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Ajohn

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Everything posted by Ajohn

  1. Some time ago I saw details on this but can't currently find any at all. There is one web site that seems to measure positions of stars actually through a telescope in order to make one. It's essentially a matter of angles, the focal length of the lens sets the scale. Does anyone know of a source of the information that is needed? The web is rather clogged up with using them rather than any information like this. John -
  2. The errors just result in some loss of contrast, That's where Rayleigh comes into things. He decided that 1/4 wave error resulted in an acceptable drop in contrast. In loose terms the max drop is at the scopes mid resolution point. The max resolution point isn't of much use on planets as the contrast is awful anyway, around 7 1/2 % of what is actually there, no problem on stars. The problem with scopes with mirrors is that the central obstruction can easily have the same effect as a 1/4 wave error and it all stacks up along with seeing conditions. I wonder if people have problems with Foucault because of the bad leads on the web and setting up. When I started looking around at slitless testers I only found one description of setting up and that didn't mention that the return image from the mirror needs remain stationary on the knife edge as the tester is moved back and forth. It has to be for the light levels to match in adjacent holes in a mask. That's the same on other forms of the tester. Also no mention of the fact that the theory is based on the knife edge and source being exactly on top of each other so the separation should be kept as small as possible. I've seen details of several where they could easily have been much closer, usually on youtube. Actually when I think about setting up the usual slitless, a knife blade half way across a led also forming the knife edge I'm beginning to think the whole thing is a bit daft. As a for instance if the tester is dead square on to the mirror the return beam will more or less miss the knife edge. The nice thing about a moving knife edge is it doesn't matter exactly where the return beam is. In fact that can accommodate a bit of an axial alignment error. Anyway I am awaiting a builder to remove and add a wall before I will have some where to work on a mirror but all things considered I'm going for a tester that can easily be converted to the sort of arrangement I have used before. I'll probably build a bath interferometer as well as a 2nd check. This bloke has a couple of decent video's on that subject but I would hold the lens against the cube rather than trying to cement it. That would need to have a shorter focal length for very fast mirrors. It's worth looking around at other designs and I reckon that camera macro slides could be used to make an xyz stage cheaply. Just need big knobs adding to allow finer adjustment. The parts needed are very cheap from Surplus Shed but the beam splitter mustn't be a polarising type. John -
  3. I've found this thread interesting and wonder if the earlier post ( which I hope was on here ) concerning noise against temperature is the important aspect. John -
  4. Not sure if it will be of interest to you Herra but full frame has been reckoned to offer 2 to 3 stops better noise performance than APS. There is a problem though. As their pixel count gets higher and higher that becomes less true. Where is was true is cameras such as the canon 6D but at the 3 stop level even that one may be dubious. In the case of levels like the D800 one of the aims seems to be to do away with the anti aliasing filter as the lenses do that anyway. It looks like this has been absent on compact cameras for some time. All very confusing though. Sensors have improved but so has noise removal software. I own an interesting example of the effect. A Nkon V1 with CX sensor. They did a cheaper Nikon 1 with less pixels and lo it has less noise too. My most used "dslr's" now are olympus m 4/3. I haven't touched aps for some time now. The 6D isn't very well rated by serious photographers - af and etc is too simple. My last ff was a 5D and no interest any more so no idea of used prices. John -
  5. I suspect the problem with suppliers and faster mirrors is time and wondering just how long it might take to reach perfection and maybe seeing them as just being light buckets for nebulae etc where as planets ideally need perfection. Great work again Raymond and thanks for including a link to your flickr pages. There are some shots on it using equipment I have wondered about on smaller scopes especially barlows. There is a shot of the eagle nebula that might interest Tim - 8" Skywarcher. Looks like you have a lot of skill in the astro photo area too Raymond. Something I am not sure I will enjoy gaining. If I can. Ordinary photography was bad enough. I've noticed that GW on youtube sometimes has a hole in the back of mirrors. I had wondered if this was to get it central on the table but maybe it's for location in the scope. John -
