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??? I'm seriously confused by what you've written here. First - ASI1600 uses MSB format - you want your flat ADU to be around 40K (actual values are in range 0-65535 and are divisible with 16 and not in range 0-4095). Now, back to above. You say that without focal reducer you need up to two seconds per filter to get to 20K, but using focal reducer you need 100+ seconds to get the same ADU level? Reducer should lower your time and not increase it by factor of x50! If above is indeed true - please check your focal reducer - it might have something wrong with it that block the light. Don't worry about short times with ASI1600 - I used flat exposures that were fractions of a second, and even milliseconds long (my flat panel is rather strong) and never had issues with flats.

That won't help much. You need something like 30-40mm in scope with such focal length - 1200mm to be able to see anything more than core. Inner yellow circle represents what your field of view will be like with 14mm ES82. Red circle is what it will be like with GSO 32mm plossl. In your case, you will only see central smudge and M32 at edge of the field. If you are very lucky and don't have much of light pollution and M31 is positioned overhead - you will see first dust lane. That happened to me only once with 8" scope and 32mm plossl in my red zone back yard (very transparent night). If you want to have any chance of getting almost whole andromeda into field of view with your scope - you will need widest possible 2" eyepiece - something like Vixen LVW 42mm or ES68 40mm Each of which will cost more than half of what you paid for your scope - £250+ (unless of course, you find second hand item). Problem with either of these eyepieces will be exit pupil - very large and I doubt you have pupils that dilate ~9mm so there will be light loss because of that. Maybe best solution for observing M31 would be to get yourself second scope. Seriously, something like ST102 will probably cost you like one of those eyepieces but it will be much nicer to use on M31: New will be £330 (don't be tempted to get it on AZ3 - it is very unsuitable mount for this scope and intended role): https://www.firstlightoptics.com/sky-watcher-az5-deluxe/sky-watcher-startravel-102-az5-deluxe.html and you will be able to get it cheaper second hand of course (although probably without a mount). Here is what this scope gives with 25mm stock EP and 32mm GSO Plossl:

There is not much difference in light gathering capacity between 5.1" and 6". If you want real improvement then go for 8" 8" dob is seriously good scope and it will show you a lot. It's a bit more bulky than 6" - with 26Kg total - split into 16kg base and about 10kg scope. It has same focal length so field of view will be the same as with 6" - not much difference there. I love my 8" dob (also skywatcher model) and it has shown me a lot. I do have to point out that most people get underwhelmed by what they see at eyepiece if they are used to "Hubble like" images on internet - things don't look like that at all in telescope - again youtube helps a bit there: https://www.youtube.com/watch?v=jI7IPPmu76U

150 model is more serious in about everything. I would not call it "beginner" scope (if there is such a thing). It is bulkier, heavier and will show you more. It also has more focal length - which is good for planets and the Moon, but prevents you from achieving wide field views. It is nowhere near "grab & go" as 130 model - which can be carried in one hand as you have seen from videos. As a contrast, 150 dob from skywatcher weighs in at about 16kg! Scope is about 6kg and base is about 10kg. While it can be carried easily in parts (telescope and base separately) - it is really not grab & go scope and is quite large.

On the other hand - there could be relatively cheap solution compared to this eyepiece but it does require use of computers (so if you don't already have a lap top - it's not cheap at all) - cheap second hand guide camera like ASI120 - and doing imaging / measurement from images?

Yes they are - way more expensive than I would imagine for a simple eyepiece. Maybe DIY option then? You really only need some sort of reticle with steps to be able to measure distance - you'll need to calibrate it anyways, so maybe solution would be a glass blank with engraving? You only need to place it at focal plane of eyepiece and field stop should help there. I wonder how much does it cost to have a piece of glass precision engraved?

Start by watching a few videos on youtube - this one in particular: https://www.youtube.com/watch?v=GHdDs2PLIrk then this one to get the idea of size of the telescope in question: https://www.youtube.com/watch?v=9Kujf1tTnAk and in the end this one to get the idea of what is involved with operating eq mount: https://www.youtube.com/watch?v=_TNrPLHB21k As a contrast to those, have a look at these - which feature 130mm dob scope: https://www.youtube.com/watch?v=FEs_MMcJ7JA or this one: https://www.youtube.com/watch?v=qVgOG5JzZGQ another one from different manufacturer but same model: https://www.youtube.com/watch?v=-muZ9KRMY40

Far from being an expert on this, but how about: https://www.firstlightoptics.com/specialist/baader-microguide-illuminated-reticle-eyepiece.html

Proper calibration is with flat darks rather than bias subs. In principle, you can get away with using bias instead of flat darks - if your flat exposure is rather short / dark current very low and your bias is stable.

