQ type mount if you want to be even close to serious. If you want to get a little bit more serious - meaning telescope + mount. Then think of those 1000$ as going towards the mount (and a bit more perhaps). Something like Heq5 will get you going (maybe even EQ5 - but most people that start with EQ5 mount - very soon think of upgrading). Nice "starter" package would consist of something like this: 1. Heq5 mount 2. 80mm ED scope 3. Field flattener / reducer for above scope 4. Guide scope (can be modified 50x8 finder) 5. Guide camera 6. Laptop 7. DSLR camera (which you already have) 8. Assorted accessories - cables, adapters, battery pack for mobile setup or different wall adapters I think there is probably around 3000$ - give or take, on the list above. You can save some if you purchase second hand items, or maybe go for different scope - like 130PDS instead of ED doublet. Most beginners don't like idea of fiddling with collimation - but since you already own newtonian scope - you probably know how to handle one. Mount is the last item you'll want to save money on - it is indeed the most important thing.

I haven't either - but I did know that there are similar ones out there so I did a quick search and that one was among results. It is fascinating - right? I particularly like material spinning around neutron star and being ejected. I've seen that in an Hubble image in ~500nm narrow band - and planned to image it myself with Baader solar continuum filter that is narrowband like - but centered around 540nm. Here it is in x-ray by Chandra:

Yes, best you can do is search for images of planetary nebulae or super nova remnants over years to see how slowly it expands when observed from a distance. Have a look at this for example: M1 expanding over years: https://www.astrobin.com/full/327338/0/ If you are really interested in transient phenomena on stars - these can also be "observed" - but it requires specialist equipment and approach. I think that @andrew s does something like that with spectroscopic observations - records how spectra changes over time for stellar flares.

Because it depends on angle and mount tracks across the sky and moves. Either it was due to something stationary with respect to mount or you have drift between subs (don't guide or guide but have guide scope and there is slight differential flexure - shifting mirror or something). How much do your subs shift over the course of the session?

Yes, definitively reflection of some sorts. If it was some sort of flare - it would take many decades to move that far away from the star. Say star is 100Ly away and largest arc is 2 arc minutes in size. Then feature size would be roughly 0.06Ly - or about 22 light days. Ejecta traveling at speed of light would take 22 days to cross that distance (not to mention that it usually travels much much slower).

https://iris-calculator.com/ (there is free version - but it does not export design - you can only note dimensions for later use) https://www.instructables.com/How-to-make-a-12-leaves-Mechanical-Irirs/ https://www.instructables.com/3d-Printed-Mechanical-Iris/ etc ...

How do you image with binoculars? Afocal method? Do you have side by side setup with two cameras to exploit both lenses?

I'm rather baffled by your images. They are object that I'm not that familiar with, so I might be wrong here. Omega Centauri globular image looks like trailing is in fact in RA direction - and that is something I would expect. I'll explain in a minute. In second image - well, I simply can't figure out what is what. I'm looking at Stellarium and Eta Carinae and I can't figure out how to match them. If you can - well, first step is to figure out direction of elongation. Now for explanation. Most people just starting out in AP when facing elongation - think, this must be poor polar alignment. I've found that in majority of cases - it is actually something else causing the elongation and drift. Most people do rather good job of polar aligning and you really need to miss by a lot in order to have drift that happens in matter of seconds. That just does not happen. What does happen is drift in RA due to periodic error. If elongation is in RA direction on the image - you can be 99% sure it is down to periodic error. Periodic error is rather difficult to overcome. One thing that you can do is to do periodic error correction if your mount supports it. Since you are using EQM-35 which is SW mount - you can use EQMod and control your mount via computer. EQmod has periodic error correction feature. That should help somewhat - but it can still be present. Second thing that you can try is to do a belt mod. Not sure if there is belt mod kit for your mount. If none of these help, and even if they do help - it is likely that they won't solve the problem 100% - you'll need to turn to guiding in order to correct that. In fact - people should not fear guiding - and should consider it from the start. Most affordable amateur mounts will need guiding. Only expensive models with encoders or with exceptional mechanical precision can do without guiding. Everyone else simply guides. Guiding does not need to be expensive - web camera and 50mm finder scope with a bit DIY skill can be turned into guide scope. Then you just need a computer / laptop, but you can even do it with Raspberry PI. HTH

Indeed - I did full workup on my Heq5 - changed bearings for SKF ones, did belt mod, changed saddle plate to vixen / losmandy dual one, placed mount on Barlebach planet - and it can now guide sub 0.5" RMS.

This was taken a long time ago - one of my first DSOs - 8" f/6 with ASI185 (sorry no DSLR). Heavy light pollution - maybe total of 2h of exposure (don't think it was more than that). Can't remember processing, but stacking was most certainly done in DSS.

I'm not entirely sure of that. Heq5 and EQ6 are same accuracy class if there is such a thing - 1.0"-1.5" unmodded / out of the box, ~0.5-0.6" modded and tuned. EQ5 - not sure if it will go below 1" RMS, will it?

Don't base your mount decision on weight alone if you are interested in imaging. You won't need much heavier scope for considerable future. Even if you opt to go for 10" scope - you will still be under 16Kg for OTA alone or 20Kg combined (both 10" RC and 10" F/5 newtonian weigh around 15.5Kg). This really means that mount that can handle something like 20Kg for imaging will be useful for quite long time. Even something like Heq5 will be step up from Eq5 in performance. What do you see as being upgrade from 150PDS? What are your intended targets and working resolution? I'd say that you should keep the scope for now - and upgrade it last and get better performing mount - something that you'll be able to guide in 0.8" RMS range and cooled astronomy camera. That will make significant difference to your images.

Maybe this thread will get more attention in Scopes / whole setups rather than Getting started with imaging. By the way - I've got 80mm F/6 triplet from TS and I'm really happy with that scope - but I'm not sure if we can extrapolate performance between these two scope lines (triplet F/6 and doublet F/7)