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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.

Yes, I know - you can't render something that has lower SNR in the image if you want to avoid the noise and similarly if you bring out the faint stuff and you don't have enough SNR you will bring out the noise. That is what I wanted to point out - In my view, good astro image will have some noise, so it won't be completely noise free. Noise just needs to be fine grained enough and controlled enough so it does not distract from the image. On the other hand, I don't think that image looses much if you don't bring out every possible detail at expense of blowing out noise. If you can't fully render arms without making background too noisy - you have two options: 1. Just don't try to get those arms bright and visible and settle for what you have captured well 2. spend more time on target until you have enough SNR on each thing you want to render. Problem with approach 2 is that you are never going to be fully satisfied - more you spend on target, more faint stuff you reveal and want to get good SNR of and then you spend some more time on target and reveal more faint stuff and go in circles

@alacant I think you've been asked this before, but here it is again: Why do you post your images in Getting Started with imaging? Image such as above, in my view, should certainly be posted in main imaging section. Now onto the criticism of the image - background again . In my view improvement on clipping, but maybe a bit too bright this time? Also, I think you are pushing data beyond what it can deliver - background is too grainy at this level of stretch. I do understand the need to show every bit captured in the image, but M101 is very low surface brightness target and good SNR is important if you are going to try to show every last faint bit in spiral arms. If you don't have the SNR - you need to make effort not to over do the stretch (at least it is effort for me - I always have to make conscious effort not to stretch too much). @ollypenrice What's with hue in that image / screenshot? Do you have some sort of color profile enabled in PS or something else? As far as I can tell - you opened above image to analyze histogram so it should be the same image, but to my eye and on my computer screen, two images are distinctly different in color - not sure if it will be seen by others as it might be issue with my computer, but here it is: Left - your screen shot, right, original image. Maybe you did a bit of curves and levels and made hue different? In the end, here is my tweak to the image, hope it's ok to do this - background made a bit darker and a bit of noise handling: First histogram - to verify it is bell shaped and nice: and image (red has been touched a bit to make background a bit more neutral / gray):

Not sure about Darwin award however, man was 64, so I doubt that genes were taken out of the pool before the chance to reproduce.

You should not be using it - period

Why are you using drizzle?

I'm not really convinced that is true. Maybe we can do math together and see if that is possible? ELT will have primary with diameter of 39.4m which means that Airy disk will be about 0.007" and maximum sampling rate would be ~0.001" - meaning every pixel would be 1mas (1 milli arc second). If we solve for diameter - angle of 1mas will give 0.010193 light minutes for object that is 2102400 light minutes away - 4 * 365 * 24 * 60, or light years). Light travels at 300000km/s so it travels 183474km in 0.010193 minutes. Earth sized planet will have diameter of about 12700km, or would occupy 1/14th of a single pixel and certainly not 9 pixels. If we take that 1 pixel is ~183500Km then 9 pixels across would be 1.6 million kilometers and that is close to Sun like object with 1.3 million kilometers. If above simulation is anything real then it is much more likely to be simulation of image of Solar diameter star at distance of 4Ly rather than earth sized planet.

