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Its not the best - but it is certainly one of the best to start with. Refractor telescopes like ED line from Skywatcher, ED80 in particular, are often recommended as the best starting scopes. This is mostly done because of newtonian collimation. This tends to be a bit scary topic for people just starting out in the hobby. varius21 already has 8" dob so I guess collimation is not something strange / scary at this point. Also, 130p was mentioned in initial post so I just naturally proposed proper imaging version of 130 newtonian. Besides collimation, ED80 has another strong point going for it - and that is dedicated field flattener that is pretty much "plug and play". When starting out with new kit, it is often case of finding exact distance (not only for novice astrophotographers) between correctors and camera. Often, if usual clamping is used (screws / compression rings) there is a risk of having tilt in optical train. This is really not important for visual and that is why this type of connection is common for eyepieces, but it can cause issues for astrophotography. It is better to have threaded connection and dedicated flattener for ED80 threads on the end of focuser tube (as far as I know) and also into camera adapter. 130PDS is very nice little scope. It is fast but not too fast at F/5. It works nicely with SkyWatcher coma corrector (it is designed for their PDS F/5 line of imaging scopes) but it also has some quirks. Collimation is certainly one. Another is that some people have issue with focuser tube protruding into optical path creating issues with stars (this depends on what camera is used with the scope). It is of course the cheapest AP option that produces very good results and it is small and light weight (in comparison to other newtonians in the line) and not much of a sail in the wind (refractors are better in this regard). It also has perfect color correction - no chromatic aberration. ED80, while having very good color correction is still ED doublet. If your camera is sensitive in far ends of spectrum you'll get some halos around bright stars. Here is example of M45 imaged with ED80: When zoomed in to 100%, you can clearly see some stars having bluish (and some red) halo. This is due chromatic aberration. It is really matter of personal preference between the two scopes - some people like spikes on stars in their images (go for 130PDS) and some don't (go for ED80)

There really is no way around it. AP is expensive. Much more then visual astronomy. If you already have DSLR type camera - that is a bonus, otherwise, you'll have to budget for that as well. Cheapest option is of course EQ5 + single tracking motor + 130PDS. You will most likely need to crop quite a bit of frame since you won't be using coma corrector, but together that should cost you something like £520. That is bare minimum which includes T2 adapter, EQ5 mount, single tracking motor (RA axis only) and 130PDS. That will let you make some images. In reality, if you want to make decent images, you are looking at following list (again, include camera if you don't have one already): EQ5 Goto mount 130PDS Coma Corrector T2 adapter / any extensions needed for proper distance Finder scope + T2 adapter for it, or dedicated guide scope Guide camera Cables Laptop (needed for guiding and imaging software). So yes, only astro bits will cost you more than £1000 There are cheaper setups, but are limited to particular type of photography. You can get for example star tracker and small scope + flattener, or telephoto type lens and that will cost you less than above, but you'll be limited to mostly wide field imaging.

No - it is Alt-Az mount and these are no good for astrophotography. In principle, it will track, but since it does not track in the same way earth rotates (it is not polar aligned) - it creates field rotation. This limits your exposure time considerably and stars don't look nice in the corners regardless of the type of scope you are using. Similar scope is quite decent for astro photography: https://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p-ds-ota.html It is version of above telescope, optimized for astro photography use. With that you'll need a tracking equatorial mount - something in EQ5 class.

How is that even a choice?

But of course we do Do we use denoising and sharpening? Those are "morphological" transform, in essence similar to healer brush on pixel level. Do we use local contrast enhancement? Again that is "morphological" transform. It can sometimes even lead to order inversion. Pixels that are higher in signal then other pixels end up being darker than those other pixels. This is partial "negative" on the image. Here is often seen example: but reality is more like this: How is that different then emphasized cheekbones

