discardedastro

The 12" approach sounds exactly like what I'm doing - I'm using my 200PDS as I'm already happy changing mirrors on that and I know it's sound otherwise. I bought a 10" kit off Stathis and so far haven't come even close to making a significant dent in the material quantities, so I'd order 1 size above. I ordered two blanks, with the back ground flat on one (the thinking being I would use #2 as a tool if tile tools didn't work out, though in practice I'd have wanted a plate glass tool to avoid chip damage I think). Definitely get the back ground flat, doesn't cost much and makes life easier. Stathis is the only EU provider I'm aware of (to the general public) of Borofloat so definitely the way to go for an inexpensive-but-sound piece of glass. I'd like to work my way up to a bigger piece of glass once I've done this one right - I might go for a 12" for a Dob next, but don't want to get ahead of myself. Still a long way to go on this one! The only bit from Stathis I am not planning to use is the pitch - I'm planning to get some Acculap from the states when I get to figuring. I like the sound of a less-smelly pitch alternate, given I know how bad bitumen smells. I'd start with a tile tool and see how you get on. I'd definitely get a good respirator if possible in the current climate, makes all the handling concerns go away (though working wet is very safe, more about moving stuff around and cleaning etc - with organic filters it also helps massively with the smell from epoxy et al). Disposable gloves likewise are a godsend for keeping epoxy off hands and making cleanup a whole lot easier. I'm still using an old potting tray as a base, just rested on some anti-slip rubber mats on my dining room table, and that's working OK (though a dedicated stand would undoubtedly be better - there's no clamping in place currently, though I think I could add this easily enough). The potting tray gets some plastic sheets laid into it to make cleaning easier. I use the same tray for epoxy work, again with plastic sheeting laid in. Dental ceramic I bought via Amazon, it's Dentstone KD - works well but make sure you get a few big disposable buckets and spatulas etc to work with. I'd also say that a "back massager" with some clingfilm over the head and gently held in contact with the surface of the wet pour is an excellent way to get rid of bubbles in the dentstone once it's poured. Sheets of 1mm plastic you can bend around your mirror blank are a must-have for making that process pleasant, too. I got straightforward arts and crafts casting resin for encapsulating the tool, which seems to work just fine; it dries non-tacky and is rigid. Get the best possible spray bottle you can since it'll be in near constant use. I use this one, which has a metal weight and filter on the end of the hose internally - this stops it ingesting air in use. Don't skimp here. I have a big bucket of water I use to get the bulk of the grit off after remaining grinding sessions. On measurement tools, I'll say the spherometer gives a huge degree of confidence that you're not screwing anything up, so well worth getting something sorted out for that. I managed to snag a more accurate digital indicator on eBay for £75 which I'll be using in future; the surface plate I got for £80 or so I think (it's small but 00 grade, so pretty flat). 3D printing the body of the tool looks to work fine (online services would be the way to go to get this done if you've not got a printer to hand), and I used M3/M4 bolt stock from Model Fixings (who are magnificent for odds and ends between M1 and M6, and BSF/UNC equivs). I've also added some ceramic spherical balls as "feet" for the spherometer, which helps (if nothing else, helps to stop me worrying about scratching the glass). I've got no optical bench or anything, though I have access to a small optical table at work. I've also bodged together (truly - rushed while a few gins in and split some of the wood with screws) a mirror test stand but it's a bit puny and I might upgrade that. I've got some bits from Model Fixings to fit levelling feet into it. Once I've got that and a Foucault tester sorted I'll be in good shape for testing.

Bit of a delay what with all this lockdown but I've gotten things moving again. Made a fresh tool and let it sit for a good long while to dry, and epoxy coated the back and front. I'm using 4mm thick tiles from Amazon - they've got some backing material which I've left on as getting it off was a real pain. I set them onto the epoxy on the front while it was still wet to try and take on the shape as accurately as possible. This was the tool ready for the wax pour, with epoxy good and dry. Tile pattern a bit irregular. And post-wax. Definitely should've poured with a dam, in retrospect, to try and get some cover in the edges but this'll do for now. I'll scrape the beeswax off the tiles and maybe remelt with a hot air gun but I'm liking the look of this so far. So in theory, back to grinding tomorrow, moving to 120 grit. I also took some pictures of the other tool with a stereomicroscope: I think that this shows that it's definitely feasible to clean these ceramic/glass tools for larger grits. I've had to take the microscope to work (got to use it to do my actual job at some point) but I'm still fairly frequently in the lab so I'm a little tempted to try and compare cleaning strategies, which should be applicable for this tool too.

