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About IanL

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    Sub Dwarf

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    Developer of the Imaging Toolbox.
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    Near Colchester, Essex, UK
  1. LBN552 appears as a small orange patch to the lower left of this image, with dark dust and reflection nebulae from the borders of Cepheus, Ursa Minor and Draco. This was a bit of a rescue job as had a bunch of problems during initial acquisition - mount lost power at one point, then auto-focus failed during the second half of the night (still dialling it in with the new scope). Polar alignment is way off as I think the pier has shifted a bit since I last used it, so lots of field rotation caused the outer 10% to be unusable once stacked. I need to make a better flats box too so this is just a crop from the centre of the image complete with dust bunnies. needs four or five times the amount of data really so the overall effect is a bit waxy at the moment, but still it is a pleasing start. Full version here: https://www.blackwaterskies.co.uk/2020/01/lbn552/ Acquisition: William Optics GT81, WO Flat 6AIII 0.8x reducer, ZWO ASI1600MM-Cool, Atik EFW2, Astronomik LRGB 1.25″ Mount/Guiding: Orion ST80, QHY 5, PHD2, Sky-Watcher NEQ6, EQMod, Sequence Generator Pro Processing: PixInsight 1.8.8 Dates: Dec. 18th 2020 Lights: L 60 x 120s, R 30 x 120s, G 30 x 120s, B 30 x 120s, Unity Gain, -15C Bias: No Darks: 100 Flats: No
  2. Didn't get any response on this, maybe being too specific Anyway for reference if anyone else has the same issue and having had time to do some trial and error I can confirm that the reducer needs to be set to at least the 9.1mn mark on the scale for a GT81, the 7.1mm setting in the second diagram is definitely too close. The extra 2mm outwards adjustment goes from visibly egg-shaped stars in the corner to visually acceptable ones. If anything I might try going a bit further out as measurements using FWHMEccentricity script in PixInsight suggest the stars are still somewhat stretched in the corners. Results with the original setting (7.1mm + 0.33mm to account for 1mm thick filter glass): Results with the 9.43mm setting (9.1mm + 0.33mm to account for 1mm filter glass): The stars are visibly rounder in the corners, measurements of eccentricity suggest a bit more spacing needed as ideally would want to be below 0.45 across the entire field. Measuring using a digital caliper, assuming a 1mm thick filter, you're aiming for approximately 90mm between the rear face of the fixed part of the reducer and the front face of the camera body (assuming standard ASI 6.5mm sensor setback), there are a few models with a different value so do check. You'd need to add a further 0.33mm for each mm of filter thickness or reduce by 0.33mm if using an OSC with no filter :
  3. I can confirm the Revelations do have the Lazy Susan bearing by default. One issue is making sure the base is level - if it is the Az action is smooth and can be a problem with the wind moving it like a sail. If not level then it can stick quite badly. With mine the Alt motion is rather too free (probably needs new hold-down springs as it is rather ancient). I use some magnetic welding weights to adjust the front to back balance depending on where I am point it.
  4. David, basic physics doesn't agree with your findings. The diagram in your linked post is absolutely correct - refraction through the filter glass moves the point at which the rays converge to focus physically further away from the reducer, so you have to add more spacing to compensate. Where you're getting confused is that 'optical distance' assumes that the light travels in a straight path from the back of the reducer to the focus point - once you add a filter or any other optical element after the reducer that assumption is broken as the rays converge less during the path through the filter. It may be that the backfocus specifications for your setup aren't correct/clear in the manufacturer's advice. I'm struggling with the same issue right now with my new WO setup, see post below. Basically WO are quoting two different figures for spacing for the same reducer/scope combination, only one (or neither) of them can be right. I'm pretty sure I need to reduce the spacing but need some clear skies to test it out!
  5. The problem won't be whether you can get a few hours out of it at first, I'd think you will. The issue will be that the battery performance will degrade fairly rapidly with repeated charging/discharging cycles. Car batteries are made to provide a lot of current for a short period of time after which they are recharged whilst still mostly full. Deep-cycle batteries are designed to be used continuously over a much longer period and will withstand repeated heavy discharge/charge cycles.
  6. You can certainly do as you propose if you use the right sort of battery. I use one of these, but any sealed 12V AGM mobility scooter or golf buggy battery would do the trick: https://www.amazon.co.uk/gp/product/B07GDPPMNP/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1 Avoid any type of wet battery (traditional lead acid for example) as they're not good for transporting and can generate explosive gas when charging. Non-deep cycle batteries will die fairly quickly if used as astronomers tend to use them To charge up I use a cheap 'smart charger' - just connect the clips to the terminals and leave it plugged in when not using and it will keep the battery charged and in good condition. You do not want the battery to discharge too much as that will also kill it (and they tend to discharge over time): https://www.amazon.co.uk/gp/product/B01MY5UT1E/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 I use a wheeled tool case to lug around all my astro gear, and the battery and charger are just fixed inside that. Just be careful that nothing metallic can sit on the battery terminals and short them out or it'll be a barbecue. You will definitely want a 12V fuse of the appropriate rating set in the positive wire as close to the battery as possible. Just add up the amps drawn by all your gear and go for the same or nearest rating up from that. Do ensure that the wiring is thick enough to take the current.