Depends what you want to show really. It takes more skill and attention to detail to show object as it really looks, but it is certainly possible. Most of the time - it is not what people want to see. You can also capture true color - as eye would see it, most of the time. In fact - you can capture it all of the time - issue is with our displays. They can't display all the colors human eye can see. For this reason we have what is called gamut of display - range of colors it is capable of reproducing. No display can properly show spectral colors for example. You can't faithfully show rainbow colors - they will always be less saturated and lacking "the punch" of real rainbow colors (which are just pure spectral colors). Important thing to understand is the fact that objects we image have such a huge dynamic range, often not supported by eyes. For that reason we need to "compress" into image - dynamic range our eye can easily see at the same time (our eyes are in fact capable of seeing extraordinary dynamic range - but not at the same time - we function perfectly in broad daylight under direct sunlight, but also in the dark under moon light - that is vastly different level of light - but think what happens when someone turns on headlights in the night - you instantly stop seeing properly in darkness). For that reason, images are often stretched in non linear fashion - to show faint detail together with bright detail. Take this example: This is the same image of M31, however left right side is the image as it would appear to our eyes in dark skies - left is how this image is usually presented to people - just because otherwise we would miss bunch of detail present in the image. As for color, well - you can choose what color you want to present, and all it takes is a bit attention to detail. You can choose 3 different "natural" color looks of the object: 1. Color of the object as viewed from Earth. This one is the easiest to achieve - but it is not "proper" color of the object. Atmosphere of the earth changes color of object - depending on altitude of object. Moon looks yellow, while it is actually grey. Similarly Sun appears yellow - but it is white. It appears orange or even red - at sunrise / sunset - because of more atmosphere light goes thru. Atmosphere scatters blue light and removes it from color of object - lower object is - more blue light is removed. 2. Object as viewed from orbit around the Sun - one just needs to remove influence of atmosphere and will get this type of color. This is still not proper color of object. There could be interstellar dust between us and object and that can cause reddening of the image. 3. Object as viewed from orbit around the object itself - and nothing in between causing issues - this would be proper color of object. It can be obtained by removing any interstellar reddening. As for getting the first step - there is something called color calibration and can be easily performed. Take calibrated display (say your mobile phone) - and shoot image of it with your telescope / camera while displaying color calibration chart. Derive color transform matrix from that. That is what is done for DSLR cameras in factory and you end up with different color balance presets. We don't need to change color balance as objects in outer space can't be illuminated with different light - we just need regular color transform matrix and you'll have "proper" color. In the end, I would say - I advocate "documentary" approach to imaging and don't really like overly processed images.

Imagine you want to split scope use between visual and astrophotography and express that split in percents. If those two are equally important to you, you would assign 50% to each. Just imagine any numbers that come to mind. If astrophotography has more than 5% - get EQ5 mount. I know that people say that you can image with EQ3 but just because something can be done (by few people) - does not mean you want to do it on regular basis. Even for purely visual - EQ5 mount is better choice for 150P/PDS type scope. If you decided on EQ5 because of AP being more than 5% - then get 150PDS. I think that you will be able to reach focus with DSLR and regular 150P, however 150PDS is astrophotography oriented version for a reason. It is not just position of the focus plane, it is also - dual speed focuser. At F/5 ability to focus precisely is important. Quality of focuser is also important - you don't want wobbly focuser where camera will tilt under its own weight and will change tilt depending where the scope is pointing (gravity always points down regardless of the pointing of the tube). Do keep in mind that EQ5 deluxe version is manual tracking mount and you want to add tracking motor to it, so that is not the final cost of the mount for imaging. You'll also want to add coma corrector at some point - factor that into account. In any case - I think your choice is very good one - probably one of few telescopes that will do it all - enable both visual and AP, for both planets and deep sky objects, but do seriously consider bigger mount.

Or combination. I need to test out another option for EEVA that will be hybrid approach of these two and could possibly allow for real time observing without stacking (or combination there of - switch stack on/off). Optically it would be the same as NV device but in operation it would be same as EAA approach. Take a scope, put an eyepiece in it. Take a camera and put a lens on it. Now stick two together Main issue with cheap astro cameras is small sensor and if you do prime focus EAA - you have relatively small FOV. This also means that for the most part you have rather high sampling rate - which dilutes light over many pixels. If properly matched, above approach can create wide field with low sampling rate - lot's of light per pixel. Say you take 4" F/5 refractor (If you want apo performance - use 4" F/7 doublet and reducer / flattener). Stick 32mm plossl in it. This will give you something like 3.33° of FOV translated into 50° AFOV. Take ASI224 and 6mm C/CS-mount lens. At this crop factor 1/3" sensor gives 53° on diagonal with 6mm lens. It will capture whole field of 50-52° plossl. Such a fast system will have a bit of field stop so you can actually use something slower. Exit pupil will be around 6mm, but most 6mm lenses are as fast as F/1.2 so only 4mm entrance pupil. I don't think one could easily get F/1 6mm lens - so this needs to be taken into consideration when putting together a setup. Another option is to use slightly larger sensor - for example ASI178 which needs 12mm lens to image 50° FOV. 12mm lens will be able to get whole 6mm exit pupil even at F/2.

Hi and welcome to SGL.

