I recently purchased a Celestron PowerSeeker 114EQ and with it I got three lenses (which I assume are low quality), a 4mm, a 20mm and a 3 x Barlow.

4mm, Barlow and 20mm

I can get pretty decent views of the moon but a very blurry, small view of Jupiter with the 4mm and Barlow. I can see the color of the storm rings for example, but barely. I've not had a chance to have a go at Saturn yet. A view similar to this...

enter image description here

I've been reading up on this and was looking at purchasing a 4-8mm Plössl lens but I'm not sure if the lens is my weak spot or some other aspect of the telescope. Another thing to note is that I've been using it in a pretty bright street, looking up very close to street lights. I've not had a chance to take out somewhere with less light pollution.

So what I'm asking is, how much difference would a lens upgrade make, specifically to my image quality?

  • $\begingroup$ My initial thought would be if those are the lenses provided along with the telescope then they are probably the most suitable ones to use. Did you try using the 20mm lens with Jupiter? $\endgroup$
    – Dean
    Commented Feb 26, 2016 at 15:33
  • $\begingroup$ Those are the ones that came with the telescope but I understand that usually that means they are cheap and not very good. I used the 20mm to find Jupiter but it doesn't really have the magnification to see anything. $\endgroup$
    – Ross Drew
    Commented Feb 26, 2016 at 15:46
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    $\begingroup$ Yeah I was just wondering if there was a focusing problem with that lens if the image was blurry, it is the best combination for magnification though as you said. $\endgroup$
    – Dean
    Commented Feb 26, 2016 at 16:38
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    $\begingroup$ Quarter wave optics on mirror and secondary? That image description sounds about right for resolving colors on Jupiter with a four inch Newtonian. The Galilean moons are nice little points, right? $\endgroup$ Commented Feb 26, 2016 at 16:43
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    $\begingroup$ Quarter wave is a measurement of how smooth the mirror is at a certain wavelength: A little: physicsforums.com/threads/wave-ratings-for-mirrors.5960 A lot: rfroyce.com/standards.htm In your case, it just means there's nothing extraordinary about the mirror. The sky may have been bad the night you went out, but I've seen Jupiter look like that plenty of times through a middle-range 105mm Newtonian. A 30cm Dobsonian will get you a better view. $\endgroup$ Commented Feb 26, 2016 at 17:46

1 Answer 1


...a very blurry, small view of Jupiter with the 4mm and Barlow...

Be aware that a 4mm eyepiece and a 3x barlow at the same time will give you a very high magnification - too high! For regular Jupiter viewing I would suggest you stick to 100x or 200x at most, unless the air is exceptionally still. (After a few sessions you'll find out what "Still" air means.)

A lot of beginner scopes like this are sold with barlows that tend to give too much power, my advice is to keep it packed away for most sessions.

So I'd stick to using that 4mm on its own, jupiter will look quite small but with practice you can usually tease a bit more detail out of the image.

I don't have one of these scopes, but my experience of comparing cheap modern eyepieces with expensive ones is that the lower cost ones are generally OK these days. 4mm is quite a high power so the extra magnification will cause a lot of blurriness and it will take patience to get the focusing at its sharpest, so don't panic if everything is looking fuzzy at the moment.

For a first stage I would suggest a few things that are nothing to do with the eyepieces at all...

  • Collimation - look this up, it just means adjusting the two mirrors so your eye is looking right down the tube in a straight line. For a long focal length scope like yours, it's not likely to be a problem unless one of them is wildly out of line.
  • Tube currents/thermal behaviour - on almost any cold night, when the tube and main mirror are still warm from being indoors, rising air currents in the tube will mess up your image and make it shimmery, at high power. Low power will look OK. It might take an hour or so for the image to improve (a guess)

Anyway, in summary my guess is changing the eyepieces straight away won't make a dramatic difference. Eyepiece makers will say otherwise of course :)

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    $\begingroup$ I've had experience with upper atmosphere turbulence. I could barely get Jupiter at all on those days. The blurry image I speak of was on a very calm, very clear night. The problem is that the telescope is quite sensitive and adjusting focus shakes it, ALOT. I'm looking at making a servo to control that without touch though. Thanks, this was really helpful. $\endgroup$
    – Ross Drew
    Commented Feb 26, 2016 at 17:51
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    $\begingroup$ For most nights, I'd tend to suggest using the 20mm eyepiece and the barlow instead of the 4mm. It's only about 2/3rds of the magnification; but inexpensive short focal length eye pieces have almost no eye relief. I rarely used my 6mm plossel because holding my eye within an mm or two of the eyepiece would often result in accidentally bumping it. $\endgroup$ Commented Feb 26, 2016 at 19:42

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