  6. LOL I didn't mean any comments people on here might make - just reviews in certain magazines that originate in more than one country but are in "english" and do not in real terms include any useful information. As good as we generally get can be found as for instance by searching iOptron 25GT review on google. Sky And Telescope did one. It does mention that an 8" SCT is "probably" the heaviest scope that could be put on it. It also that it was "mostly" used with 4" refractors. The standard tripod was mentioned too - a common problem really. No results though and no detailed information such as the fact that the worm and wheel are held in contact with a spring which means that there isn't any back lash in that area. A web search would reveal that people may benefit from re aligning the worm and wheel - down to "Chinese" assembly. A fairly common problem. They do however try to use decent sized worm wheels and have also tried to do something about the silly centre of gravity of typical GEM heads which were initially developed for use with long focus refractors mounted on very rigid piers. The position of the north leg on the tripods in relationship to the weight always causes me some amusement but at my latitude it doesn't matter. They have always been like that so why change. Some I have seen don't even allow settings for all latitudes. Some even push the centre of gravity further out than it need be simply to give more clearance on the weight Anyway being serious just from curiosity I decided to see what I would buy if it was permanently mounted in an observatory within the budget that was implied. Given the OZ reports the EQ8 would be the clear winner for me but that's me. While I would like an Astrophysics mount of similar proportions for a head only it would probably cost me 3 times as much just for a bare head that needs extras. The EQ8 seems to be available less stand for circa £2500. For lots of people that is very significant and is why skywatcher have produced it. I'm inclined to say good luck to them and hope to see some sensible engineering type rather than instrumental design appearing at some point. Doubtful really as certain aspects have always been like that and in some cases copied from other manufacturers so good luck to iOptron too. John -
  7. I couldn't find any real info on what is belt driven on the Linear Olly just going on looks. The dec axis does look all belt. Not easy to tell on the other but it looks like belt reduction to worm would fit and not sure about the other way round. The do show a shot which seems to be with the side cover off which looks like it would need a right angle drive eventually. I'm getting the impression that manufactures aren't so careful on the dec drives. Take the EQ8. That appears to use a direct worm drive to the dec and a belt to worm on the ra. To discover that I looked at a video by some one who I suspect lives in one of the ex Russian satellite countries and a German video just swinging the head around. Dec was far more noisy. Neither were in English. The "Russian" video threw up what looked like an unguided plot at the end, pass on the amount but it was pretty smooth. It's sad really that all we generally get in English is blase reviews that don't really tell potential buyers anything of any use at all. That applies to all sorts of things. For instance the only place I am aware of that will give me some idea of what a camera lens may be like really is in Poland plus one that doesn't add many lenses of late in Germany. Oddly Australia as well for some things in that area. John -
  8. True Oly but a 25GT doesn't really reach the level of the mount that Lee "doesn't" want to buy. It seems to me that people are happy with their larger mounts. I reckon that the main problem with the 25GT is the tripod it comes on. The 2" shouldn't be an option and well the clutches are different and in my particular case I am not at all keen on their idea of goto alignment but suspect it does allow a high degree of precision. It's really difficult to get decent information on mounts. I did find one informative test on the Avalon Linear in French. In a pdf unfortunately so hard to translate the lot but 2 snipits. Fig.7 and performed without homing has an amplitude of ± 7 arcsec corresponding to the values given by Avalon. When the curve is observed, although it is difficult to determine with certainty, we would note repeatability over a period of 10 minutes (9mn and 50s). The curve is smoothly and very low spreads observed are probably due in large part to the turbulence. There is some flexibility on both axes whenimparts a rotation of the tube with both hands to eachend. The size of the tube and the wind are they settingstake into account?The curve is pretty smooth compared with some that use gears for a lot of the speed reduction. Smooth curves make life much easier for autoguiding. I think the last part is related to the length and weight of scope that could be used with it. Homing is autoguiding. They used a CN212 scope on it and an SBIG STL 11000M camera. Also a G11 stand rather than the tripod it comes with. A pier I assume.Then there is