101 replies to this topic

[Jeff B]

When my friend and club member picked up his Zhumell Z10 OTA that he let me evaluate and test:

 

https://www.cloudyni...zhumell-10-f49/

 

He dropped off his Orion XT8, 8" F6 OTA for similar care and feeding.

 

The mechanical quality and fit & finish are, IMO, on this sample, not quite on par with that of the Zhumell's, but certainly very serviceable and very good for the money.  It required collimation tweaks of the secondary and primary but both went quickly.

 

Unfortunately the optical quality at full aperture was rather below par on this sample.

 

As the DPAC images at full aperture show, there is a significant turned edge with an overcorrected zone over the outer 70% to 80% of the surface.  The surface is otherwise fairly smooth if a little lumpy in spots.  The owner confirmed to me that the images with the scope were not really sharp at high power and focus is a bit vague.  However, as this was his first scope he really had no other experience or point of reference to say the optics were sub par.   I saw no signs of astigmatism, which is good and the fully illuminated FOV seems generous.

 

I then retested it with a 7" aperture stop over the front.  This greatly improves the overall DPAC performance, though at the smaller aperture.  The outer portion of the surface is still overcorrected a little but it covers less territory and, importantly, the turned edge is almost entirely eliminated.  That overcorrected outer zone blends smoothly into a more neutral correction towards the center but the overall system figure is still mimics mild over-corrected.   Overall though, at the 7" aperture, I image the scope should give rather sharp images at high power when properly collimated and thermally stable.  

 

It's too bad it falls down at full aperture.

 

Jeff

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[ngc7319_20]

Great stuff!  Thanks!

[Mitrovarr]

Oof. That's not a good edge on that one.

[spongebob@55]

Is this an older or newer production scope?   

Thanks for posting.

SB

[scotsman328i]

When my friend and club member picked up his Zhumell Z10 OTA that he let me evaluate and test:

 

https://www.cloudyni...zhumell-10-f49/

 

He dropped off his Orion XT8, 8" F6 OTA for similar care and feeding.

 

The mechanical quality and fit & finish are, IMO, on this sample, not quite on par with that of the Zhumell's, but certainly very serviceable and very good for the money.  It required collimation tweaks of the secondary and primary but both went quickly.

 

Unfortunately the optical quality at full aperture was rather below par on this sample.

 

As the DPAC images at full aperture show, there is a significant turned edge with an overcorrected zone over the outer 70% to 80% of the surface.  The surface is otherwise fairly smooth if a little lumpy in spots.  The owner confirmed to me that the images with the scope were not really sharp at high power and focus is a bit vague.  However, as this was his first scope he really had no other experience or point of reference to say the optics were sub par.   I saw no signs of astigmatism, which is good and the fully illuminated FOV seems generous.

 

I then retested it with a 7" aperture stop over the front.  This greatly improves the overall DPAC performance, though at the smaller aperture.  The outer portion of the surface is still overcorrected a little but it covers less territory and, importantly, the turned edge is almost entirely eliminated.  That overcorrected outer zone blends smoothly into a more neutral correction towards the center but the overall system figure is still mimics mild over-corrected.   Overall though, at the 7" aperture, I image the scope should give rather sharp images at high power when properly collimated and thermally stable.  

 

It's too bad it falls down at full aperture.

 

Jeff

That’s awesome Jeff. Wish I could get my optics tested. Love to see what I’ve got in reference to a mediocre, standard or superior stock mirror. Very cool! 

[Bean614]

Actually Jeff, that's an XT8-Plus, and the Optics are from GSO, not from Synta. All the Orion basic XT Dobs, with Springs and not Tension Handles, have Synta Optics.  So do the Intelliscope models and GoTo models.  The Plus versions and Skyline versions are from GSO.

   And, my experience with these (I've had many dozens) mirrors your tests.  Of the 40 or so Orion Synta Dobs I've owned, bought new OR used, the worse optics I've had were "above average".  However, of the 30 or so GSO Dobs I've had (the above mentioned Orion models, Apertura models, Zhumell models, and GSO models) it was much more hit or miss ---- some quite excellent,  some nearly unusable above 100X magnification. 

   Of course, all of my samples were perfectly collimated before EACH use, and all were placed outside hours before use, WITH fans running.

[scotsman328i]

Actually Jeff, that's an XT8-Plus, and the Optics are from GSO, not from Synta. All the Orion basic XT Dobs, with Springs and not Tension Handles, have Synta Optics.  So do the Intelliscope models and GoTo models.  The Plus versions and Skyline versions are from GSO.

   And, my experience with these (I've had many dozens) mirrors your tests.  Of the 40 or so Orion Synta Dobs I've owned, bought new OR used, the worse optics I've had were "above average".  However, of the 30 or so GSO Dobs I've had (the above mentioned Orion models, Apertura models, Zhumell models, and GSO models) it was much more hit or miss ---- some quite excellent,  some nearly unusable above 100X magnification. 

   Of course, all of my samples were perfectly collimated before EACH use, and all were placed outside hours before use, WITH fans running.

