discardedastro

Not an expert, but the W deepening stroke as described here? https://stellafane.org/tm/atm/mirror-refs/strokes.html#The W Edge Deepening Stroke

What cjdawson is describing isn't quite platesolving - just star tracking (track stars near the North and you can calculate the PA error, and then correct it).

Thanks! I've considered some shorter exposures and might revisit at 120s and see how it goes - I've done some HDR before which might work quite well for this. Quite a few stars are at saturation. I haven't tried Ha yet on this target.

Really wanted to revisit this after a successful first pass last month and finally got a few hours in. ~40x300 L + ~20x300 R, G and B, 200PDS w/ ASI183MM-PRO at -10c, Baader LRGB filter set. Processing was with PixInsight and followed my usual routine - calibration, subframe selection w/ weighting, integration (using PI's LinearFit for RGB and ESD test for L, all with local normalization), cropping, MureDenoise, DBE, deconvolution with a DynamicPSF-generated PSF, ChannelCombination, PhotometricColourCalibration, SCNR, MultiscaleLinearTransform denoise w/ linear mask, histogram transformation, LRGBCombination, some slight tweaking of curves for contrast, and final TGVDenoise.

The 200PDS is absolutely a capable AP telescope - but the mount makes it possible. It's not a great 'scope for planets, though it can do that. What are you looking to photograph? What sort of images really attract your interest? Wide-field, deep-field, planetary? Get a copy of Turn Left at Orion (in advance of buying, if you ask me). "Every Photon Counts" is another great book for beginners of AP and a great resource. In terms of achieving focus with any camera the basic idea is to put the focal plane at the focus point. The back focus on a 200PDS is quite generous, so you'll need an extension tube - one 2" extension is supplied with the scope and that may suffice. You'll either need a 2" to T2 connector adaptor as well as a T2-to-Canon-mount adaptor, or you can go direct from Canon to 2" - I'd go for the T2-mount adaptor as you'll find that things like coma correctors and filter wheels commonly use the T2 thread/format. Baader also do a thing called a "Varilok" which is a variable extension tube that's quite handy to get the backfocus set perfectly if you do put a coma corrector in, for instance. My 200PDS uses an ASI183MM - this has very little backfocus (11mm) from the thread to the sensor. This is attached to a filter wheel, then a Varilock, then a coma corrector. The coma corrector has a 2" front so drops straight into the focuser, without an extension. That all sums up to around 65mm of length, which lets me achieve focus. With an SLR you may have to aim for much less length depending on how far back the sensor is - on my Nikon D1X that's about 56mm, on the Z6 it's much less. So it really does depend on the camera.

At $dayjob-1 we did something similar for "surround video" research (back before VR was a thing and all the cool kids started waving headsets about) which used a projector shining onto a cheap reflecting hemisphere. Definitely not as good as a fisheye lens, I'm sure, but did I mention it was very cheap? Publicly funded research department didn't have funds for fancy optics! The main thing I'd be thinking about is power and noise - most cheap projectors will be regular bulbs which have loud fans to cool (LEDs aren't much better). Plus power and bulb consumption factor in.

That does indeed all make complete sense! I think from the sounds of it I should get away with it, but I do have a relatively low areal coverage on the tool. Will have to see how I do I suppose. I've practiced my glass-breaking and I can do smaller bits for the next tool, should it be needed. I'll refine the bevelled edge - I haven't touched it since I put it on initially. Also going to cut some channels in the tool with a Dremel and a diamond disc. Cleaning it for the finer grit is going to be painful - starting to really see the value in making a plaster disc, sticking glass onto it and using wax as a surface, I think.

Well, I'm getting somewhere! Definitely making progress with removing material now. My grinding down of the sharpie marks at the edge suggests I'm pretty symmetrical overall but doing basically no grinding near the edge. One of my glass chunks let go of a bit but this didn't leave a mark on the mirror - the shard just got pushed around a bit and I washed it off. So, so far so good, I think... just more grinding to go!

