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digital_davem

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Everything posted by digital_davem

  1. I started this astronomy lark just over a year ago with the help of ebay and very little money. First, I picked up a classic 3" Japanese 1970s achromat refractor with a 1250mm focal length f/16 focal ratio (so very forgiving of eyepieces). Branded Prinz 660 and originally sold by Dixons. I paid the princely sum of £27 for the scope. Picked it up from the seller from a motorway services car park. It came with various accessories, including half an EQ1 mount, eyepieces and a big wooden coffin, none of which were any use! I decided to refurb it by replacing the old 1" eyepiece holder with a modern 1.25" visual back and got a small collection of decent budget plossls (£20 a piece). It cleaned up very nicely and gives excellent views with pinprick stars and good contrast. However.... it's 4 feet long and hard to mount steady at high magnifications. I have learned that mounts are very important as a wobbly view drives you nuts. And mounts can be expensive even if the telescope can be cheap. It's worth considering that big, long telescopes need solid mounts. My second purchase was the 130p reflector mentioned a few times already. I picked mine up mounted on an EQ2 for £45 in excellent condition except for some paint missing from the counterweight. It's pretty good. The tube is very light and the F/5 short focal length is easy to mount. I can pick the whole thing up and carry it and it fits in the boot of a Golf. For £45 for the tube, mount, tripod and two standard skywatcher eyepieces I was quite chuffed. It's easy to get carried away in a high priced hobby but for beginners it is still possible to get a good starter without too much financial investment. I did make one mistake - I got a vixen porta ii mount from ebay. It is not strong enough for the long Prinz 660. It's ok until you touch it then it vibrates too much and too long. Better than nothing but I should have saved my pennies for a Skytee or a EQ5. But then again, you don't find out until you try :-)
  2. Update I have managed to make some improvements. The locknut that holds the cog gear tight against the worm presses down on a nylon washer which presses on a big washer under which sits a thin mis-shapen washer which I guess is intended to act like a spring that is compressed by the big washer when the nut is tightened. I have removed the spring washer and the nylon washer and I can now tighten the locknut much more firmly. The push bearings and slow mo still work after this surgery, so I'm not entirely sure what the importance of those two parts is. Anyway, the mount seems more stable. There is still some movement at the eyepiece but it seems to be flex of the whole mount and tripod rather than the worm drive and I suspect that is inevitable given the length of the scope and the lever effect. Looks like the skies are clearing slightly after a miserable day, will try it out. I bet short scopes like the Skymax 127 would work better on the Porta.
  3. Hi guys Thanks for the replies. I've cleaned out the old grease and dirt from the alt mechanism and re-greased it which has made no difference at all. I'm not sure what the problem is exactly. The worm mechanism is very smooth when you operate it, so that isn't the issue. The main symptom is that if I grip the barrel or drum (or whatever it is called) that the puck bolts to with one hand and the other half with the other hand and twist, there is a millimetre or so of flex and it makes a click as you twist it back and forth. Tightening the main bearing has no effect. Looking at it dismantled, it looks like the big aluminium cogwheel that sits over the central spindle wobbles slightly even when it is not being turned. There is a tiny amount of play. There is a gap either side of the spindle just below where the locknut sits that looks like it could take a shim which might stop the spindle rocking. But I would guess there is supposed to be some flex to allow it to mesh with the worm without risk of seizing? The problem is only really troublesome when focusing, the millimetre or so of movement makes the scope wobble too much for easy focusing. This is the only mount I have experience of apart from the EQ2 on my 130p, so I'm not really sure whether it is normal for there to be some minor play. Perhaps I am just asking too much of the lightweight Porta to mount a 3" 1250mm f16 classic achromat? Maybe I need something stronger like a Skytee? As for replacing parts, I would need to know for sure it would fix it, otherwise I'll risk wasting cash that could have better gone towards a stronger mount. What do think, is this normal for a Porta? Dave
  4. Astroboot have brand new 130p OTA only for £45. Looks like they even have a 2" focuser! Obviously you would want an eyepiece to go with it but they can be very cheap for a basic one. They have dovetails fitted so you fit them easily enough to a cheap mount/tripod if you can find one. There's even a standard one for £35 quid without the dovetail. Useful if you can find someone is selling their 130p mount and rings.
