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Showing results for tags 'refractors'.
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I have been using a Skywatcher Startravel 102 for about a month now as a grab-and-go scope. I also intend to use it as a travel scope for holidays, but I've yet to try it in that capacity. So I thought I'd record some of my thoughts about this scope. Initially I purchased the ST102 with an AZ3 alt-azimuth mount, but I quickly found I didn't get on with the AZ3. On the plus side, it is very compact and lightweight and would make an excellent travel mount. However, I found the friction bolt arrangement for setting the altitude tension to be unreliable, and the mount was difficult to use near zenith. So, I changed the mount to a Vixen Porta II, which is much more comfortable to use. The Porta II tripod does seem to vibrate a bit more than the AZ3 though (especially on concrete), so maybe I will change the legs for something more substantial one day. Onto the telescope itself. The optical tube feels very solid and substantial. There is a large dew shield fitted, which is held on with a simple push fitting held in place by a felt band. Removing the dew shield reduces the OTA length significantly, but unfortunately the supplied lens cap won't fit over the front cell without the dew shield in place. This is a pity, as removing the dew shield would make the scope very compact for travel. The 102mm doublet objective has a blueish-looking coating, that seems evenly applied. The OTA assembly is supplied with decent tube rings and a dovetail. If you buy the scope in a kit with the AZ3 mount it comes without a dovetail, and the tube rings bolt straight onto the mount. The focuser felt quite smooth but a little tight straight out of the box. Initially there was no play in the focuser and the drawtube was well aligned. However, the focuser does prove to be a weak point on these scopes and I will return to this later. Now on to the important bit - performance! The OTA came supplied with the usual 25mm and 10mm MA eyepieces. The 25mm is quite a good budget eyepiece, but the 10mm could be better. However, since I already have a set of reasonably good eyepieces I put the supplied EPs to one side. Also supplied with the OTA and AZ3 kits is a 45-degree erecting prism. This is useful for terrestrial observation, but not really of sufficient quality for astronomical work (although it is OK at low magnifications). I replaced this with the excellent Revelation 2" Quartz Dielectric diagonal. This scope excels at wide-field views of open clusters and brighter DSOs. With a 25mm X-Cel LX eyepiece the whole of the Pleiades can fit in the field of view, which is a stunning sight. I also have a 32mm Panaview 2" eyepiece, which offers a whopping 4.4 degree field of view, framing the Pleiades beautifully within the surrounding sky. Under a dark sky the view is quite breathtaking. Other open clusters such as the Beehive also look superb with such a wide field. Best of all, this scope gives me the best view I've had of the Double Cluster in Perseus, with both parts of the cluster beautifully framed within the FOV. Large DSOs are also a strong point for this scope. M31 (Andromeda) looks fantastic under a dark sky, and dust lanes are visible. Dimmer DSOs are quite within the reach of this instrument, with M1 (Crab Nebula), M33 and M51 all visible under dark skies. Globular clusters also make good targets, although perhaps a little more aperture would be useful here to see them at their best. Working at high magnification, the ST102 is quite capable of splitting the "easier" double stars such as Castor and Sigma Orionis. A 5mm EP works well here, and a Barlow can help to increase the separation on brighter doubles. The dim companion to Rigel can just about be made out under good seeing conditions. You may notice that I haven't mentioned CA (chromatic aberration) yet. That's because, for clusters, DSOs and most double stars it simply isn't an issue. For planets and lunar observation, however, it's a different matter. Yes, the dreaded purple haze is there, especially noticable on the limb of the moon and on bright planets such as Jupiter. In fact, the ST102 is quite capable for casual lunar and planetary observing, but if the solar system is a primary interest for you then you might look elsewhere. Although the optics are pretty sharp at high magnification, I really feel that the CA damages the contrast for planetary and lunar observation. This is my first refractor (my other scope is a 10" Dob). I have to say I'm now a refractor fan! There's something about the ease of setup and the contrasty, pinpoint stars that appeals to me. I also like the short-tube concept from a portability point of view, and these scopes are very capable deep sky instruments. Yes, CA is a problem on bright objects at high magnification, so it's not an all-rounder like an APO, but for the price it's fantastic value for money. I mentioned the focuser earlier. After some use, the focus tube developed some vertical play. There are two grub screws on the top of the focuser which are used to tension the drawtube. I needed to tighten the front (i.e. closest to the objective) screw to take up the slop, and also tighten the rear screw to remove any remaining image shift. After this adjustment the focuser worked fine again. I have now had to do this twice, so it seems that periodic adjustment is required. After the second adjustment cycle the focuser was very stiff, which I resolved by slackening off the screws that tension the spring in the focus pinion assembly. Now the focuser is nice and light and smooth, but I anticipate further adjustments will be necessary in future. We shall see! This is really a faff and the only real annoyance with this scope. There is a dual-speed Crayford focuser available which is a drop-in-replacement for the original R&P focuser, but at around £129 I'm not sure it's worth it on an OTA costing £169! All in all, I really like this scope, apart from the cheap focuser. In fact, I like it so much I'm wondering what the 6-inch ST150 would be like on DSOs and clusters! Ed