Sorry - I'll try harder, I'm not great at explaining things and this isn't my absolute forte! Target average ADU as in the average value of a pixel within an image - so if every pixel were set to 10,000 you'd have an average 10,000 ADU image. If your maximum full well is 17k ADU then beyond that value your pixels will potentially not behave linearly, so you need to stay well clear of that. Atop of this there's scaling to consider - your camera's analog-to-digital converter will have a bit depth for each pixel's reading - 8 bit, 10 bit, 12 bit, 14, bit, or 16 bit. The SX-694 is 16-bit so there's no scaling involved. If you had a 12-bit ADC then your 17k full well might actually be a fair bit below 17k in the readout in the software. Basically, if you aim for the average intensity of your image to be around 10,000 you'd be fine. If SGP can draw a histogram you should find a fairly narrow peak forming (with even illumination) somewhere between 0 and 65,355 (maximum 16-bit readout). Adjust your exposure time till it's sitting around 10k. Dark frames will always help, even with low-noise cameras, and their inclusion is easy - plus they're portable between shoots so you can use some cloudy nights to record a large number of frames, make a master, and that's your dark frame for the next 6 months at least! Same goes for bias frames. PixInsight has a "superbias" feature which will take a master bias frame formed from a goodly number of bias shots (50 or so) and effectively extrapolate the overall bias of the sensor - might be worth an experiment if you have PI or can post a master bias for someone who does to process.

Not sure about SGP but Ekos/KStars lets you provide a target average ADU. The key thing is to avoid nonlinearity in pixels, but otherwise as high as you can manage. Depending on the bit depth of the camera that will vary and may be tricky to calculate. In general I've seen recommendations of around 30-40% of max ADU being a good ballpark; personally on my ASI183MM setup I target 10k ADU and that seems to work well. As to the rest - if you can maintain your setup's state (including filter positions, etc) between sessions flats are reusable. I've gotten away once or twice reusing flats between nights even when taking the camera out to do collimation just by making sure I got the camera back in the same position by eye, but it won't be perfect. If you're running in an obsy then placing the flat panel on the wall somewhere and having the scope slew to point at it can achieve a pretty good result (just make sure the panel is "flat" in attitude with respect to the scope, as far as is possible). You need some way to turn the panel on/off, of course. It's been a while since I played with DSS but are you making master flats and calibrating them with dark/bias frames? I think DSS can do this automagically, but worth checking. Using uncalibrated flats could lead to problems.

Yup, that sounds about right. Plus I don't have any way to mount an actual eyepiece in the tube - the threads are all Odd, so not something I've got lying around. Work's dumped a load of meetings on me tomorrow anyway, so I shall be watching everyone's results on here from inside a darkened office...

Like I said, didn't manage to get anything out. Making a note for 2031 or thereabouts to get myself properly sorted out for solar imaging - in advance! Setups above look much more sorted - best of luck...

I just tried to set up a little projection rig using an old 9x50 finderscope I didn't mind incinerating, some gaffer tape and some card I had handy on a photo tripod: I did not, despite the immense resources at my disposal, achieve any view of the sun - I used the shadow of the scope to align, lacking any finder. I do have a 60mm guidescope to hand, but I'd really rather not cook it, and getting it accessible is a faff. If I denuded my main scope+mount rig I could use the EQ6 (the guidescope's on a vixen ADM dovetail bar, so that works), but only for projection, and I've only got 8mm and 2.5mm eyepieces lying around the place. Should've nabbed the £350 Lunt 35a on eBay last week... but it was showing as likely completely clouded over 😞

I've had my EQ6-R plus 200PDS and electronics, cameras etc mounted outside under a Telegizmos cover for well over a year and they're all absolutely fine and rust-free. I'm not near the coast or anything though. Just pop the cover off, lens caps off, dew shield on, run out the mains cable and 12V supply and plug that in - everything else is already set up and good to go, though being on a tripod it does need polar alignment once in a while. Only gotcha is that while I can get insurance for everything, weather isn't covered unless it's in an observatory! The pier looks fab and solid. The tube approach I've seen done by a few people now and it looks a great way to contain the concrete.

