Zermelo

Hi Mat, I think you realize by now that your “question” was really several questions in one, which have been teased apart by previous answers. But to summarize: - sensible to choose between visual and imaging (and you have prioritized visual for now) - tracking and goto are separate beasts (and you seem minded to forego both for now) - wifi is just a variant on goto mounts, some use a handset instead - imaging (especially long exposures for DSOs) really needs a good equatorial mount, not an alt-azimuth, though the latter can sometimes be adapted with a “wedge” - a tracking motor can sometimes be added afterwards to the RA axis of a manual equatorial mount - the sky darkness at your location (or your most likely viewing location) may affect choice – because more light pollution > harder star hopping > more benefit from using goto Some further thoughts from me (though bear in mind I have much less experience than some of the other contributors above, check out our respective ratings) : It sounds obvious, but think very carefully about how you are likely to use your scope. If I had been using mine on my own, I might well have opted for the largest dob I could afford, and been content with nudging. But I have a partner who wants to share the hobby, and I also do some outreach work with schools, so a tracking capability made a lot of sense. I can see less, but I can find more, and I can share it with more people. Only you can decide how much you will value the actual finding of astronomical objects. For some people, the thrill of the chase is as exciting as finally looking at the target, and so for them, goto may be beyond the pale. For others, life is too short. They want to spend their time observing the objects. There is nothing "wrong" with either view. Do remember, though, that even with goto, you will still need some basic sky sense. The tech doesn’t work every time, and even when it does, the identity of the object of interest may not be immediately obvious in your low power eyepiece. You’ll still need to be able to compare the view with a chart, know which way is East, etc. There’s no substitute for that. If you do decide to go with a goto scope, don’t be tempted to think of it as a substitute for finding your way around the sky, i.e. recognizing the main constellations, their relative positions, the way they move through the night and change through the year, getting used to the angular distances in the sky. I came late to practical astronomy after a lifetime of reading about it and was amazed how little I knew about how the sky actually worked. If you think there’s a risk of that, consider holding off for a while, get some binoculars and spend some time just watching the changes. Another point is that a good knowledge of the sky will help when performing alignment of the goto mount (because you need to find some known stars to fix on). Some comments were made about the difficulty of use of goto tech vs a manual setup. There is something to this, based on my experience with a Skywatcher wifi mount. I felt the instructions were not as clear as they could have been, and it took me a while to get used to the app and sort out issues like maintaining dark adaptation, though I have now sorted everything out. I can see that there might be sufficient hurdles to put off some newcomers. Comments were also made above about the noise of goto mounts. I share the concern, and generally there’s no way to avoid a goto operation running at the mount’s maximum (and hence noisiest) slew speed. But with the SW mounts at least, the dual encoding capability (if you choose to use it) allows you to manually position the scope close to the prospective target, then use the goto for the remaining part. I’ve been doing this successfully and it’s much quieter. Good luck with whatever you end up with.

barlows ... yes, it's generally true that the more glass you put in the path of the light, and the more surfaces it has to navigate, then the more likely it is to degrade the image. A cheap barlow will almost certainly do that to some degree. Counter-intuitively though, a decent barlow combined with an average eyepiece *may* perform better than a single eyepiece with their equivalent focal length. This is because the barlow has optical characteristics that are "opposite" to those in eyepieces, so they can have the effect of reducing some of the aberrations present in the EPs.

Hi, I'm not sure from the thread above if you've quite given up on your original Orion Starseeker, but it seems to be almost identical to this model available in Europe (Synta make for both Orion and SW), though the Orion tube is described as steel, whereas the SW 150i is ABS. The Starseeker is also available in the wifi version like the 150i, if you are happy to work with a phone app rather than a dedicated controller, and will save you a few dollars. I have the 150i so I can comment on some of the points mentioned above, and I think they apply equally to the Orion. The tube is within the capacity range of the mount. The Orion appears to be slightly heavier than the SW, but I've not had any issues, and combined with the steel tripod I've found it to be very stable. The short F/5 tube is also important here - a longer one, even of the same weight, would not be so stable (though there are several reports of people pushing the Star Discovery mount beyond its rated capacity). Yes, the main mirror is fixed. I was initially concerned by this, but apparently this is not a particularly recent feature and does not seem to be causing issues. Note that the secondary mirror can still be adjusted if necessary. I have not needed to do so as yet. Yes, it is generally true that faster scopes will be less forgiving on cheaper eyepieces. But I was surprised how usable some of my stock EPs were with my SW, so if you do go with the Orion I would try them out first before splashing out, and even then don't assume you need to spend a fortune. The weakest point on the 150 is the focuser, and it looks like the Orion has the same one. With some EPs I find it can be difficult to focus precisely, as the "in focus" range is very small and the rack is tight.