I'm sure they will - but I was just making a point that whole system can be packaged into eyepiece sized device. Don't really follow how intensifier can perform better when both devices operate on the same input. No device can produce more light than there already is. In fact - intensifiers don't do longer exposures, right? I mean standard ones - based on photo multipliers. That is why there is so much photon noise in intensified image as each photon is represented as a small flash of light. Would we loose anything by doing 30ms exposure? I guess in wartime conditions - yes, you want the best interaction with environment as possible - but for astronomy? I don't think most people would mind even 100-200ms exposures, it would still be considered real time.

But is it really? Have you seen this device: https://www.omegon.eu/digital-night-vision-device/omegon-alpheon-nv-5x40-night-vision-device/p,47286#tab_bar_0_select Here is a quote from description: and resolution is quoted to be 640x480 ... Best night vision device is not one with photo multiplying tube - but rather just the above - good sensor with high QE over the whole spectrum and into IR. High density display with high contrast ratio and clever software in between. I would not be surprised that 3/4 gen devices use the same approach. I read once that there is bloom suppression in one such device - and I can't help notice that is easily done in software. In the end - it is just how one optimizes the size and everything is already small enough to pack into eyepiece sized package, but it is still - sensor and display and computer and some optics to make it work nicely together.

Sure you can. Even if you don't center it properly - it won't change operation of the mask - only intensity of each spike (but not angles).

Maybe try to asses "speed" at which gradient is progressing. If it is at sidereal rate (exposure length x 15" = progression) then it could be due to tracking. If it does not look like cloud then it is probably some sort of light shining down the tube (or in case of newtonian can sometimes be from other side if mirror is exposed for ventilation - but you don't have any spikes in the image so I guess not newtonian). It could be reflection of something rather than direct light - maybe piece of rain gutter reflecting street lamp or something? What is your environment like? There is easy way to figure out if it is the light or shadow. Light will raise background values but leave stars the same intensity - shadow will block both background and stars. One is additive (adds light), other is multiplicative (only percent of light reached). Measure intensity of the same star over range of images to see what is going on (if you are really interested in that sort of thing ).

Good thing about stepper motors is that you can actually count the steps - you don't need encoders to do that. With servo motors, I think you have shaft encoders that help drivers put servo in proper position - and I believe those can be used for counting purposes as well. HEQ5 for example - has no encoders but it "knows" where it is pointing - at least when you align it properly and start off from home position. If you want to move scope manually - you loose pointing information. AzGTI on the other hand has freedom find - which is exactly opposite - as it has (low precision) absolute encoders - you can turn the scope and it can figure out where it is pointing. It would be interesting exercise to calculate how much tracking error there would be if you had very loose pointing information. I was thinking of getting myself SkyTee 2 mount. It uses same worm gears as EQ5 so steppers are easily added. I just want point and track feature with a simple controller, but I don't want to have database of objects and have the need to select them. What I figured is this: - I create simple manual setting circles with 1-2° precision in both alt and az - I point the scope where I want and then read off two numbers - az 0-360 and alt 0-90 and enter those in hand controller and hit go - it will start tracking. I wonder how good the tracking will be if there is uncertainty of 1-2° in initial position? Additionally - I would want correction feature - so I let the mount track and I have up/down/left/right commands. So after a while - my target is drifted a bit and I recenter it and hit "sync" - and firmware figures out from initial position and tracking and correction - how to correct for everything and reduces error significantly.

Why would you update tracking rate so rarely? In each iteration - move mount where you think it should be, update its coordinates accordingly and then continue iterating. This should really be millisecond period (depending on resolution of stepper motors). I have AzGti mount and it has very nice feature - it is called point and track. It does not need alignment in order to be able to do that. For example - you point the mount to Jupiter and you say - I pointed mount to Jupiter now and I need it to track (you select Jupiter / point and track in SynScan app). What that does is set initial coordinates as app knows where Jupiter is at the moment - it knows its alt/az so if scope is pointing at Jupiter - it must have those alt/az coordinates and it then just starts tracking. That is all it needs to know - start alt/az and it will continue for hours without making too much error (provided you have your mount level).

Just wanted to share - it is very nice / simple way to do it, but it does require a bit of specialist gear. Have planetary camera that is sensitive in NIR and all sky lens or similar? Get NIR light source, lock yourself into dark room, wait a bit and take an image: Maybe hold ruler next to your eye so you can read off scale.

Sometimes, when I tell my wife that I'm going to observe something, she asks me: "Haven't you seen that already?" On the other hand - she can "observe" TV channel on interior decoration for hours - while I think to myself - "Well, haven't you seen that one already" This just shows how people have different interests and respond differently to things that capture their interest vs something else. Interesting thing - while I was always interested in astronomy (I even had astronomy lessons back in school) and had multiple chances to participate in astronomy related activities (like visits to local planetarium and using telescope as well as later witnessing Venus transit back in 2004 - my employer at the time was also amateur astronomer and had his own observatory) it was not until I was having a walk one evening and while looking at the stars I thought: "I wonder how much telescopes cost these days?" that I even contemplated doing amateur astronomy. I was brought up believing that telescopes are very expensive devices - mostly out of the reach of common folk . I guess back in the day they were expensive indeed, but luckily things changed and here we are - quick online query showed that telescopes are much more affordable than I thought.