That sort of thing I had in mind. Btw, above procedure is applicable to regular session if one wants to see a difference between for example 2h vs 0.5h or similar - you just stack fewer number of subs in one stack.

Not much point in saying that to a certified pixel peeper like myself - my instant reaction is right click / open in a new window / zoom to full size - even typing it seems long in comparison to motions now firmly set in muscle memory

I find it good idea to view a few youtube videos of people handling said scopes to get the idea of the size/bulk involved. More than once I was surprised by the size of telescope in person versus the idea of size I got from looking at pictures of a given telescope on the internet - they always look smaller on pictures for some reason 150p is large enough to be life time telescope, and so is 200p but I do believe they will be too bulky for you to start with. Also, advice on additional eyepieces is sound one, but you don't have to rush into it - there is plenty to see with stock eyepieces.

Dobsonian mount is very well regarded with amateur astronomers for its simplicity of operation. It is also often recommended and used because it is the least expensive type of mount - so more of the budget goes into the optics. If you have more money to spend, then I would say have a look at this scope: https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-150p-dobsonian.html There are some drawbacks to that scope - it is much larger to carry around, but will fit in car without too much problems. Only advantage that EQ mount offers is - it can track object with motion in only one axis, and this motion is uniform - so it is well suited to adopting motors to drive it. It has other benefits that are much less important for observing and much more for imaging - like lack of field rotation and such. Issue with EQ type mount is that cheap models are really shaky and light weight. They are a bit awkward to use for beginner - you need to polar align them and motion of the telescope tube is not straight forward to grasp. With EQ type mount, newtonian (mirror) type telescopes often end up in strange positions for observing - you need to rotate whole telescope in its rings to get eyepiece to suitable position. With telescopes aperture is very important factor in what it will show you. For this reason, beginners often go with newtonian type telescope as it offers the most aperture for their money. Because of newtonian construction - they are well suited for alt/az type mounts - that thing with eyepiece being in awkward positions. And in the end cheapest alt-az mount is dobsonian mount. From all of that you can see why dob mounted telescope is recommended for beginner. Now, 130P flex tube is very lightweight and portable scope, and only drawback is that it is open / truss tube design and my recommendation would be to fashion some sort of shroud for it to stop stray light from entering it. Larger scopes become less portable really fast. They also tend to be fairly bulky really fast. Here is comparison of different sizes of telescopes and a grown man with height of about 6'. If you can handle the bulk of 150mm dob (or even 200mm - it is just larger diameter and heavier but same height as focal length is the same - 1200mm) - then go for that one, if not, 130mm will serve you very well.

How about this then: https://www.firstlightoptics.com/dobsonians/skywatcher-heritage-130p-flextube.html It is 130mm, very portable, costs £142 and only "modification" I would do to it would be adding a black fabric shroud when observing in light pollution areas. or can be cardboard based:

Second one obviously better and certainly what one would expect from more exposure. I agree that both images should be processed the same. In fact, if you really want to do good comparison - try making a split screen scenario. Take both images - preferably stacked with the same method, bin/scale to same resolution, align them the same (register one to another) and equalize them, and then, in the end, compose one image by taking left part from one image and right part from the other image - while still in linear stage - and process resulting image. This will provide excellent way of seeing the difference between the two.

Well Heq5 is rather basic mount - which means you'll need to get your hands greasy if you want to keep it running in a good shape. Have you done any modding to it? I changes bearings, did tuning and re-greasing, belt modded and changed tripod and saddle plate on mine and now its decent - but not as good as I wanted. I have a feeling that Cem60 would be as good if not better without all the fiddling about. I'm against the EC version as I think it is too expensive for what it brings and I also heard that people had issues with it when guiding (probably sorted out now). EC version is probably very good for anyone not guiding, but if you guide - you won't tell the difference in performance to regular mount, and cost of EC version is very fast approaching mounts like Mesu200. What I'm trying to say - if you don't mind DIY and want so save some money - do a round of tuning on your Heq5 and possibly belt mod if you have not done it yet. If you don't want to mess around and have the budget - I think Cem60 is better solution. EQ6 class of mount (regardless if it is AZ or regular 6 or 6-R) I see as same performance as Heq5, only higher payload capacity. Cem60 is a bit better than these from what I see.

@Adam J From what I can see in your signature, you own a Heq5 mount? Are you looking for an upgrade? Not sure what your budget is, but if I were looking for an upgrade from my Heq5 - I would aim at Mesu200, but that's not the point - mount in between, much closer in budget, that I would consider would be Cem60 (non-ec version). Have you considered that one?

