Carbon Brush

If you look here... Michael had the wisdom to individually fuse the outputs.

@markse68 The long explanation. Courtesy of NASA. https://mynasadata.larc.nasa.gov/sites/default/files/2018-12/Measuring the Temperature of the Sky and Clouds.pdf Bottom line. Clear sky is colder than surrounding objects, builds, or clouds. HTH, David.

Rigels are great. I have two of them. David.

The tube inside is almost black paint as standard. This reduces internal reflections, improving image contrast. Just how 'almost black' being in part determined by the price tag. Unfortunately some scope insides seem to be smooth black, rather than matt black. Many folks use black flocking material to overcome these issues. The tube inside is therefore the best heat radiator. A white outside being poor for radiation. But as the tube is thin, there is good heat transfer from outside to inside so don't get worked up about colour. Tube colour is as much as anything to get us to buy the latest model. Are Skywatcher green dovetail bars mechanically better than the black ones? Does a William Optics Redcat refractor work better because of the colour? I'm sure my LS60 solar scope gathers more detail because of the red trim.😕 Before worrying too much, give your scope a few runs to get the measure of the problem. If you observe downwind of the local duck pond, you will be in moist air and dewing will be more of an issue than on a hill top. The same goes for being downwind of a central heating boiler flue. As you get a feel for the magnitude of the problem, you can take whatever steps are necessary to avoid the dew. If you don't stay out for hours on end, it may not be a problem. Keeping eyepieces in warm pockets avoids condensation. I made a 12V heated box for eyepieces some years back and posted pics on this site. For some reason it provoked zero response. Perhaps because I made it from scratch, rather than adapting a standard product. Advice on dew heaters does of course depend on your scope type. HTH, David.

Going back to earlier posts. A few general comments. Not nexessarily appicable to the OP. I would avoid running the mains cable in the same duct as control/network cables. There is the tempation to run an 'ordinary' mains cable. If it is not armoured, then accidents while digging can allow a mains to network connection. The absence of a screen/shield on the mains lead means it is easier to get noise and interference coupled to the network cables. By having the cables laid riht next to each other, or touching, there is potential for cross coupling. Powerline adapters can be OK. However, they work by putting high frequency (radio) signals onto the mains. If you have a long cable run, the core/core capacitance attenuates the signal. I use powerline adapters in the house <10M). Garage at a push (>10M). But they can't handle the longer cable run (25M) to the observatory. HTH, David.

Yes it can be a problem! Consider a reflector scope with a thick mirror, stored in the warm house. You take it outside and the main mirror starts to cool. The mirror cools in an uneven manner. Edges and the thin centre lose heat more rapidly than the other regions. This causes the mirror to distort a little. It is no longer a well figured parabola. This prevents you from getting pin sharp stars. Next problem the warm tube and warm mirror cause rising air currents in the tube. The difference in refractive index between warm and cold air means you get image distortion that varies with time preventing good viewing. When you do focus, the warm (steel or ali) tube is longer than a cold tube. As the tube cools the focus has to be adjusted. Once the entire scope has cooled to near enough outside temperature, everything becomes stable and you get good performance. Next problem. The clear sky is cold. A weird statement. If you look around with an infra red thermometer, you will find the sky is colder than the nearby walls, hedges, ground, etc. This means that as time passes, the scope mirror continues to cool towards sky temperature. Ever wondered why sometimes in the morning your car windscreen is icy but not the side windows? Side windows, being near vertical, are at surrounding temperature. The sloping windscreen points to the sky, so cools towards sky temperature. This is the point where your scope glass gets dewed up, but not other things. Though there are nights when everything suffers condensation. If you can heat the important glass bits, just a little, you prevent condensation. Just a little is the important bit. Too much heat and you are back to the problems seen when you first take the scope outside. A red light torch on glass will help you to see condensation before you notice poor viewing. That is the point when you nudge the heater power up a little. If you use a dew heater on the glass and put only enough heat into it to prevent dewing, there is minmial heating. The glass does not distort and the tube does not suffer significant wrm air currents. A blast from a hair drier over the front of a scope is enough to lose the image. The hair dryer is really a last resort. Or for drying everything off before packing away. Hope this helps, David.

