symmetal

I've made several modules to help protect circuits from power supply problems, to see how well they perform. They all use mosfets with a very low 'on' resistance, to minimize their impact on being used. 1: Over voltage, under voltage and reverse polarity protection This uses the LTC4365 IC which is only available in a small surface mount package. I first used surface mount resistors and mosfets which made a small module but found the mosfets got a bit warm over 5A as they tend to need thermal vias through the board for power dissipation which is tricky for home made boards. As size isn't a big consideration I used standard components where possible. I used 2 resistors in series for each voltage threshold to enable a more accurate voltage to be set. With the values shown if the power supply drops below 10.5V or over 15.0V the Mosfets will turn off isolating the power supply. The circuit will withstand a power supply going from -40V to +60V and only pass the voltage if it's between the threshold values. There's around 1V hysteresis after shutting down so an overvoltage trip at 15V won't reset until the input volts drops to around 14V. This avoids it rapidly switching on and off, if the volts hovers around 15V. If polarity protection isn't required then only mosfet Q1 is needed, and Q2 can be replaced with a shorting wire link. My test load is a 1.5R 100W resistor fixed to a thick aluminium plate which is why 8.8A is the test current (from a 13.8V supply). I soldered wires on the current carrying tracks to reduce their resistance but they aren't really necessary below 8A, just a thick layer of solder would do. The mosfets just act as a low value resistor so the voltage drop depends on the current. Without the wires the total resistance was 0.015R compared to 0.010 with them. The heat sinks on the mosfets aren't necessary up to 15A or so but added them as I had them. As it is at 8.8A everything stays cold as the whole module only dissipates 0.8 watts. The tiny LTC4365 is on the back of the board and I thought I'd have trouble hand soldering it but I've made around six modules using ICs this size and they've all worked. 😀 🙂 I'll add the other modules I've made at a later time. 😀 Alan

Thanks David. It is for imaging over several sessions, but as the image centre coords are saved as part of the target sequence, selecting slew and then centre will automatically point the scope correctly so there should be no need to check the framing is correct. I think it's best if, as previously suggested, I run the sequence with slew and centre enabled and then pause the sequence, and turn off slew and centre to stop it repeating if I need to stop/start the sequence later. I am just used to using SGP and hoped NINA could behave the same. 😀 I used to use auto-focus with filter offsets to save refocussing as you say, but found the offsets weren't consistant from one session to the next and some filters would not be at best focus, so I always auto-focus on a filter change now. Thanks scrufy. Yes, that's what I found. You can manually centre and auto focus in the imaging tab but not slew. There are all the work arounds suggested but they require sevel clicks and screen switches. 😬 Thanks Viktiste, Yes that'll work, but requires another click/switch/selection on top of the other requirements. 😉 I'm currently sticking with SGP at the moment as I don't have to think about what I'm doing. 😁 Alan

Oh! I agree vlaiv that the more captured frames is better. If Tippon's camera can't do video centre cut-out then the 720p at 120fps will give a very small image of the planets, and Jupiter's rotation effect likely won't be resolved even with a long video. 2 mins at 4k vs 30s at 720p would give the same 900 frames to start off with for stacking, and the 4k will give a much higher resolution image, and the rotation effect, if visible, will be small. My advice was to go for resolution if centre cut-out wasn't available and fps if it was, particularly for planets. For the Moon you may as well go for resolution as video duration is not such an issue, though depending on the accuracy of Tippon's motor drive the target may drift off frame on a long video. Alan

It also depends as to whether you camera just downscales the full sensor resolution to the specified video format, or it enables you to use centre crop video instead where the video format just uses the specified resolution cropped from the centre pixels of the sensor, ie no downscaling so no loss of resolution. Canon DSLRs can use the MagicLantern firmware to enable centre crop video, and also uncompressed video, if it doesn't have it normally. If you can't use centre crop video then 4k will give the highest image resolution. A 5000 x 4000 sensor for example downscaled to 720 means a 5 x 5 pixel area of the sensor ends up as 1 pixel on the video. For planets in particular you need the highest resolution you can use. If you can use centre crop video then use a resolution that best matches the target. Probably 720 for planets, and 1080 or 4k for the moon. 4k using more sensor may show some coma effects so 1080 for the moon may be preferable. A higher frame rate just lets you capture your 1000 to 2000 frames or so quicker, it doesn't give you a better image. 🙂 Alan