Have no idea about different mount names - as far as I can tell there was only one AZEQ6 model, so I assume every one of those names is for the same mount. I don't know exactly about PPEC. What I do know is following: I do VS-PEC on my HEQ5 mount and yes it is very beneficial to guiding results. Since it reduces total P2P RA error and smooths things out - it enables me to use longer guide exposures without fear of mount drifting too much away from target position - smaller P2P in one worm period means smaller RA drift rate. Longer guide exposure means less variation due to seeing. It helps both with how aggressive corrections need to be and with longer exposures for seeing. Issue that I have with my HEQ5 is that it does not have encoders - on RA nor on motor shaft. That means that PEC relies on EQMod tick counting (micro step counting) to determine where in worm cycle mount is currently - which in turn means that I need to park mount after each session - so that EQMod/VS-PEC is properly initialized next time with tick count of 0. It takes me about 2 hours to record PEC data and power outage when you are in the field - not only ruins session but makes your mount do power cycle without parking to home position - thus loosing PEC sync. It also means that I can't use my mount for visual without computer - with hand controller only as it has no park to home feature. For this reason I prefer the idea of PPEC, although I have not worked with one so far.

According to this: http://eq-mod.sourceforge.net/prerequisites.html same gear train, same stepper motors and same resolution. I do believe that AZEQ6-GT has some sort of encoder and has PPEC - not sure about EQ-6R, so that could be advantage. It looks like EQ-6R also has PPEC, but not dual encoders.

I also have this mount and at some point want to mess around with it and do some light imaging. I purchased it to be moon gazing mount because it is light weight and tracking and I have Mak 102 sitting on it, but will do some EEVA at some point with it. Still need to get all the bits needed to do EQ conversion - wedge and counterweight ... If you can manage 1"/px semi regularly (which would be great) then that would be perfect for 2.34"/px. I think that even with 1.5" RMS you will be ok, but at 2" your images might start to feel a bit soft because of mount.

Have a look around these forums for images taken with Samyang 135mm F/2 lens for exceptional examples of wide field astrophotography. For starters there is whole thread dedicated to this particular lens: Point of course being that even 135mm will produce some amazing shots of heavens. When we talk about AP we don't really talk in terms of focal length (although telescopes and their focal length are integral part of the story) - we talk about arc seconds per pixel - as measure of resolution. Loosely speaking, we can divide AP into 4 categories - very wide field / milky way and constellation shots, wide field AP, "medium" field AP - although this term is not used very often - probably because it is just AP or regular AP, and high resolution work. In terms of arc seconds per pixel - it goes something like this: high resolution work would be everything above 1.2-1.4"/px, regular AP would be 2-3"/px up to 1.2-1.4"/px, wide field ap would be above 3"/px and really wide field / Milky way shots and constellations is no longer thought in terms of angular resolution per pixel but in terms of Field of view - more than about 5-6 degrees and we can start fitting constellations into FOV. Just for a comparison 200mm lens paired with Canon 500d will have ~4.8"/px so it fits perfectly to wide field category, and if you want - you can also do really wide field by dropping to something like 50mm or smaller FLs.

Are you interested in astronomy in general or just AP? Do you have any other astronomy kit? I'm asking because up to £400 - your budget is seriously tight. You won't even be able to get 130PDS and EQ3-2 and motorize it. Goto version of EQ3-2 with motors is already at the top of your budget at £400 new. This means that you either want to purchase second hand, or possibly go with regular unmotorized mount and add motors - as separate purchase or DIY project (if you are into that sort of thing - stepper motors and a bit of arduino skill is all that's needed). To answer your question - all of mentioned scopes - 150 models, are best suited for heavier mounts. 150PL model has 1200mm focal length and is generally not recommended for beginner to start imaging, although can be used as good imaging scope. PDS line of scopes by skywatcher is meant for imaging - they are equipped with 2" focuser with microfocusing and have larger secondary mirrors needed to provide good illumination for astro photography. I would recommend 130PDS over 150 models in your case if you choose EQ3 mount. Larger scopes simply require larger mounts to be stable enough for imaging. Having said all of the above, I would actually recommend you that you start by getting to know what is involved with AP - maybe a book on astro photography first? If you are keen to get started - question comes - will you be able to add more cash later to this hobby? If answer is yes - just spend all cash you have now on largest mount that you can afford, and for the time being just mount your camera with regular lens on mount and start doing images and learning. Scope like 130PDS is really not as expensive to be added later when you feel more comfortable and already know what you are doing. If not - then my suggestion would be the same - get EQ3 class mount, see about motors but try to save some budget for later purchase of scope - and start with camera and lens.

