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90mm ST vs WO 90mm

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18 replies to this topic

#1 CHASLX200

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Posted 27 March 2019 - 06:09 PM

I really like both of these scopes.  I am not sure what one i will keep.  The the ST90 is dead sharp showing the trap in M42 with a 3mm Delite.   But M42 is pretty washed out vs the WO 90MM F/6.9. Both scopes are very sharp, while color is much better in the WO.  

 

11094wp.jpg


Edited by CHASLX200, 27 March 2019 - 06:12 PM.

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#2 B 26354

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Posted 27 March 2019 - 06:42 PM

Apologies for my lack of knowledge. Who makes (made?) the ST90? If no longer in production, when was it made? Could you possibly include some basic stats? I tried looking it up, but couldn't find it.

 

Thanks!



#3 Tyson M

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Posted 27 March 2019 - 06:45 PM

Keep the scope you use more.  



#4 CHASLX200

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Posted 27 March 2019 - 06:46 PM

Apologies for my lack of knowledge. Who makes (made?) the ST90? If no longer in production, when was it made? Could you possibly include some basic stats? I tried looking it up, but couldn't find it.

 

Thanks!

It is a Discovery brand.  Kinda like the Orion ST80, but 90mm. I think it is F/5.6. I don't know much about the ST90 since not many were made. Saw it for sale and jumped.  It was cheap so why not.  I think it was made around 2000.  At F/5.6 color and FC is a problem like with all fast Achros.

 

If it had a 2" focuser it would make a killer sweeper.



#5 petert913

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Posted 27 March 2019 - 07:30 PM

I don't see much similarity between the scopes except the aperture.  I would take the Williams any day of the week.


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#6 CHASLX200

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Posted 27 March 2019 - 07:34 PM

I don't see much similarity between the scopes except the aperture.  I would take the Williams any day of the week.

The speed does set them apart. I find both give great wide FOV.  Less FC at lower power in the WO 90mm.  Much cleaner looking images also with the WO 90mm since color correction is much better.  But the ST90mm for $150 smackers does a good job for the price.



#7 homerdt

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Posted 27 March 2019 - 08:15 PM

Don't know much about the "Discovery" I've got a WO 90mm that I like a lot. I'd pick the WO but I guess I'm a little biased.



#8 Jon Isaacs

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Posted 28 March 2019 - 03:59 AM

At F/5.6 color and FC is a problem like with all fast Achros.

 

 

Field curvature is an identical problem for APOs... No difference there unless the scope is corrected for field curvature, quite rare.

 

I'd keep them both or sell the ST-90 and replace it with an ST-80 with a 2 inch focuser.  I have an ST-80 with a 2 inch focuser for the widest possible views plus an AT-80 LE which is an 80mm F/6 FPL-53 doublet which provides up to 5.5 degrees with very good color correction, slightly wider than is possible with the ST-90 with a 2 inch focuser.  

 

And then there's more.  If you really like ultra wide field sweeping and dislike field curvature, one the TeleVue Modified Petzvals would do the trick. The older ones have some false color, the newest, none.  The NP-101 has a 540mm focal length, only 40mm longer than the ST-90 but a flat field and excellent color correction.  These will do 4.9 degrees with a 41mm Panoptic, 4.45 degrees with a 31mm Nagler.

 

Jon


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#9 knight_parn

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Posted 28 March 2019 - 05:27 AM

The WO 90 is in fact f/6.2. The earlier revision had it mis-printed as f/6.9 which was corrected in the later ones.

 

Compare 504mm to 558mm focal length, the difference in fov is pretty small. On the other hand the optics on the WO is a high quality FPL53 doublet which under normal circumstance should be vastly superior to the fast achro found in the 90ST.

 

For me this would be a no brainer if I were to pick one of these two to keep.



#10 CHASLX200

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Posted 28 March 2019 - 05:35 AM

The WO 90 is in fact f/6.2. The earlier revision had it mis-printed as f/6.9 which was corrected in the later ones.

 

Compare 504mm to 558mm focal length, the difference in fov is pretty small. On the other hand the optics on the WO is a high quality FPL53 doublet which under normal circumstance should be vastly superior to the fast achro found in the 90ST.

 

For me this would be a no brainer if I were to pick one of these two to keep.

