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So I just recently bought a Celestron Powerseeker 127EQ 12.7 cm f/7.87 Cassegrain telescope and I inserted a 20mm eyepiece and the telescope with the Moon.

That eyepiece seems to work fine, but when I use it with a 3x Barlow lens the moon seems to look a bit blurry compared to the 20mm eyepiece itself.

It gets worse when I use a 4 mm eyepiece and I can't seem to get the focus correct. Any fixes to this?

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    $\begingroup$ Your issues may be similar to this recent questioner astronomy.stackexchange.com/questions/49286/… $\endgroup$
    – James K
    May 6 at 18:59
  • $\begingroup$ Welcome to Astronomy SE! I have a question about "look(s) a bit blurry". Is the blur static and fixed, or is it wavy with time. Depending on your location atmospheric effects can severely limit the image quality. Astronomical seeing takes some getting used to. It can be much worse some nights than others and depends on local geography, altitude and how hot it got during the day or cold it's getting at night. But if the blur is mostly fixed and static, then it's definitely optics-related. $\endgroup$
    – uhoh
    May 8 at 19:58
  • $\begingroup$ Maximum focus doesn't focus all the way and it looks fixed $\endgroup$
    – InfinitySwordofDiamond
    May 8 at 23:31
  • $\begingroup$ also see this answer astronomy.stackexchange.com/questions/10957/… $\endgroup$
    – Aaron F
    May 9 at 17:16

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Truth be told, there are a few factors:

  • The 4mm eyepiece that comes with the Powerseeker just isn't very good, unfortunately.
  • Neither is the Barlow that comes with the Powerseeker. This is a serious issue by itself - all Barlows degrade the quality of an image somewhat, even very expensive ones. But the one that comes with the Powerseeker is not fantastic.
  • The 4mm is going to give you a magnification of 250x, which is already quite high for being able to control the Powerseeker on its mount, or see through it given its design. Blurry pictures are an extremely common report for this model.
  • Problems with the focuser are also somewhat notorious for the Powerseeker series, and it would be unusual in my experience for this to be fixable at-home.

And, as Kavin Ishwaran says - Barlowing 3x up to 750x power is almost certainly going to cause you to see almost nothing. I would not generally dare push that high on a much larger, much more stable telescope. A rule of thumb is that atmospheric conditions will limit your seeing to 400x on an extremely good night - and even on good nights, I try not to push views that hard unless I can seriously justify why I'm trying to do so. So, I'm not shocked you're having trouble with it - it isn't normally possible to get good views with that power at all!

Here are my recommendations:

  • Overall, if you are having trouble getting the image to come into sharp focus during the course of normal usage, I'd pack the scope up and return it as defective. (Note: "normal usage" does not include Barlowing the 4mm!) A few people I know have tried their best to correct the focusers on these telescopes via shimming, and despite their skill at telescope making, have had limited success actually improving it due to the design of the telescope.
  • Avoid using the Barlow that came with the Powerseeker. More generally, I would recommend avoiding using a Barlow at all at this point, unless you have a very particular reason for doing so. While it might seem like an attractive option, most hobbyists only use 2 or 3 eyepieces almost all of the time, and a Barlow is really a speciality piece of equipment. If you want a specific power, you'll be much happier with a dedicated eyepiece for that power, unless you have a special need for one (generally only if you'd need a very short focal length eyepiece).
  • Similarly to the above, if you do continue using the Powerseeker, I'd recommend backing off the 4mm eyepiece - Goldlines, such as the 6mm version, are perfectly good eyepieces, doubly so for the cost.

Overall, bluriness and unsteadiness are, unfortunately, among several highly common frustrations with the Powerseeker 127EQ series that do not appear in other telescopes in the price range. They are a consequence of the construction of the telescope - the way its optics are designed to work, the way it is mounted, and the overall build quality.

I know this isn't advice everyone wants to hear, but if you have the funds available, you may enjoy a different telescope more - for example, a Z100 will have better control, better optics, a more stable mount & base, and will generally allow you a bit more liberty when learning. Check out this guide for more information - really, anything with a Dobsonian design. Or, frankly, a pair of binoculars in the price range of the Powerseeker will do you better as well.

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You will experience this issue if the barlow is not designed for the particular telescope you are using. the manufacturer mentioned the maximum effective magnification as 300x which is a bit optimistic, the maximum effective magnification you can obtain is around 260x. And if you are using a barlow that is not designed for the telescope or it is not an universal barlow lens, then you will definitely face this improper focus issue. If you are using the barlow that actually came with your telescope but couldn't able to achieve focus on a "closer" target like Moon, you should try using the setup targeting terrestrial target and see if you can see a clear image of something, if you still see blurry image, then there is a problem with your optics and you cannot blame the sky. Using 4mm eyepiece with barlow on this telescope will definitely make your viewing experience a disaster because the focal length of your telescope is 1000mm, dividing it by the eyepiece's focal length will give you the magnification you will obtain, in this case you will get 750x magnification when using 4mm eyepiece with the barlow lens (1000/4 = 250x with 3x barlow = 750x) which is like overkilling your telescope as well as killing your viewing experience.

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  • $\begingroup$ The problem is that I am just either using the 20mm eyepiece with the barlow lens or the 4mm eyepiece itself and it is already quite blurry $\endgroup$
    – InfinitySwordofDiamond
    May 7 at 18:00
  • $\begingroup$ I've never known Barlows which only work with a specific telescope. Unless you're talking about the Bird-Jones correctors, which - yes - are designed for a particular telescope. All Barlows (and powermates) I've seen and used are telescope-agnostic. (I'm not downvoting, btw, because you hit upon the answer in your last sentence) $\endgroup$
    – Aaron F
    May 10 at 18:11
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    $\begingroup$ @AaronF The optics used in barlow lenses of the same variety is not going to change. The thing I mentioned that it should be designed for the telescope is the barlow's design (tube length lens arrangement etc) should either be set for Fast telescopes or for slow telescopes. If one use a barlow lens designed for slow telescopes in a fast ones, one may not be able to achieve focus. In this case the barlow's height has to be adjusted. And this is what I meant there $\endgroup$
    – Kavin Ishwaran
    May 11 at 4:34
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    $\begingroup$ aha I see! yes the focuser might not extend enough to accommodate such a Barlow, it's true :-) $\endgroup$
    – Aaron F
    May 11 at 15:36

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