The dim frames you mentioned may have been screenshots from Windows 7, where you had much greater control over window item colours with the 'Window Color & Appearance' dialog box. Windows 8 and later removed that option and you have the default white/light grey with only the title bar and pixel wide border colour selectable by 'Settings/Personalisation/Colours'. In order tochange the other windows item colours, it seems you have to edit the registry to do it, as shown here. Alan

Thanks David. 😀 When I load in the sequence which had been previously created in the framing tab the actual coords used will be slightly different to the centre of the target name, in order to get the best framing. Having to select the target again in CdC to transfer it across seems an unnecessary extra step, and the previous framing centre will be overwritten if I use 'replace as sequence'. Just clicking the 'slew' button next to it would be better in that case. Also after transferring the coords from CdC you have to wait for the image to load from the Sky Survey if it's not cached. The correct coords are already there in the sequence, It's a pity they can't be used with one click for a manual slew. 🤔 Alan

Made the light box and drilled the perspex board. Had an old unused metal project box, probably 30 years old or more. Chassis looks like galvanized steel. Mounted 2 fibre panels on the front and 2 12V, 20W, cob led array panels on the back panel. Each fibre panel hold 24 fibres so for the minimum 25 stars needed two panels. I'll add extra stars if it's successful to give a fuller field. A constant voltage / constant current buck converter powers the led arrays and I removed the constant current adjustment multi-turn trim pot from the module and wired a standard rotary pot on the front panel in its place to quickly adjust the current / led brightness. The converter is rated at 20A so is just ticking over in this project and stays cold. As I didn't want to exceed the maximum 1.6A to each led panels I wired a meter in the led supply. A 0R47 2W resistor is put in series with each panel in order to balance the current between them. As the leds get hot at full power they need to be mounted on a metal panel/heat sink. As it is, after 2 minutes at full power the rear panel is too hot to touch. High brightness is only needed for bahtinov focusing and not star shape assessment, and focusing won't need full power anyway I suspect. I used the perspex panel in the end as it's stiffer than the foamex though the foamex would be quicker to work with as it can be cut with a saw and drilled easily. It's robust and waterproof though quite bendable so would need bracing across the back if used as the star board. I did drill the edges of the perspex to fix some aluminium angle for added rigidity though it probably isn't necessary. I should have made the stars the same distance apart H and V but drilled the A2 as a 5 x 5 array without thinking. A 6 x 5 or similar would have been better. I did drill extra holes between the 5 x 5 array to add extra stars if I need to. Fibre couplers fixed to panel. They're the red protective boots on the end in the photo. Just need to connect up the fibre cables now and take it for a spin. 😀 Alan

Have you checked the scope is well collimated Ryan? I'm not a reflector expert as I've never used one, but I assume collimation needs to be done without the CC present and should return the point of best focus/stars to the centre of the frame. At the moment it's well off towards one corner. You need to get that right before adding the CC which is possibly compounding the problem. Edit: Just noticed you said the collimation was checked between the two images, though may not have been done right. My previous post mentioning to do checks pointing straight up to avoid gravity tilt, doesn't really apply to reflectors. Alan

Oh! I don't expect that the MGEN has an ASCOM driver to acess the camera output direct so I don't think you can use Sharpcap Annie. Is it just the star alignment that's always off but the long exposure images look OK without elongated stars? If your polar alignment is off then the long exposure image will slowly rotate around the guide star giving more elongated stars the further they are from the star used as a guide star. The further the polar alignment is out the worse the effect. Alan

If you're using Windows and have a separate guide scope I would recommend the Polar Alignment tool in Sharpcap Pro. It's only £10 for the Pro version and is well worth it just for the Polar Alignment tool itself. 🙂 It's easy to use and is quick and accurate. The tool's built in plate solving needs a FOV of around 1 to 2.5 degrees from the guide scope, so may struggle with an OAG. Alan

