Carbon Brush

Hi Steve. If you buy any of the small refractors used, you can always sell them on a minimal loss if they don't work out. I used to have an ST102. Always considered it performed very well for the money. If you don't have a really steady mount, then you aren't going to be splitting doubles and the like. So CA may be tolerable. Or if you spend more you can get an 80mm with better objective to help with CA. A curved ball to throw in. A long time ago I got a lot of enjoyment from my ETX90. I still have it but it has not been out of it's case (except for inspection) for years. It was very good for pullng out of the box, drop on the tripod and show non-astro visitors Saturn, Jupiter, moon craters etc before they got cold or bored. These scopes seem to have fallen out of favour nowadays. Though some have been neglected so you need to check befoe buying used. But they are rucksack/backpack size with the mount included. Use goto, or leave it at home. Stand on a table, or use a tabletop tripod, or photo tripod, or a full size tripod. With the flip mirror it is good for astro or terrestrial. Then again a Vixen VMC95 (or similar) gives great image quality and being lightweight can go on a porta mount. Flip mirror again. I have a VMC95 that goes on overseas holidays. Sorry to throw choices (or is that information overload) into the thread. David.

An observatory is not necessarily a bad place for a computer. If it gets hot during the day (as mine does) the computer is going to be unpowered. So the innards temperature is only similar to a house/office running temperature. If you work in there during the day, you are going to leave the door and/or roof open for your own comfort. When it is cold, not in use, no harm is done. When it is cold and in use, there will be some self heating. Generally this ensures the innards are taken up to a temperature so they work within specification. If running really cold (well sub zero) there is the possibility of timing drift on crystals, DRAM refresh, etc. Having said that, I have not seen any issues caused by cold alone in assorted computers over 10+ years. The only issue is condensation and moisture absorption by components. If you do not power up for a long time (weeks) and do not look after moisture, there is the chance of innards being damp. If the innards are dusty, the moisture forms a slightly conducting layer that will stop things working. There may be issues with low power switching. For example monitor controls not working. I once had a monitor that showed some pixel width vertical lines when cold and damp. After a few minutes running, it always sorted itself. It is good idea to remove the covers from the computer annually, take it outside and give the innards a blast from a compressed air line. Just watch you don't overspeed the fans. Wedge them. Make sure your air line doesn't spray watery rust as well! Getting rid of dust will avoid the observatory damp issues described above. Getting rid of dust from your house computer will let it run cooler and therefore last longer. The above comments apply to electronics built on a glass fibre circuit board with solder resist. That is computer motherboards, hard disc controllers, network boxes, etc. If you have a piece of equipment that is built on SRBP (brown paxolin type material) that absorbs moisture. Also the board tends to be unfinished. No solder resist or laquer. They are prone to condensation. Examples are toys and shoddily built electronics. If you have to use these items, remove the boards and leave them on a radiator for a day or two to thoroughly dry. Then mask off connectors, etc and spray with a PCB laquer. Hope something in here is useful. David. .diain

Yes I was supposed to be there with my son. Actually on the way when I got the message my grand daughter was being taken to hospital in Hull. Nothing serious thankfully. But enough to make us miss the event. Were there just two empty chairs?

Alernatively, which planet is closest to earth today? I did a variant of this years ago for a quiz question. When Pluto was still a 'proper' planet but inside Neptune's orbit.

A balloon that is under pressure (well inflated) will weigh slightly more than one that is not under pressure. Back to a scuba example. Aluminium air tanks, when full (200bar) sink. When going on towards empty (50bar) they float.

Amazing picture. Sadly I was completely clouded over.