an autoguided testHoming performed on M13Laying 15 minutes with fluctuationsmaximum of ± 2 arc secondsStar height in FWHM3.18 ''More and more people seem to be using much shorter exposures than that. I do wonder if the Linear uses a worm drive on the RA axis. One thing that is noticeable on the rather high end mounts that do is that the worm wheels are rather large. There is a pretty simple reason for that. Say it's possible to get the teeth in the correct position to 2um. That represents a larger error at say a 50mm dia worm wheel than it would on a 150mm dia one. The 150mm one can have a lot more teeth too = less or even no gearing before the worm. Going back in time the ideal was considered to be a worm wheel of the same diameter as the scope that was being used.I don't suggest mounts either only mention them. If I don't own it I can't really comment. My better mount is an old Meade LX750. I did think about changing it until I talked to some one who kept up to date on high end Astrophysics mounts.Looking around and for an observatory at this price level I think I would be going for the EQ8. It's rare to see tests so thorough as those youtube video's. As these days I am more interested in light weight I would look at more mounts but it looks like the Linear would be the one I would buy. Not the sort of 1/2 fork ones they make though.John-
  9. Maybe I should expand on tangential having read the web site mentioned. The centre grub screw sets the worm to wheel spacing but the 2 screws either side of it set the angle it's at / the worms tangential angle to the wheel. If they are tightened by different amounts the worm angle will change so the axis will need to be rotated slightly to get the 2 to mesh again. The change of worm angle will also reduce the clearance. I'm not suggesting that they should be finely tweaked this way, which might be possible to a very limited degree. Just pointing out what happens and that the axis needs to be rocked by hand as they are meshed - that will cause the worm to be at the correct tangential angle when there is no clearance. The worm will fit firmly on the wheel as more than one tooth should be in contact. It's possible to feel when they are meshed this way. The 2 other "horizontal" bolts limit the range of angles that the worm can be at. All just things to think about and bear in mind while adjusting them. It might help. I'm about to do an EQ3 Pro when the grease comes. The adjustment on the dec axis seems to be ok but the ra rocks by a degree plus. Not totally sure about the grease I've ordered but it is synthetic and intended for something like maintenance free general purpose applications. From the temperature range I'd guess that it wont be too thick. Ebay number 281074391607. John -
  10. There are only 424 images taken with an Ioptron 25GT on astrobin. Clearly they must have been lucky. Or were they? I'd guess it's more a case of what some one mounts on it. Just like others. More powerful drive might work out on very short scopes. Edit anyway iOptron isn't the subject of this thread. John -
  11. Edit - looking around a bit more the EQ8 uses a toothed belt to drive RA and direct by the look of it for DEC. Can't help being curious. Just in case I move house and area and build an observatory. John -
  12. Yep. Looks like you would need another £2000 for direct drive or even direct encoding.. This video might interest you He explains why there is the odd bump in tacking. He has a pretty good review of the entire mount in these https://www.youtube.com/channel/UCPd7bXRv2QGeMAKHZvG1PsA/search?query=eq8 It seems to be a direct drive from a stepper to a worm wheel with no other gears in the way. Pity all mounts don't use large worm wheels to obtain all of the speed reduction. There are a number about that do use large worm wheels as it improves the accuracy of the drive. Astrophysics for instance lap them to make them even better and also program PEC directly into the mount. Might be worth checking that it is done like that if the mount interests you. John -
  13. I never look at the "more" expensive mounts but given your needs I would at least look around at any direct drive mounts that are available also those that use the same sort of encoding directly on each axis. I only visit this forum from time to time and am pretty sure that a few people have owned mounts that use this style of encoding for some time now. Maybe some will comment. I have no idea at all what these or the one you mentioned actually cost. There are some technical details on direct drive here http://planewave.com/technology/mechanical-design/ I expect this sort of thing especially the encoders may move down the range eventually. John -
