Eyepiece image looks blurry.

[Manali]

Help! I have a zhumell z8 Dobsonian and everything through the eyepiece looks blurry. I tried using a 30mm wide angle lens from which I could see some stars. As soon as I switched to a 9mm lens, everything was super blurry. I tried collimating using an SVBONY Laser colimator and it is supposed to be correctly colimated. I am not able to understand the extreme blur I am seeing. And yes I focused the image but nothing changed at all.

[johninderby]

Hi

First thing is that your laser collimator may itself need collimating.. Many in the price range of the Svbony can be way out.

 

[Starwatcher2001]

Hiya and Welcome to SGL.

Your scope seems to have a 1200mm focal length at f/5.9, so the 9mm will give 133x magnification which should work perfectly fine with that scope.

Does it work okay during the day when looking at objects a good distance away?  What make of eyepiece is your 9mm, and do you have anything in between the 30 and the 9?

Are you using a diagonal with the scope.

If you start with the focuser all the way out, then move inwards all the way in, what happens? Usually an object (like a star) will start out blurry, gradually get better and better, snap into focus and then get more and more blurry.  I know you're not seeing the moment of focus, but does it generally behave like that?  The other thing that might be happening is that you change the focus from one end to the other and it gets better and better, but never quite gets there. If that's the case, you may need to add or remove an extension to get the right focal point.

[Louis D]

Try looking at distant (1/4 mile or further) object during the daytime or wait for the first quarter moon at night.  Take the eyepiece out of the focuser and look at the aerial image in the focuser from a distance of a foot or so.  It's sort of like looking in a shaving mirror.  Does the object appear sharp?  If so, we'll assume you have a good mirror.  Next, on the moon at night, put a couple of strips of frosted tape across the empty focuser tube center and see if you can bring the moon to a sharp focus on them, sort of like focusing on ground (frosted) glass plates in view cameras of old that were then replaced with a film plate.  Next, lock the focuser (there should be a thumbscrew on the side of the outer tube for this purpose) and remove the tape.  Last, put the 30mm eyepiece in the focuser and see if the image in the eyepiece is nearly in focus.  Unlock the focuser tube and slowly start moving the focus wheel forward or back, depending on which way causes the image in the eyepiece to get smaller and less fuzzy.  At some point, it should razor sharp.  If it doesn't ever reach a sharp focus and instead starts getting more bloated again past a certain point, you've either got collimation issues or a really bad figure on your mirror.  I doubt that your eyepiece is to blame.

If you can't ever get a sharp image of the moon on the frosted tape, note at which position of the focuser the image is smallest.  If it is all the way in/down, you'll need to move your mirror forward/upward in the main tube to push the image further out the side of the tube.  If it is all the out/up, you'll need to add an extension tube to reach focus.  You also might be able to get away with not inserting the 30mm eyepiece all the way in the focuser when trying to focus with it.

If you can't ever get a sharp image at 30mm, forget moving up to 9mm.  It will only get worse.