discardedastro

That's a great shout. I'll have to give that a try. I'll be picking up some ply to make the cover tomorrow. Made good progress - have been slowly but more aggressively cleaning the mirror (fingertips only) and there's clearly still *some* debris on it, so just trying to get that gone without making things worse. Mixed results so far but it's better for it. My plan is to remount the mirror for now and run it till probably next summer - then I'll ship it off to OOUK to get it measured since it predates their Zygo. If it looks good optically then I'll recoat, if it's iffy might consider a new primary. The tube now has better steel/rubber trim, a plastic handle for maneuvering, and I've attached both the new finderscope mount and Telrad mount with M4/M3 bolts. The dew heating system is starting to go in, too - I'm just putting cable tie anchors down the length of the tube (avoiding the region where the tube rings will contact the tube) to secure all the cabling. The fan with its damaged wiring is on the workbench to repair, and I'm also going to adjust the barrel jack - the supplied one is clearly not compatible with the mounting plate of older OOUK scopes so will just 3D print a clip to hold it at the edge of the plate instead of passing through. Tube rings and cradle are both looking better with some smooth Hammerite, which I've also used as a first-pass coating to blacken the ends of the stainless bolts/nuts which are securing everything. Going to take a few more coats to get it all properly sorted but it's already massively improved from where it was - all the exposed metal is now well covered.

So long as you're applying them properly, calibration frames done right rarely make matters worse. Almost all cameras benefit from dark frames. Many benefit from bias. All optical systems benefit from flats. Dark flats and variations like that get a bit more application specific but honestly capture bias+dark+flat to start and go from there. Even if your camera has "low" dark currents/amp glow etc, it won't be zero.

Match the light frames for your darks, of course, as above. Then just take as many as you can in a session, at the right temperature and definitely dark. Ideally pop a cap on your camera and put it in the fridge. I usually take mine on cloudy moonless nights, with the telescope under cover (and itself capped and pretty comprehensively light-blocked), so I don't invalidate the flats by demounting the camera. Capture-wise I just have KStars capture 50 and I repeat till I get bored, so my average master dark is 100+ frames combined. The ASI183MM is very amp-glow-heavy so benefits from good calibration. Structurally I keep my master darks/flats only in a folder named by capture date and I generally do darks/flats prior to imaging. I've got quite a bit of data (3000+ light frames) so I've got my own database system built on top of all that which manages which lights need which calibration files, etc. But most generally I try and calibrate as soon as I've done capture, and then store (in addition to the raw frames) calibrated light frames so I can always go back and re-integrate etc.

Really depends how you want to image! If you're happy hand-guiding etc then consider something with smaller pixels/sensor to get a narrower FOV and stick to the Dob - you don't need big light-bucket pixels for planetary. You could pop in a Paracorr or similar barlowing coma corrector to give improved coma performance as well as a mild barlow - lots of APs use Paracorrs and similar without issue on Newts/Dobs. Paracorrs are pricey though, so might be better off going down the pure Barlow route which can also work well. Second-hand Televue Powermates can be had from time to time if you're patient, but they're £300 new for 2"; I've heard good things about the ES barlow at around £200, though. I'd definitely consider what you might want to do in future, though. Barlows are definitely one-trick tools - I haven't touched mine except to use it in collimation in over 2 years, since I've not been trying to image targets that need it.

Assuming this is similar to the EQ6-R... The grub screw under that cover shouldn't need to be anything more than nipped up - if memory serves it's pressing against the top Dec bearing to make sure that it's under tension/load. If you undo the top three bolts holding the saddle on you'll be able to see the other side relative to the top Teflon washer and bearing. If you've got friction in Dec, then I would start at the other end of the axis. It could be the end nut is too tightly tightened or the bearing lubrication isn't in good condition. If it's the end nut, that's a really easy fix and very simple to adjust by releasing the grub screws and backing it off a smidge, then nipping up and securing the grub screws.