  7. I'm working on setting up my new WO GT81 (the current 2019 version) with the WO FLAT6AIII flattener/reducer. I'm struggling a bit to understand the correct spacing as the diagrams and drawings provided by WO are pretty unclear and also inconsistent. I've got slightly elongated stars in one corner and edge which tells me that the spacing is not right and possibly a slight tilt somewhere in the train. So the setup is: GT81 -> FLAT6AIII (screwed directly the the M63 thread on focuser) -> OAG/EFW2 (screwed to M48 thread) -> ASI1600MM (screwed to M42 thread) The diagram below suggests that there should be 55mm between the back face of the 6AIII body and the sensor which is 6.5mm inside the front face of the 1600MM. I also need to allow a further 0.35mm to account for the 1mm thick filter (approximately) so the distance is actually 55.35mm. To get there I thus a spacing between the back face of the 6AIII and the front face of the 1600MM of 48.85mm (55mm - 6.5mm + 0.35mm). So having done that I have as close to the 55.35mm 6AIII to sensor spacing as I can get. I know it should be good since it's a straight swap of train from the M48 thread on the back of my SW80ED + 0.85x reducer to the M48 thread on the GT81 and FLAT6AIII M48 thread. The rear of flattener to sensor spacing for both setups is 55mm or so, and the ED80 setup was giving good results. Next I need to set the 6AIII adjustment per the table in the above diagram. The diagram below shows how to set the adjustment: This uses the Z81 (not GT81) as the example, but if you subtract the 55mm spacing from the 58.2mm spacing for the Z81 (both in first diagram above) you get 3.2mm (per the second diagram). So for the GT81 following the same maths you take the 60.1mm 'Backfoucus' value, subtract 55mm and thus set the adjustment to 5.1mm. All good, except there is a second diagram floating about showing different values: This diagram says the back focus for the GT71 is 64.1mm (not 62.1mm per first diagram), and for the GT81 it is 62.1mm (not 60.1mm). So in both cases it says another 2mm of adjustment is required. This is backed up by the 'adjust distance values of 9.1mm and 7.1mm respectively. I'm just wondering if anyone knows which of these two values (62.1mm or 60.1mm) is the correct one. I've currently gone with 62.1mm which isn't giving a great result (worse than my SW80ED and 0.85x reducer). Of course I can keep adjusting until I get it right, but due to the fact you need to screw the 6AIII in or out to adjust, it is painful as I need to unplug all the cables and remove the extension tube from my guide scope for each attempt, then reconnect it all and take a new sample image. I've got limited time and even more limited clear skies so was hoping for a bit of advice to try and get this nearer to right second time around? Thanks for any help you can offer.
  8. With regard to the RA finder, the dew shield is usually totally inadequate, mine dews up very quickly. You could try making an extension out of some craft foam or similar, just cut a length, roll it up and use an elastic band to hold it on the end, or self-adhesive velcro for a better job. The eyepiece end is a total disaster, facing straight up at the sky usually with no protection. Keep it capped unless using it and ultimately yes you may need a dew heater for it. For the rest of the eyepieces, you can certainly use a dew heater, but keeping them in warm-ish pocket and swapping them regularly usually works for me. Some people make heated eyepiece boxes which do the same thing more effectively. For the XT8, it's probably only the secondary you need to worry about in most circumstances. That tends to get cold more quickly but to be honest I don't have many issues with my 10" Dob. The primary mirror in a closed tube Newt generally won't dew up unless conditions are extreme or you have been out all night since the tube acts as a giant dew-shield. You don't really want to be heating the primary since it can create a boundary layer of turbulence on the front of the mirror ruining the view. Some Dobs have built in fans to keep this layer moving and also cool the mirror. The moving air also prevents dew forming in the the bargain. Mine has one but I have never needed to use it (yet). Search for "Newtonian Fan" and you'll get the idea. Definitely do not heat the tube body, that will set up air currents that will ruin the views.
