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Revision as of 20:02, 16 April 2008
76mm reflector telescope F70076
I'm a complete beginner, what concerns telescopes and astronomy, so I thought that my experience about telescopes might be useful for other beginners.
Manufacturer
This telescope was produced by the German company Telescope-Sevice, the parts of it were though likely produced by the Chinese company Wuhan Siwei.
Price
This is one of these less than $100 telescopes, it is very similar to Celestron PowerSeeker 76 AZ, which at least in Amazon.com costs $64, and to Orion SpaceProbe 3, wich costs $99.95 at the Orion site, Bushnell, Tasco, Bresser and other companies also produce a similar telescope. This telescope did cost 64 EUR plus shipping costs, which also is less than $100, depending on the exchange rate. But there often is no choice for one who lives in Europe, other than to buy goods from Germany, as shipping them from America is first expensive, and there would be troubles with customs formalities. So it can be said, that this is the European version of this family of 76mm reflector telescopes.
Comparison with other cheap telescopes
It is the rule, that a reflector with the same aperture, always costs less than refractor. This is true also concerning the cheapest telescopes. A 60mm refractor costs almost as much as this telescope, all 70mm refractors are much more expensive. So it is likely the best choice for the cheapest telescope. Refractor is not better than reflector in any way, except some expensive apochromatic refractors, different from what some may argue, there is no reason whatsoever for the light going through the lenses to have anyhow higher quality, rather in a reflector with the same aperture less light would be lost. The biggest advantage of refractors seems to be that they almost don't need any maintenance, and they are also almost eternal, while the reflector mirror would corrode after 30 or so years. But the maintenance like collimation of the reflector telescope is not difficult at all, and is some fun also, so being maintenance-free may be important only for these who know nothing about any technical things, I would not agree to have more than 10mm less aperture for that reason, and it is not so extremely important to me that a cheap telescope would be inherited by my grandson after my death.
Newton reflector
Newton reflector is the best and cleanest optical system for a reflector, which an ordinary person can afford. The others, like Maksutov-Cassegrain and Newton reflectors with extended focal length, all have some additional lense or glass, where the light should go through. Also the almost 1/10 focal ratio is good, as it enables eyepieces with greater focal length for high power, which gives higher quality images, and also all possible aberrations are almost not noticeable at that focal length. It gives also a reasonably wide view at lower magnifications. Well the Newton reflector was first made in 1672 by Isaac Newton, and this was a 2 inch telescope, and had an inferior quality metal mirror, so our 3 inch telescope with glass mirror is much more powerful. To these who doesn't know what is Newton reflector, Newton reflector is the simplest mirror telescope design where the primary mirror is in the bottom of the tube, and the image is reflected to the focuser at the front of the tube, by a flat diagonal (secondary) mirror. The construct called spider holds the secondary mirror in place, the spider is the first thing you see, when you look into the telescope tube. This spider also cause a little trouble, as it cause spikes in the form of the spider at the brightest objects. This is though not that bad, the spikes can be seen only at the brightest objects which are surrounded by complete darkness, like the brightest stars, and these are considered normal on the astronomical images.
What was inside the box
All the parts seemed to be high quality, all the screws were also nicely tightened, the mirrors and accessories were not damaged anyhow. The assembly of the telescope was extremely simple and didn't take almost no time at all. There were 2 Huygens eyepieces 20mm and 12.5mm, and one Super Ramsden eyepiece 4mm. The eyepieces all looked decent, the lower part of them is made of metal, and the lenses are all glass (different from some other similar telescopes like these made by Bresser, where the lenses are plastic). There was also Barlow lense 2x, and erecting lense 1.5x. These both were made of plastic, and the lenses are also plastic, but the image through them doesn't in spite of that seem anyhow bad or darker. The Barlow lense is quite small, but the erecting lense is a long tube, the telescope looks nice though with that in. The images through all the eyepieces were crystal clear, somewhat the eye has to be in the right position to see the whole field, but there is no problem when one gets used to. The image through the 4mm eyepiece together with Barlow lense (350x magnification) was already too pale, but through the 4mm eyepiece alone (175x magnification) it was nice and sharp, and there was no difficulty in looking through that eyepiece at all. There also was a moon filter, and a metal triangle to use as a screwdriver. The scope has a nice cap to close the front of it, and especially good that there is another cap in the center of that cap, opening that cap makes collimation somewhat easier, as there are less reflections then. The focuser was good, entirely made of metal, and standard 1 1/4 inch diameter, so all standard eyepieces can be used. The telescope had a nice smell of rubber inside its tube. This is also in a way an exceptional cheap telescope in that nowhere on the box appear any advertisement that this telescope has 350x power, or such. Also, it is said in the Telescope-Service site, that using 2x Barlow lense and the 4mm eyepiece together is useless. 350x is indeed a useless magnification, it is considered that a maximum useful magnification of a telescope is two times its aperture in millimetres, for this telescope therefore 152x, but really, 175x using the 4mm eyepiece, in spite that this is slightly beyond that limit, gives a good and sharp image as well, at least at daytime, but likely also this eyepiece should be useful for viewing bright objects, like moon and planets.