No, visible-wavelength >1mW <=5mW is a class 3R laser, which is not eye safe by default. 3R requires special handling to maintain eye safety. In practice, both class 3R and 2 lasers won't cause any eye safety issues if diffused by a windscreen even a bit at the sorts of distances involved due to optical path loss in free space but the bright light it would create would of course distract which is normally the main issue. That doesn't stop a class 3R laser being dangerous to handle on the ground, though. For reference once your organisation goes above handling class 2 lasers you need a designated trained laser safety officer if you're operating commercially - class 3R is well into the realm of stuff that can cause permanent eye damage. Windscreens get scratched. Scratches diffuse and stop total internal reflection. Almost all aircraft windows are plastics rather than glass for weight and safety reasons, and dust and dirt will over time pit and scratch any surface. High powered laser pointers are technically legal in many jurisdictions and enjoyed by some enthusiasts and laser hobbyists but definitely aren't suitable for normal outdoor usage - they're for safely controlled use in a shielded setting and require the use of safety goggles etc.

I thought the Pi has its own polyfuse internally? I use a DC-DC converter too, vandalised a USB-C cable to just supply it on the usual connector rather than soldering on etc. For an all-sky I'd definitely be looking to use a PoE hat so I can drive it off my usual IP camera switches. For an enclosure, just planning to get a spare bit of flat plate glass from my mirrormaking stock and use that as a "lid" over a simple project box, epoxy to hold it in place on top. Glass means nice and easy to clean and simple enough to keep above dew point, and I think I could sink enough power over PoE for a dew heating circuit plus the Pi etc...

Think I'll give it a punt. Need to work out how best to power it and keep it all dry, but I have some thoughts on that front, and can test easily enough on a dry night. Just going to get the "default" lens and I can go buy a C-mount fisheye later if the exposure settings etc work. Edit: never mind, The Pi Hut are all sold out! Guess demand is high. Will watch the internet with interest. Also, I would've thought for basic use the indi_webcam driver would work for the Pi camera out of the gate - it's exposed as a v4l device.

Ooh, that's interesting. The main issue with using the old camera boards - apart from the sensor - was lack of long exposure support. I hope this has been addressed in the latest release or it'll still be no use for all-sky applications.

On the 200P, something like an ASI183MM with considerably smaller pixels will undersample (e.g. 0.5"/px on my setup) which imho is ideal for detailed imaging of galaxies, but Olly is right that actually using this requires perfect seeing and guiding which rarely happens - I guide around 0.8"/px and seeing is of course usually worse. But I find it works well for me overall.

That's a very good shout. PHD2 has been complaining about Dec rate variance lately and I will pop off the covers tomorrow and have a look at the belt tension - it's a super easy fix if required!

I'd always recommend PC on the mount/scope with wired Ethernet off to the house. It'll be 100% reliable and pain-free. Either use remote desktop if you're running Windows et al, or just run INDIserver on the scope PC and run KStars/Ekos indoors for the glorious Linux world (which means the scope PC can be as little as a Raspberry Pi). USB3 at a distance was not meant to be; the technology can be sort of cludged into making it work but generally you're going to need powered repeaters and at higher speeds like USB 3.1 these are really expensive not to mention sensitive and fragile in terms of resistance to interference etc. Ethernet on cheap Cat5e cables is good for a gigabit per second at 100 metres. Beyond 100m, the only way to go is fibre optics, which are an entirely different ball game but actually quite straightforward if you stick to buying pre-terminated cables made up to your required length (which isn't that expensive to have done) and just swap it back to copper Ethernet with media converters at each end. I'd never suggest making up Ethernet patch cables (e.g. terminating male plugs) - you can buy 50m, 75m or even 100m "patch cords" for pretty low prices on Amazon and they work just fine (I use these for some of my garden cameras and to connect my scope up in its current semi-temporary position). If you need to make up an Ethernet cable, do it with punch-down (IDC) modules on each end and terminate in wall boxes. This requires only a £3 plastic tool and some diagonal cutters (sidecutters), will be neater in most cases, and it's much harder to get wrong in a way that'll cause a problem. For shorter links, chaining powered hubs might be the way to go, but I'd still be using Ethernet for a shorter run between scope and warm room with the PC on the scope.

