windjammer

>>Do you have pictures of it? Here are some views of it - it is 'agricultural', no lathe required. I could never fabricate anything high precision, but coupled with closed loop guiding the electronics would fill the gap. Main scope is the SW 150mm F5 achromat in DSO configuration with 2.5x barlow at F12.5, motorised Bahtinov mask in front. Blue thing is a SW 90mm F10 guidescope and 2x barlow at F20. The guidescope has a motorised XY stage to move the guidecam around the focal plane to get a decent guidestar. It needs a mag 9 or brighter to work best - the guidecam refreshes every 1/3rd of a second or so. All the controls are slaved, an umbilical runs down into the office so you can be in for the duration in comfort. Its called Kevin.

Hi Interesting discussion. I have been thinking about how to fix guidescope sag and guide algorithm hunting about its equlibrium position giving elliptical star images. I had a couple of occasions when the errors happened to be such that the star trail ran horizontally across the frame. Which triggered a few thoughts about a simple case- Suppose we determine from the elliptic star image that the light is smeared equally over L pixels - equivalent to a constant sagging over the exposure duration, say left to right for the sake of argument. Suppose the true intensity at the i'th pixel is Ni or N(i). The camera records N'i = (1/L) Sum(Nj), j=i, i+L. At the adjacent pixel k = i+1, the camera records N'k = (1/L) Sum(Nj), j = i+1, i+1+L so (N'i - N'k) = (1/L) (N(i)-N(i+1+L)) So if we knew just one of the N(i+1+L) values we could work backwards and untangle the whole row to produce all the Ni values. The edges of the frames would be boundary conditions where things go differently - but might have a redundancy to enable an estimate of a starting or ending Ni to be made... but brain goes blank at this point. There is a subtraction of one pixel from another, which would double the noise. Simon

Here is my spring collection - and first processing efforts with PixInsight. Rig is a SW Startravel 150mm F5, 2.5x Celestron Luminos 2" Barlow, Atik 460EX mono. Location is London UK (deep inside the M25). Mammothly long exposures for the mount, a DIY GEM, and still ironing out guidescope sag and guide algo hunting around its equilibrium position. Exposures this long on these kinds of DSOa are a bit of a first for me - 10 or 15 minutes is ample time for the gremlins to strike! M53, a Globular Cluster in Coma Berenices R 550-725nm: 17x 600s 1x1 binning G 500-600nm: 12x 600s 1x1 binning B 420-520nm: 13x 600s 1x1 binning Total exposures 7 hours, 26 April 2020 to 21 May 2020 M57, Ring Nebula R 550-725nm: 10x 600s 1x1 binning G 500-600nm: 10x 600s 1x1 binning B 420-520nm: 11x 600s 1x1 binning Total exposures 3.5 hours, 30 May 2020 to 01 June 2020 M64, Black Eye Galaxy R 550-725nm: 12x 420s 2x2 binning G 500-600nm: 13x 600s 2x2 binning B 420-520nm: 10x 600s 2x2 binning Ha 656nm: 29x900s 2x2 binning Total exposures 12.5 hours, 5 April 2020 to 22 April 2020 M66, a bit noisy unfortunately R 550-725nm: 15x 300s 2x2 binning G 500-600nm: 11x 420s 2x2 binning B 420-520nm: 20x 420s 2x2 binning Ha 656nm: 7x 900s 2x2 binning Total exposures 6.5 hours, 22 March 2020 to 26 March 2020 Simon

Hi I use SCb2000s as video viewfinders on my rig. Exposure setting on the widest field of view cam (about 30 degrees of arc fov) is about up to 1 second. The night sky is bright w. light pollution (London skies) so much more than that saturates the camera. So I would suggest as long as possible exposure without overexposing. I would suggest turning the DNR3 off - this is an exponential moving average gadget that will just confuse your video with fast moving objects. Also turn the sharpening setting down - it tends to make hot pixels look like stars, confusing. Basically start with the all the controls off except for manual exposure and AGC on High. If you don't have one, I recommend a UTC (up the cable) controller which allows remote control of the cam via its video cable. They are only a few quid. Or else solder wires onto the switches at the back and make a wired remote control. It makes life a lot easier in the dark. You will need to capture the video stream onto a PC or video recorder to analyse later. Google 'meteor capture software' - loads of links come up. This one looks quite useful https://www.britastro.org/node/12239 HTH Simon