  5. Hi Anyone have any experience with reducing backlash in worm gear slow motion mechanisms? I have a vixen porta ii mount. I've replaced the aluminium legs with DIY non-adjustable height wooden legs so the tripod is very solid. However, I've noticed some unwanted play in the altitude axis of the mount. I took apart the mount to see how it works. There are two separate motion mechanisms on each axis. The first is the 'push' mechanism provided by a simple rotating bearing. This can be tightened with a hex bolt to adjust the amount of resistance to taste. Loosen them completely and the axis spins freely; lock them tight and axis cannot be pushed at all. In between settings provide resistance. The second motion is the slow motion control. This is provided by a brass "worm" and an aluminium gear. Turn the end of the worm, and the gear moves, adjusting the position of the axis. These two mechanisms are completely independent - if I lock the push mechanism bearing bolt tight, no movement is possible by pushing the scope but you can still move it using the slow motion control. There is no way to lock the worm drive in one place. The push mechanisms are fine on both axis with no unwanted movement. On the az axis, the worm drive is good as well. I can lock the push mechanism down and there is no play in the slow mo worm drive. However, on the alt axis, the slow mo worm has some slop. Even with the push mechanism locked, there is still movement if move the scope. What this means in practice is with my long classic f/16 refractor the mount is permanently wobbly in the alt axis. Given that the az axis is fine, this isn't simply a case the mount isn't up to the job - it is a fault of some kind in the worm drive. Anyone got any idea how to tune it? Cheers Dave
  6. Completed around 3 hours of observing mostly of moon and jupiter with 130p/650 f/5 and 76mm/1250 f16 classic refractor. Moon comparison: At 100x both showed essentially the same detail but the frac was a little crisper and contrastier. Not so much that you would really be able to tell unless you were swapping back and forth. Jupiter comparison: Again at around 100x both showed the equatorial bands clearly but the frac also hinted at some polar texture missing from the newt. Again, there was a slightly crisper/contrastier view from the frac. Also, the Galilean moons were rendered at points by the frac but the newt made them slightly starburst like. Star test: According to this site: http://www.garyseronik.com/?q=node/238 you can check collimation by defocusing a brightish star and examining the "donut" blob this creates. If you see a central dark area surround concentric rings with the dark spot dead in the middle then you OK. If the dark spot is offset, things are not square and need adjusting. Happy to report that my dark blob was a perfect bullseye in the centre of the blob. Still can't quite get over the perfect polar alignment entirely by luck!
  7. Doing a comparison between the 130p and my 3" classic refractor tonight using the Moon and Jupiter. Both seem at the crispest around 100x and there isn't much (anything?) between them on the Moon. It's suddenly gone cloudy; if it clears again I shall try Jupiter. Then a star test though that will be pure experiment as I'm not sure what to expect. I did notice that if I totally defocus Jupiter it becomes a big circle with a black circle in the middle with cross hairs - looks remarkably like the view through the collimation cap! p.s. I shoved the eq mount out in the garden randomly this evening and am amazed to discover I have achieved an excellent polar alignment by sheer chance. Can track target perfectly with RA manual slow motion control! Bet I'll never manage this again on purpose.