For processing of lots of large images, particularly with well-multithreaded software like PixInsight, the AMD offerings are worth a look. Lots of RAM and NVMe storage are the real key though. I'm dealing with 24MP frames on some of my work (with a full-frame Nikon Z6) and that takes a fair bit of time to crunch through 50-100 exposures on a 3950X (16 core) with 32G RAM and (fast) NVMe storage - probably 5-6 minutes per integration of 100 frames. Once past integration though CPU and storage are king - at 24MP this combo can do most things in 10-20 seconds on a 24MP image, with prompt previews. I think 62MP will scale more or less linearly in terms of compute time, if not a little worse, so an i5 may struggle depending on your patience, but with 12G RAM you should do OK! AMD also has a huge benefit over Intel in I/O performance which is important - PCIe 4 drives are starting to arrive, and AMD chips have many more PCIe lanes available than the more expensive Intel equivalents, as well as PCIe 4 support across much of the lineup. Little disappointed to hear of the vignetting with the ASI6200's default setup - full frame is a big sensor for sure but you'd think they'd consider that in the engineering of it all...

Welcome! The main difference is aperture - the f/ratio is a byproduct of that as they're similar focal lengths. The light gathering ability of a larger aperture increases massively as a function of diameter so the 250 will pick up much fainter objects - for photographic use this means shorter exposure times needed. However, these are both Dobsonians, which are (for most applications, except some planetary and a few other things) visual telescopes only. Dobsonians are actually a type of mount but sort of integral to the telescope tube in most cases; the actual telescope type is a Newtonian reflector. Photography of fainter objects like galaxies, nebulae etc requires long exposure times which requires a scope that can track the motion of the earth. Dobsonians aren't easily motorised and because they're alt-azimuth mounts (i.e. they move up/down/left/right relative to the ground, as opposed to an equatorial mount which moves north/south/east/west relative to the rotational axis of the earth) even if you do motorise your mount or get one with GOTO the image will actually appear to rotate as you track an object. No problem for visual, but a dealbreaker for photographic use. I would absolutely opt for a more expensive equatorial mount like an EQ5/HEQ5 and a smaller telescope to start out - you'll find that it's much easier to do photography with! There's a lot of those mounts floating around the second hand market due to their popularity if you're looking to save cash. Small telescopes like the 130PDS are a great place to start, or you can go for a refractor for a wider field of view. https://astronomy.tools/calculators/field_of_view/ is a really helpful tool for FOV calculations. The more expensive the mount (generally) the better the tracking will be. How critical this is depends on your field of view - wider field photography with things like 60-120mm refractors or camera lenses don't need great tracking. Smaller FOVs that are common with big Newtonians (like the Skyliners) need better tracking as they can "see" the movement of tracking errors more readily. Beyond a certain point you need to assist the mount in tracking by using a guide system, which actively corrects the mount to keep your target centered. The other option would be - if you already have cameras/lenses that are suitable - something like the Star Adventurer mounts, which are designed to just hold a camera and track the rotation of the Earth so you can do long exposure shots. These are much cheaper than full-blown mounts but for widefield photography are a great tool. Not so helpful for deep space objects etc. If you want more specific advice then talking about the sorts of images you want to take will help a lot, as well as your budget and any existing kit you might want to make use of!

Not that I know of. If I get brave I'll have a go this summer.