As a rule of thumb, a fuse will pass the rated current indefinitely at 25C. PTC polyfuses, PTC thermal fuses and similarly named devices have the same characteristic. So do circuit breakers. All the devices become more sensitive at higher temperature and less sensitive at low temperature. That means a 1A fuse at room temperature becomes a 0.9A fuse in your central heating boiler and a 1.1A fuse inside your deep freezer. For astro use, this is not a big issue. You are out to catch faulty wiring, not try to catch something going 10% over current. If you apply a (nearly) short circuit to a fuse, it will blow at anything from a few seconds at 2x rated current, to milliseconds at 10x rated current. You can buy fuses with different time lag characteristics. But remember the characteristics vary between manufacturers. Many sellers describe fuses as 'anti surge' or 'time delay' but you can get a 2:1 variance on time by changing manufacturer. If you buy a named fuse (for example Littelfuse) you can look up time/current data. If you buy from a retailer/ebay etc, you have no idea what the characteristic is going to be. A word of caution here. I have seen equipment sold on Amazon and made in China that had dangerous fake fuses in the mains side. I always swap out mains fuses for something with known provenance if in doubt. Circuit breakers are tending to fall out of favour. They can be expensive and require front panel work to fit them. They have the benefit that it is easy to see when they have tripped and you can buy different time lag characteristics. Looking at the polyfuse type of solution. These have a time/current characteristic determined by the manufacturer and are not generally available in different time lag variants. These again tend to trip in a few seconds at 2x rated current and a fraction of a second at 10x rated current. They are ideal for astronomy because if you get a wiring short, all you need to do is remove power, fix the short and away you go. No hunting for a replacement fuse. All fuses, circuit breakers and polyfuse devices have a maximum fault current. That is the maximum current that is allowed under fault conditions before something unwanted happens. If you take a glass fuse and have a big fault current (for example using it on the mains) then it can explode spectacularly. Glass fuses are best thought of as having a fault capability in the tens of amps and low voltage. Circuit breakers vary considerably in their ability to deal with a fault. The (physically large) breakers in your fusebox at home can handle hundreds of amps fault current without failing. Other breakers for inside equipment may have a life of tens of operation with a fault current of 30A or so. Polyfuse type devices have a maximum voltage rating and a maximum current break that needs to be checked. Very often a polyfuse will have 40A max breaking. But if you put one straight across a 12V lead acid battery you can get a couple of hundred amps. Usually if you do this a few times the polyfuse has increased sensitivity as part of the body becomes open circuit. Eventually it fails completely. If you exceed the voltage rating the device may break down can explode - a bit like a glass fuse. Don't forget that when tripped, a polyfuse self heats with a low current through the load. The polyfuse body tends to remain about 125C or a little hotter until you remove the load (faulty wiring) or incoming supply. Not hot enough to melt solder. But don't put it next to a bit of soft plastic. HTH, David.