Well, I'm pretty sure it's coating damage... Took some better photos with a macro lens on the D1x after all the cleaning - not quite done yet, as you can see some streaks below - along with a lot of what's definitely starting to look like coating damage. The streaks in this area were a last-ditch drag with a cleanroom-grade lint free wipe, which failed to shift anything. I've fingertip washed this area twice now, too. Here's the whole thing. Interestingly, one edge appears to have been spared and cleaned up readily, top left through to centre. No idea why. Storage position? Still a few bigger particles I've been unable to shift here and there. So I think the right course of action is to ship this to OOUK for recoating. But I've not got that sort of cash floating around at present - so for now, I'm going to leave it and focus on mechanical repairs and improvements.

I've not yet but am going to once it's dried after tonight's wash. Tried doing half the mirror with acetone neat as a last-ditch measure to move some of the organics, so we'll see how that goes. It's allowed me to gently move off one of the bigger bits (the one in the last photo), so some progress! Rinsed down thoroughly with dilute IPA and then distilled water and we'll see how it goes. Had a bumper delivery of wipes to try today - the Kimwipes did well, but the CERNATA critical wipes were better at removing material with less force. Kimwipes had a tendency to "adhere" lightly to the mirror so were hard to drag off whereas the critical wipes had enough rigidity to just rest on the surface lightly.

Absolute goals! This has already had a focuser upgrade to a lovely Feathertouch which I've further upgraded with the Really Big Fine Focus Knob. Not sure how the default OOUK focusers are (or were!) but having gone from the default Skywatcher dual-speed focuser to a Steeltrak to a Feathertouch I'm now officially ruined! Rinsed the primary once more with water this evening. Looking better. I'm probably going to leave the really hard to shift spots if I really can't get them gone, but am a tad nervous they may damage the coating if left in situ so will give removing them a gentle go. Annoyingly the handles I'd ordered aren't going to ship for another month so will have to get some other ones. Just simple plastic ones for shoving and pulling the tube around to point, so not the end of the world and they'll find use on another project in due course. Going to drill out the holes in the tube for cable anchors tomorrow. Finishing up the CAD for the tube caps/fan holder this evening but dithering over attachment methods for the bottom plate - ideally want something easy so I can drop it off to collimate. On my 200P I removed the locking bolts for the mirror cell and used those threads in the mirror cell plate as the anchors for the back plate I added, and given I don't tend to use the locking bolts here I might repeat the exercise (with cutouts for the collimation nuts), just have to see how the clearances look for the fans!

15 years is pretty good going! I'm not sure quite how old this one is, but from a bit of internet sleuthing I think this was a "OD400 De Luxe" model with 1/4PV optics and Hilux coating: https://web.archive.org/web/20090417025321/http://www.orionoptics.co.uk/DOBSONIAN/dobsonian400delu.html That was gone from the OOUK website by 2011, replaced with the VX16 with 1/6PV optics as standard, so at least going on for 10 years!

You could certainly bin with that, yes, but it's still a pretty long FL - you definitely need to be guiding if not already. I'd start with the Wave 80 and optimise for that - it's a good FL for a lot of objects. Something with a bigger sensor would be better suited to both, but you'll need to check the flat field size in both - bigger sensors might well need optical flatteners/correctors. Don't forget you'll want more than just the camera - a basic LRGB set is a must-have I think but don't sweat the narrowband to start. Also consider processing and acquisition software - if you want to get seriously into the nerdy nuts-and-bolts then you may want to drop some cash on PixInsight or other commercial software. There's lots of good free acquisition tools these days though with filter wheel support. A reasonable autofocuser (so long as it's a stepper) is also a huge quality-of-life win, if you ask me. If you can save some cash on a second-hand camera and keep an eye out for second-hand focusers, filter sets/wheels etc you can get a good set of bits in that budget!