I think that such mount can do below 1" RMS for a limited amount of time if there are no significant outside influences and seeing is really good. Seeing needs to be good enough not to cause corrections in position that are larger than single step of stepper motor, and 0.6" shift of guide star in longer exposure - like 1-2 seconds requires really poor seeing. If there is no wind and vibrations are low - it can keep the mount at about 1". You also need to have good guide resolution to be able to properly measure 1" and below RMS error. I would say that you need to have at least 4"/px guide resolution for something like that. With camera like ASI120 or ASI224 - that would mean at least 190mm of focal length in a guide scope.

This is quite right, it can be otherwise as well. I think that it depends on gradient of curve at particular points. Steep curve will make larger difference then it is (in percentages) while shallow gradient will make smaller difference thus de saturating color - that happens on very bright things if curve has common shape often used to stretch. In my above post I wanted to say that green color in ending image might: 1. not be green color at all 2. could be quite mundane occurrence in universe. Consider following - I'm not sure what exact filters and camera you used for above image, and I'll be using your signature - Astrodon RGB filters and SX Trius 814 camera. Let's consider very simple nebula with dominant Ha/OIII emission. M57 type of object, or much larger molecular cloud complex like M42 - point is that emission from such source gives Ha, Hb and OIII lines in spectrum as dominant light because it contains lots of hydrogen and oxygen gas. Now, first obstacle is finding exact QE curve for Sony ICX814 sensor - internet search gives different results - but let's go with this one: and filters (lets go with gen2): If you take a look at following lines - 656nm, 495/500nm and 486nm - Ha will go into red, OIII will be split between green and blue and Hb (H gamma and all other significant H jumps) will be blue. QE of sensor is relatively same for these lines with small variations, so it is very easy to see that object consisting only out of two gasses and three spectral lines would produce: R: 1.0 , G: 1.08 and B: 1.03 But what color should such light have? In the image it appears green, is that to be expected? This is Cie xy chromaticity diagram. On outer edge of this diagram - every point represents a single wavelength source, so our three lines will be on that outer edge. Planckian thermal sources lie on so called Planckian locus - also depicted on this diagram as line going thru red/orange/yellow part and ending in blue - it has temperature in kelvins marked onto it. In this diagram - if you have three sources of light with known coordinates - all colors that we can see that are mix of these three colors lie in triangle inside of those three points (it holds for any two points - all colors that are made out of combination of two sources lie on line connecting those two points and by extension to three points as well). From this, we can see that simple Ha (and Hb/H gamma and so on - all that are in visible part of spectrum)/OIII can produce - red, orange, white, bluish and greenish colors to human eye . We can't see pure grass green nor deep blues or deep yellows from this combination. Btw - real colors in this diagram are more saturated on outer part of the diagram than monitor is able to display - rainbow has more saturated colors than this. In fact, most likely computer monitor will only display this region: All other colors are beyond the gamut of sRGB capable display and can't be reproduced. Red, green and blue pixels that monitors use have coordinates of triangle points in above image - hence all colors monitor can produce lie inside that triangle (like what I've marked above). So if we want to show what colors can be produced by Ha/OIII combination and also displayed on our monitor as distinct colors - we need intersection of two triangles like this: So in principle - Ha/OIII region can be even turquoise / dirty aquamarine in our RGB images if we process data correctly (btw - this is where my color knowledge breaks down - once I'm expected to assign common name to particular hue ).

I would say that you are probably mount limited rather than seeing limited. With AzGTI, I would be surprised if it could do less than 1" RMS. In fact I think that stable guiding below 2" RMS is very good achievement with it. It's just a small mount and not very precise. According to this: http://eq-mod.sourceforge.net/prerequisites.html It has about 1/5 of precision of Heq5/Eq6 class mounts. Those have 9024000 stepper ticks per revolution - which makes their stepper motors have resolution of 1296000 / 9024000 = ~0.143617" per micro step (1296000 being number of arc seconds in full circle or 360 x 60 x 60). If AzGti has 2073600 ticks per revolution, then resolution of motors is 0.625" per micro step. You can't really expect mount to have below 1" RMS if it can't keep DEC precision below 0.625", and two to three times this value is more realistic or 1.5"-2" RMS. Btw, resolution in above link for AzGti is given to be 0.0625 - which is less than 0.143617 that of Heq5 - which I believe is a typo with 0 added as is clearly shown by above calculation.