That's right, the Takahashi TAKSD1 premium 1.25” star diagonal. After reading William Paolini, 3/6/2014 in-depth review on various prism and mirror star diagonals, I've been searching for the right diagonal for my Celestron C80ED, 80mm, f/7.5 grab 'n go refractor. The Baader/Zeiss prism was the one that got high marks for planetary images. But at $450, it's way out of my range. Another highly rated diagonal in the review, covering lunar and planetary viewing was the Takahashi 1.25" prism diagonal - the one I just purchased. And it is reasonably priced at about $170. I will say this: Compared to the other diagonals I have accumulated, some prisms some mirrors, some 99% dielectrics, of varying cost, the Takahashi TAKSD1 does put up a somewhat better image with less scatter - in my above mentioned scope. It isn't night and day, but it is noticeable and I think short of using no diagonal at all or getting the Baader/Zeiss model, this is the best I'm going to do. I found it very interesting that most of the diagonals for sale are the 99% dielectrics, followed by (and this really floored me) correct image diagonals! Then there seemed to be a some offerings of right angle prisms which ranged anywhere from $35 to the aforementioned $450 and up to about $900, if I recall. Also, I have to say that regardless of the price, registration of the prism or mirror in its housing is not always good. I had purchased a Baader T2, 1.25" prism diagonal with the micro focus. Very nice diagonal and substantial. But, my sample was noticeably out of registration and rather than play with it and make it worse, I sent it back. But the images were good with this diagonal and background scatter very well controlled. It is the non Zeiss model and a good performer in my scope. I used the 'Cheshire, through the prism/mirror and out the nose piece to a flat mirror test' and only a few of my diagonals were right on target. And even the ones that were, when putting them in the scope was another variable that often threw the alignment out of whack. Without a diagonal, using a Cheshire tester and a covered objective lens, my scope is just about right on target. But putting the diagonal in, even the ones that are well registered, often ended up in an off registration situation. So you ask, if both the scope and the diagonal are aligned properly, how can this happen. 1 1/4" inches is not the same everywhere and for everything. Some diagonal nosepieces fit snugly, most very loosely. And when you tighten the thumb screw, things change more. So if you want a spot-on registration, you have to perhaps do some shimming, or use Howie Glatter's clever alignment gadget to get it just right. One last thing. The Takahashi TAKSD1 uses a very nice compression type clamp, similar to a plumbing compression fitting. And it works quite well. But, if your eyepieces have that tapered part so they won't fall out, the compression ring may not tighten completely on the eyepiece at this less than 1-1/4 part. Easy to fix. Just take the plastic compression ring out, snip about 3mm off one end, put it back and it has more range to tighten on the sub 1-1/4" part of the eyepiece. Thought I'd just share my diagonal experiences. If anyone wishes to comment, please do so. If not, I hope this information helps someone.
I have read and studied as many reviews as I can find on refractors. I am now down to what I believe to be the final three that would meet my needs but would appreciate some final advice from the experienced members of the forum. Scope Requirements. The scope will need to satisfy the following criteria. An aging 66 year old that wears glasses. Back garden observing in an area of medium light pollution. My eye pieces are Vixen SLV's Mainly solar system targets with DSO's occasionally. Solar white light observing with a strong possibility of moving to Hydrogen Alpha in the near future. Scope fitted to a Skytee Mount. Short List of Scopes. 1. AA Starwave 152mm V3. F/5.9. Cons small FL 2. SW Evostar 120mm ED DS PRO F/7.5 Cons Focuser could be better therefore more cost to upgrade. 3. Explore Scientific 127mm APO Triplet. F/7.5. Cons Unknown quality. Any final thoughts please as to which of the above would suit my criteria would be much appreciated. Unless their is a scope I have missed bearing in mind my limited budget. Thanks for reading. Garry
I got a few recommendations from Sky Watcher that seemed reasonable: http://skywatcherusa.com/ed-apo-refractors/proed-doublet-apo-refractors/proed-80mm-doublet-apo-refractor.html http://skywatcherusa.com/maksutov/sky-watcher-maksutov-cassegrain-102mm.html http://skywatcherusa.com/maksutov/sky-watcher-maksutov-cassegrain-127mm.html The 80mm looked fairly tasty but I don't really know if a refractor is the right choice for the AllView. I really wanted to step up to the 100mm refractor but it is to long for the mount. Sky Watcher indicated there may be a competitors 100mm that might be short enough but... isn't the 100mm designation the width of the tube or the length of the internals? Could i find a better choice than the ones listed or should I just pony up for the 80? For that matter I dont even know if the 127mm Mak-Cass would be the better choice. I want to be able to see as far as possible. I want Saturn's rings, the great spot of jupiter, and potentially some galaxy, nebula or whatever is reasonable for that telescope. Some fov would be nice but I am beginning to gather that that is a trade off. I made a questionable purchase of the AllView, pleasse help me maximize it's usefulness. thanks Jonathan
Item on the BBS News Science & Technology site Flat lens promises possible revolution in optics See http://www.bbc.co.uk/news/science-environment-36438686 Apparently, using chip-fab techncology it should be posible to make super-quality lenses 30 cm dia or more for pence (cents). Big, cheap refractors here we come? Regards, Doug
Not much written on these compared to Barlows. They seem ideal for long fl scopes to get wider fov and lower mags from an ep for Cassegrains and refractors. Are there any that can be recommended for good optics that can take 2 inch eyepieces. For use with SCTs etc, would image quality for optical be much worse, and would an ep's limitations be more apparent?