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William Optics Zenithstar 81

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14 replies to this topic

#1 AlienRatDog

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Posted 22 December 2020 - 11:23 PM

Does anyone have the WO Zenithstar 81 with the flattener? If so, what are your experiences?

#2 DJL

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Posted 23 December 2020 - 12:46 AM

I have the somewhat similar WO GT81 with the same field flattener. My experience with the adjustable field flattener was that I somehow overlooked the fact that I had to adjust it! Once I did the adjustment, it worked really well. Were you just asking about the flattener or the scope as well?



#3 AlienRatDog

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Posted 23 December 2020 - 07:44 AM

I was asking about both. I’m going to sell some gear and plan on using the Zenithstar 81 on one of the new CEM26 or GEM28 (whichever is available at the time of purchase) to do more astrophotography with my daughter. I’d love the GT81, but it’s a bit out of my price range.

Edited by AlienRatDog, 23 December 2020 - 08:14 AM.


#4 DJL

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Posted 23 December 2020 - 10:22 AM

Understood. I considered both the ZS81 and GT81, and had decided on the CEM26 but they were all out of stock or back ordered.

 

ZS81 same as GT81:

Both have handlebar - fantastic for holding the scope while mounting, as well as mounting UniGuide 32 guide scope or other guide scope

Both have Bahtinov mask - very handy until you get an EAF

I'm assuming the focuser is the same and it's night and day after using SLR lenses, not usable once EAF is added

EAF fits easily on the GT81, I assume this is the same for the ZS81.

Both have mounting points on the barrel where I mounted a red dot finder and my ASIAIR Pro.

 

Differences:

ZS81 is a doublet and costs less; GT81 is a triplet and costs more - triplet is supposed to be better across the frame than a doublet, since this is my only telescope I can't compare.

ZS81 has a longer focal length and therefore a bit more magnification - check this out in Stellarium using the camera view

GT81 has the rotator which I am finding really useful now that I am doing HaRGB with sessions on different nights and framing and alignment have become more important.

GT81 will fit in its case if you remove the field flattener. ZS81 may (?) require more disassembly to fit in its case. Either way, if you are taking it on a trip you may want more than the free case that comes with it and leave accessories and camera mounted.

 

Re the mount, I could not find a CEM26 in stock, but I did find an HEQ5, and since so many of my YouTube heroes use the HEQ5 I went ahead with that.

Comparisons:

CEM26 may be physically lighter.

People say you should not move the CEM26 with the telescope mounted on it

 

My current setup has the HEQ5 on dolly wheels which I use to move it out of the house and then kick out from under the tripod feet. The telescope stays mounted and balanced, meaning less setup time.

 

It may be useful if a ZS81 owner could post an example. Here is my M31 taken with the GT81, ZWO ASI071MC (an APS-C camera) and the field flattener.

 

 

 

Attached Thumbnails

  • M31_L.jpg

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#5 AlienRatDog

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Posted 23 December 2020 - 10:37 AM

Thank you so much! That is a beautiful picture!! (I have the same ASI071MC)
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#6 Beaverpond Astro

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Posted 23 December 2020 - 11:16 PM

I love my GT81...just upgraded from the MarkII version to the new Mark IV with the camera rotator...in Space Grey.  Very cool.

Just imaging M31 as well a few weeks ago with the GT81 and ASI071...

M31 stack 47l 20d 11 15 20 processed 3 crop

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#7 bulletdodger

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Posted 24 December 2020 - 06:51 AM

ZS81 will be fine for viewing and I doubt you would see a difference with the naked eye. I actually prefer a well corrected doublet to a triplet, however, if you use it for imaging the GT81 would be the better choice IMHO.
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#8 wizer

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Posted 25 December 2020 - 03:26 AM

I have the ZS81 with flattener and I’m very happy. I’m sure a triplet would be “better” for my photos, yet I couldn’t point out any issues right now.

I use it mainly for narrowband imaging where the double also seems to matter less. I might have still gone with the GT if I’d do it again, but based more on what others say rather than any real problems I’ve had.

WO produces great scopes and I’m eyeing the FLT132 next.

#9 AlienRatDog

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Posted 25 December 2020 - 09:56 PM

If I could swing it, I’d get the GT81 but I also need to get a good EQ mount, so my budget is limited. I really like the looks of the mechanics on both scopes

#10 wizer

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Posted 26 December 2020 - 01:59 AM

Two sample images I took with the ZS81 + Flat6AIII. I am not super thrilled with the M33 but its RGB so you can see something other than narrowband.