I'll need to do some testing for this. I remember one occasion where we put 4" vs 8" scope on galaxies in Markarian's Chain. 8" F/6 scope used 28mm 68° eyepiece giving ~ x43 and exit pupil of 4.72mm I can't remember what eyepiece F/5 4" scope used - probably 17mm plossl? But it was no contest at all Dob showed all of the galaxies and ST102 showed only 3 main ones.

That is the part that I don't understand. Why do you think that 16x50 would work better than 16x100 on any particular night?

I understand what you are saying, I'm just not sure how resolution impacts all of this. Maybe it would be best to limit magnification range to x15-x80 for example. Here aperture size and resolution won't have much impact. We are looking at extended objects of relatively uniform surface brightness. Say we have nice elliptical galaxy and we want determine which scope makes it possible to see furthest extents of it at same magnification. Take example I gave with a telescope and eyepiece and aperture mask. Same scope, same eyepiece that natively gives 7mm exit pupil - 4 different cases: - dark sky no aperture mask - dark sky 50% aperture mask (3mm exit pupil) - LP sky no aperture mask - LP sky 50% aperture mask (again 3mm exit pupil) Can we make definitive ordering on furthest extents of nebulosity seen and explain why is that?

Magnification would stay the same, won't it? Larger aperture just means more light collected - both LP light and target light. That is the part that confuses me. Larger aperture collects more of both LP and target light and their relative intensities remain the same. We know that larger telescopes simply work better, and for fixed magnification - that means larger exit pupil. That line of reasoning says that large exit pupil should make it easier to see. On the other hand people say they see easier with smaller exit pupil. So confusing.

Not sure why resolution is discussed here - atmosphere limits resolution so there will be not much difference between 16" and 20" at x200. I think that contrast is maintained across exit pupils, isn't it? Say you have brightness A for target and brightness B for sky at exit pupil of 6mm. Getting exit pupil down to 3mm will make both target and sky reduce apparent brightness for same amount - thus their ratio is maintained, isn't it? Why would then contrast increase? Only explanation is that it has something to do with "nonlinarity" of human perception. Maybe two times brighter does not look like same contrast if absolute amount of light changes. But I never heard something like that for stellar sources. Two stars having magnitude of difference in brightness between them - have the same "contrast" regardless if they are mag5 and mag6 or mag11 and mag12, right? Or to put it in another words - contrast does not change with distance. Distance determines absolute amount of light hitting our eye - further away from sources we are - less light is reaching us, it changes with square of distance. Standing next to billboard and looking at it from half a mile away - makes no difference to contrast on the image (except for atmosphere, but on a very transparent day).

If you happened to have 16x100 binoculars on that particular night do you think image would be even better? Would you be able to see more / or at least would it be easier to see what you saw? 16x50 binoculars give 3.125mm exit pupil. 16x100 binoculars give exit pupil of 6.25mm I think that main issue is that people look at things from - fixed aperture point of view. If you fix another parameter - like magnification, then it becomes obvious that best view will be provided by largest aperture on that fixed magnification. What I do have issue with is the fact that people prefer 2-4mm exit pupil in some cases and I can't figure out why is that. Possible reasons: - Contrast thing due to sky brightness. If this is the case then something highly counter intuitive would happen. Imagine you have f/5 telescope and 35mm eyepiece. This combination gives you 7mm exit pupil. If magnification is proper for object that you are viewing - it follows that using aperture mask on telescope - thus stopping it down to create narrower exit pupil - would make image better. This is the main problem that ties my head in the knot - reducing light makes image better somehow. - Angular size / contrast thing. It is known that human vision system does not equally perceive contrast on different frequencies. This would mean that magnification is responsible for better image rather than exit pupil. But then again, changing magnification would create better image on same aperture, but then, adding more aperture would again improve things?? I simply can't understand why best images are at 2-4mm exit pupil and not 7mm. Maybe that is just a myth?

That has very interesting consequence. Any scope that is above F/8 is really not optimal for deep sky observing unless it can't adopt some sort of reducer. This is of course if we assume 7mm exit pupil and 56mm eyepiece as being max (at least affordable maximum). It also limits usability of telescopes with 1.25" focuser to about F/5.7 (40mm plossl). That puts whole new twist on things, doesn't it?