Interesting to know. I have an Orion XT8 Plus I purchased in Autumn, 2019. The optics are very good on mine. Planetary detail has been very, very good but a little soft when using 9mm and below focal length eyepieces. Most all applications present fine pinpoint stars, excellent detail on objects like the Ring Nebula, nice wisping of nebula on M42 and incredible lunar detail when we’ll collimated. I’d still love to have my GSO primary tested though. I know I’ve received a winner of the batch, but by how much? Be very interesting to see just how well made my primary came out of a batch of mass produced mirrors from China. 

[Bonco2]

Great timing. I've recently posted here on the forum about masking my Synta 8 inch Orion. Was not satisfied with star images and planet detail was soft. So I masked it to 7 inch. After several nights of testing I'm very satisfied with the visual results. Star images and diffraction images are significantly improved. It now has me satisfied. Of course i would rather have a better 8 inch mirror. But I don't want to spend what it would cost. The masking cost me nothing.

Thanks for the post.

Bill  

[Jeff B]

Actually Jeff, that's an XT8-Plus, and the Optics are from GSO, not from Synta. All the Orion basic XT Dobs, with Springs and not Tension Handles, have Synta Optics.  So do the Intelliscope models and GoTo models.  The Plus versions and Skyline versions are from GSO.

   And, my experience with these (I've had many dozens) mirrors your tests.  Of the 40 or so Orion Synta Dobs I've owned, bought new OR used, the worse optics I've had were "above average".  However, of the 30 or so GSO Dobs I've had (the above mentioned Orion models, Apertura models, Zhumell models, and GSO models) it was much more hit or miss ---- some quite excellent,  some nearly unusable above 100X magnification. 

   Of course, all of my samples were perfectly collimated before EACH use, and all were placed outside hours before use, WITH fans running.

LOL, you're right...I just looked at the sticker, it's a "Plus", well actually, in this case, a "Minus". 

 

Thanks for the background Bean!  Seems the Zhumell Z10 sample I tested came out a "Plus".  

 

Jeff

[Jeff B]

Great timing. I've recently posted here on the forum about masking my Synta 8 inch Orion. Was not satisfied with star images and planet detail was soft. So I masked it to 7 inch. After several nights of testing I'm very satisfied with the visual results. Star images and diffraction images are significantly improved. It now has me satisfied. Of course i would rather have a better 8 inch mirror. But I don't want to spend what it would cost. The masking cost me nothing.

Thanks for the post.

Bill  

Your welcome Bill! 

 

Funny, when someone gets basically an identical result or observation that validates mine, I typically say "great!" but that does not seem quite right in this case.   

 

But it seems you now have an excellent 7" F7 scope.   Great!

 

Jeff

 

BTW, the fully illuminated FOV at 7" aperture is very large and the resulting F7 focal ratio is more "eyepiece" friendly too, making for excellent wide field views.

 

Jeff

[Jeff B]

Similar to what I did in the Zhumell Z10 thread, here is a comparison between this sample XT8 Plus optics at full and 7" aperture and a sample of an 8" F7 newt system of known excellent quality (R. Fagin primary).   This provides perspective on the XT8 Plus.  First image montage is at focus.  Second montage is at outside of focus.  

 

The quilted pattern on the Fagin mirror was about 1/50 to 1/60 wave as a rough (no pun intended) estimated by CZ (it has since been eliminated), but no significant zoning and the "jail bars" are about as straight as you could ask for with a great edge.  An honest, smooth 1/10 wave system.  The XT8 Plus is rather smooth but, has that over-corrected zone towards the outer span of the diameter.  However, at 7" aperture, it ain't that bad actually.  I've requested the owner drop the XT8 Plus base off to me so I can do a visual assessment as well.

 

Jeff 

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Edited by Jeff B, 28 January 2021 - 01:54 AM.

[helpwanted]

Actually Jeff, that's an XT8-Plus, and the Optics are from GSO, not from Synta. All the Orion basic XT Dobs, with Springs and not Tension Handles, have Synta Optics.  So do the Intelliscope models and GoTo models.  The Plus versions and Skyline versions are from GSO.

   And, my experience with these (I've had many dozens) mirrors your tests.  Of the 40 or so Orion Synta Dobs I've owned, bought new OR used, the worse optics I've had were "above average".  However, of the 30 or so GSO Dobs I've had (the above mentioned Orion models, Apertura models, Zhumell models, and GSO models) it was much more hit or miss ---- some quite excellent,  some nearly unusable above 100X magnification. 

   Of course, all of my samples were perfectly collimated before EACH use, and all were placed outside hours before use, WITH fans running.

Interesting info, can you tell us your source? Also, where are other Orion reflectors made, such as the 190 Mak-Newt?

[Bean614]

Sources are Orion, Synta, GSO.   After the tumult which caused the Orion Lawsuit, which led to Meade's Bankruptcy Filing in November, 2019, Orion now buys from several different Manufacturers, mostly in Taiwan or China.

[Jon Isaacs]

Actually Jeff, that's an XT8-Plus, and the Optics are from GSO, not from Synta. All the Orion basic XT Dobs, with Springs and not Tension Handles, have Synta Optics.  So do the Intelliscope models and GoTo models.  The Plus versions and Skyline versions are from GSO.