The fuse in a 13A plug should always be rated with consideration for the expected load. Given that the smallest fuse you can buy is 1A, that equates to 240watts. That is a lot of scope power, dew heating, etc. What is actually needed for dew heater fire prevention is protection in the 12V side of things. Take this hypothetical setup.... You have a mains to 12V 10A power supply. That is 120watts You might think a 1A mains fuse should be good. 240V & 120W = 0.5A. In practice, inrush current and fast acting mains plug fuses (long explanation so just accept it) mean you may have to go up to a 2A or 3A plug fuse. In other words the plug fuse is only useful for serious failures within the power supply. The power supply should (but may not) have some sort of current limt on the output circuit. If you overload the output it may well limit around 15A. Or it may struggle along as best it can (20A? 30A?) until an internal thermal trip or big fuse goes. If you consider a 4 channel dew heater, without taking it apart you often do not know what internal current limt measures are in place. For example, you might have a controller claiming to deal with 5A per channel with a car cigar plug on the inlet. The cigar plug may or may not have a fuse. If it does, it is probably going to be 20A. In practice, wire fuses tend to blow in a few to 10 seconds if the current is double the rating. In other words with a 20A fuse, you need 40A for a reasonably prompt blow. If you exceed a fuse rating by 50% it will probably taqke all day before it thinks about blowing. But if your power supply can't deliver enough current to blow the fuse, it fuse will never blow. So what about the dew heater output channels? The situation depends on the controller. The cheapest way to build a controller is to simply have a transistor that is turned on/off to determine the heating. No fuses. No thermal protection. No current limit circuit. In general, if you overload a transistor and cause it to fail, it will fail permanently on. Not always. But that is the most dangerous condition. There are measures that can be taken at design to shut down a channel if there is an external fault. But these cost money and we all look for the cheapest box. With my hypothetical setup, if the wires at the dew heater short together, then you will get a fire. Quite simply there will be 10A and more flowing through (in all probability) a few strands of wire and you will get localised intense heating. Even if there is not significant localised heating, the wires running from the dew control to the heater will get warm, possibly starting to melt insulation. If you want to know what 120 watts (or less) feels like, just get hold of a light buld. That is a filament lamp. Yes you will get burnt. Unless you know the innards of your power supply and dew heater controller, you need to add your own protection at the outputs of the controller. That could be a small box containing 4 fuseholders. Put a fuse in each holder that is rated a bit higher than the heating element. If you change your setup, you can change the fuse value. If you use 20mm or 1.25" fuses and holders then you can buy fuses in any value to suit the application. Alternatively you can make something using PTC thermistors but these mean soldering. Or if you ask the controller manufacturer about his overload protection? Is a flaming dew heater an issue? In itself probably not. It is outside and low cost. But do you want to melt your guidescope, telrad, OTA lens cell, etc? If you look back 15-20 years, there was little scope electrical wiring. As it was more specialised, users tended to think more and ask more questions. Nowadays there is lot more scope wiring. This gives much more opportunity for problems. There is pressure on equipment price so effective overload protection may be unaffordable. Further, there is tendency for us to buy a power supply, a heater control and the heaters without thinking of the complete assembly 15 years ago we might have bought everything from one dealer and had the over the counter advice about wiring techniques, protection, etc. Today we are more likely to buy the items online, from different places. Each 'box' or part of the system may well be built to a standard and be CE (or whatever) stickered. But is the combination of devices fit for purpose? David.

Cold is not a damaging condition. Well having said that, if you have a lead acid battery based powertank, the battery won't be quite so good sub zero. I have not experienced any DSLR issues from cold, and have not heard of anyone who has. In fact some people deliberately cool (using peltier pumps) cameras to reduce sensor noise. The problem when viewing is the condensation on the glass bits. There are lots of threads on dew prevention. Condensation on low voltage (12V scope, etc) circuits is not a huge problem. If you run a mains supply outside, that does need thinking about. At the end of the session, you need to bring everything back up to house/storage place temperature. Preferably without subjecting a cold scope to warm and moist house air for a long time. The worst thing you can do is take your cold scope and accessories indoors and box them up while cold. The condensation stays there. There are good aruments for taking the scope into (for example) an unheated garage and warming it using a hair dryer. Once up to 20C or thereabouts you can take it indoors without condensation from your humid house. Lots to think about. But nothing too difficult to sort. David.

Network cable should be good for a 100M run. Whether from router or a computer, or a switch. CAT6 has the benefit of lower signal loss than CAT5, which shows on long lengths. In practice the loss restricts speed, rather than losing data. Nowadays most network routers/switchers check the line for signal integrity and adjust their speed to suit your cable capability. So if you have a slow router, you probably won't see the benefit of CAT6. But if you have fast router, signals will be slow on Cat5, but fast on Cat6. However when I say slow or fast, this only matters if you are transferring huge files between computers. If considering connection to the internet, this is usually the slowest part of data link. I would use Cat6 if planning for the future. New network 'boxes' generally support higher speed data transfer. USB is best considered for linking devices that are next to each other. The cable linit is 5M unless you use a buffer/convertor of some description. Further, a lot of USB leads do not work all that well. Buy a known name not the cheapest. Electrical earthing is a subject often misunderstood by water, gas and electrical people. Yes you are supposed to earth water and gas pipes. If there is a mains item on the steel pier, it should be earthed. In other words if you have a 13A socket on the pier, then the pier requires an earth bond. If you have a goto mount, that is all low voltage kit that is isolated from the mains by the (usually) mains to 12V power supply that is often away from the pier. In this case a safety earth is not required. Earthing is about ensuring everything metal is at the same electrical potential. In addition, the bond should be strong (thick) enough to withstand the prospective short circuit current until the circuit breaker (protecting the cable) trips. In this case, taking the braid from the armoured mains cable to the pier is adequate. But if you clamp onto a single strand of the cable, it won't be. Think of a single strand as being a piece of fuse wire. This has to remain intact until the circuit breaker in the onsumer unit trips. Any elecrician should understand about this. If the installation allows, ask the electrician to provide a separate circuit breaker and residual current breaker to feed the observatory only. You don't want the house telly to go off because a mains socket in the observatory has got damp. Sorry if this confuses more than helps. David.

