discardedastro

Definitely looks like a gradient to me, yes. But a really good image! Beautifully framed and tons of detail, very sharp and nice round stars. Lots of cloudy nebulosity visible. Incredible photo for a second attempt at imaging! I took the liberty of throwing the image through PixInsight's DynamicBackgroundExtraction and it spits out this nice orange gradient which looks like textbook sodium light pollution to me. Subtracted gets you this:

So, here's my next challenge - cleaning out this tool. I've been going at it with a fine point needle and some running water. The tiny little pockets of grit are the ones giving me most concern - it's very hard to get in there and clean them out. I can get a dremel and start just widening all the holes out etc, but not sure it's the best plan. I can backfill all the pits with wax or epoxy. There's also a bit of 80 grit being held in the epoxy around the edges - I think some gentle sanding should get rid of that though. That or I could just pour a fresh tool and make it with thick glass tiles epoxied on top and wax between the tiles so I can effectively clean the whole thing properly between grits without spending a few days digging increasingly tiny bits of grit out of the tool surface.

The most important thing to spend the money on for AP is not the telescope! It's the mount. Long focal lengths require good tracking and normally guiding, so cost ratchets up rapidly. I'd be looking to save up a bit more if you want to go for a telescope that can do DSO imaging. Or as Carole says, go for a standard DSLR camera and a Star Adventurer or similar for wide-field - wide field requires less perfect tracking (though I'd also look at the iOptron camera tracking mounts which have a nice in-built polarscope for ease of alignment). Second hand mounts are definitely a good place to start out. EQ5 and above will do well for pretty much anything up to and including a 200mm Newtonian but ideally you'd go to something a bit beefier at that. Refractors and cameras with shorter focal lengths will definitely be an easier way in at that price point, especially if you've already got a suitable camera.

Now I have a way to measure, even roughly, I've been making good progress - it helps to be able to "see" what you're doing. I've got everything down to about .41-.42mm pretty evenly now, which is about where I need to be I think. So I'm going to clean everything up and start on 180 grit. My main concern at this stage of things is the tool. There's a lot of small bubbles and voids containing grit. I'm hopeful I can get it all cleaned up, but I might struggle to get it completely clean, in which case I'll either have to attack the tool vigorously with a dremel and a diamond bit, or cast a fresh tool (and I will use epoxied-on glass rather than embedding it this time, and use the wax trick in the gaps). Much rather get things into a sustainable position for fine grinding now rather than later. If I can get it completely clean I might try and do a wax covering to fill all the voids. I have a better set of vernier calipers on the way to improve my spherometer measurements along with a 0.001mm dial indicator - hooray for eBay, both used-but-good-nick digital Mitutoyos for under £30. And last but not least I've got all the bits to make a mirror mount for Focault testing, and assembled a rough-and-ready Focault tester stage with some foamcore - I just need to rebuild this in wood/plastic print and then get a little X/Y stage to mount it on.

So I currently have my 8" Newt and that's permanently on imaging duty. I'm trying to now design a complete new rig centred on a Skywatcher 300P non-goto scope (which will be my first non-goto scope) for a telescope I can take out and use for visual observing while my imaging rig does its thing. Plus I'm going to an event (EMFcamp) in July where I want to have something a bit more outreach-friendly alongside the imaging rig! A 12" truss feels about right in terms of portability and storage space requirements. That kit list includes a Powermate 2x which I might use on the imaging rig but I'm mostly thinking of it as a more versatile way to get more flexibility out of a good eyepiece. I've also thrown in a Paracorr though this is mostly for the 8" to replace an MPCC Mk3 for imaging, and a Baader Steeltrak NT because the 300P only comes with a pretty basic focuser and I've liked the Steeltrak on the 8". While I'm trying not to break the bank I'm keen to go for a good-quality eyepiece - I much prefer doing a couple of things well rather than lots of things "okay" and I don't like buying something I know I'm going to upgrade/replace when I can! To avoid things becoming too expensive (more than they already are) I'm only looking to pick up one good eyepiece to start things off on this rig. I've got the 28mm that came free with the 200PDS, plus a Pentax 12mm. I don't find myself reaching for the 12mm often. However, I'm struggling to visualise how, say, a 17mm TV Nagler would look in that dob compared to my 28mm in the 8". I've got little experience with "serious" eyepieces like the Televues and not so much experience in visual observing anyway. Basically - any advice for the best focal length to go for as an all-rounder EP given access to a 2x Powermate? Edit: Forgot to add, I'm also keen to stick to the TV eyepieces for the Dioptrx support as I wear glasses but would prefer not to and use a Dioptrx lens to correct my astigmatism...