Ref Vlaiv: Average person has weight difference about 5g between inhale and exhale (about 4l of air having 1.2g each) As our lungs are always open to the air, there is no weight change. We simply redistribute our mass between collapsed and extended ribs. In a closed system, there is a difference. If you take a deep breath, block your airway then compress your chest, the pressure in your lungs increases. The mass/unit volume in your lungs is therefore higher, so you weigh a little more. DO NOT try this at home! Crushing your chest can cause life threatening injury. An analogy is a bottle weighs the same whether the cap is loose or tight. It is much easier to understand these changes when scuba diving. When you inhale a 4 litres of air, your buoyance changes by the water mass displaced (5Kg) minus air mass inserted (5g). With correct buoyancy control you can make small ascents and descents by breath control only. If you were rotated rapidly on a turntable then the state of your chest might be able to be measured by the speed changes, or changes in energy input to maintain speed. This being a consequence of (expanding chest) mass moving away from the centre of rotation when inhaling. Back to the original question. If you are on scales with a spring or other bendy measuring device, you weigh less when the moon is overhead. If you are on a balance (like those seen in clincs) your weight is compared to lumps of metal. Both you and the metal are equally affected by the moon, you therefore weigh the same. The chocolate mentioned is naother matter. If you stuff yourself with a large mass of chocolate, like 1Kg in an hour, then you cannot possibly digest it fully and absorb all the fat. The rule of mass being proportional to chocolate intake is only valid for low intakes. In other words, stuffing yourself silly with chocolate does not pile on the pounds (sorry kilogrammes). Some of the above is absolute rubbish. Some is valid science. Some is - well - inbetween. Have fun separating the good stuff from the rubbish.

Does this help? The thread also links to techniques others have used. Hope this helps, David.

A vote here for Dell - if you have to buy another computer. We have been using them at work. Approximately 10 computers bought at vrious times in the past several years. Some old boxes were taken out of daily front line use are because they can't handle some new applications that needs lots of RAM, etc. They continue to work on test fixtures, simple machine control, data backup, etc. I really hope I haven't jinxed anything now!

You are working with a high light intensity. This means you don't have to spend on a super sensitive camera for the PST. But of course if you are into night sky imaging.....

This is a really good price. Well under 50% of new price and a hard case included. A scope that is immune to light pollution and can be used in warmer weather has to be of interest in the UK! Good luck with the sale. I'm not buying as I already own one and don't want to try a binocular mod by fastening two togther!

On behalf of the SGL members, thank you for your honesty in describing the state of the finder. In my opinion, the chip in the objective is nothing to worry about. I doubt it will spread and will not affect use. As for the loose threads to attach the diagonal. Again not a big issue and there are solutions. PTFE tape to tighten the threads. Good repair that will last indefinitely. The scope can still be dismantled for whatever reason. I mention these because there are a lot of threads (excuse the pun) on SGL about people having big problems and wondering what to do about minor damage on scopes. If the screw thread was worse to non existent, then a couple of layers of self amalgamating tape on the outside would make a tight grip collar. But tape lacks showroom elegnce. Who cares in the dark? Or if it was really bad, I would drill/tap the body and diagonal to fit (probably M2.5) screws. On the O ring. I have just ordered a lifetime supply of O rings for my finders from fleabay for a few pounds for this very reason. Despite RACI finders being my favourite type, I won't be making an offer on this one. I already have enough in my shed as a result of buying them at full price! David.

In my wooden obsy shed I run a dehumidier. The waste heat from it is very pleasant if I am working in there with the roof closed.

Yes stay warm. Several layers of clothes everywhere. As mentioned above. Batteries are the first item of equipment to suffer the cold. This is one reason (there are others) that big lead acid leisure batteries have been used for astro work. You might use 2Ah to 10Ah of battery in night running a mount and some dew heating. If you 100Ah battery that is peforming really badly in the cold, so what? You are not asking for more than a tiny fration of the capacity. Also if you have the battery nice and warm in the house before starting, it takes a long time to cool being large. A small NiCd or NiMH pack is completely different. You expect to use a significant proportion of the capacity in a night, so loss of performance in the cold does matter. Being physically small, it cools quickly. There are good arguments for keeping any batteries for astro kit in the warm house for charge, then in an insulated box for use. Remove from the insulated box for charging of course. Hope this helps, David.

Thanks Alan for the advice. I will print it so it is to hand when in the garden. I will have the scope on a tripod ready for any gaps in the cloud this weekend. Being new to this scope type I plan on running single stack initially to get used to things. Pics will follow. David.