A steel wire armoured cable should be OK buried for years. It is affordable. Mains electricity will still be in use. If you are bothered about getting it 'signed off' just have a chat with your chosen electrician. Basically you bury the cable, pin to walls where required, etc. The electrician terminates at each end and tests. Most electricians would rather be involved in 'clean' jobs. Not working trenches. The only problem you might find is that some domestic electricians are out of their depth when involved in outdoor cabling or anything 'non house'. If the electrician says it can't be done, it is worth asking for a second opinion. Data cables are another matter. You can buy multicore data cables with steel armouring. If you have to ask the price, you can't afford it. Money is better spent on scope kit! I would be tempted to use 'drainpipe technology' for data and control. Buy readily available water pipe or drain pipe. Don't be afraid of going up on size. It will be hidden. It is all cheap and cable requirements have a habit of breeding as new devices come along. Run a length of good quality rope through the duct. Every time you pull a cable through, run another rope. I would start with 2 off CAT5/6 network cables and a low power (not armoured) 6/8 multicore screened- as a minimum. It is not expensive in the grand scheme of things. The multicore cable can be used for simple heating or dehumidifier on/off control. Use low voltage relays to isolate the mains. It can also report intruder alarm status, etc. Hope this helps. David.

Suggestion that may keep a roof over your head and avoid surgery. Buy a used PST. This can be about 50% of new cost. It is as near to 'grab and go' as you are going to find in Ha solar. See how you get on. When you sell on, the loss should be small. My PST kept me from further spending for several years. For Mercury transit in the work car park I had my LS60 alongside a colleagues PST. He had the easier setup and equal view. On the day the sky limited the view rather than the scope. David.

Slightly off topic. But prompted by Vlaiv. I have seen instances of heatsinks debonding from integrated circuits (chips) following a transatlantic air freight journey. This prompted me to look into the shipping conditions. They are quite worrying for expensive scope parts. Imagine taking a room temperature item and boxing it for shipping in the UK winter. UPS/DHL/TNT/Fedex collect it from you. It spends the rest of the day in the back of a van - unheated. Taking the parcel to near freezing. After a short time in the depot, it goes onto a trunk vehicle for delivery to the airport, again unheated. At the airport it is in an unheated warehouse for a short time. It may even spend time on the tarmac in an aluminium cargo container. By the time the parcel gets onto the flight, it is definitely around 0C. Many cargo flights have an unheated and unpressurised hold. Presumably no money (weight) is spent on insulation. We all know the outside air temperature at altitude is -35C or even -50C. We know that flights follow great circle routing (give or take war zones, politics, etc). This means a transatlantic flight (8 hours or more) spends several hours in really cold air. Transiting over Iceland, Greenland, Northern Canada. Your delicate optical or electronic parts are going to be chilled to -40C or cooler. Further, the pressure at altitude is only about 20% of surface pressure. This means any sealed components containing air are at almost 0.8 bar above ambient pressure. Pressure change is no problem for a Lunt pressure tuner. What about other things? Unintended air bubbles in assemblies? I took a glance at the Lunt and Coronado web sites. Telescope storage temperature and pressure limits are not specified - unless this is hidden somewhere. This means you can buy a new scope, store it near absolute zero and take into space without problem! As for me. On cold days (sub zero) the probability of solar viewing is quite low. With the sun a 26deg above the horizon at noon mid winter, and a clear sky......... David.

Please tell us more.... Are Lunt saying the scope BF may be damaged by extreme cold? Or is this just dew prevention? I can understand keeping the grease warm and O rings pliable.

I will compare with my cg5 this evening. It may be that prying off the black cap will allow internal access to the terminal. David.