 

NGC1499 Ha Crop AstroBin

 

M33

 

The NGC1499 (Ha only) is a rather large mosaic, the scope doesnt have that wide a FOV.



#11 Sedim

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Posted 25 January 2021 - 10:05 PM

Understood. I considered both the ZS81 and GT81, and had decided on the CEM26 but they were all out of stock or back ordered.

 

ZS81 same as GT81:

Both have handlebar - fantastic for holding the scope while mounting, as well as mounting UniGuide 32 guide scope or other guide scope

Both have Bahtinov mask - very handy until you get an EAF

I'm assuming the focuser is the same and it's night and day after using SLR lenses, not usable once EAF is added

EAF fits easily on the GT81, I assume this is the same for the ZS81.

Both have mounting points on the barrel where I mounted a red dot finder and my ASIAIR Pro.

 

Differences:

ZS81 is a doublet and costs less; GT81 is a triplet and costs more - triplet is supposed to be better across the frame than a doublet, since this is my only telescope I can't compare.

ZS81 has a longer focal length and therefore a bit more magnification - check this out in Stellarium using the camera view

GT81 has the rotator which I am finding really useful now that I am doing HaRGB with sessions on different nights and framing and alignment have become more important.

GT81 will fit in its case if you remove the field flattener. ZS81 may (?) require more disassembly to fit in its case. Either way, if you are taking it on a trip you may want more than the free case that comes with it and leave accessories and camera mounted.

 

Re the mount, I could not find a CEM26 in stock, but I did find an HEQ5, and since so many of my YouTube heroes use the HEQ5 I went ahead with that.

Comparisons:

CEM26 may be physically lighter.

People say you should not move the CEM26 with the telescope mounted on it

 

My current setup has the HEQ5 on dolly wheels which I use to move it out of the house and then kick out from under the tripod feet. The telescope stays mounted and balanced, meaning less setup time.

 

It may be useful if a ZS81 owner could post an example. Here is my M31 taken with the GT81, ZWO ASI071MC (an APS-C camera) and the field flattener.

Nice gear and photo DJL. I am new to all this and just ordered the GT81. Quick question: Where and how did you mount the ASIAIR pro and Red Dot finder on the barrel?



#12 DJL

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Posted 26 January 2021 - 06:53 PM

On the top of the scope are 3 pairs of screws. Leave the middle pair alone. The left and right pair can be removed and used to mount accessories. I used this cross slot clamp to mount the accessories. You can find similar ones with different numbers of slots and holes, but the 4 slot version allows the most flexibility in positioning.

https://agenaastro.c...nder-xfurb.html

The screws that come with the clamps are a little longer than the ones that come with the scope, so keep the originals in a safe place.

Here's a photo of the scope showing the ASIAIR Pro on the left and the holes where I had mounted the red dot finder on the right. I had to remove it to reuse the clamp for a different equipment configuration.

Note on red dot finder: the higher up the target, the lower you will have to get to see through it, so it's really just a backup in case something doesn't work.

Hope this helps, and enjoy your new scope!

 

 

 

 

Attached Thumbnails

  • WO GT81IV accessory mounting.jpg

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#13 Nate1701

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Posted 26 January 2021 - 07:29 PM

I love my GT81...just upgraded from the MarkII version to the new Mark IV with the camera rotator...in Space Grey.  Very cool.

Just imaging M31 as well a few weeks ago with the GT81 and ASI071...

Thanks Steve for selling me your type 2.

Still waiting for a good night to get out with it. waytogo.gif


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#14 Sedim

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Posted 26 January 2021 - 08:24 PM

On the top of the scope are 3 pairs of screws. Leave the middle pair alone. The left and right pair can be removed and used to mount accessories. I used this cross slot clamp to mount the accessories. You can find similar ones with different numbers of slots and holes, but the 4 slot version allows the most flexibility in positioning.

https://agenaastro.c...nder-xfurb.html

The screws that come with the clamps are a little longer than the ones that come with the scope, so keep the originals in a safe place.

Here's a photo of the scope showing the ASIAIR Pro on the left and the holes where I had mounted the red dot finder on the right. I had to remove it to reuse the clamp for a different equipment configuration.

Note on red dot finder: the higher up the target, the lower you will have to get to see through it, so it's really just a backup in case something doesn't work.

Hope this helps, and enjoy your new scope!

Thank you DJL. This really clears up a lot .



#15 Beaverpond Astro

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Posted 29 January 2021 - 08:57 PM

Thanks Steve for selling me your type 2.

Still waiting for a good night to get out with it. waytogo.gif

You are quite welcome!  I'm still waiting for first light on the MkIV GT81 - maybe this weekend!




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