Best of luck Ryan. 🙂 You could try taking an image with the scope pointing straight up as that should minimize any droop due to gravity and see if the stars look more similar overall, circling the point of best focus which should hopefully be near the centre. Perhaps take some images say 10 degrees off straight up in different directions to introduce slight gravity tilt in that direction which may indicate what direction the tilt is at a minimum. Correcting tilt is one of the more challenging problems. Your 6D being full frame means getting alignment correct is even more critical. You'll probably still end up with some star distortion nearer the corners even at the optimum alignment, as correcting over full frame is probably beyond the ability of a medium cost CC. It should be a lot better than you have at the moment though. To get the best focus in the centre it may be worth doing the tests I just mentioned without the CC present as the CC is complicating the resultant effects seen. Without the CC the stars towards the edges should at least be a similar shape, circling the best shape stars. You want to adjust the tilt so they are the same size as well as the same shape with the best stars in the centre. Easier said than done. 🙂 Then put the CC back on and see what things look like. Alan

The first image shows the best stars towards the top left, while the second has the best stars towards the bottom right. If the camera was mounted with the same orientation wrt the scope then it looks like the focuser is drooping a bit, and you did a meridian flip between the two images. If everything was aligned on axis then the best stars should be in the middle and any spacing error effects should look similar and get worse towards the edges. Your images indicate one corner is too close spacing wise while the opposite corner is too far and only where the stars look reasonably good is the spacing right. Is there any movement if you hold the scope steady and try and move the camera left, right or up and down. This lets the focuser droop under gravity causing tilt although the problem you have does look excessive. Alan

This looks like the distance spacing between the coma corrector and the camera sensor is incorrect, usually called back-focus though the term has different meanings depending on what it's referring to so can be confusing. The MPCC coma corrector has the 'standard' 55mm required spacing between the rear flange of the CC and the camera sensor. With a Canon EF mount the Canon EF to M42 'T2' adaptor which I assume you have to attach the camera to the CC has a thickness of 11mm. The distance from the camera front plate to the sensor is 44mm, (also called back-focus 😉), giving a total of 55mm as required by the CC. Do you have anything else in the image train after the CC apart from the Canon-T2 adapter as this would cause effects like you are seeing. The effects differ quite considerably between the left and right sides of the image implying the sensor is also not square on to the incoming light from the scope, usually called tilt. Coma Correctors introduce 'opposite' coma to what's incoming to cancel it out and that is designed to work at a specific distance from the CC. Alan

FS order arrived today. Got enough fibre stuff to make 25 stars in a 5x5 array for the moment. 😀 The maximum thickness board on which the ST couplers can mount is 3mm. 3mm black foam board doesn't seem to be available in A2 and would be a bit fragile in any case. I've ordered a 3mm A2 sheet of black perspex, and a matt black A2 3mm sheet of Foamex Foam PVC, to see which is more suitable. Both similar price of around £20 each. 😲 The perspex is gloss black but that may not be a problem as there should be no actual light shining on the backing board. For the leds I've ordered several COB led panels in different sizes and a couple of constant current LED driver buck converters from ebay. All fairly cheap. The COB led panels will need mounting on heat sinks. Alan

Thanks Peter, yes I think leds are safer, and cheaper. 🙂 Light efficiency and loss isn't really an issue in this project and the increased light spread from the exit fibre if fed from a wide light source probably simulates a real star better after having gone through atmospheric disruption. Put the order in today and FS has said it's been dispatched. I ordered this LC Multimode panel as I'm using multimode cable but suspect I could have used a LC Single-mode panel instead and saved £5. If you or discardedastro can confirm they are mechanically the same, or not, that would help when I compile the list of materials needed, and possibly save a bit of money for those wishing to make one. 😀 Alan

The external 12V is needed if you want the cooler to operate. The USB power is only used for the camera. Some cooled cameras, the ASI071MC being one, if given 12V for the cooler will also power the camera from that 12V and disable the USB from powering the camera. The anti-dew heater on the protect window, if it has one, will still work if just powered from USB 3 I believe, as it only needs 300mA for that. Alan

Excellent, thanks for that info. I'll order single mode couplers. This project isn't critical so FS will be fine for the bits. 😀 As part of the test yesterday I tried defocusing to see whether that would effectively give larger stars but it actually gave more star distortions as well as larger stars so it looks like optimum field flattener distance is only specified for focused stars. It seems defocused stars would need a different flattener distance to appear round. Here's the defocused test. Alan

Can discardedastro or PeterW (or anyone else who knows 🙂) say whether the ST multimode cable fits into the ST-ST Single-mode coupler as the ST-ST Multimode coupler will take 2 weeks to arrive as it isn't in stock locally. It appears the guide hole inside the coupler is just for the end ferrule which is specified as 2.5mm diameter for the ST connector. Is it just the end cap colour that's the difference. If it is I'll order Single-mode couplers to get them sooner. They're the same price. I don't know why FS are so low cost, £0.60. I thought I could get some from ebay for less but the cheapest there are £3.50 each. Farnell £6.00 each. 😲 Alan