I only lost a smattering and I have originals for the lot. For those looking for more reliable backup methods, if you've got a reasonable internet connection (>20Mbps down) then online backup is probably the way to go. I use Backblaze ( https://secure.backblaze.com/r/01u648 for a shamelss referral link that gives you and me a month off, https://www.backblaze.com/ otherwise ) and have successfully restored from it once or twice when a disk failed. Doing local backups onto a NAS/mini-home-server is fine so long as you're maintaining it and it has redundancy. And don't forget that RAID/mirror disks are not a backup - it just buys you time to fix a drive. Amazon S3, which Astrobin uses, is highly resilient and won't lose your data - but if you accidentally delete it, it's gone! I use Backblaze in addition to my main store which is a ~30TB 16-drive array using ZFS, which can tolerate 3 disk failures before I lose any data.

The TG365 covers work great but I would try and get everything sealed up as well as you can and ideally get some dessicant into the tube of the scope if you're leaving it outside for an extended period.

I had this exact problem and I had an online laser cutting company cut me a rear cover which is held in place by the small collimation locking screws - they don't seem to do much good anyway and I've not missed them. You can still adjust the primary collimation knobs, though it's easier to get a firm grip by taking the plate off first - only takes a minute. I used https://www.ponoko.com and I've attached the file I sent in. I've not had any worries about light leakage around the primary since. Cost about £10 I think. The before and after in daylight: tubecap.svg

Well, this worked out okay for a first attempt! The clamping isn't ideal and is a bit off-center but it's fairly stable - I'll shim the barrel out a bit with some bits of plastic. The "ridges" were an attempt to try and give this otherwise quite thin structure some additional rigidity but it's actually very solid - I printed this with a 30% gyroid infill in ultimaker Tough PLA, using PVA supports for the holes. The clamping just uses a captive M4 nut. I've attached an STL. My indicator is only a 0.01mm accuracy device so will want to upgrade that sometime. At the moment the feet are just the bolts, but I've got some ball bearings coming which I'll glue onto the bottom of the bolts. Measurement-wise I saw 0.37-0.38mm at the edges and 0.36mm in the centre. So plugging this into an Internet Calculator I'm seeing 1773mm ROC - so fairly close to target 1500mm! But I think more 80 grit to go before I switch to finer stuff. spherometer-v7.stl

Where I live I have pretty low light pollution - I've got bortle 4 skies, by the maps, though I've never gotten a SQM and measured it. However there's a few nearby industrial locations which I think are keeping their lights on all night and which I think are the source of quite a bit of the local skyglow; I'm keen to engage with them to ask them to cut back and switch to eco-friendly lighting with better control and/or switch their lights off overnight. Obviously one can hop in the car at midnight and go look to see which places are staying lit up all night but I'd like to be a bit more empirical and scientific about it, if nothing else to evidence my requests and provide a basis for comparison should I be successful. I did a project a couple of years back for my company using laser mapping with GPS to scan terrain for excavation planning, and I think I could use a similar approach for mapping out the local light pollution. My objective is to make a fairly detailed local map that will clearly show sources of skyglow in a fairly defensible and comparable fashion. And also not to spend any money, of course 🙂 My first thought was to take a survey-grade GPS receiver I've got lying about and assemble that alongside a cheap machine vision camera with a narrow field of view lens of some form pointing straight up, with some shielding to prevent stray light from headlights creeping in. Potentially also an infrared temperature sensor to let me measure cloud cover in some form, since that'd have a direct impact. The MV camera I could lock off in terms of exposure time, gain, etc. I can assemble this onto a magnetic roof mount on my car and drive around, logging data on a laptop in the car. I don't have many streetlights around but I figure I can probably exclude those in post if they're sufficiently bright compared to the rest. However, thought I'd ask if anyone's done anything similar and if there's any more sensible approaches to consider - should I just use a SQM instead of the camera? Is the approach of measuring the sky directly above a sensible one? Should I consider angular measurements? Any other suggestions?

For a short run I'd just go for conduit or UV-stabilised cable. Currently my telescope sits permanently connected under a TG365 cover on the end of a 50m UV-stable patch cord which goes into a switch in my greenhouse. Super simple, super cheap, will last for years. £30 of cable - kind of hard to beat.

The easiest way to do cabling if you have complicated internals and can drill holes in the house is to drill out and tack the cable on around the outside of the house. All you need is UV-stabilised Ethernet cable and either crimp-on connectors or a wall box and module plus a crimp tool. Quite straightforward to do without too much faff - bit of fiddling at the ends but that's all. EoPL is broadly an evil thing and best avoided - WiFi will achieve far better speeds. The other option you might have - depending on the signal you can get at the back of the back of the house - would be to use just one of those WiFi bridge devices at the observatory end. If there's enough link budget spare you don't necessarily need two high-gain ends.

No, they'll all suck in the same basic way - it's what powerline does. The problems with it are intrinsic. If you're up on the first floor and have line-of-sight from the house to the observatory (or near it) then a wireless bridge is the correct answer. Ubiquiti do a range of perfectly good radios e.g. https://linitx.com/product/ubiquiti-airmax-nanobeam-ac-network-bridge-19dbi-gen2-nbe-5ac-gen2/15056 which will link A to B with reliable high speeds. They'll even work through some vegetation.