I took the data from this project: and combined it with another night's worth of data, captured largely unattended overnight last night on the same rig - details in that thread. I kept processing simpler this time, but stuck with the super luminance strategy. Total was 30x300 L, about 20x300 R, G, B. No deconvolution this time, and masking only used in the final colour saturation adjustment pass. Denoised and DBE'd masters before a final DBE pass after background normalisation and PCE. Definitely a cleaner image than the last, and the detail in the core started to come through without deconvolution. I was a bit more creative with curve adjustment to try and normalise the core a bit (plus a very light pass of local histogram transformation) but at 300s the star is pretty bloated and won't get much smaller, I don't think.

Rother Valley seem to have the ES in stock and have done me well before, though I'll still be going for EPs from FLO I think. From reading up on them, looks like common mods are to fix some problems with rivets fouling on the az bearings and completely surround the secondary holder, but focuser gets good reviews and overall looks alright. Not averse to some scope mechanics DIY if the optics are basically sound. Do you find the offset spider vanes produce odd spikes?

Longer subs are better than shorter at some point - you need to have "enough" SNR in your subs, or you'll just be multiplying too much noise in each frame. But there's no real hard limit on the number of subs you can combine. In practice, more subs means more memory and storage space, and your computation will be more difficult/complex/time-consuming. But shorter subs will of course be less prone to tracking errors, etc. I've done 200 5s frames on a Z6 with a 24-70mm f/4.5 and stacking is fine in PI (this just on a tripod, no motion). I'd definitely be focused on getting tracking of some form though - you'll need longer exposures to get any nebulosity or detail preserved. Maybe a homemade tracker or a Star Adventurer etc?

Righto, so - trying to finally decide on a 12" dob kit for <~£1k. I've looked at the usual suspects and FLO will just about get me there on a Skywatcher 300P FlexTube plus shroud and dew shield, but I think I need to add a focuser as I know I'll get annoyed with a single-speed focuser, so that knocks things up to £1300. I think this is likely to be a reasonably good option in that I know the SW glass will be OK and the FlexTube is going to be a nicer thing to store than a full tube etc. Being a popular model it's also something quite a few accessories are available for with easy mounting solutions, such as encoders - these I'll add later with a Nexus DSC, rather than using GOTO. The focuser will be a Baader Steeltrak Diamond NT as I've been very impressed by the Steeltrak Diamond I'm using on the imaging 200P, so I know that'll be a great thing and work well. However I know there's other options out there - the Meade LightBridge has a dual-speed focuser and looks fairly sensible otherwise, Explore Scientific's Ultra Light second generation series looks quite promising and similarly has a dual-speed focuser included, and GSO's (non-truss) 12" Dob also has a dual-speed focuser and what looks like a better bearing system. Price-wise they're all there or thereabouts and look like they might be better options. This is purely for visual use - I have the 200P/EQ6-R Pro rig for imaging - hence going for a big (but not silly) Dob. Moving it isn't an issue but I figure 12" is the sensible limit for solo maneuvering in and out of an awkward house. Demounting the camera and converting everything back to visual is a fairly lengthy task (esp to demount the focuser etc) so not something I want to be doing. I'm going to be doing this rig in stages like I did for the imaging rig but good motion control and focus control to me feels like a prerequisite to not getting annoyed at the kit during a session. Would welcome any thoughts or suggestions from more seasoned observers than I!

Yes - I tried to fix these but I think I had a sequencing error with when I applied my denoising and so didn't denoise near stars. I was doing the processing ad-hoc during my workday in breaks, need to have another go properly focused on things. I've struggled to have good results with wavelet regularisation/noise reduction settings as a means to protecting backgrounds, though doing a gentle MLT denoise pass first helps somewhat. Range masks help a lot, especially on RGB masters where there's a lower SNR and more background noise.