   And, my experience with these (I've had many dozens) mirrors your tests.  Of the 40 or so Orion Synta Dobs I've owned, bought new OR used, the worse optics I've had were "above average".  However, of the 30 or so GSO Dobs I've had (the above mentioned Orion models, Apertura models, Zhumell models, and GSO models) it was much more hit or miss ---- some quite excellent,  some nearly unusable above 100X magnification. 

   Of course, all of my samples were perfectly collimated before EACH use, and all were placed outside hours before use, WITH fans running. 

 

 

 

I think the XT-8 Plus is a Synta scope. 

 

I have been following the Orion XT series and GSO Dobs since they were first introduced in 2000.  The original XT-6, XT-8 and XT-10 were manufactured by GSO. In a year or two, Orion switched to Synta. I think I have pretty good eye for identifying Orion Dobs made by Synta and Orion Dobs made by GSO and to my eye, everything about the current XT-8 series points to Synta/Skywatcher as the manufacturer.  Here are some of the obvious reasons:

 

- The XT-8, the XT-8 Plus, the XT-8i and the XT-8G use mirrors made from "low thermal expansion Borosilicate glass".  GSO Dob mirrors are made from BK-7.  This is very telling. 

 

- The XT-8 Plus does not have a GSO focuser.  It has the upgraded two speed that comes with the XT-8G and other Synta scopes.  Only the Skyline has a GSO focuser.  

 

- The XT-8, the XT-8 Plus, the XT-8i and the XT-8G OTA's weigh 20.3lbs-20.8 lbs, the Skyline 23.8 lbs. This has always been a good way to tell the difference. 

 

- The XT-8 Plus does not use the GSO altitude bearing design, it uses one very similar to the XT-8i.  

 

I could go on but I think it's clear that the scope Jeff tested was manufactured by Synta/Skywatcher.  

 

We all have our favorites and our own experiences but the beauty of the DPAC is that the pictures tell the story and this one is a clunker.  

 

Look at the photos, compare the specs:

 

Orion XT-8 Classic 

 

Orion XT-8 Plus

 

Orion 8 inch Skyline

 

Orion XT-8i

 

Orion XT-8G

 

Jon

[Chucky]

Jon, all this reminds me of the phrase "Keep them guessing".  And like shopping for mattresses.....almost impossible to compare various brands. 

 

You did a really nice summary in Post # 14.

Edited by Chucky, 28 January 2021 - 10:09 AM.

[helpwanted]

Jon, all this reminds me of the phrase "Keep them guessing".  And like shopping for mattresses.....almost impossible to compare various brands. 

 

You did a really nice summary in Post # 14.

or like shopping for a plossl

[CHASLX200]

Lots of hit and miss with these cheaper made scopes. Same for SCT's.

[Tyson M]

I had an Orion XT8Plus and it was fantastic optically once cool down- outstanding scope.  The 10" Orion I had was good but not quite as good- but it was faster.  Still no slouch.

 

Obviously sample variation is going to come into play with these options.

[CHASLX200]

Last time i had a mass made Newt was a 10" F/5 Celestron and it was just ok at best.  Nothing i would be happy with.

[Mitrovarr]

I'm starting to wonder about my dobs, honestly. I wonder if they're just not all that great and that's why I have a rather dim view of dobs for planetary use.

[scotsman328i]

I'm starting to wonder about my dobs, honestly. I wonder if they're just not all that great and that's why I have a rather dim view of dobs for planetary use.

LOL..I feel you, Brother. After seeing this thread, I’m paranoid that my mirror sucks and the world might be flat after all! 

[Mitrovarr]

Maybe I'll look into a testing and recoat and maybe refigure. The 12" dob is starting to have coating failure.

[CHASLX200]

Maybe I'll look into a testing and recoat and maybe refigure. The 12" dob is starting to have coating failure.

My Zambuto and OMI optics in all my Stamasters and Obsessions will blow you away on the planets.  Just unreal how good they were.

[junomike]

I'm starting to wonder about my dobs, honestly. I wonder if they're just not all that great and that's why I have a rather dim view of dobs for planetary use.

Possible, but IME the difference you speak of is more drastic than one sees between the common Dob mirror and premium Dob mirror.

[Jon Isaacs]

Possible, but IME the difference you speak of is more drastic than one sees between the common Dob mirror and premium Dob mirror.

 

Getting the good planetary views out of any Dobsonian requires some effort on the part of the owner/operator/observer.  I am wondering how much attention Mitrovarr pays to thermal equalibrium and collimation.  Even in San Diego's mild climate my 10 inch GSO Dob with a sealed back fan running takes well over an hour to be cooled down enough to provide to provide seeing limited planetary views.

 

And Boise probably doesn't have the best seeing.. And these past few years, the Jupiter and Saturn have been low on the horizon, no more than 25 degrees in Boise.  

 

Getting good planetary views means being prepared for those nights when the seeing is very good to excellent. 

 

Jon