  8. I've read a lot about collimation and much of it makes it sound like trying to develop a theory of quantum gravity! Two resources make it sound so simple it's child's play: 1. A youtube video made by two guys in a telescope shop who start off by loosening everything so badly that you can't see anything then use a laser collimator to do the secondary and primary collimations in about 2 minutes flat. 2. This website http://www.garyseronik.com/?q=node/169 which says most resources grossly complicate things by going for perfect collimation when a basic collimation is good enough for most purposes and very simple. He says use a collimation cap to collimate the primary only as that will do for most people. I followed these instructions by: 1. Drilled a hole in the focuser cap 2. Made a hole in a circle of white paper which I put inside the eyepiece cap 3. Removed the backplate of my 130P/650 to expose rear of mirror 4. Loosened the 3 tiny allen locking bolts 5. Adjusted 2 of the big silver phillips head bolts while looking through the hole in the collimator cap After this I can now see: i) the whole of the primary mirror, including the 3 mirror clips ii) The black circle of the secondary centred in the middle of the primary ii) The secondary vanes (look like cross hairs) ii) A doughnut shaped white circle positioned right in the middle of the black circle of the secondary mirror I stopped at this point and re-tighted the allen head locking bolts. As far as I can make out from Gary's website, this should be good enough to start. The thing that worries me slightly is that he says I should be able to see a black dot in the middle of the doughnut (the reflection of the hole in the collimation cap). I don't see this because the view is too dark in there. - Should I worry? - Have I pulled off a basic collimation or not? How can I tell if it's correct? Can you tell in daytime with terrestrial viewing or is a star test the only true test? Thanks Dave
  9. Big Thank You to Everyone Loads of useful info on this thread and in the links. A special thank you to Peco4321 for the DVD which was quite good and very helpful. Collimation next....... ;-)
  10. Couple more questions... 1. When moving the scope around the dec and RA axes it moves very smoothly most of the time but there seem to be some positions where the is a slight resistance to moving and you have push it harder. Is this normal? 2. What's the metal thing that is next to the slow motion knob on the RA axis? It's a piece of thin flat circular metal about an inch is diameter with a notch on one side and a sticky out piece. It is bolted to the mount such that it swivels freely most of the time just behind the slow motion knob, but in one position it touches the slow motion shaft. It looks almost like it was supposed to be some kind of crude brake but it doesn't seem to have an obvious use. It is not mentioned in the manual,although it appears in the diagrams.
  11. Thanks, folks. I managed to get out and look at the moon and jupiter briefly last night but I was just pushing and shoving the scope randomly! What I've learnt so far: - an EQ mount has 4 axes: left/right to local horizon; up/down altitude for setting latitude; RA; declination. - the first two are just for set up, the latter for actually pointing the scope - there is a big silver wheel attached to a worm drive on the RA axis - this is slow motion control for tracking targets. This had a strange piece of tin next to it (a thin round plate with a notch cut out of it and a bit sticking out to move it with. No idea what this is for, looks too flimsy to do anything. - the RA and Dec axes have setting circles but the DEC one is fixed while the RA one spins round. No idea why. - There are large knobs on the RA and Dec axies that appear to release the mount and allow free movement. Presumably you release these to swivel to your target, then tighten and track with the slow motion control? - I obviously need to align the scope to Polaris somehow but the guides I've looked at quickly don't seem entirely clear how this is done. Will need to study them more carefully - I need to do something with the counterweight to balance the scope but the guides seems a bit handwavey as to exactly the steps to follow. Need to study this more carefully. It's a second hand scope previously used by a young lad for astronomy GCSE. Probably need to check collimation before serious use, so another thing to learn how to do. It's a bit more complicated than my Vixen Porta 2!
  12. Hi I've just acquired a skywatcher 130P 650/f5 on a Eq2 outfit for the princely sum of £45. And I have no idea how to use the EQ mount (used to Alt-az). It's got a lot of knobs and scales but where to start? There are no instructions but even if there were I don't think they would be helpful judging from the online version which devotes 2 sentences to set up... Cheers Dave
  13. I've tried varying the light polution setting between 1 good and 9 terrible and I can't say I can see any effect of the view through Occular with it set up for my gear. Take jupiter for example. Throught my 3" f16 achromat using a 7mm eyepiece, I see the top and bottom equatorial belts as faint thickish lines. No irregularity, no spots or blobs, no colour and such low contrast that they are only fractionally darker than the disk. Using occular on the most hostile settings, there is far more detail, colour and massive contrast, like it has been heavily sharpened in photoshop. The main moons are big disks in occular but pinprick points in my scope. I don't much similarity at all between the view and the simulation, to be honest. Occular seems "glammed up" to me.
  14. I find this simulation interesting because I have a pair of Royal Astro 20x80 bins and the view of Andromeda looks nothing like either of the images above. Instead, what I see is a shapeless grey smudge. No central hotspot, no surrounding disk gradatuating lighter as you move outwards, just a featureless irregular smudge. Pretty much how it appears through my 3" classic refractor as well. I reckon my London suburban skies are to blame. Stellarium needs a sky pollution filter to give more realistic simulations.