  14. There has been various methods mentioned here http://stargazerslounge.com/topic/259330-cleaning-optics-in-telescopes/ I actually wonder if some one tried an anti fogging substance in a newtonian I recently cleaned. A very light finger touch left smears that wasn't down to grease on my fingers. The mirror in an LX90 was interesting as well as was the corrector. It's has improved significantly since I cleaned it. What I think is important irrespective of method is to make sure things are very wet as this significantly reduces the chance of dust causing scratches. Using a blower bulb first helps too. Then as little as possible pressure. Sadly getting refractive optics very wet isn't a good idea at all as it may run into the cell the parts are held in. Edit One thing I will add is that there is all sorts of gunk kicking about in the atmosphere and it does settle on optics over time and it wont come off that easily. In some areas where optics are used they get cleaned every 12 months to ensure that they never get that dirty. Some optics need it more often than that. The solution ideally used for this is nothing other than triple distilled water and some sort of wetting agent. I've no idea which one. John -
  15. It might be a good idea to take photo's as you do it just in case you forget what goes where. They aren't that complicated but ........................... One of the things that is important one worms and wheels is that the worm is precisely tangential to the wheel. Personally I think "feel" is the best way to do that, no rock when there is zero clearance. It's also best to check that there is no binding over a full revolution of the wheel. Gears are designed to run with a certain amount of clearance so some back lash is essential really. The question is how much. If correct they will revolve smoothly without any " jumps " or binding and the next teeth will start engaging as the current one starts to disengage.. John -
  16. The nice thing about temperatures like these is that as the sun goes down lots of water vapour freezes and falls out of the atmosphere making it clearer. The crystals that form are pretty after a fashion. The water vapour hangs around most of the time in the UK and many other places. The snow presumably reflects more light pollution upwards but it has less to hit thanks to this. That's how it seems to me anyway. I used to spend a month in the early part of the year working on automotive ecu's in Arjeplog in Sweden which is not many miles from the Arctic Circle. I probably needed more thermal gear than locals but it was pretty pleasant really as the sun was often out all day and around -10C then. As a break from work there was no problem spending a couple of hours fishing in a hole cut into the ice for dinner. All ok so long as people breathed through their nose. Every now and again some one forgot and spent a couple of days in bed on antibiotics - ice crystals formed in their upper respiratory tract. Seemed most likely to happen at -15C and below, especially under -20. John -
  17. I can't answer that so over to some one else. I have a Vixen GPDX which the EQ5 is said to be based on but it's on a pier not a tripod and some reckon that the Vixen mount was one of the few which will take more load than they rated the mount at. Somebody has already mentioned why you should buy the HEQ5 if you are interested in photography. You have also seen shots taken with a 150mm Newtonian on an EQ3. If you want to read various views on the 2 eq5 mounts there are a fair few available from this google search https://www.google.co.uk/search?q=HEQ5+site%3Awww.cloudynights.com&oq=HEQ5+site%3Awww.cloudynights.com&aqs=chrome..69i57.22064j0j4&sourceid=chrome&es_sm=122&ie=UTF-8#q=HEQ5+site:www.cloudynights.com&start=0 Be inclined to take more notice of people that have posted a lot and actually used it. If you add tracking to the search some one may have done both to see how they compare. On the other hand I am not sure if it's possible to buy an EQ5 with synscan other than via an upgrade kit. The lightest Astrophysics mount come in at just under £6000 bare by the way. John -
  18. Save up for the HEQ5 as it's your only mount and the eq3 pro doesn't come with the EQ5 tripod. The HEQ5 should keep you going for a some time providing you don't put too big a scope on it. Also keep your eye out for a used one and be aware that later people may well tell you that you need an HEQ6. There is no end to that aspect. Look at Astrophysics mounts to see what I mean. John -
  19. I am too Matt. I just bough a used EQ3 Pro Synscan. There is some AP posted in a thread funnily enough that mentions EQ3 and photography in the title. There are links to yet more with a number of "things" on it. Perhaps people who have tried and failed have suffered operator error. Must admit I have only examined mine with an EQ5 tripod on it plus a 6" F5 newtonian. I am aware of how tough gem's are on the tripod and from past experiences don't trust the one it comes with. The Pro should have the same tracking abilities as the HEQ mounts. I've owned older low EQ number mounts before. One so low that I binned it rather than selling it on. They seem to be making a much better job of their mounts these days but "that" tripod looks just the same so pass. I do have it. The head might well eventually be grafted onto a pier, legs in the bin. It looks like it needs a strip and regrease especially the drive and I have just found that something is obscuring the view through the polar scope. I need a right angle camera finder