At 3m distance the 9um fibre, terminated both ends, only fully illumated 2 pixels while the 50um fible, bare at the board end gave a fuzzier edged star with about 5 pixels diameter fully illuminated. With a proper terminated end this should be cleaner edged and a bit wider I would think. I chopped the only 50um cable I had so can't test it terminated both ends. Alan

Hi Ian, 125um is the diameter of the cladding surrounding the actual optical fibre core. In the pursuit of a genuine point source it was considered that 9um would be best. I was using 9um core in the latest tests and were the items listed in the shopping list you mentioned but as I found out last night the 9um core is too small when used a useable distance from the scope as it illuminates insufficient pixels to determine its actual shape. I think the 50um cores will therefore be better as the star should cover several pixels. It'll also be brighter and have a wider viewing angle. In proper usage 9um cores are usually illuminated by a laser while 50um cores are illuminated by a LED. Also for your colour camera the larger star would be helpful as the 9um stars may just illuminate a single random colour pixel. I would think the working distance is dependant more on the focal ratio rather than just distance so a slower scope could be tested with the board closer I imagine as the light cone is not so broad to start with. As you say it may need to be set up in the garden to get the distance, but I can go weeks without seeing any stars and the only 3 nights I've had where stars were visible since buying the ASI6200 were taken up trying to get the spacing right as it's so sensitive to distance. If I could have got it right or very close using the fibre star field, on the cloudy nights I could have had 3 nights of imaging. 🙂 Alan

Is that the main reason you would like a useable star field simulator Dave? For the price you would have hoped those issues wouldn't arise. Unless you rebuilt it wrong. 😉 Alan

I could always set up a heater in front of the board to simulate seeing and get bigger stars that way, but I think 50um fibres are an easier solution. 😁 Alan

No, I'll keep on trying Dave. Oh...., that binning. 😁 That would give even more undersampling as your pixels are 4 times bigger. If I bin my flt98 images the poor corner stars aberrations almost disappear. Alan

Good news. Took some test images down the hall tonight at a distance of 6m compared to the previous tests at 3m and the elongated stars seen on the 3m corners have gone apart from the top right which agrees much more with the actual star image. 😀 So it looks like the flattener incident light angle at 6m is close enough to the infinity light angle for it not to affect the outcome to any significant amount. At least with the ZS61. Here's the test images composite: Now the not so good news. At 6m the 9um stars are undersampled only illuminating 1 pixel fully. This leads to the surrounding pixels getting some light the spread of which seems to vary on successive frames in a random pattern which can tend to appear as a slight star elongation in a random direction. As seen on the centre star on the corner test. The Top right elongation is greater though and is consistant between successive frames. At greater than 6m the stars will be more undersampled so I'm thinking that 50um fibres may be a better bet. The errors on the 50um stars in the 3m tests were just as apparent as the 9um stars at 3m. At a distance of 15m the 50um stars will be the same as the 9um at 3m. 50um fibre is multimode compared to the 9um single mode but that shouldn't matter in this application. Multimode vs Single-mode. Here's the 50um LC-ST multimode duplex OM2 patch cable that should be suitable. Here's the LC multimode duplex OM4 adapter panel I assume the OM2 cable will fit in the OM4 panel OK. ST terminations are only available in OM2 cable. OM4 is just a more expensive higher bandwidth cable it appears. Following on from my previous post query would the LC-ST OM2 multimode patch cable fit in the OM2 single mode patch panel anyway. The only difference is the colour? Awaits reply from the two experts. 😁 Alan

Thanks Peter, Yes, prices have thankfully come down. 😀 I don't know whether a more collimated light source will affect the star aberration results. It'll give a narrower exit angle compared to an area light I imagine, but is that a bonus in this case? We'll have to see. 🙂 I chose LC over SC in the end as you can get 24 LC fibres in the panel frame verses 12 SC fibres and ST patch cables seemed to be more common to LC. I was wondering if the different LC panel adapters specified for OS2, OS4, single/multi mode, UPC/APC etc are physically the same and just the colour is different to identify its use, or are they actually different and an LC cable of one specification won't necessarily fit in another? Same with SC adapters. 🤔 Alan