Good input from everyone. A short tube refractor is good - though I would suggest alt az mount. The ST80 glass quality is OK for this application. CA will be acceptable for low magnification viewing. The 130 flextube, or slightly smaller, or rigid tube version are also good choices. A small dob needs (or has the benefit of) a table top and chair for comfort. Table for a book, etc. No need for an unwieldy tripod. Chair alongside garden table? Or garden table + bench one piece? More difficult to knock over than a tripod. A 90 Mak is good again. Decision...decisions.....

Hi Neil. Welcome to SGL. The best astronomy forum. Age is no barrier to astronomy. Enjoy the learning journey. You will finds lots of helpful people on the forum. +1 for 'Turn Left At Orion'. My copy (some years back) was money very well spend. Are you happy with state of your scope now you have straightened it out? I'm sure if you ask, you will find someone local to you who would be happy to check it over. David.

I have found generally that plastic/synthetic rubber life expectancy is a bit hit and miss. Not just in astro kit. The rubber tyres on the Skywatcher focus wheels are a good example of degrading rubber. I use O rings instead. I reckon that less than scrupulous manufactuers (of components not complete equipment) let it out of the door if it is the right colour and texture. Chemically it may not be up to the job. The varnish will certainly help bond things together. It may also delay further degradation by keeping oxygen and moisture off the rubber. But that depends on the varnish. HTH, David.

Can yu npost a photo of the situation?

+1 for john's comment above. I have the Vixen version. Quirky little things. Great for a grab and look. Good to take on holiday - being small. Note you need your eyeball quite close to the glass. Definitely no specs. If you have only a long/short correction (not astigmatism) then you can take it up with focus. HTH, David.

How did I miss this when it was first posted? It is an amazing video. A real wow! At 53degN the only green lights I see are from idiots shining lasers at clouds. This video should be compulsory viewing for the (word deleted) at Nottinghamshire County County Council who are gradually changing our skies from sodium orange to LED white.

For me, it is about using the minimum amount of scope heat to prevent dew - rather than remove it. That avoids the loss of focus from a hot air blast. Generally I reserve the hot air for ensuring kit is warm and dry at the end of a session. This autumn is though a bit different. The garden is really soggy and there is often almost 100% humidity on the (rare) clear nights. HTH, David.

At work for overseas shipping we use mainly UPS. But also TNT and DHL sometimes. Always through one of the 'middlemen' as it costs much less than booking directly. Provided you have the actual carrier tracking number, you can track the parcel. The nice thing about these (international company) services is that you can get a good idea of where the parcel has gone. For exmple I can track a UPS parcel from pickup to delivery in for example the USA. I can get times of events at the local depot, the outbound airport, the USA arrival airport, customs progress, then the local delivery network. As a general rule there are never any 'ask again in 3 weeks' response. Yes parcels can go astray, or get delayed, but at least you can a quick answer and nail down the event. Unfortunately usually RM does not link in with the delivery partners overseas and 'ask again in 3 weeks' is the general response to a non delivery enquiry. Hope this helps, David.

Regardless of scope type or size, you need something well baffled with a black tube. That is the best way to deal with the off axis stray light. As an experiment, to simulate light pollution, shine a red light torch across the end of any scope, just grazing the lens on a refractor, or the corrector plate on a compound scope. Or just illuminating a bit of tube in an open newt. Look through the eyepiece, and the sky background is red. Just how bright red depends on the scope. Considering a newt. If it has not-very-black paint, then the scattered light is well reflected. If it is really black or flocked, there is little light scatter. Clearly a long FL with dew shield helps. The same applies to a refractor. The difference between a newt and a refractor (or compound scope) is the ease of improving the blackening. Flocking or painting a newt is easy. But do you want to dismantle a complex scope? A more expensive scope tends to have better paint and baffling. A side by side of similar refractors will show, and the better contrast from better lens coatings. I once did a side by side of an ST102 and WO80 at 3x the price. A world of difference in contrast. Under polluted sky the smaller WO80 would have shown more. I used to own an Orion Optics UK 8" newt. Excellent glass. It gave super views. But the tube inside was best described as dark grey. Under polluted sky contrast (or lack of) made it like a cheap scope. Hope this doesn't create confusion. David.

Dew shields, heaters and hair dryers are cheap. Good refractors are expensive and still use metal & glass. If you are happy with the 130 (apart from dew) why not preserve the wallet? Just my random ramblings. David.