Yeah - the respirator I bought at the start of this has gotten a lot of use - dust kicked off while making the tool is plentiful, and as the respirator's got a reasonable degree of organic compound filtering in the A1 cartridges you can't smell a thing while doing the epoxy. It's similarly good when unblocking sewerage lines, as I found out last week! I've got a back porch so I've done it all in there and left it out there - it's bloody cold so it'll take a while to cure, but it'll get there. I think I'll do one more try at the embedded tool before I give up and epoxy glass to the front of a ceramic tool (or cave in and use the 21mm 8" blank I have as a tool). The wax trick is neat - for the coarse stuff it's visually pretty clear where it is but at finer grits I can imagine it'd start to be a bit of a nightmare to clean out.

Yeah, pretty chunky! I had a look at my local B&Q and while they have some glass tiles they were all 3-4mm or so, which I thought would be marginal. I've just finished the epoxy coat on this tool - it won't have quite as much consistency/glass directly in contact, there's quite a bit of plaster in the overall front surface. Not ideal really. I think I can make smaller tiles. Nonetheless I think I should be able to get some work done with it so I'll start grinding again this weekend once the epoxy is cured. 10mm thick "tiles" should work fine though!

UT, of course, is not UTC - UT1 is an Earth rotation based time standard, UTC is a coordinated standard based on atomic clocks. GMT generally refers to UTC. Your timing for the purposes of the transit, though, could use any or either and be close enough 🙂 there have only been 27 leap seconds so at worst you'd be 30 seconds out.

It's in the FITS headers, MaxIm DL. MaxIm also puts the licensed user name in the header as well as the serial number - that's not great! Looks absolutely on the money for an ASI183xx, having one myself, and the FITS header reports 2.4um pixel size which is a match. But definitely something wrong there as pointed out above. For a 50 second dark frame on an ASI183 you'd expect to see the usual bloom on the centre right hand of the image.

How thick are the tiles and where did you get them? All I could find online or at my local tile place was thin (2 or 3 mm) "corrugated" tiles. Bit late for this tool but would be good to know. That all makes lots of sense. My glass scorer was a cheap thing off eBay that looks to be a Silberschnitt clone of some sort, and seemed to do the job ably. I worked on a flat work bench with a towel for the first bits and that worked very well - felt is what I've seen most people use on t'internets as a base but a towel is pretty close mechanically. I tried leaning the cut across the edge of the bench but putting something below the glass and leaning sounds a good plan - the "pro" thick glass cut running pliers look to have some pads arranged on the inside of the jaws to produce that effect. Anyway, tool now on a drying rack above a radiator to dry out - looks to have come out okay, but a couple of bits of glass "floated" to the edge during the pour (despite my efforts to keep everything still) and there's a ~2cm long section of the side which has the exposed glass chunk as an edge. Shouldn't be an issue once the epoxy goes on, I think.

See earlier in the thread where I made the tile tool and ate through the hard bit of the tiles in less than a week of evenings! Glass tiles I did consider but this approach should last much longer.

Right - well, glass cutting basically worked! I've ended up with a mix of sizes of chunks of glass which I think should be okay. I've managed to do it in a sufficiently controlled fashion that I've got plenty of undamaged glass left to hack on if I want to take another ago at it all. The sheet as it started out... Scored it twice, once more firmly than the first time, after I failed to get the score to open with my pliers. In the end it turned out my first score was fine, but the pliers weren't going to do the job on 10mm thick glass. Very gentle tap with the pictured hammer did the trick, though. The break followed the first score after a bit, and the 10cm ish chunk I wanted came away fine. The rest of the glass went back into its packaging for safe keeping. Then it was just a case of repeating a few times. I wanted various sizes of chunk to ensure some irregularity in the tool. I had another 10 pieces or so but this was the set that I was happiest with in terms of fitting everything up on the mirror with few gaps/nothing poking the edges. Mixed up 1.5kg of Dentstone KD with 450mL of water and gave it a good mix, agitated once poured to get the bubbles out, and it's curing now. Used some plain card for the mold walls but didn't tape all the way down and had a little bit of buckling at the joints which won't look pretty but shouldn't be structurally relevant. Now just to wait a week!