to use that. More work making something to clip it on with. The polar scope will probably need aligning with the mount as well. My 110mm APO has a losmondy plate on it at the moment. I would have guessed that this would be too much for it but I might have a play out of curiosity. At 4.5kg it might work out but it will have a more unbalanced weight distribution than the newtonian. I took the 4.5kg newtonian with me when I bought the mount as I had doubts about it being able to handle it. If things don't work out it should make an excellent guided camera platform but Astobin suggests that with some skill it will work out and I have heavier mounts anyway. I also looked at an AVX but couldn't agree a price. Judged just by feel always a bit dubious my impression is that EQ3 plus EQ5 tripod weighs more than the AVX. It would be interesting to check that out. Looking at the weather in the midlands of late I wonder why I bother but some decent stuff might come along one day - I hope. Edit LOL I have a GS too. Maybe that's our problem. John -
  20. There are lots of cheaper routes into astronomy. Adding costs tends to make the scopes easier to use and may well offer better performance generally. Upgrading say an EQ5 to an EQ5 with goto works out more expensive than buying the mount with a goto. Rather than repeat myself I posted some thoughts in EQ3-2 suitable for photography thread. They apply to any mount you might buy really. It also explains why some one who is interested in AP is likely to finish up with goto and an auto guider of some sort. Manual guiding can be done with a drive fitted to a basic mount but alignment is going to be pretty critical. It takes a while to set up a mount well. Also something of a learning curve. I made a couple of newtonians completely and used all sorts of odds and ends I could get my hands on before I bought a commercially made scope. I went for an 8" full fork mounted SCT. Fork because I knew for the same weight it would be more stable than a german equatorial. They are easy to use and easy to manage. I still feel that these are an ideal first scope but budget probably puts many 1st time buyers off. In some ways these scopes maybe easier to upgrade later according to need than others. eg Some one might buy one with alt az mounted with full forks. They can buy an equatorial wedge for it, also counterweights actually as odd as that sounds. There are even focal reducers / correctors available. Light pollution permitting these will show plenty of nebulosity even at 8" but it can be a disappointing experience as there wont be any colour really, nothing remotely like photographs as our colour vision in low light just isn't good enough, I don't think I have ever used any mount that doesn't shake a little when manually focused. I manage, practice but guess many go for electric focusing. The same applies to manual guiding via knobs on the mount. I wouldn't even try that. It would need a massive mount. What is important is damping time. I've had my dob days. I'm more interested in a scope I can use without even going near it - once I have set it up. What dobs offer really is larger mirrors. Much larger while still being moveable even if mechanical aids are needed. They gain in the same way as fork mounted sct's do as far as the mounting is concerned. No hefty weight dangling on the end of a long thin pole. When shaking about that has rather a lot of influence on what happens. Heavier scopes mean the the weight is even further out. Maybe a bigger tripod might help people with that problem. People starting shouldn't forget the used market either. There used to be a saying that only problem scopes finished up on ebay. I don't think that is true these days. Then there are the other web sales facilities anyway. Scopes new or used may need aligning. Personally I prefer to travel rather than buy privately mail order as the scope may get damaged during transit. Smaller APO's are likely to survive but others can really suffer. Dealers are bit different - if things don't work out they would have to sort it out. Personally I wouldn't rule out older equipment that is in good condition either. Astronomy is another area where used prices drop significantly when a new model comes out even though the gains may be small. There might also be a case for just buying something to get some experience. That is very likely to allow people to make a better choice next time unless they have very deep pockets. Many people have to be more realistic even after gaining the experience. John -
  21. Concerning an earlier comment. I should get the manual out and check but I'm pretty sure that Meade use the scope level and running east west on gem's as that still allows the use of a polar scope. Much the same as older Vixen. Not sure what the newer Vixen do but I have gained the impression that star alignment requirements are now more stringent, a pity really. John -