  15. It would be interesting to hear what Ed Witten or Brian Greene have to say on this subject. Or, another way of putting thiis is: your postings on this idea are vague and hand-waving. You should re-cast them as a rigourous mathematical framework, demonstrate that they accurately reproduce the known characteristics of the universe to the same or better level pf precision as current theories AND that they then make testable predictions of things that elude current theories. Then get it published in a reputable peer reviewed academic journal. Sharing it here is just pub talk, entertaining at best. You should also be wary of insulting every professional physicist and insitution as a tactic to get your idea accepted. It won't work, you'll simply get ignored as a crank alongside all the other millions of people who behave similarily.
  16. There are reasonble theoretical reasons for WIMPs being the correct model but obviously no guarantees. Your implication here is that WIMPs are the only game in town as far as the dark matter community is concerned and that the whole community is doing nothing else but spending money searching for them. Which is clearly ridiculous - many other avenues have been and are continuing to be explored eg asymmetric dark matter, Axions, dark matter free ideas like MOND, MOG, TeVeS etc. I can't help but think that whenever I see statements to the effect that "the physicis community is incapable of understanding" this or that, that, it is a red flag to a personal agenda at work. The physics community is a very large group of individuals, not one entity, it makes no sense to dismiss them as if they were a single obstinate, blinkered conglomerate. If your ideas have merit, they will be being worked on by people, it's as simple as that.
  17. A more pertinant question might be: - according to an estimate by Physics Today, there are approximately 1 million practicising physicists in the world today. (http://scitation.aip.org/content/aip/magazine/physicstoday/news/the-dayside/one-million-physicists-a-dayside-post) - according to you, 999,999 of that cohort are brainwashed and can't see the truth of the most fundamental theory they have devoted their lives to the search of despite it being right in front of their faces. - Except you, of course. Yet, despite having exclusive, sole access to something the entire community would stew their grandmothers to possess, no one, bar 3 members of an obscure part of an amateur star gazers forum, gets to hear this revelation. What's going on?
  18. The OU video materials pronounce it "de broil" but who knows.
  19. Lol, I hope I have got it right then. seriously though, I remember the first time this was explained to me and the simplicity of that equation and the idea that, what I like to think of as the stickiness of space (permittivity and permeability), fixes the universe's speed limit. It just blew me away it was beguilingly intuitive. Of course Maxwell was the genius that took us to that point of understanding, no wonder Einstein credited him so much. Jim Phyicists will (and do) consider every imaginable idea in the competitive fight to make a breakthrough. There are endless examples of conjectures, partial theories and speculations that phyicists are trying and working on. There is no lack of effort, imagination or willingness by professional physicists to consider each and every approach that can be dreamed up. But there is always the problem of making every new idea that solves one problem fully consistent with everything we already understand well. And so far, most ideas, no matter how promising, fall over at some point. Amateur enthusiasts pushing one approach or another seem to consider themselves immune to the requirement for their theories to meet the challenge of not only solving the immediate issue but maintaining consistency with everything else to endless numbers of decimal places of precision that experiments have achieved. If there really was a theory sitting in full view that a member of a stargazing forum could spot, don't you think the thousands of top physicists all desperate to make their mark, would have picked up on it? The only other mechanism that could be proposed to explain a lack of enthusiasm for these obvious ideas is some kind of conspiracy to suppress the truth for unknown reasons. That kind of thing seems to appeal to some people, but holds no interest for me. What is more likely do you think: the Theory of Everything invented by Everyman is being suppressed by the Ilumminati or that it is just plain wrong?
  20. That's its orbital period, its rotation period is 59 days. That's its orbital period, its rotation period is 59 days. Oops! Thank you, careless cut and paste error.