As I understand it, your symptoms may be due to multiple connections of ground to the neutral wire. So making another ground connection may not help. There should only be one connection of ground and neutral in the house, usually to a substantial metal item stuck in the earth etc. Multiple connections give rise to ground loops where large currents can flow. I have this problem as well, and I suspect some chinese made electronic gadgets (wall warts in particular) I use with ground/neutral connections are the cause. The cure is to methodically remove stuff (gadgets, wired extension cables etc) until it stops. I think there are also some fairly cheap test instruments you can get to sort this out. Every once in a while I get the steam up to try and fix it, but so far not much success ! Simon

I keep my rig outside all year round under garden furniture covers - three layers, top one lasts a year before UV kills it. Being basically large plastic tents dew and condensation are a problem. I run 12V from a power unit inside the house, out to the scope with a high current pond cable, like this: https://www.screwfix.com/p/nexans-pond-flex-3183p-3-core-2-5mm-10m-black/5002t Inside the tent I have mounted power resistors to make a warm air blower: https://www.rapidonline.com/aluminium-clad I use four 6.8 ohm 50W resistors in parallel at 12V on heatsinks with a small fan to blow warm air inside the telescope covers. It generates 80W or so, and takes about 7 amps. It works a treat. I have mounted a greenhouse remote RH and temp sensor (ThermoPro TP60s Wireless Thermometer): https://www.amazon.co.uk/ThermoPro-Thermo-hygrometer-Thermometer-Hygrometer-Temperature/dp/B07G2YM494?ref_=s9_apbd_otopr_hd_bw_b5zxl5j&pf_rd_r=M1YG8Y42H5YYTJ6DWBY5&pf_rd_p=dd27ab4b-5b90-57e6-98da-609b80414dcd&pf_rd_s=merchandised-search-10&pf_rd_t=BROWSE&pf_rd_i=5496263031 on the scope. Whenever the RH goes above 70% I turn the heater power on from inside the house. I would not want 240V mains anywhere near the scope. If you are OK with that, you could always put a 100W incandescent bulb under the cover - should work.... Simon

Thats a very nice lathe! - actually I never bought one (though came close many times, and regretted many times) because I didn't want to be sidetracked from doing astronomy ! Perhaps you should go into business supplying us all with pukka worm gear sets - seriously, how much ?! Agree on the fire risk overnight, not so much at the scope, more inside the house where the power units are. The resistor idea is a very low intensity method to provide local heat to the bearings. I read about them used to heat lathe beds in damp workshops to keep the rust off - so it could work for you. A cheap idea to try anyway. Dew heaters (mine are homemade, 330ohm 1/4W resistors in parallel wrapped in duct tape ) work well but you are right, they do take an age to clear once the dew has condensed, but very good at stopping it in the first place. So I tend to leave them on all day when I am present and the RH is high. Condensation is a big problem I worry about a lot - I have previously found the dew to be quite damaging to the lens coatings. Simon

Re: >>The last thing I want is rusty bearings from exposure to damp in a constantly cycling temperature regime. try screwing power resistors (like these) to your metal work: https://www.rapidonline.com/aluminium-clad You could power them with a dew heater. A small amount of heat would keep the damp off. I use four 6.8 ohm 50W resistors in parallel at 12V on heatsinks with a small fan to blow warm air under the telescope covers. It works a treat. I have mounted a greenhouse remote RH and temp sensor (ThermoPro TP60s Wireless Thermometer): https://www.amazon.co.uk/ThermoPro-Thermo-hygrometer-Thermometer-Hygrometer-Temperature/dp/B07G2YM494?ref_=s9_apbd_otopr_hd_bw_b5zxl5j&pf_rd_r=M1YG8Y42H5YYTJ6DWBY5&pf_rd_p=dd27ab4b-5b90-57e6-98da-609b80414dcd&pf_rd_s=merchandised-search-10&pf_rd_t=BROWSE&pf_rd_i=5496263031 on the scope. Whenever the RH goes above 70% I turn the heater power on. On worm gears - have you thought of turning one on your lathe ? I understand (don't have lathe!) hobbing a wormwheel is quite hard, turning a worm screw is a lot easier of you have a screw cutting lathe. You could choose your material of choice, brass or stainless, with shafts as long as you like. I recommend this magazine, Model Engineers Workshop and forum if you need info - they are always running articles on gear hobbing etc which will be in the digital archive if you subscribe. https://www.model-engineer.co.uk/editorial/page.asp?p=250 Yes, projects are never finished ! But how can you avoid long periods of downtime while you make and install new stuff ? So you need TWO versions - one up and running so you can use it, and a second in development to swap over when commissioned, then start all over again! Simon