You can create acetate rings to overlay onto your printed atlas as described above, or here's an alternative I use. I downloaded Michael Vlasov's Sky Atlas and I'm selectively printing off and laminating the pages I need as I go. I use dry wipe markers to temporarily highlight objects in the evening's observing plan, which might just be an arrow if it's an obvious target, but could be a simulated finder or telrad circle, drawn by putting the marker into one of those old fashioned compasses with a "claw" grip. I worked out that (on my printer at any rate) my 7 degree finderscope corresponds to a 6.1cm diameter circle, and then a standard telrad set would require 4 degrees at 3.5cm, 2 degrees at 1.75cm and 0.5 degree at 0.44cm, though the last would be quite fiddly to draw with compasses, as would any circle corresponding to any eyepiece except those with the widest TFOV.

The potential upgrade to the 200P would be the deal breaker, as that would rule out the AZ GTi and similar specs, but then your budget would be stretched too. On the other hand if you're going to concentrate on the 130P, then with my limited experience so far I would agree with those saying that the AZ GTi's dual encoding for the axes ("Freedom Find" in SW jargon) is a great feature allowing you to mix and match star hopping and goto, even in the same session. I didn't actually go with the AZ GTi, I bought the Star Discovery mount as part of a package with the 150i, it has the same wifi and dual encoding but is a bit chunkier and came with the steel tripod rather than the pressed aluminium model. It took me a while to learn the app, but now it's simple to do a 2-star alignment. As I'm usually out in the early hours at the moment, and concious about noise, I'll often either find targets manually if I can, or else slip the clutches and use the scope in "semi push-to" mode to position roughly and then use goto for the final part. So far, I've never had the mount give me any issue with pointing accuracy (i.e. targets have always been within the field of a 21mm EP, however much manual slewing I've been doing). I've replaced the small red dot finder with a 6x30 finder and strapped a Telrad at the other end, so that it's still balanced. The Star Discovery has a 5kg limit which should be OK for the 130P, but certainly not for the 200P.

Another vote for the Plus version of SkySafari. The free version is also fine, but I've been very impressed with how well SkySafari integrates with the SynScan app to extend wifi scope GoTo control into SkySafari. I can drive my whole observing session from my planned list, selecting each object in turn. SkySafari also gets position information back from Synscan and updates its chart with the scope direction in real time, it's beautifully put together. And you can seamlessly sync your observation notes to a free LiveSky account in the cloud. You need the Plus version for the scope integration but well worth it in my opinion. I'm on Android btw, I think I read there was some issue on iPhone that needed resolving.

