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Zhumell/GSO 30mm SuperView looked bad for terrestrial - normal?

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#1 Nuages

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Posted 30 April 2021 - 09:13 PM

Hey everybody. After finally collimating my Z8 dob (or at least doing a first pass), I couldn't wait to try it even though it was still daytime. Popped the Zhumell 2" 30mm eyepiece in, aimed the scope at some trees & houses about a mile away, and. . the view was bad. Could not focus and lacked clarity. I thought I had not collimated right, and/or it was very bad seeing. But then I decided to try a 32mm 1.25" Plossl that was on hand. . and it was fine. Tried the Zhumell 30mm again just in case it was the mirror adjusting to outside temps, but had the same bad result. Am I doing something wrong, is the Zhumell 30mm just not good in this application or could it be defective?

 

Thanks & CS

 



#2 Jon Isaacs

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Posted 30 April 2021 - 09:17 PM

When you are looking at objects that are relatively close, the focal plane is further out.  That can mean you need to slide the eyepiece part way out of the focuser just to reach focus.  The 30mm GSO Superview does focus outward of most Plossls so it possible this could the issue.

 

It's not a great eyepiece but it should be OK in the center of the field during the day.

 

Jon


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#3 wrnchhead

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Posted 30 April 2021 - 09:45 PM

What John said (per usual haha) if you never got a sharp view, are you sure you had focus? Also, I love that eyepiece. Not saying it’s premium, but I use it often and it makes me happy.
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#4 Nuages

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Posted 30 April 2021 - 10:14 PM

Thanks guys. I had thought that I was moving the focuser through a range that would have included the focal point, but perhaps in fact I wasn't. (This will be the first season I use more than Plossls.) It's getting both dim and cloudy now but I will try again another time.


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#5 clearwaterdave

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Posted 01 May 2021 - 06:06 AM

As Jon said.,Lift the eyepiece about 1/2" up and clamp it there.,Then it will come to focus for you.,It had me very confused when I got mine.,cool.gif .,


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#6 hcf

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Posted 01 May 2021 - 11:56 AM

Loosen (a lot) the bottom knob of the focuser. That should give you the extra distance to get the 2" 30mm to come into focus. Or as Dave said, put the EP halfway in the focuser. The Apetrura AD8 (same scope as the Z8) includes an extra entension tube for such cases these days.


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#7 SeattleScott

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Posted 01 May 2021 - 12:09 PM

Normally 2” eyepieces require an extension tube to reach focus in a Dob. Or leaving the eyepiece sticking partway out.

Scott

Edited by SeattleScott, 01 May 2021 - 12:09 PM.

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#8 ravenhawk82

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Posted 01 May 2021 - 03:18 PM

I agree with the others, it sounds like it was just a little outside of the focus travel. That was the primary eyepiece I used in my old Z10 with great results. Just be aware that without a coma corrector you'll probably have some oddly shaped stars near the edges of the field of view but that's just a quirk of Newtonian optics. The center should be tack sharp. 


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#9 Nuages

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Posted 01 May 2021 - 06:06 PM

Yes - I was able to find focus by pulling the focuser all the way out, plus pulling the eyepiece out some from the focuser. Might have taken me a while to think about doing this since I've pretty much used 1.25" Plossls thus far. Thanks everybody.


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#10 Jon Isaacs

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Posted 02 May 2021 - 03:59 AM

Yes - I was able to find focus by pulling the focuser all the way out, plus pulling the eyepiece out some from the focuser. Might have taken me a while to think about doing this since I've pretty much used 1.25" Plossls thus far. Thanks everybody.

 

:goodjob:

 

At night, it might not be necessary to pull the eyepiece out part way.  The closer an object is, the further out the focuser needs to be.  

 

Jon


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#11 Jim1804

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Posted 04 May 2021 - 01:32 PM

:goodjob:

At night, it might not be necessary to pull the eyepiece out part way. The closer an object is, the further out the focuser needs to be.

Jon


This eyepiece focuses fine for me at night in my Z10.
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#12 joker23

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Posted 04 May 2021 - 04:37 PM

I have a similar telescope, the Apertura AD8.  It came with an extension tube.  I found that when looking at the moon with the extension and the 30mm eyepiece, I could not quite reach focus one way.  Without the extension, I could not quite reach focus going the other way.  I use my glasses when using the finder, but not while looking through the eyepieces.  Maybe that's part of my issue?  I found that if I put the 30mm eyepiece in just enough for the brass ring to grab a hold of it when I tighten the screws, it works great.


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#13 OIC

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Posted 06 May 2021 - 09:20 AM

I found, on my Z8, that the 30mm was not of good quality. Even when in best focus (yes, pulled out) things were not as clear as through my ES eyepieces. We are all different and maybe my tolerance is not as accepting as others. Enjoy what you have for now, but think about upgrading.


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#14 Nuages

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Posted Yesterday, 04:34 PM

Yeah. I'm not surprised if the 30mm doesn't measure up to $200 eyepieces, but for something that came with the scope, I'm not complaining and will use it for a while at least. Tuesday night was less cloudy here so I was able to go out for a while, looking at some stars. IIRC I still pulled the eyepiece out a bit to focus, though not as much as I had with close terrestrial targets. I probably wasn't testing its limits but the stars looked all right. Was more disappointed in the light gray sky, and also realized I should get a Quikfinder or something to make it easier to point the scope. When it's just stars it is hard for me to tell one from another in the finder scope.


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#15 jwaldo

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Posted Yesterday, 08:54 PM

This thread is interesting to me. My GSO SV 30mm is an old 1st-gen model, purchased ~10 years ago. Their barrels were longer, so much so that they focused fine in the daytime and many scopes didn't have enough inward focuser travel for them to focus at infinity! I knew they'd shortened the barrel after I purchased mine, but it seems maybe they corrected the problem a little TOO well. It's a solid eyepiece; there are eyepieces that beat it, but they're  costlier and heavier, and so the Superview has stayed in my EP case.


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#16 Jon Isaacs

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Posted Yesterday, 09:11 PM

Yeah. I'm not surprised if the 30mm doesn't measure up to $200 eyepieces, but for something that came with the scope, I'm not complaining and will use it for a while at least. Tuesday night was less cloudy here so I was able to go out for a while, looking at some stars. IIRC I still pulled the eyepiece out a bit to focus, though not as much as I had with close terrestrial targets. I probably wasn't testing its limits but the stars looked all right. Was more disappointed in the light gray sky, and also realized I should get a Quikfinder or something to make it easier to point the scope. When it's just stars it is hard for me to tell one from another in the finder scope.

 

waytogo.gif

 

For an eyepiece that is included with a scope, it's the best one I know of. It's not a 31mm Nagler but it's a good finder eyepiece and provides some enjoyable if imperfect views.

 

Jon


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#17 vtornado

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Posted Yesterday, 09:31 PM

Also using a wide field eyepiece in a f/6 reflector during the day, can show the shadow of the secondary in the view..

It is kind of annoying.  That is why most folks use a refractor for terrestrial viewing.


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