Huygens eyepieces
Huygens eyepieces are the oldest design, and up to the middle of the 19. century all good telescopes had Huygens eyepieces. Some say these are bad, and recommend not to buy telescopes which have Huygens eyepieces, because these eyepieces have always a low quality. Of course more expensive eyepieces are always better, but Huygens eyepieces are not necessary bad when the focal ratio is small (like focal ratio almost 1/10 which this scope has). It seems that in spite the eyepieces were Huygens, they are high quality Huygens, the daytime images were very clear and sharp, and I never noticed any chromatic, spherical or other aberration, at all. I'm very satisfied with these eyepieces. There might be some truth about the advice that Huygens eyepieces may have a low quality, so one should be careful while buying a telescope when it is known that the eyepieces are Huygens, as I have seen some cheap telescope like these made by Bresser, where the eyepieces are whole plastic, together with lenses. The eyepieces consist of two lenses, but in more expensive eyepieces like Kellner and Plössi, these lenses consist of two or more lenses glued together, like achromatic objectives in refractors. In Huygens eyepieces, and also in Super Ramsden eyepieces, both lenses are simple, and the lenses also didn't seem to be coated.
Moon filter
The moon filter made the image of the moon kind of green and ugly, and I didn't see more details with it, than without it. It is likely that with some 10 inch telescopes the moon would be too bright and a filter is necessary, but with this telescope it seems to be just useless.
Finder scope
The finder scope is a simple 5x24 all-plastic scope. The finder scope is very useful, you should move the telescope so that the object is in the center of the crosshair, and the object is then visible in the eyepiece. I couldn't find the objects any other way. The finder scope should be aligned first, for that srew out its upper alignment screw, align it with two lower ones, and then tighten the upper screw again. I for example moved a corner of a house into the center of the eyepiece and then aligned the center of the finder scope crosshair to that corner.
The mount
The tripod is sturdy when the legs are kept short, and almost no shaking from the tripod is noticeable then. The telescope can be nicely used that way, sitting near it. Whenever the legs would be made longer, the shaking caused by the tripod would be noticeable, that shaking is especially nasty in that it ends only in 15 seconds or so after touching the telescope, and making the legs longer should therefore be avoided, whenever possible. The telescope has a fork mount, all the cheapest telescopes have such mount, likely it is more expensive to make any other joint, so there is no joice anyway concerning the mount. Such mount cause shaking after moving the scope or focusing, but this shaking ends in one second, and the telescope is completely stable after that. This time is short enough, so that it enables the normal use of the telescope, and it is possible to get used to and live with that. The shaking is caused by twisting the base of the fork, and cannot be avoided anyhow, for no shaking a very massive or wooden fork would be necessary. The movements of the telescope are smooth, and it can be moved very exactly. The fine adjustment rod is completely unnecessary, and cause uneven altitude movement even when the tightening screw is completely open, so I use the telescope without that rod. The azimuth movements are smooth also, but I first had to oil the azimuth joint. Concerning the mount, there was a warning on the box, not to tighten the srews too much. Likely, at least the screws screwed into the aluminium, would become loose when screwed in too much, and would then fall out. Therefore, when the screws are well tightened, there is no need to touch them any more, and then they would stay permanently in. More about the mounts, you may regret that the mount is not equatorial, but it is said that the cheap equatorial mounts are by far not precise enough to use them to position the telescope to a star, and such mounts are mostly even more unstable, only causing an additional shaking, so it is not good to buy a cheap telescope with an equatorial mount.
The size and weight
By the shipping information, the whole set of the telescope weighs 6.2 kg, the telescope together with the mount therefore likely less than 6 kg. It feels to be very light, and it is no problem to carry it, holding from the fork. It is the best to hold the telescope mounted, it doesn't take much room even so, and it also looks nice, so you don't exactly have to hide it behind the corner. The telescopes bigger than this are much bigger and heavier, much more difficult to carry, and therefore also less useful, as one most of the time would use a telescope which is easiest to carry. There are some smaller "table telescopes", but the problem with these is that they almost always need something with a proper height, to put on, some made some special stools for that, and they still have to carry that telescope together with that stool, so not easier at all than carrying this telescope.
