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I have a Celestron Firstscope telescope and like it overall for my location and the amount of observing I do. I am disappointed in my view of the planets with the scope. What would be a good eye piece to purchase for this telescope to improve planetary observing. In keeping with my limited budget, it should not cost more than the telescope.

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To clarify, do you mean that it should not exceed the cost of the telescope? –  Grant Thomas Jul 2 '11 at 21:12
    
Correct, I am hoping there is something in the $20-30 range. –  Blake Jul 3 '11 at 1:16
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8 Answers 8

I'm not sure what eyepieces come with the Celestron FirstScope. I have the very similar Orion FunScope, which came with 2 eyepieces: 20mm and 10mm focal length, yielding 15x and 30x respectively. I have found that the 10mm is around the upper limit of what this telescope's optics will support, and would not recommend any eyepiece giving higher magnification. In fact, most of the time, I use only the 20mm because the views are better.

Small telescopes like these are generally not capable of very high magnifications. To get a satisfactory view of the planets you need to spend more than $50. This telescope is fine for what it does, wide field views of the Moon, planets, and large deep sky objects, but simply is not capable of the magnifications (150x to 250x) needed for good planetary views. For that you need at least a 4-inch refractor or a 6-inch reflector.

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I am not so concerned with magnification, as I am with clarity. The planets appear fuzzier than I would like. I had a department store refractor that actually had reasonable optics. (It was painful to find anything with.) It actually gave me clearer images than the FirstScope when I could point in the right direction. –  Blake Jul 3 '11 at 1:21
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The problem with the FirstScope is its spherical mirror. At a short focal ratio of f/4, this produces massive spherical aberration, which smears the image. Magnifying more only magnifies the smear. –  Geoff Gaherty Jul 3 '11 at 17:13
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I also have an Orion GoScope 80mm refractor, and it performs much better than the FunScope: better contrast and a much sharper image. Of course, it costs twice as much: $100! –  Geoff Gaherty Jul 3 '11 at 17:15
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There is an additional lens, called a Barlow lens, that can be added in front of an eyepiece to increase the magnification by 2x or 3x. It's basically a negative power lens that reduces the convergence of the rays from the primary, thus simulating a longer focal length. They're cheap, so you might try one with your Firstscope just to see if it helps. Of course, any imperfections in the primary mirror and wobbles in the mount will also be magnified.

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I tried a 5mm Hyperion from Baader Planetarium (great eyepiece) on the FirstScope of a colleague but the thing was too heavy and it became difficult to keep the telescope stable. So since you're dealing with an extremely light telescope you should also take weight and balance issues into account.

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Why would you do that? It's like bolting a Mustang engine on an oxcart chassis. The 5 mm Hyperion is a big, reasonably well corrected eyepiece, made for much bigger instruments. The FirstScope is a toy. –  Florin Andrei Oct 17 '11 at 22:51
    
Because I own such an eyepiece and a friend owns a FirstScope. It was an experiment to find out how good the FirstScope could be if you used a better eyepiece instead of the included ones. –  xmjx Oct 18 '11 at 6:10
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Here in the UK the SkyWatcher "Ultrawide" series fits your budget and is a decent improvement over the stock eyepieces included with budget telescopes. The branding is rather misleading, as "Ultrawide" conventionally refers to eyepieces like the TeleVue Nagler series that have greater than 80 degrees apparent field of view (AFOV); the SkyWatcher ones are significantly below this. However, despite this, they are reasonable quality, have longer eye relief which makes them comfortable to use, and perform acceptably on-axis at f/4 (off-axis performance suffers a bit, but f/4 is very demanding and only very expensive eyepieces retain good performance to the edge of the field in very 'fast' telescopes).

They are available here used for well under £20, which suggests that they would fit your budget if they available in the US.

Another good option are clones of the Burgess/TMB planetary design, which are again long eye-relief designs optimised for planetary performance. They're a little more expensive, but should be at the upper end of your budget - here they're about £25-30 used. The Burgess/TMB-branded versions have better cosmetic finish and are more expensive, but the actual optics appear very similar.

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The SkyWatcher UltraWides are available under their own name <skywatcher.com/swtinc/…; from some dealers in the USA, and also from Orion as "Expanse" <telescope.com/Accessories/Telescope-Eyepieces/…;. I tested the 15mm and 6mm and they are quite decent value for the money, better than cheap Plössls. –  Geoff Gaherty Aug 6 '11 at 13:37
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Another issue that hasn't been mentioned yet is collimation - it's very important for a fast Newtonian, and if the telescope is out of collimation it won't matter how much you spend on an eyepiece, the views will never be good. I found my son's Firstscope rather hard to get right as adjustment of the secondary mirror wasn't easy, but got there eventually.

There are lots of guides to the process online, I used

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

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It's on the far end of your price range, but the "Super Abbe" line from University Optics has a good reputation. You don't say what size your current eyepiece is, but their 7.7mm would probably be a good bet. You don't want to go too high on magnification, as you'll have trouble keeping things in view. When looking at Saturn with my 6" Newtonian and a 5mm eyepiece, it drifts out of my field of view within about 30 seconds.

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Those cost as much as the entire instrument, and still don't solve the spherical aberration of the existing mirror. It's a waste of money. In the FirstScope, maybe try a decent Plossl, hoping it works better than the original glass. Maybe. –  Florin Andrei Oct 17 '11 at 23:03
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Zhumell from telescopes.com makes a great kit that you will not out-grow as you can use it on up-grades. But for just one lens that's higher quality but not to expensive, I love the Zhumell 12.5mm. Just got through looking at a double star cluster in front (South) of Cassiopeia. Just brilliant on the firstscope.

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You're not going to get much more than that out of this instrument. It's cheap, it's a very fast f/4, and to top it off - it's spherical! At f/4 even a well-corrected parabola would be very challenging for any eyepiece except cream of the crop $400 glass. A sphere mirror only adds its own issues on top of that.

Short instruments look easy, but are tough on the eyepiece. People should stick with f/8 or longer for their first scopes. That's not difficult for any eyepiece, and it doesn't matter if it's a paraboloid, or a "mere" sphere.

Maybe try a decent Plossl eyepiece, there's hope they are better than the originals. But don't expect miracles.

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