Looks great! I've used the fingertip method when cleaning my 200PDS and thought I'd give it a try after an experimental bit of cleaning with dilute IPA and a water rinse. I kept running distilled water flowing above my fingertips and slowly worked my way across the mirror. There's quite a lot of stuck-on debris still, but this got rid of all the pollen and organics - mostly. Still looking much better than it was! This is the surface covered in dilute IPA: It's still fairly clear to see some of the debris (white spots middle right, etc) and some of the "dusty" appearance (bottom left). And yes, all the tools above on the shadowboard are secure! I've got nowhere else to put anything. Still one or two bigger bits of debris, too: Just going to try rinse+soak a few more times for now and then it'll be on to the wipes - but it's already dramatically improved from where I started!

I've not done soapy water yet - giving that a go before even dilute acetone is a good shout! I've also got some dilute IPA so will try that too.

The good news is I don't think the coating's gone! I gave the whole mirror a bit of IPA 99%, then washed with water. Then using some Sticklers fibre optic endface cleaning fluid - which is just a slightly more sophisticated IPA style solution for optics and glass fibre, so should be safe on SiO2/Al - wetted a lint-free cloth and with very light force dragged the fluid over a square inch or two of mirror and then rinsed with water. What's left below is a perfectly clean mirror surface with no apparent coating damage - I'll get some magnification on it and take a close look before I go further. Definitely streaking/smearing of the contaminants, which makes me think organics of some sort. I'm going to try some dilute acetone tomorrow as a rinse and see if that helps to break down the organics without damaging the surface - my risk now is that if the contamination smears and doesn't lift with cleaning wipes, I'll have to do quite a lot of repeated dragging across the surface and risk damaging what's left. I really want to avoid damaging the glass at all costs - I'm quite sanguine about the prospect of recoating the mirror at OOUK given it's quite an old thing, but if the glass is damaged then I've got no chance.

I managed to get in touch with John at OOUK and he's confirmed this is a very old mirror for them, likely polished to 1/4PV, so starting to think that recoating the primary is going to be a sensible path. Started cleaning with 99% IPA today to try and shift some of the organic contaminants - currently still looking fairly grimy. I think I'm going to get a couple of discs of plastic laser cut, with one sized to fit in the tube and one to fit over. The one to fit within the tube I'm going to have cut with some ports for 120mm 12V computer fans and mount in the base over the top of the mirror cell like I've done for my current imaging scope. The one to fit over the top I'll put some dowels in around the edge to let it just rest on the tube without slipping off which should work OK as a "lens cap"!

On the C8, you'd be massively oversampled with the 183s at about 0.25"/px; the 294 would do better, but is still strictly oversampled at around 0.5"/px. Practically you'd want to look at sensors with bigger pixels - but with a C8 you're going to be struggling to avoid considerable oversampling. The wave 80 does much better being a shorter focal length system and would be comfortably undersampled with any of the above. What are you trying to image, though? The C8 would do well for planetary/lunar with a fast camera, whereas the wave 80 is better suited to DSOs and wider field with a cooled slow camera.

I've used the Caloclean spray on some regular DSLR lenses and I find it really hard to avoid getting smearing/streaks, using their microfibre cloth. I usually have to follow up with something else to finish off (I've used Sticklers fibre optic cleaning fluid, since I usually have some around the place, and this works flawlessly). It does work well for lifting debris though. I've bought some of https://www.thewipeshop.co.uk/product_info.php?products_id=345 as well as a couple of cheap lint-free wipes off Amazon - if I get a spare 30 minutes in the lab I'll stick 'em all under our stereomicroscope and take some comparison photos!