I see there are already accounts within these pages of several, very accomplished power tank projects, hence the title of this piece. The other reason that this was a ‘modest’ project is the intended purpose: servicing a SkyWatcher Star Discovery 150i – an EQ6 it is not. But I thought it might be worth documenting in case anyone else was in a similar position. Context We have recently upgraded from an entirely manual first scope to the 150i, which has tracking, goto and wifi control. The default power option is an internal 8xAA battery pack delivering 12V. Unwilling to keep buying alkalines, I’ve resorted to NiMHs, but these give only around a total 10.4V fully charged, and that’s on warmish summer evenings. Opinion suggests that the mount’s goto accuracy can be impaired if the voltage drops, so I wanted to get off the internal batteries. As an alternative, the Star Discovery mount has a 12V power input socket, and I had already bought a cable with the standard car cigarette lighter plug at the other end. Apart from powering the mount, the other requirements are currently uncertain, but possibly include an electric dew heater or 12V hair dryer for the same purpose, which I assume will probably connect to a cigarette lighter socket. Also, given that the scope control relies on a phone app rather than a handset, a USB charger outlet would be useful for emergencies (and other gadgets might well also run off USB). The one thing we won’t be doing is running a laptop all night, which is what seems to really burn the juice. Choices So we needed, at minimum, a 12V power source with a cigarette lighter socket, and ideally a second socket and one or two USBs. The offerings from astronomical suppliers seemed expensive, and often included gadgets we didn’t need. Standard car batteries were on the heavy side, and would need adapting and connecting. Car jump starters were a bit cheaper than astro kit, but were optimized for short, heavy loads. So I decided to have a go at making a bespoke power pack, where I could choose the physical size, capacity and outlets. The basis would be a smallish sealed lead-acid battery. I settled on 9AH as a reasonable compromise between weight, cost and capacity, but the design allows this to be doubled if necessary. I considered buying a ‘deep cycle’ battery more suited to the observing usage pattern, but decided on a cheaper, standard model for alarms, UPSs, etc. Time will tell if this was false economy. For the casing, I used a 5 litre plastic crate from the Really Useful Box range. I chose these because (a) they are quite robust as boxes go, and (b) they are more nearly rectangular than most. The 5 litre box comes in two versions – I bought the ‘XL’, the only difference being a taller lid. The battery will live at one end of the box, but there will be a similar space at the other end for another if needed. For sourcing the electrical outlets, I found a number of sellers on eBay and Amazon that offer essentially the same range of instrument panels that run off a 12V supply, for installing in cars/motorbikes/boats, at reasonable prices. In particular, I found that a 2-by-2 panel of these instruments just about fitted onto the side of the plastic crate. I ordered one of these sets that included a cigarette lighter socket, twin USB charger, LED voltmeter and on-off switch, though I ordered a separate, second lighter socket to substitute for the switch. All of these sockets and instruments seem to be standard sizes and can be swapped in and out of the panels. The sockets also come in weatherproof versions that have integral rubber plugs, which is ideal. I thought the voltmeter might be useful to show how the battery was dealing with the load (an ammeter would also be useful, but I haven’t seen one that would fit this panel). Usual caveats apply to ordering online, there’s a lot of variation in vendor reliability. And a caution about the voltmeters – red now seems to be the hardest colour to find, most seem to be bright blue (not ideal). Build I chose the particular plastic box because the battery fitted lengthways across it quite nicely, but I knew I’d need to do something to stop it slipping sideways when being carried. My first thought had been to glue in some stout plastic sheeting to create internal compartments, but these boxes are polypropylene, so good luck trying to get anything to stick that. Instead, I decided to create a separate internal frame that would slip inside the box and wouldn’t need to be glued to it. This would create compartments for the batterie(s) and also stiffen the sides where the outlets would go. I had a piece of 6mm ply that was about right – thick enough to do the job, but it still fitted around the battery. I cut out four pieces to create the frame, all of which are 10cm deep (I would have reduced this a bit if I had not been using the 'XL' version of the plastic box, as there's less head room). As the box isn’t quite a cuboid, the longer ones are actually trapezia (or trapezoids if you’re reading this from the US) measuring 28.5cm and 29.5cm on the shorter and longer lengths. The shorter cross-pieces are 15.2cm long. The other pieces are softwood I cut up to brace the joints; there’s no way 6mm ply is going to be joined at right angles without some help. At this point, I used the instrument panel facia to mark out the position of the socket and screw holes on the long side of the plastic box, and cut them out: I then used the holes to mark the positions onto one of the long frame pieces and cut those out. With hindsight I think it might have been better to cut the frame holes, assemble it and then mark and cut the plastic box. I did find it quite fiddly – you need to be careful with the frame, because the outlet holes have to be big enough for the sockets, but if you make them too big there won’t be enough for the securing nut to purchase on later. The holes in the box aren’t so critical because nothing depends on them and they get covered by the facia. Also, assembling the frame inevitably shifts the positions of the holes slightly, causing them not to line up any more. Anyway, in the order I did it, the pieces were assembled in stages, measuring up to ensure there was enough space in the end compartments for the batteries. The softwood pieces form the corners for the ply, so you need just one good 90 degree corner on each one. I used PVA, panel pins and some very small screws (pilot holes to avoid splitting). A picture frame clamp proved useful to keep corners square. When the clamps were removed, the frame was checked for fit inside the box and I gave it a couple of coats of paint. It won’t win any beauty competitions, but it won’t be seen. The four devices can now all be inserted, passing through the facia, the plastic box, and the frame, and secured from the other side with the large plastic nuts (careful not to cross-thread). I added some rubber O rings of the right size that I had, so that the nuts didn’t take the paint off; large neoprene washers would be even better. These devices will hold the panel securely as it is, but the four screws that are supplied for the facia are worth fitting (and also for aesthetic reasons). Right sized pilot holes required so as not to distress the ply. I found the screws to be too long by about 6mm, so cut off about 3mm and then as I screwed them in I held a small rubber grommet against the inside of the frame to receive the tip and brace it still further (a small fibre tap washer would work well) but actually it bit surprisingly well into the ply. All four of the devices in the panel need 12 volts, so they need wiring in parallel, both positive and negative, which needed some thought. One option would have been terminal block strip, but I wanted to use fairly chunky cable as I wasn’t sure how much current might be drawn in future, and that didn’t lend itself well. Instead I created a couple of multiway connections using ring terminals connected by small nuts and bolts – I used locking nuts and spring washers to keep the joints tight – these were all bits I had lying around. The instrument panel kit came with spade connectors and insulators. The result is quite compact. An in-line fuse holder is a must – I managed to short out the battery terminals fairly quickly. At the moment I have a 2A fuse fitted (I put a multimeter on the 150i mount and measured the current at about 0.6A on maximum slewing speed) but I’ll review that according to future use. With the cabling attached, the box looks like this: For now, the other battery compartment is empty, but I used “piggy back” terminal connectors on the battery leads so I would need only to run two wires across the top of the box to add a second battery in parallel. And here it is all working: The lid overhangs a bit, so provides some extra rain protection for the panel. It cost about £40 altogether, half of which was for the battery.