>>Taper roller, thrust bearings, or even axial thrust, ball bearings, on the worm shafts would be better. Sadly, the worm shaft extensions are miserably mean Maybe a small live centre pushing into a dimple on the end of the worm shaft would do the trick, either fixed or sprung - something like this: https://www.arceurotrade.co.uk/Catalogue/Centres/Mini-Live-Centres The one on the 10mm plain shank looks suitable. No extra length on the worm shaft required. Simon

Very interesting ! I had thought that Beacon Hill had gone - as of a few years ago I was searching for parts and they had disappeared. I googled their web site now and they still have a catalogue with worm gear sets listed. Sounds a bit hit and miss though. Nice looking worms. What gear ratio are the worms and belt drives ? Is the stepper motor microstepped ? The Tollok bushes look absolutely enormous ! I was able to bolt my gears directly to the DEC bearing plate (RA gear) and the saddle (DEC gear). Here are some older pics of my gem during construction for comparison: https://www.flickr.com/photos/31131978@N00/albums/72157683523839235 More stuff has been added since those pics - the GEM now carries an 150mm F5 refractor and a 90mm F10 guidescope, plus 3 video viewfinders at different FoVs. I have put up some more detailed stuff as contact sheets here: If you fiddle with the full screen mode and + icon you should be able to see the individual pics at a reasonable size (I hope the links work...). https://www.flickr.com/photos/31131978@N00/albums/72157712988317928 These two pics show how an M16 threaded rod is mounted inside the 2inch axis shafts: https://www.flickr.com/photos/31131978@N00/49493473818/in/album-72157712988317928/lightbox/ https://www.flickr.com/photos/31131978@N00/49493472653/in/album-72157712988317928/lightbox/ These two pics show the RA axis attached to the DEC bearing plate through the drive gear: https://www.flickr.com/photos/31131978@N00/49494189772/in/album-72157712988317928/lightbox/ https://www.flickr.com/photos/31131978@N00/49494188827/in/album-72157712988317928/lightbox/ That was not quite strong enough,so I fitted a key - first version: https://www.flickr.com/photos/31131978@N00/49493975151/in/album-72157712988317928/lightbox/ But the screws sheared off, so stronger pins added: https://www.flickr.com/photos/31131978@N00/49494183267/in/album-72157712988317928/lightbox/ These three pics show the attachment of the saddle to the DEC axis through the drive gear: https://www.flickr.com/photos/31131978@N00/49494186572/in/album-72157712988317928/lightbox/ https://www.flickr.com/photos/31131978@N00/49493471228/in/album-72157712988317928/lightbox/ https://www.flickr.com/photos/31131978@N00/49493470093/in/album-72157712988317928/lightbox/ Looking forward to your next installment Simon

