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Showing results for tags 'refractors'.
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A random musing for a Sunday evening. The lenses in my spectacles are plastic. They correct my short-sightedness and astigmatism perfectly. Has anybody or any company tried creating lenses for serious astronomical use using plastic, the equivalent of apochromatics, for instance? Obviously, I’m not talking about the lenses in cheapo refractors from department stores. I assume there are good technical reasons why this has not already been done, rather than using exotic and expensive glass; I would just be interested to know the reasons.
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From the album: WPF Observatory Images
The Elephant Trunk Nebula - IC-1396 Telescope Equipment: Mount – Celestron CGEM DX - Hypertuned Scope – Canon 70-200mm EF @ 135mm, f/4 Guider- Orion StarShoot Autoguider Imaging System: ZWO ASI533MC Pro – Gain 100, Offset 70, Temp -15°C Filter – Optolong L-eXtreme Image Details: Light: 48x300s Dark: 24x300s Flat: 24x17.3125s (25,000 ADU ±5%) Dark-Flat: 24x17.3125s Software: Image Capture – Astro Photography Tools (APT) – PhD2 Pre-Processing, Stacking, Stretching – Siril 1.0.3 Starnett ++ v2 – to separate nebula from stars Post Processing – Adobe Photoshop CC, Astronomy Tools Action Set for Photoshop Image Taken: July 10, 2022 Photographed from the When Pigs Fly Observatory© © David Aylsworth - WPF Observatory - Earth
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From the album: WPF Observatory Images
The Veil Nebula (aka - The Cygnus Loop - Sh 2-103 Telescope Equipment: Mount – Celestron CGEM DX - Hypertuned Scope – Canon 70-200mm EF @ 135mm, f/4 Guider- Orion StarShoot Autoguider Imaging System: ZWO ASI533MC Pro – Gain 100, Offset 70, Temp 0°C Filter – Optolong L-eXtreme Image Details: Light: 64x300s Dark: 25x300s Flat: 25x1.62812s (25,000 ADU ±5%) Dark-Flat: 25x1.62812s Software: Image Capture – Astro Photography Tools (APT) – PhD2 Pre-Processing, Stacking, Stretching – Siril 1.0.3 Starnett ++ v2 – to separate nebula from stars Post Processing – Adobe Photoshop CC, Astronomy Tools Action Set for Photoshop Image Taken: July 31, August 2, 2022 Photographed from the When Pigs Fly Observatory© © 2022 - David Aylsworth - WPF Observatory - Earth
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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
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one of my friends is a little bit confused in between these scopes - 1. TS-Optics PHOTOLINE 80mm f/6 FPL53 Triplet APO - 480 mm 2. TS-Optics CF-APO 90 mm f/6 FPL55 Triplet APO Refractor - 540 mm which will be better for imaging ? not for visual. Which glass is better for imaging , FPL 53 or FPL 55 ? Have anyone used either of the scopes? what is the performance of each of them? Please suggest.
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I have a redcat 51 which is my travel scope. Now i want a refractor triplet in a range 70-80mm. But i don't want to loose the focal length by using reducer [removed word] flattener. In india not many branded scopes are available. I have to choose in between WO / TS Photoline / Explore Scientific /Sky watcher . WO triplet scopes have problem that they use their own reducer [removed word] flattener in GT series. So the focal length will be decreased, which I don't want. Please advise.