Had another 20 mins of grinding on 80 grit this evening doing a normal stroke with 1/6th overhang each side and it is slowly making better contact and bringing the curve out to the edge - slow progress now but promising. My friend-with-a-mill hasn't gotten to making the spherometer body I designed, but work's got an Ultimaker S5 on loan and I'm going to print one off for now - it should be accurate enough. I'll be using M4 bolts with ball bearings epoxied to the ends as measuring feet and the body should be good and rigid; tweaked my original design to give me a pocket to fit a nut for clamping the indicator stem.

By very rough measurement I'm there or thereabouts in the centre (2.5mm is the target)! Still not quite out to the edge, though. I spent today's session grinding with roughly a 1/6th overhang as a chordal stroke. I think from now on I'll work with a normal stroke with no overhang to get the curve out to the edge. At present I'm seeing grinding taking place everywhere except the middle ~50mm diameter, which is being ground a little but nowhere near as much as the rest. I also improved my bevel - it's now about 2.5mm side-to-side consistently around the mirror. I'm keeping a closer eye on that now. The tool hasn't worn down much at all so should be good for fine grinding - will just have to be very careful about getting it clean once I'm done with the 80 grit.

You may need a more sensitive camera for OAG - the 120MC is OK with a guidescope, but might be hit-and-miss on an OAG. https://www.talkunafraid.co.uk/2019/04/adventures-in-differential-flexure/ I ended up replacing my guidescope rings with some solid machined blocks of aluminium and that eliminated my flexure problems almost entirely as a cheaper fix.

36mm tends to be unmounted - some filter manufacturers prefer it, and it does give you quite a bit more usable filter (the 1.25" filter will actually have less than 1.25" of usable filter diameter - check the spec sheet for the filter) because there isn't a mounting ring taking up some of the space.

Back to it this year - had to get the tools out of the house for Christmas and I've had a heck of a busy new year. I ground some more bevel on but need to do some more - takes quite a while with the whetstone. But I am getting there on shape, broadly - this is a (slightly exaggerated due to light positioning) sagitta, so it's out to around 3cm of each edge.

Generally your FW mounts direct onto the camera, so look at the diagrams for your desired FW and camera - they'll both have sensor-plane-to-edge/filter-mount-to-edge dimensions.

If you're going to do narrowband at any point or think you might then go for a 7-slot EFW if you can: L, R, G, B, Ha, O, S. 1.25" filters are fine for a lot of sensors - once you go to larger sensors then you'll get vignetting. There is a handy calculator here: https://astronomy.tools/calculators/ccd_filter_size

Nothing exciting optically, but as I'm making a spherometer I need something to calibrate against, so a small-but-highly-accurate surface plate arrived today! Good within a micron across the surface, so can't argue with that.

Sounds like a plan. I can gaffer tape the filter in place as an added mechanism for security, or drill some securing bolts through. Thanks all.

Understood on the Ha not being a proper etalon - I know from some research that NB filters can help a little with contrast in WL, hence things like the Baader continuum filter. Only looking for white light - I'll go buy a Quark/Lunt if I want to do solar properly, but that takes a budget! The heat load and overall safety of the system was the main thing I was worried about. It's a lot of aperture compared to most solar scopes and it gave me pause.

Hi, So I've got a 200PDS Newtonian and I've been using it exclusively for DSO work - for which it works great. I'd like to do some basic solar observation and the lowest cost entry point would seem to be a full aperture solar filter like the Baader Astrozap filters: https://www.firstlightoptics.com/solar-filters/astrozap-baader-solar-filter.html My question is - will this plus the Ha filter in my filter wheel be safe for the camera in a 200PDS? Would I need to throw an IR/UV filter into the front of the coma corrector? I'll be using my ASI183MM to do the actual capture. The other option I have is to get some Baader filter material and tape it securely to the stopped-down aperture in the dust cap, which feels a bit safer in terms of aperture/heat gathering, but would this make a material impact to the amount of detail/resolution I'd be able to get out of the system? And lastly, if the 200P isn't suitable, would a low-cost apo with the same filter setup do the job?

Yeah - I started out thinking I'd still bring most things indoors frequently but not having to re-do polar alignment, flats, etc every night and having everything cabled up permanently is a helluva drug. Run out 13A, plonk the 12V supply down and plug in two cables, shove the dew shield on and off to the races! I've got a plan for how I might house the 12V supply and a 230V extension more permanently but haven't gotten to it just yet. From the looks of it, an Arduino/ESP32+BME280 pressure/temp/humidity sensor would do all I need for control of a relay, and then I'd just need a heater. Working out how much heat would be required is a bit of a guessing game...