  9. Placing the scope close to the house will delay the onset of dewing not make it happen sooner. The air contains a variable amount of gaseous water vapour, which will condense in to liquid water when the atmospheric pressure and air temperature meet certain conditions. We can't control the amount of water vapour or pressure, so primarily we care about temperature. When the temperature falls far enough, water condenses in to clouds or fog. In temperate latitudes with less water vapour, the air has to get quite cold for this to happen, but in the humid tropics, condensation can occur when it is much warmer. In the case of the telescope, if the lens or mirror cools enough, the adjacent layer of air also cools and water condenses on to the surface of the scope since it needs a nucleation site to start condensing. The mirror or lens mainly cools by radiation. Heat is lost to the environment in the form of infra-red radiation, but it is also gained from the environment by the the same means. The scope is radiating at + or - a few degrees or tens of degrees C, as is the ground and nearby objects like buildings. When the sky is clear at night, space is radiating at about -270 C. So there is a rapid net loss of heat from the scope to space. Placing the scope next to the house blocks some of the sky and will greatly slows the net rate of heat loss since the house will actually heat the scope by radiation. If you park your car next to the house, the windows facing it will dew/frost far less than those facing away since they experience a net heat gain whereas those facing the sky experience a net loss unless it is cloudy (clouds are warm vs. space). Placing the scope by the boiler vent would replicate the tropics, hot humid air, but otherwise the house is not the issue, quite the opposite. The keys are: - An insulated dew shield (e.g. foam) since this blocks the lens from seeing most of the sky (except the bit you are observing) and thus reduces the rate of net heat loss. Metal dew shields cool quickly so are less effective. - Cap the lens or tube until observing for the same reason. - Keep eyepieces in a closed, insulated box until using them. - Use a dew heater to offset the net heat loss. Heater is a bit misleading though, it should only be warm enough to keep the surface above the dew point. If it feels warm then it is too warm and will create local 'seeing' issues. - A bit of breeze is ideal, since air is a good insulator and if it is moving it won't stay in contact with the cold scope long enough to reach the dew point. You car won't dew up and (radiation) fog doesn't form on windy nights for the same reason.
  10. Depends on how you are connecting the mount to the battery. If you add a 12V cigarette lighter socket wired to the battery you will probably be OK. The cigarette plug that may have come with the mount should have a fuse inside to protect against a short. (To change the fuse you usually unscrew the silvery ring on the tip of the plug). If you are running cables direct from the battery to the plug that goes in to the mount then I would add a fuse to the positive wire. You can get round fuse carriers and blade fuse carriers (that take standard car fuses) online. Check the mount's rating (in amps) and use the same value for the fuse or the next value up if not available. The thing to understand about batteries is that whilst the voltage is safe, they can supply a lot of amps, so if you get a short things can melt or even catch fire.
  11. WO 61 definitely ticks all your boxes. Bought one for the Mrs recently and it is a delight to use; solidly build, focuser is super smooth, views are very good - no appreciable colour fringing on the Moon for example. Works well on the cheapo photo tripod as it is so light and compact. With dewshield retracted it is very portable, not quite a pocket scope, but definitely fits a moderately sized handbag. The only question would be mounting it for piggy-backing. It has a single tube ring with a vixen-style "foot" complete with a pair of tripod screw holes. Very handy for grab and go, but not so conventional for mounting on another scope.
  12. The US legal system has the concept of punitive damages which isn't (generally) the case in the UK. So you can make a claim for way more than your actual losses and the court (or jury) can award them as a discouragement to others thinking of trying something similar. They generally get whittled down through a series of appeals after they are awarded, so initial claims tend to shoot for the Moon not expecting to get anything close to what is being claimed. Question is whether anti-trust regulators will decide to take a look at this whole mess and dish out fines or other sanctions. May be they'll consider the market to small-fry to bother with, but either way it is us consumers who suffer when companies behave like this.
  13. Absolutely certain which is why I am just as surprised. Can only think there is a short somewhere or the pinout on the mount connector isn't as I'd assumed. Will figure it tomorrow when I open up the mount to see what's what. Suspect one or more of the chips will be fried though, so likely to require a swap out.
  14. Ok well that was a complete disaster. Tested the mount output and found GND and 12V in the pins as shown in the AZ-GTi manual. Wired up the buck converter and tested fine. Was only getting 4.3V maximum on the output side after adjusting the trimmer. The battery pack was only putting out 11.4V so not too concerned. Wired the WiFi chip to the converter and TX and RX lines. Triple checked for shorts, solder bridges, etc. Plugged it in, powered on mount, small puff of smoke and now have a dead mount board (no response on both axes error). Will have a look in the morning when less annoyed, but cannot see what I got so wrong. Will take a look at the board tomorrow to see if anything can be repaired but doubt it, otherwise it's 50 quid for a new board and still no WiFi
  15. I haven't taken mine apart, but other AZ-Goto users report that the RX and TX lines are connected on the mount board, so it's a half duplex setup. Hence my wondering about the potential flow control line as usually for bi-directional comms on half duplex you need a control line to ensure that both ends aren't trying to send at once. On the other hand the AZ-GTi wiring diagram suggests that only the power and RX/TX lines are actually connected. I do wonder if the AZ-GTi is full duplex, but I guess I'll find out soon enough.
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