Fusion 360 is definitely, hands down, the most accessible CAD system out there which has real power. They're tweaking the features/licensing at present but it's still a very good option (and free). FreeCAD and things like OpenSCAD can be great but have a very steep learning curve in my opinion.

Well, once I've done the "simple" 8" f/5, who knows... The glass has arrived for the glass tool along with the various tools that I hope should suffice for cutting it. Nice big chunky 10mm thick slab delivered in impeccable packaging - tons of cardboard and bubble wrap. I've had a long day at work so my current level of inebriation precludes glass cutting, but it's looking like it's "on" for the weekend or tomorrow evening. Need to make some space on the workbench and then my plan is to score a reasonable (10cm) strip off the side and then subdivide that strip irregularly - should limit working on the whole sheet to a minimum and if I cock up anything with the small strip the damage is limited. Only ~£25 though, so not the end of the world if anything happens - just potentially very messy! The economics of it are interesting. Once I have a working mirror I'm happy with I'm definitely going to take the existing mirror on the 200PDS and measure it as well as I can. The objective in my mind is to produce a mirror of better quality than the commercially available mirrors. As for coating I'm currently planning on shipping it off to OOUK for a Hilux coating - seems a sensible enough option and won't break the bank, plus I know OOUK can do a reasonable measurement on their Zygo as a final QC step prior to coating.

Just a single short night's data, and wasn't entirely sure how the capture was going, but it turned out alright! Shot on my 200PDS/EQ6-R Pro with ASI183MM-PRO and Baader LRGB filters. ~10x300s each RGB, 24x300 L. Guiding in PHD2 with a 120MC on a 60mm Primaluce guidescope, was around .9" RMS all evening. Image scale is 0.5"/px. Post-processed in PixInsight following a pretty standard LRGB workflow using a light deconvolution on L only and MureDenoise on all, photometric colour calibration, etc.

If you're going to stick to reflectors (and lots of people do!) then I would strongly suggest going down the off-axis guider route if you need to do guiding. It may require a more sensitive camera than a guidescope but it's a lighter solution and mostly immune to differential flexure, and with modern CMOS cameras it's not a big deal to get sensitive enough. For DSOs, a reflector will give you more aperture for your money, and it's probably the way to go. On a HEQ5 I'd probably stick to a 150, but well-balanced you might get away with a 200. You will need to collimate so include that in your budgeting. A decent laser (and a Barlow if you've not already got one, so you can do the Barlowed laser trick) and a sight tube are all you need to do a pretty good job of things. Other than that, Newts aren't that hard to care for. If you're in a cold area then a cheap dew shield will eliminate most/all dew issues, but you may need a heater if you add a coma corrector down the line. This blog post I wrote sums up most of my learnings from being an AP newbie through to being vaguely "sorted": https://www.talkunafraid.co.uk/2019/02/how-to-fail-at-astrophotography/ - I've since "fixed" my flexure issue with some custom guide tube rings and replaced my focuser, but I've not really added anything else and I can make halfway decent images (some of which are at https://www.astrobin.com/users/discardedastro/ but more on this place). The focuser was a huge improvement - I wouldn't say you have to do that at the outset but if you can get a cheap focus motor and a dual-speed focuser to fit it to (the 200PDS and Sesto Senso or ZWO focus motor are good options) it'll change your software control. Getting the mount into software control is a huge win - this is easily done with an eqmod cable. The open source software stack is these days very good - INDI/KStars will get you a very long way and it'll save you a bunch over things like SGP/SharpCap/etc. Once you get the mount pointing itself and plate solving locally you'll find it much easier to get things framed and focused. It is a tricky thing to start in but it's an awesome hobby, at least if you ask me - you will be able to achieve great things with any of the scopes listed. The only real limit is to avoid non-APO refractors, at least for DSO work - there's no real fix for chromatic aberration. But awesome astrophotography is done at all scales of cost and scope - don't feel you have to splurge on a huge scope to get fantastic results. I'd absolutely go for a smaller scope (though I'd stick to the Newts) and appoint it well in terms of tools and accessories. Those are all portable, so if you fancy an upgrade, you won't throw it all away!