Andrew, the link to your primer article now seems to be dead?

Hi ScouseSpaceCadet , if you have time could you identify the kit you've added here? And do you have any idea how much weight it added?

Hi, you may be interested in a thread I kicked off recently, as I was in a similar position and ended up buying the 150i: https://stargazerslounge.com/topic/356514-advice-please-choice-of-next-scope/ You can still adjust the secondary on the 150i. As it happens, when I did get hold of the scope it was slightly off collimation, but close enough not to need tinkering with the secondary, see: https://stargazerslounge.com/topic/357345-how-far-off-collimation-is-this/ As others have said, the mirror itself is the same, decent-quality parabolic that SW use in their more rexpensive models. And as you have identified yourself, if the primary doesn't actually need adjusting, then that's certainly a plus in my book. The 150 is a clever compromise to be sure; the mirror and the tripod are more than you might expect, while the focuser is probably the weakest feature; but for the price I paid, I'm happy so far. Be aware that instructions for the GoTo are a bit confusing, as those supplied are for the non-wifi version of the mount. There are many threads in these forums that are helpful with the various alignment procedures.

Update. I managed to get a test on Arcturus last night at just over 200x with my shortest EP + barlow. Unfortunately my phone camera refused at those light levels so I'll have to describe the view. When defocused, I saw approx. 6 concentric rings, inner ones dimmer and outer ones brighter. It was shimmering about a bit, but I wasn't surprised at that magnification. At any particular instant there was some random distortion in one direction or other, so I looked over a period of time at (i) the "average" shape of the rings and (ii) their "average" distribution relative to the centre. As far as I could tell, (i) they were circular, and (ii) showed no directional preference. I take this to be good news. As a more real-life test, I included the Lyra double double in the observing schedule later on. I thought it might be a good test of the mirror and alignment, as each pair would be on opposite sides of the FOV, when blown up enough to split them. (I've attempted the double double before with a small refractor, but never succeeded). Impressive. Both pairs split as perfect dots, no tails, orientations at right angles to each other. Based on these tests, I'm not going to bother adjusting the secondary. I'll just check it now and again against my original photo.

OK, I was a bit prematurely worried then. I'll try to do a star test tonight, and depending on the result (and how brave I'm feeling) I'll give it a tweak.

Thanks John, but is that a secondary adjustment, or primary (which I can't do on this scope - at least, not unless I try to emulate the factory process)?

150mm F/5 Newt, as received new, view down eyecap collimator (no adjustments attempted by me): I've read a couple of intro guides, so I'm led to believe that the off centre image of the secondary in the primary is normal for a fast reflector. The whole image of the primary in the secondary seems to be reasonably central too. My concern is obviously that the black dot from the collimation cap is not within the "doughnut" centre marking from the primary. I've tried here to superimpose a circle with centre lines, but I'm not sure if I've got the circle itself correctly positioned (I'm not sure what I should be lining it up against): Now, the interesting thing is that it's one of those jobbies with a sealed, non-collimatable primary. But I believe the secondary has all the usual degrees of movement. Does it look likely to be far out? I can try a star test tonight (first time for that too).