I'll give that a bash out then! Must've had a bump at some point in its life. Primary has had its first rinse in distilled water (about 2L) to get the worst debris off, though still a way to go clearly. The mirror cell came apart readily, though the big screws on the mirror clips required some persuasion and one refused to budge (note the precision engineering tool on left of photo!) so I left it and slid the mirror out instead, and have applied some lubricant to the reticent one. In moving the mirror cell around I snagged the half-fit fan and managed to damage the wiring so am going to get a replacement rather than risk installing something that'll short when it's a bit dewy - or will replace the damaged wiring, soldering job looks trivial. The fan I got was from OOUK but the DC jack they've supplied won't actually fit the hole in the plate, so I'll need a thinner one of those or to drill out the hole a bit. The new edging worked a treat, though has left the joint of the tube exposed - I'll apply some Plasti-dip or something to protect this bit. The new edging is steel reinforced rubber and is much more elastic, should actually protect the end of the tube! Little bit worried about the state of the primary, but have only just started on cleaning, so will see how much of this comes off easily. Worst case it'll be back to OOUK for a recoat I guess!

Practically, for ease of calibration, I'd want to have flats for each rotation position (and maybe stick to a few common rotation positions if possible if you're able to and don't want to be taking flats all the time). I know that my flats generally correct more than just what's in the optical train and that tilt of the train isn't going to be exactly nil (e.g. vignetting etc won't be perfectly symmetrical). Better to be safe than throw out a bunch of exposure time, I think. I also don't think you'd want to do synthetic flats e.g. rotate your existing flats to calibrate the flipped ones. This has the risk of correcting correctly all the optical train artefacts but incorrectly correcting for the scope. After flips you don't strictly need to rotate the camera - there's no downside to rotating the image in software later, and then all your calibration data will match with only one set of flats. Obviously having the rotator is really helpful between subjects, though. And while lots of people do suggest flats after every session I practically do just fine with everything left in place for months at a time with occasional imaging. I redo flats on occasion just to update for any new dust or debris!

Well, all the awful weather we've had lately has driven me to take the opportunity to take my VX16 apart rather than wait for summer. The primary really needed a clean - which was the main trigger for this - but there's a bunch of other problems I want to resolve to make this scope a really reliable "daily driver" for my use, which is purely visual observation with little setup time in quite a humid area. The scope lives outdoors all year round under a cover. Things I'm going to try and do: Mount the Telrad base properly with screws (the adhesuve strips don't actually suffice on their own, hence tape below) Replace the finder shoe for compatibility with the finders I have Remove the tube rings and renew the felt lining Repaint all the scuffed and chipped bits on the scope mount with new Hammerite Renew all the PTFE bearings on the mount Drill and tap the mount for encoder mountings so it's ready for that (if Astro Devices ever get back to me!) Finish flocking the inside (it was part-done by a previous owner) Fit the primary fan properly in the primary cell (part-done but can't finish it properly without taking the mirror out of the cell) Renew the spider and secondary hardware with stainless steel thumbscrews to avoid corrosion issues from condensation, after finding them rusting after some wet months Fit dew heaters for the primary, secondary, Telrad, and eyepiece Fit screw-mounted cable tie anchors down the length of the tube to properly manage dew heater and other power cables Paint all remaining exposed surfaces with heavily pigmented black paint (Stuart Semple's Black 3.0) Replace all the tube edging (it's cracked and failed) Make a non-fabric tube cap out of wood with some simple quick-release retention mechanism I've also got some tidying up to do on the secondary which was flocked around the edge for some reason, and cleaning of all the mirrors. Dew heating is definitely going to be a big upgrade - by far the most common reason I've had to stop play when using the scope, even with the fan. I've got a set of Lynx heater straps and a 4-channel controller to make it all work. Should be fun. The assembled scope after demounting from the cradle for mirror removal. Inside of the tube, looking from secondary down, after mirror hardware removal. It's a bit dusty and only part-flocked! This is a bit concerning - where the rolled tube is formed together it's flattened out quite severely. Going to try and bring this back to a vaguely circular profile. This is after removing the tube edging - which just kind of fell apart in my hands as I took it off. Only glued on in about two places with a tiny dot of glue, but the material's also very brittle - I've got some rubber-and-steel edging trim to replace this. This is the primary, still in cell (which is quite an early OOUK one, I think - it's not their modern cell design for sure). Lots of large debris on this, as well as some regions where it looks as if the coatings might be failing - I'll inspect this in a bit more detail once I've got it out of the cell and the crud off. Definitely needs a clean, either way! Spider came out (with a bit of careful bending!) and the secondary looks fine, though also like it would benefit from a gentle clean to get some dust off. The main purpose of taking this out is to get the secondary mounting out for fitting of the dew heater, painting of the vanes, and replacement of the screws with stainless parts. Will post updates as I go for anyone interested - I'm curious to know if any other OOUK dob owners have noticed the flattened section of tube above or if this is a damage/defect.