Hi Great thread, can't wait for the next installment. I finished my own monster bearing block GEM about 18mths ago and have been enjoying it since. Its carrying about 30kg now as bits have gone on. But starting to collect parts, materials and ideas for a mark2! I used 2inch pillow blocks, and as you say, ended up fixing them to flat plates. I looked at the flanged bearings and couldn't see a way to make them work without welding up a bearing box (not in my skill set unfortunately!). I am amazed that your bolted up boxes are strong enough - they are very elegant solution. A problem I came across in previous models is that if the scope is unbalanced and heavy then the slow motion drive ends up winding up the metalwork and bracketry rather than turn the shaft. When the tension in the metalwork gets high enough, the shaft lurches round and the winding up starts again. So preventing twisting is key, as you say. I looked at 2inch ground solid shafting - cost alone put me off that, never mind the weight of it! It speaks well of your design that the bearing boxes can carry this. I went for 48mm scaffolding pipe with 5mm wall and shims to fit into the 50mm bearings. My research seemed to indicate that tube was actually more rigid than solid bar? Being hollow one can fit barrel nuts into the tube to attach gears and plates to the ends. Your shaft clamps look huge - did you look at taper bushes with bolt on hubs ? I thought I might experiment with these in Mk2. Very interested to hear about the drive arrangements you have used. Those worm wheels look very handsome - did you hob them yourself on the lathe? I did not find wormwheels and worms at a reasonable price (for what might not workout) so went for straight cut MOD1 spur gears. Two problems with these: unbalanced loads get transmitted back through the gear train in a way that the worms don't, and the very devil of backlash - which means having a friction brake on each shaft to control slop is mandatory. As it happens, I wanted a design where the gearing could be uncoupled so that the axes rotate freely - so having friction brakes was needed anyway. I found it difficult to get motors to respond over the speed range for tracking and slewing. If,say, you want an axis to slew at 1 turn in 2 minutes and track as well (1 turn/24hrs), that is almost 1000:1 speed range. So I ended up with 2 motors per axis - one for slew (DC motor) and one for track (stepper) and a remote controlled gearbox to swap motors. Making 4 motor controllers got very boring! - but in the end what sounds OTT has ended up as very reliable. How did you manage this aaspect ? The wedge has ended up being the weakest point of my effort - rigidity, and its size and shape have given rise to collision issues when pointing south at higher elevations. The way you have angled the yoke arms is clever. It is impossible to imagine every position the OTA can take and arrange the metalwork accordingly! Your huge refractors must make this an issue ? I pivoted the wedge around an M16 stud like yours. I think perhaps it is not beefy enough. I was toying with the idea of using a short length of 2inch pipe rotating on V blocks as the pivot. A high end mount I saw at a show made intriguing use of a dividing wheel to adjust the wedge angle. Thinking about this brings back hilarious memories of weekends trying to machine stupidly large chunks of metal in a small drill press. Drilling and tapping M16 into steel and aluminium is quite something - watching huge curls of swarf come off the drill while frantically squirting cutting fluid onto it. Great stuff. Looking forward to your next episodes Simon

Ok, so its not really the Barfing Dog nebula, just looks like a floppy ear, a wild eye and suspicious yellow patch... Narrowband Horsehead and Flame Nebula, IC434: https://www.flickr.com/photos/31131978@N00/49459941343/in/photostream/lightbox/ Rig: SW Startravel 150mm F5, 0.8x Orion Imaging Reducer, Atik 460EX mono Darked and flatted in Dawn, stacked in Registax5, processed PSE10 Astronomik Ha filter 41x180s Astronomik S2 filter 56x180s astronomik O3 filter 43x180s Total exposures 7 hours, 18/19/20 January 2020 Ha mapped to green channel, S2 mapped to red channel, O3 mapped to blue channel. Greens morphed to yellow, the blues/cyans emphasised, magentas suppressed. Monochrome narrow band images: https://www.flickr.com/photos/31131978@N00/49459941088/in/photostream/lightbox/ Untweaked RGB overlay: https://www.flickr.com/photos/31131978@N00/49460651432/in/photostream/lightbox/ A couple of colour balances: https://www.flickr.com/photos/31131978@N00/49459941608/in/photostream/lightbox/ and: https://www.flickr.com/photos/31131978@N00/49459941608/in/photostream/lightbox/ Simon

HI James That may be his view, but that is not what his video is about. In the video he asks what is the shortest sub exposure you should take to get most of the noise benefit of a single exposure. The single exposure SNR is best (he says) because there is only one hit of the cam read noise, whereas subexps have multiple hits. By saying, OK, I will accept a subexp that is only X% worse in absolute noise level (not even SNR!) he then comes up with a value for subexposure time - based on cam read noise and LP noise. It is elegant, granted, but according to this calculation you would use the same exposure length for snapping the sun as for your dimmest DSO! I do not have Sharpcap, and I am sure there is loads of good stuff in it. But as to what exposure time to use on any given object I am stuck on the recipe I posted earlier. On the topic of CMOS gain which he moves onto, I have no experience (CCD). But it does seem complicated! Simon

Hi Rather late to this thread, but if you are still thinking of rolling the beast, the trick is to have the castors on jacks and the feet rigidly attached - which is the reverse of what is normally done. To move, wind the castors down so it is off the feet, move it, then wind the castors up so it stands on the feet. Jacked feet will just wobble. There may be some merit in 4 wheels. I had three, and rolling over soft turf was seriously weird if it bogs down... Re your dome: are you sure it is worth the bother - they are cramped. My scope I abandoned the garden and moved up to the roof, a small one metre wide strip of flat roof: A couple of pics - and and The thing is covered by 3 of these garden furniture covers, one inside the other: https://www.amazon.co.uk/Woodside-Outdoor-Garden-Furniture-3-25ft/dp/B00CQ4DOK6/ref=sr_1_6?keywords=woodside+garden+furniture+covers&qid=1574722227&sr=8-6 Quite water proof, about half an hour to uncover or pack up. Bit of a laugh if the wind is up.