  21. Perhaps a risk of sounding pedantic but I can't accept this description. True, all motion is relative and you can seem to negate it by choosing an appropriate reference frame that is matched. However, in ordinary speak that is not what we mean when we talk about a planetary body's axial rotation. For example, if you were in a space craft that was in geostationary orbit, your orbital motion in synchronised with the rotational motion of the Earth such that you hover over one spot on the ground. To you, the Earth would not appear to rotate. But it would be Quixotic to deny that the earth rotates on its axis. Billions of people on the ground experiencing the day/night cycle would disagree with you. And indeed, if you were to raise your eyes from that spot on the ground to observe the background starfield you would see it spinning around you proving that you and the Earth were indeed experiencing axial rotation. When you sit up all night and watch the starts swing across the sky you are experiencing the Earth's axial rotation. You would experience exactly the same thing if you were to try it on the Moon except the night would last (Earth) weeks. Likewise on Mercury (with an even longer night). The existence of rotational motion of a planet is not dependent on the additional orbital motion of an observer, that merely creates lines of sight "stationary appearance" effects. The moon, Mercury, all the planatary bodies all rotate on their axis with respect to the background universe, always have and always will.
  22. On a practical note, even if we were somehow to be transported to these planets, they are not believed to have solid surfaces so there wouldn't really be anywhere worth navigating too ;-)
  23. Physics is often very subtle and takes considerable skill to think about correctly. The lay person, without the requisite training, having an amateur stab at it, can sometimes get in an awful muddle and come up with seemingly incomprehensible paradoxes that are actually perfectly satisfactorily understood by experts. This is the normal state of affairs and popular science writers are accustomed to dealing with muddled enquiries from enthusiastic, but untrained readers ( one, I remember saying he keeps a list of the top 100 most common blunders made by amateurs who believe they have dispproved Einstein and simply responds to the regular letters he receives my returning the list with the appropriate numbered error ticked). The infamous scientific "crank" is someone with an obsessive and deep seated belief in some pseudo-science idea they have dreamed up that makes no sense to an expert. Professional scientists,if they were inclined to sacrifice the time to do so, could falsify these ideas without difficulty but they often have a very attractive allure to some lay people, particularly those with some kind of need to be different. The Internet is obviously a fruitful channel for expressing these ideas for people who in the past would have no recourse other than vanity publishing. Speaking of which, I have a wonderful self published tome in my possession by someone called Michael Pinder who declares himself the President of the Decimal Time Society. It starts off quite creditably and is well argued but before long, a simple idea (that we should decimialise time units rather than sticking with the familar base 60 seconds and minutes) morphs into a philosophical treatise into how the switch to decimal units would solve not only economic problems, but all the social ills you could imagine. And by the end of the book, even the text is no longer your familar fixed with set of letters but devolves into blocks of letters of all sorts of strange shapes and structures and the prose converts into rambling poetry. I'm sure there must be some intention behind this design but for something presumably intended to be persuasive to the makes of public policy, it resembles quite strongly the work of (at best) an amusing eccesntric or (at worst) a lunatic. Physics attracts many people and ideas of similar standing - presumably people drawn by the consideration of the infinite. Or something like that. Real physics is hard enough without the distraction of well meaning but silly psuedo-science.
  24. Planets get their rotation from their original formation and will retain it forever unless something interferes. In the case of moons that show the same face to their planets (tidally locked) they still rotate but their rate of rotation ("Day") has been slowed by tidal effects so that it matches the rate of their orbit ("Year") so they show the same face. They are still rotating though. I have no idea why you think their rotation has anything to do with holding them together. If anything, rotation would threaten to disrupt if fast enough (Saturn for example is significantly flattened at the poles because of its fast rotation). ps @Bomberbaz The Moon rotates just fine (if slowly) as does Mercury: Rotation period: Moon: 27.3 days Mercury: 88 days The slowest rotational period in our solar system is Venus: 243 days (which is longer than its year)
  25. The important thing is that we work on understanding the formation of the solar system. Pluto and the other KBOs have an important role to play way beyond what they are called. The weirdest factoid of all for me is that the current favoured planetary formation model (the acretion model) appears to be impossible as, while it is certainly possible to explain how dust particles combine to form pebbles, there is no known mechanism by which metre sized rocks colliding at 40,000 mph can acrete into a planetesimal...
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