Thanks all, for the replies. The "saddle" I have is actually integral to the mount, it's one of these: https://www.firstlightoptics.com/skywatcher-mounts/sky-watcher-star-discovery-wifi-az-goto-mount-tripod.html so I don't think there's a way to replace it with a third party version. dobblob, the bar/puck attached to the OTA has no overhang or holes, it has an identical section along the entire length (hence my concern about its ability to slip unhindered through the mount). But your point is valid: I could probably drill and tap a single hole at the eyepiece end of the bar, insert a machine screw, and that would catch the OTA against the saddle if it did slip. It might still shake up the optics a bit though! (but the closer I placed it to the saddle clamping screw, the less it would fall).

I have a new scope on a Skywatcher mount with a Vixen dovetail type mount. The scope is a lightweight F/5 150mm Newt. The mount has a single screw that braces the inserted OTA 'wedge' against the opposite side of the dovetail recess. There is no other mechanism to prevent the inserted wedge slipping, so it's basically relying on friction (and on a single, unlocked screw) when the scope is vertical. The first time I used it, I had tightened up the screw as tightly as I dared, but half way through the session I felt the scope slip slightly when pointed upwards, and managed to catch it, but only just! I'm not very happy with this design. My previous refractor had a similar dovetail arrangement, but it had a slightly recessed area to receive the screw, which meant it was more secured against slipping out. I'm thinking of doing something similar with the new scope - countersinking a *very* shallow hole in the centre of the OTA wedge to give the screw something to bite into. An alternative (or additional) ploy might be to line the inside of the mount dovetail recess with some variety of thin, rubbery self-adhesive strip that would grip the OTA wedge more firmly than the existing, smooth metal-against-smooth metal. Is there any reason I shouldn't perform this mod? (other than voiding any warranty, obviously). Clearly I'd be establishing a "preferred" position for the OTA in the mount, so if I needed to rebalance it in future, for whatever reason, then I'd need to repeat the procedure (the OTA has no rings, the wedge is attached directly to the tube).

After another round of agonizing, I've ordered the Star Discovery 150i from FLO. (and also a Hyperflex 7.2-21.5mm zoom, which seems to be well thought of in these parts) Thanks again to everyone who chipped in to the discussion, and I apologize in advance for the obligatory spell of cloudy weather that will hit the south western UK in "approximately 10-15 working days time".

Also remember there are two "ends" to the problem. You want to try to cut out as much of the light that shouldn't be there, but you also want to let through as much as possible of the light that should be there. The characteristics of the first of those is fixed, depending on the pollutants in your environment (and as others have said, LEDs are difficult) but the second is variable according to your current target in view. You can only ever cut out light with a filter (from the target object and the pollutant), but the aim is to selectively remove the right wavelengths so as to improve the contrast between target and background, even though the image as a whole is dimmed. For nebulae in particular, a filter that does this trick best for one object may not be the best filter for a different object, because the spectra differ. People have spent a lot of time comparing lists of objects with different filters and made recommendations, e.g. https://www.prairieastronomyclub.org/filter-performance-comparisons-for-some-common-nebulae/

OK ScouseSpaceCadet, I suppose that's no great surprise at that price, and that link is useful - I'm sure I can tackle that. I've also read that thin PTFE plumbers' tape (which I already have) can help with excessive play. Thinking cap on again.

Good point Shaun, I keep forgetting about exit pupil.

"... a member changed the focuser to a GSO low profile one" happy-kat, do you have a link to this please, I couldn't find it.

Yes, I admit I'm wandering all over the place, Geoff! But I half expected my thoughts to be upended. It's all grist to the mill.

ScouseSpaceCadet, "The focuser is pants" - as in, not as good as on the 150P / 150PL? collimation cap - so, no need for a cheshire, even though this is an F/5? Because we only need to check the flat?

The more I look at it, the more I like the Sky-Watcher Star Discovery 150i as a lower cost interim choice. If you can look past the ABS shell and lack of collimation (or conversely, if you believe that it won't require any, then it actually becomes a bonus) then it has an awful lot going for it. And at that price, we'd still have a chunk left over for some EPs and a power tank. Use it for two or three years, and then we'd be in a better position to decide whether we want to spend our serious money staying on the visual route (perhaps move to an 8" by then) or else into imaging. And even then, the 150i would still be a nice, compact, easy to use alternative to keep around for the right occasion.

"£600 could be tricky as you stipulated GOTO as a requirement" yes, it could be, jonathan, but we can go a bit extra if we need to. I'll have a hunt for the CG-4, thanks for that steer. I agree fully with your last point, and I have been putting in some hours with my existing, (very) manual scope, so I although I class myself as a newcomer, I won't be completely at the mercy of the tech 😂