Hi I watched the video and I get the maths but don't understand it. The good doctor comes up with an exposure time with no reference to how dim or bright the object is. Only the cam read noise and light pollution flux. I don't agree LP is only shot noise, more properly considered as a mean flux <p> plus sd Op. What is wrong with exposing so the brightest bits just saturate and the LP lurks at the bottom ? Then just take loads of frames and stack - though would be nice to compute when the marginal benefit of the next frame is pointless. To go after the faint detail, overexpose the bright bits and hope you capture counts from the fainter bits before the LP comes chasing up from the bottom and saturation comes down from the top.

Hi - it is definitely not the end of the world. I use a SW Startravel 150mm F5 doublet - with a mono cam and filters: RGB and narrowband. It works well, just that an L filter is a mush of out-of-focus light. No reason why you should not use RGB filters with a colour cam. Just a bit more work processing ! I found that the focus positions (Bahtinov mask) of R and B light is very close, and G is quite different - which I was not expecting. B is difficult, it needed and an L3 astronomik filter stacked on the quite flabby astronomik B to get acceptable blue exposures, and even then stars tend to bloat badly when images are stretched - but the photoshop carboni star tools fix this. On the other hand narrowband Ha, SII, OIII, Hb are all sharp. Here is an Ha of Flame and Horsehead (bright star by the Flame shows collimation a bit off) https://www.flickr.com/photos/31131978@N00/49098502228/in/photostream/lightbox/

Hi - I think thats quite a good result for M31 esp, if a first go at it ! I have similar issues with simple RGB overlay - weird gradients and patches of unphysical colour. For me, I concluded it was because I processed each colour filter separately, processing each colour as far as it would go as a monochrome. So the different colours became uncoupled from each other. I use Photoshop Elements for the tarting up after the serious stretching elsewhere -PSE is only 8 bit. My most recent recipe for making the separate RGBs congruent as follows (in PSE speak, but hopefully you will get the drift): Pick one colour (obviously all the colours are monochrome images at the moment) as the reference, say G. Compute the flat F(R-G) ie. Green overlay with Red with blend mode 'difference'. Blur the difference using 'Dust & Scratch removal' at maximum settings. This removes fine detail from the difference and just leaves the broad wash of intensity differences across the frame. Then compute R(new) = R - F(R-G) ie. overlay the Red with the above flat with blend mode difference. If you get a bit twitchy about this, you can vary the opacity of the flat to vary the volume of the adjustment. Do the same with B, and compute flat F(B-G) and proceed to create B(new). Construct the colour composite (Rnew, G, Bnew). For any major colour tinge remaining, adjust the hue to be pleasing. For me, green is the most common overall tinge which I adjust to a sun yellow, or a red adjust to a gold. For any small non-physical colour patches, adjust the hue in either saturation (make it more colourful if it brings up physical detail or decrease to damp it down) or increase intensity (pushing it to a more harmless simple luminosity). So this is what I made of M31 from an outing mid October... https://www.flickr.com/photos/31131978@N00/49053267023/in/photostream/lightbox/ Simon

Hi I leave my stuff outside all year. I use garden furniture covers (about 13 quid each) as a tent to keep rain off. Three layers - top layer lasts about a year before UV kills it. Top layer breaks the force of the rain and wind, second layer stops remaining water and inner layer is belt and braces. Luggage straps round the pier keep all in place. Electronic packages are at the scope pier and stay dry. Umbilical runs inside some flexible ducting to the house from the pier with power (12V and 24V only), remote control cables and video/USB camera feeds - also outdoors all year round. I built a hot air blower out out of 50W power resistors strapped onto heatsinks in an aluminium box with a 8inch computer fan blowing over them - it dissipates about 100W and sits inside the tent. I found some pond cable that would take the current (about 8 amps). I installed a remote greenhouse temp and RH monitor (thermo pro T60s - amazon, 17 quid) inside the tent that has a radio link to an inside display. Whenever the RH goes above 70% I put the blower on. Also put silica gel desiccant packs taped inside the lens covers. Stick with it ! It is quite possible to get to a permanent installation without a dome or shed - and it makes a huge difference to making the most of observing time. Simon