Another "what can I do in a night?" job. Tried a few new things in post for this one, and in capture - captured in batches of 5 per filter with a few extra L batches, worked pretty well with the Baader filters all being parfocal. This was all on the 200P, ASI183MM-PRO, as per my usual. LRGB only, no Ha. The processing for this I stuck broadly to form on - but I stacked L, R, G, B and then stacked those stacks to form a super luminance. I then did denoising and then per-master deconvolution with a RangeMask as usual, and used the PSFImage script to come up with the PSF (which worked really well - amazed something like this isn't in PI natively). Then I did channel combination, denoised again, LRGB combination, the usual tidying up and whatnot. Quite happy with the result for a mere few hours of exposure - tried to pull more detail out in the centre, but didn't manage much without it looking a bit odd, so left it. The dust and clouds I can't pull more out of without more exposure time I think. Still quite a pleasing result I think.

Might be worth flagging up that Dark Sky, the data source for forecasting for Clear Outside, has just been purchased by Apple. They appear to be aiming to gradually shut down the API. https://blog.darksky.net/dark-sky-has-a-new-home/

That's right, so collimation is unaffected. I might make them a little wider around the large bolts - they can be rotated but it's a bit tricky to get a grip on them. Another 1mm around the edge would make a big difference.

The little screws are totally safe to remove - they don't really do anything but allow you to put tension against the big screws, and in practice they're irrelevant; I've seen no movement between sessions of the mirror other than the usual tiny amount of mirror flop/sag you'd expect in a 3-point mirror mount. The disk is trivial to fit using those little screws - all of 30 seconds to drop it into place and do the screws up. It's continued to work flawlessly as a mod for the last year, by way of a progress report.

Yeah, canned air is risky because if you're near the end of a can or hold it wrong you can quite easily dump a load of very cold propellant out on the surface you're trying to clean, which can induce damaging temperature differentials. Plus the velocity is high, so it can cause scratches (is the received wisdom). Blowers/puffers don't suffer either of these issues.

Amazon stock them in bulk, or RS supply them in lower volumes: https://uk.rs-online.com/web/p/multi-purpose-wipes/1223087/ Chemtronics also do these which are effectively the same thing premoistened with isopropyl alcohol: https://uk.rs-online.com/web/p/fibre-optic-cleaning/2361981/ Both are lint-free and will work great for cleaning optics. Using a blower to remove any large-scale debris is always a good starting point though. There's a lot of hearsay around cleaning optics - I have a spare AR-coated clear Baader I might sacrifice to science while I have a high-zoom stereomicroscope on hand since I have boxes of fibre optic cleaning supplies lying around along with coarser options.

Definitely - OAG is preferable for guiding a Newtonian (as it lets you account for mirror movement) but is a lot more fiddly, not always possible with backfocus available, and requires a sensitive guide camera. Flexure in guide rings can be a huge issue - I went to the extreme of having a friend CNC-mill a friction fit set of rings for mine, which more or less fixed it: But you can still be at the mercy of flex elsewhere - e.g. the helical focuser on the Primaluce Lab scope will move laterally if you let it, so cable anchoring is a good move regardless. I use velcro and a bit of gaffer tape. I'd echo the wind comment above, too - I see huge difference in guiding between calm and windy nights. Calm nights I can achieve <0.8" RMS, windy nights can push that up to <2" RMS (and imaging at 0.5"/px, that can be a bit problematic) Good PA helps but to be honest I can get <0.8" RMS with just the polar drift align in PHD2. There's no perfect alignment between guidescope and telescope (not that I can adjust it!). This is also just using as 120MC (in mono, so much like a MM). Rigidity and stiffness is king, basically.

There's a handy calculator here http://www.wilmslowastro.com/software/formulae.htm#Dust which will tell you har far away the dust is from your sensor plane - worth making sure you know which bit of the optical train needs cleaning before you go at anything. Everything including the sensor cover on an AP camera will have some form of coating and be sensitive to scratches, but cleaning isn't impossible - you just need a very soft lint free cloth (disposable) and isopropyl alcohol. For loose dust, compressed air can work but can also cause scratches depending on how you use it, so I'd stick to very careful use of disposable lint-free cloths. When you have your optical train in bits, do so in a dust-free environment and keep everything face down or covered with dust caps. With that much contamination, particularly the thing going on bottom right, I'd probably be looking to clean that, myself. While dimming from dust shadows will get taken out in calibration, blockages won't, and you are throwing away perfectly good light if you have shadowing across too much of the glass.