Cleaning the mirrors
I don't know much about cleaning the mirrors, and I have only cleaned the secondary mirror. It was easy and fast, really, though I cannot assure that I did it in the most correct way, but taking care of such telescope cannot be too complicated, so we should use easy solutions. I rinsed the mirror, took a piece of cotton, made it wet, and added to it a bit of soap. Then I wiped the mirror slightly, one cannot use any pressure at all. Then I rinsed the mirror thoroughly, and just let it dry. I found that that way there was much less residue than when trying to remove the water droplets anyhow. The best is to rinse the mirror with distilled water immediately after rinsing it with ordinary water, so that there would be no residue. But when you have no distilled water, just rinsing with water should be a satisfactory enough solution. The most important is not to touch the surfice of the mirror never. Also, the mirrors should be cleaned as rarely, as ever possible, or never if there is no serious reason.
Collimating
There are several methods of collimating, it can be done using a laser, or by the diffraction rings around a star when the telescope is slightly out of focus. I though satisfy with only the easiest collimation, as I think that taking care of such telescope shouldn't take too much time. Collimating is aligning the primary and secondary mirror. The mechanism which enables collimation is really the most simple, I would even say primitive, and this mechanism is the same both for primary and secondary mirror. There is a plate with three screws on it, which are called the collimation screws. These screws go against some support, which is the bottom of the telescope tube in case of the primary mirror. This simply means that by adjusting these screws by few turns, the tilt of the mirror can be changed. And there are other screws called locking screws, which simply fasten the plate to the support. There are three locking screws for the primary mirror, and one locking screw for the secondary mirror. Naturally, for adjusting the tilt of the mirror, the locking screws must be loosened. For the primary mirror, you should loosen all screws first only slightly, and then all almost by the same amount, as doing that unevenly would cause one screw to become too tight. The collimation screws are in triangle, which means that for tilting towards one screw, the two opposite screws must be evenly screwed in. Collimate the secondary mirror only when the telescobe tupe is in horizontal position, to avoid anything to fall into the tube, which may damage the primary mirror. The first thing which you likely should do for collimating, is to look through the focuser (in the lowest position and without any eyepiece in) whether you can see the whole primary mirror. If you cannot, you should either adjust the tube axis position of the secondary mirror, or the spider (with what the secondary mirror is fastened to the tube) so that the mirror would be closer to the focuser. For that you may need to remove the spider, and adjust the length of its branches, all are also screwed into the center, so the can be adjusted that way too. It seems to be the problem with these scopes, that secondary mirror is only then close enough to focuser, when the center of the spider is not exactly in the center, or it seems to be a bit too small. Then collimate the secondary mirror so that you can see the whole primar mirror. Then collimate the primary mirror so that the spider is in exactly the same shape as you see it when you look into the tube (unfortunately we cannot say in the center). There is also a thing called collimation cap, which for example can be made of 35mm photo canister, by making a small hole in the center, putting it into focuser, and looking through that hole, the only purpose of that is to ensure that your eye is in the center. But we can satisfy with less precision, and therefore don't use even this additional tool.
What can I see through it
To be written when the nights would not be cloudy, and I can use the telescope for the first time for looking at the night sky. I don't really have much idea what I can see through that telescope, but Charles Messier who made the catalog of 110 deep sky objects (galaxies, nebulas and star clusters) in 1780, had a telescope which may be equivalent to today's 3 inch telescope, so I should see all these objects at least somewhat. But of course the skies of Paris were not so light polluted at that time, when there were no electric lights yet, than the skies of the cities today. More than that, Hodierna found 19 deep sky objects already in 1654, using only a Galileo telescope with 1 inch aperture.
April 15, 2008. Tonight, my telescope saw first light. But the sky is still not clear enough, so I could only observe the moon and one comet. The moon was an almost full moon, I saw clearly the craters and the edges of the craters were kind of rough, so I was able to see even more details. I saw the moon with all eyepieces, with 12.5mm eyepiece the moon covered almost all the field of view. I saw craters through the 4mm eyepiece as well, but I was not able to focus properly, because I observed the moon through the window, where I had not enough room to move properly, and the 4mm eyepiece needs a very fine focusing. The comet was a bright but small comet, with a very small tail, I observed the comet through the 12.5mm eyepiece with 2x Barlow lens (110x magnification).
Astrophotography