  22. Subject to reading again it looks like the alignment star filtering is easier to use on the alt az versions of these mounts. Suggesting that people who buy equatorials don't have excessive light pollution in certain directions where as alt az people will have. Here's me with the S in front of B'ham in my location signature so Skywatcher seem to think I should only buy an alt az mount. North for me from the garden is something of a no no. For others it might be the same in any direction. Weird really as the software for this facility seems to be in all of the handsets. John -
  23. There are some people about now that reckon that there is no need at all to integrate for anything like that length of time but "short" exposures can still be used. A few pages come up for the EQ3 Pro too. John -
  24. Last time I elaborated on the difficulties beginners face buying certain things the thread was closed. So I'll try and be gentle. Is something like an EQ3 suitable to be the only mount some one owns? The answer is yes and no with a lot of no. The first thing they will want to do is add a drive as tracking manually is something of a pain. As alignment is likely to be off it may even need two hands on the knobs so they will need to learn how to adjust it according to how the view drifts even with a drive. A polar scope will help but the platform the mount sits on still needs to be very level. Less no now. If goto is added the scope is aligned and the controller calculates positions accounting for errors within limits = a lot less no. Then comes payload - how big a scope some one may want to put on it. The length of the scope comes into this as well. For the same weight a longer scope is far more likely to cause the whole thing to shake about. Electric focusing helps with shaky set ups as there is no need to touch the scope. A puff of wind might cause things to move around though. While the manufacturers mention an arc second there are several gears used to cause the mount to move and track. It would be interesting to calculate what this means in terms of tooth pitch errors. PEC can remove a lot of it but generally only on the gears that drive the final worm drive and maybe not all of those. If some one want to get into AP then autoguiding is going to be needed unless exposures are extremely short. This used to be done manually and still could be. Some of the now old big observatory perfectly set up scopes used a mechanism Ritchey (RC fame) came up with. It used the observers hands, feet and mouth. There is no need to be as extreme as that. The best option is one that uses the main scope, next a guide scope. People did have sufficient dedications to use these methods in the past. Even piggy backing cameras on their scope and using the main scope for guiding manually. So really providing the mounts perform as advertised a decent set up is very likely to include go to especially if some one envisages photography and at least a drive if not. The size of scope then more or less sets which mount some one should buy. Photography has it's complications as well. In some ways it favours smaller scopes as the focal lengths of these can be short enough to get angular fields that could for instance cover all of M31 at the available sensor size. It might not even be possible to see what is being photographed visually through the scope in the extreme. Goto and pray sort of thing. This site is useful for getting some idea what people have achieved with a given scope or mount. On the EQ3 synscan they reckon 10" periodic error. Maybe the EQ3 Pro is better maybe not. http://www.astrobin.com/gear/149/sky-watcher-eq3-synscan/ It's a pity more people don't make more use of this site in relationship to mounts. Actual telescopes usually have a lot more shots associated with them. Looks like some people have used the EQ3 as a camera platform which interests me actually. There are also a few shots taken with a 150mm F6. I doubt if that was an apo. It would be easy to knock up a platform to carry a camera and finder with a guider for it. A small longer focus scope might be better for guiding as it will have a bigger image scale. That was a standard consideration when manual guiding was used. Usually using a higher magnification via an off axis guiding set up. John -
  25. Must admit I am a bit of a Meade man Ronin. The first goto I really used was a Meade gem fitted with their 5" F9 APO. Dark site and I used the scope rather than the finder to try and align it. So many stars in view I had no chance of telling which was which so pressed ok and same with the next. It was close enough to use. Vixen used level and east west orientation on the gpdx s 2k if I remember correctly. Also align on anything, moon, planet, fuzzys. Personally I see that as very user friendly allowing some degree of alignment in any old conditions. I don't think that Meade and others use a virtual star. It more like a fixed initial reference that doesn't move - like Polaris nearly is. I haven't fully digested the manual but wonder if park could be used to achieve the same sort of thing but really it would be best to have it in the controller. That assumes park can be customised but the previous alignment correction factors are probably retained so it wouldn't be ideal. John -
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