I'm having difficulty understanding their explanation, some of the things they've written don't make much sense to me. I'll outline what confuses me, maybe someone will understand and explain to us what they meant so we can get to the bottom of this green color in the image. So far, so good - I agree completely, if you want to document true color of the object - you can, and same as them, I object the notion that "color is arbitrary" in astrophotography. It can be arbitrary - but by choice only. Emphasis on last sentence is added by me as it is root of my misunderstanding of what they are saying. They say that they want to exclude human vision component - that is ok, light reaching sensor is physical thing and as any thing in nature that we measure - we should exclude our subjective sense of it. This is where things go south ... In introduction we are talking about measurement and we are excluding notion of human vision and such, and yet tool itself does - what they describe as white balance and most of document is about choosing reference white balance value. Here is the thing - white balance is directly tied to human vision and perception. Absolute color spaces like CieXYZ does not have a white balance. It does not need white balance. White balance is used to define how color of particular object would be perceived by observer under certain illuminant. Our brain is funny thing. In an environment where we don't have pure white color - we choose closest color and that becomes white balance reference for our brain. All other colors in that scene are perceived "shifted" in hue to match that white point. Our brain does a bit of color balancing - although we have same spectrum - we perceive color as being different. Astronomical images don't need white balancing in this sense - this is typical sense of daytime photography - we do white balance to adjust colors and convert our perception from environment that image was taken in to environment that image is viewed in. This is why we have different presets in cameras - like sunny, cloudy, incandescent light, fluorescent light, etc ... to tell the "camera" what was illumination like and then camera will convert that to "standard" viewing conditions. In astronomy we don't have illuminant - we have sources of light and those don't depend on if it is sunny or cloudy day or we are using artificial illumination. No white balance is necessary or wanted. What we want to do in order to produce what we colloquially call color balanced image is color space transformation. From raw tristimulus values produced by our camera sensor - to some standard color space tristimulus values. One can either choose to perform conversion to CieXYZ or to sRGB Linear - as there is well known linear transform matrix between the two. For final color that is displayed on our computer screens we need to do sRGB standard gamma correction - and voila, we will get true color, or rather - we will see on our computer screen closest representation of that particular color. If we don't want to go as far as display - we can stop at CieXYZ value - that describes color well enough and is standardized, or we can choose to represent color in some other "color space" like BVR from UBVRI where we would use BVR filter response as matching functions instead of XYZ matching functions of CieXYZ color space). What we should not do - is take tristimulus value that we have - arbitrary assign that to RGB and then wonder why such RGB triplet is green when displayed on the screen. Back to the actual color of that thing: We have R_raw, G_raw and B_raw to be (1, 1.06, 1.03) and this is our starting point - we have camera, I suppose it is Starlight Xpress Trius SX-814, and we have Astrodon RGB filters that produced these values?

Do you have any idea of what "units" PCC is in? Or rather what color space it is in? I wonder how almost equal values in red green and blue (green being only 7% higher and red and blue equal) can suddenly change to red being 33% less than both G and B?

Difference between doublet and triplet scopes can be due to F/ratio of the beam - it too can have an effect as well as distance and type of the filter. Btw, this is something I suspected for a long time now, and often advised people with this issue to change the distance if they can to see if it will lessen the effect. I even argued with some people who maintained that this effect is independent of the filter and is product of cover window and micro lens and as such - always present. Valuable work on your part that shows that one can still impact effect to some degree.

In principle it is not, however good NB filter will cut LP at a rate of about x50-100 - for example 3nm NB filter will eliminate 99% of LP from 300nm range (400-700nm is full spectrum). x100 less light is 5 magnitudes. Natural sky brightness is about mag22, so yes, good NB filters make difference as moving from bright city center to best skies available - from mag17-18 to mag22 (4-5mag difference, or about x50-100 less light). Moving from mag19 skies to mag21 skies is only 2 mag difference and that is about 6-7 less LP light - effect of UHC filter maybe?

If you are using lens - then just ignore my comment above Just realized that you might be using regular lens with camera - not sure about that and dew shield - could be that it is vignetting because of that

Could be due to EF-M / C adapter, but it is almost certainly not due to dew shield / LP shield. Field of view is at most a degree or two wide here and there is no chance that this amount of vignetting is due to 1 degree light cone being clipped on side. Odds are that dew shield is larger than ota diameter and lens/mirror is certainly less than ota diameter - so even that one degree is questionable. Here is diagram of what is happening: Let's assume that mirror is exactly the same diameter as dew shield: If a star is one degree of axis, then parallel rays coming down at aperture will create very small shadow on primary - marked with arrow - rest of the mirror will receive light. At most, only very small fraction of the mirror - less than 1% will be in shadow. You should not be able to detect that in the image, or it would be very very small effect. Usually mirror is not the same diameter but smaller a bit - just enough to still be fully illuminated. You are free to use dew shield - LP shield. If you are using newtonian scope - it will improve contrast even if there is no street lights around - It is often said that extension in front of focuser should be at least x1.5 diameter of tube, and today's scopes often have very small section of tube in front of focuser. Marked section of scope needs to be at least 1.5 x 130mm = about 200mm or 20cm and it is clearly not that much so yes, dew shield is a good thing to add contrast with newtonian. Refractors have focuser on the other side of the tube so they provide very good contrast by design, especially if they have tube baffles as many do.