Kimwipes (the lint-free ones) and lens paper like https://cvp.com/product/tiffen_lens-cleaning-paper are what I always use when cleaning any coated optics using the once-and-bin approach. We use both lots of both at work both on photographic lenses and laser optics/fibre optics with no issues whatsoever. The Baader fluid will work fine but I'd never use a microfibre cloth on a lens/mirror surface I cared much about - the risk of dragging debris across the coating is too high. Fine for "disposable" lenses like eyeglasses which you expect to be taking a bit of handling damage, but unsuitable for long-life things you're trying to maintain at a very high standard. I'd avoid Kleenex and similar face tissues because they've often got lots of additives for comfort and produce copius quantities of dust (and definitely aren't lint-free!). Night and day under a microscope compared to a professional cleaning wipe for the application.

Depends very much what you want to image and your field of view! If you're looking to do deep sky imaging then guiding will help a lot as it will mean longer sharp exposures. With a 72ED you'll have a fairly wide field of view with most cameras (use https://astronomy.tools/ to check any planned setup) and that means it won't be so sensitive to misalignment and drifting. If you're looking to image smaller dim targets with a narrow field of view it's a must-have. It also depends where you're setting up. If you've got a permanent location to set up under cover (e.g. a Telegizmos cover or similar) then you can take your time to do a really precise polar alignment (drift alignment). If not, you might better spend the money on something like a Polemaster which will help you get a pretty good polar alignment very quickly and easily.

The radiator was the last really critical physical thing - if they couldn't get the two side mirror segments in they'd have less aperture to use but with the adaptive optics could still do great science. But fingers crossed for the last two bits - feeling good about it though given everything else! Then still a lot of cooling and cryo to be done, along with all the mirror segment alignment, but home stretch...

As you can see from the pictures I posted there is absolutely no way that they shield the light escaping. There really is no excuse apart from saving money on putting screens/blinds in place. The pictures of the blinds has already been shown in the local press to be a red herring. Apparently according to some staff the blinds are there in a couple of their greenhouses but don't get closed due to lack of maintenence. Yeah, it really doesn't look shielded. It should be a legal obligation (though given enforcement rates of, say, waste discharge into rivers, that might not be worth anything these days). Really disappointingly bad.

Found this: https://www.thanetearth.com/Content/pdfs/Thanet Earth and lit production 2019.pdf 40MW of lighting! It is apparently shielded, in part, unlike the football stadiums - they have a photo of their blinds. (edit: though apparently not all their greenhouses...) They apparently generate all the power for this from their own waste on site through a CHP plant, so not as bad as it could be on that front, but still not great or renewable..

Winter growth of plants does need lots of light. Wembley and Twickenham show up on various news places because of their winter grow lights which are incredibly bright - and as with the above, entirely unshielded, they just light up the entire surrounding environment. Strikes me that the all-party parliamentary group on dark skies could propose this as a really easy win on light pollution - put a bill in that expressly requires operators of these sorts of lighting systems to take measures to prevent light from escaping into the environment. It's quite mad this is allowed. Edit: This system is what Wembley use: https://sglsystem.com/EN/Lighting/860/LU440 FLEX - 63kW of HPS lighting per unit and they use 12 units, so about 756kW total draw...