I always factor money into it.  I have too many scopes as it is and never know what scope i should use on any nite  Just looking at M42 the WO blows the 90st out of the water. I do notice some color on Venus with the WO.  I need to thin them down some and for the price the ST90 is not bad for a grab and go.  Not like i would ever look at planets with the ST90 when i got much better scopes for that.


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#11 KerryR

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Posted 28 March 2019 - 09:53 AM

I always factor money into it.  I have too many scopes as it is and never know what scope i should use on any nite  Just looking at M42 the WO blows the 90st out of the water. I do notice some color on Venus with the WO.  I need to thin them down some and for the price the ST90 is not bad for a grab and go.  Not like i would ever look at planets with the ST90 when i got much better scopes for that.

I think this kind of answers the question.

I dig "cheap" scopes- It's extremely impressive what can be had for comparatively very little money these days. However, when thinning the herd, it's advisable to keep the scopes with the best optics. While low-power sweeping is joyful, it's very handy to be able to throw power at a double star or small planetary when you want to. That's what separates the low-end achros, as impressive as they are, from the higher end ED's.

One additional caveat: Often, the low-end achros are much lighter than the higher-end ED's. This affects mounting dramatically. The WO90, which is pretty heavy for it's size, really benefits from a beefier mount than many of the lower-end (and lighter) achros. Consequently, I spend more time with the lower end scopes, simply because they work on a much lighter rig, even at larger apertures. I've always been amazed at how much better any scope performs when adequately mounted such that the point of best focus is easily seen and stopped at- rigid mounting makes any scope perform better, to the point that the mount is almost as important as the glass.

 


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#12 knight_parn

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Posted 28 March 2019 - 10:50 AM

I always factor money into it.  I have too many scopes as it is and never know what scope i should use on any nite  Just looking at M42 the WO blows the 90st out of the water. I do notice some color on Venus with the WO.  I need to thin them down some and for the price the ST90 is not bad for a grab and go.  Not like i would ever look at planets with the ST90 when i got much better scopes for that.

You would lose more money from selling the WO than the achro. ED doublets can only fetch about 50 - 60% of their original brand new prices from re-sale unless they are Taks or some other premium brands. On the other hand fast portable achros like ST80 can be bought relatively cheap and sold with only a small reduction in price.

 

The WO being f/6.2 is still on the fairly fast end for a ED doublet, so minor CA is to be expected on very bright objects like venus. It is heavier than a similar aperture achro, but for only 3.1kg and ~50cm in length it is still very much grab'n'go.


Edited by knight_parn, 28 March 2019 - 10:52 AM.


#13 SteveG

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Posted 28 March 2019 - 11:09 AM

Apologies for my lack of knowledge. Who makes (made?) the ST90? If no longer in production, when was it made? Could you possibly include some basic stats? I tried looking it up, but couldn't find it.

 

Thanks!

It's a Synta constructed scope. My friend had an Orion version (Short Tube 90) that I spent some time with. Very cheap construction, poor focuser, but good light grasp in a very lightweight tube. Best suited for low powers only.


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#14 B 26354

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Posted 28 March 2019 - 04:16 PM

It's a Synta constructed scope. My friend had an Orion version (Short Tube 90) that I spent some time with. Very cheap construction, poor focuser, but good light grasp in a very lightweight tube. Best suited for low powers only.

Thanks! Already having what I really like, I'm not overly interested in either scope. I was just curious...and thought there might also be a number of other readers who wouldn't necessarily automatically know what an "ST90" specifically is.



#15 CHASLX200

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Posted 28 March 2019 - 06:14 PM

I think this kind of answers the question.

I dig "cheap" scopes- It's extremely impressive what can be had for comparatively very little money these days. However, when thinning the herd, it's advisable to keep the scopes with the best optics. While low-power sweeping is joyful, it's very handy to be able to throw power at a double star or small planetary when you want to. That's what separates the low-end achros, as impressive as they are, from the higher end ED's.

One additional caveat: Often, the low-end achros are much lighter than the higher-end ED's. This affects mounting dramatically. The WO90, which is pretty heavy for it's size, really benefits from a beefier mount than many of the lower-end (and lighter) achros. Consequently, I spend more time with the lower end scopes, simply because they work on a much lighter rig, even at larger apertures. I've always been amazed at how much better any scope performs when adequately mounted such that the point of best focus is easily seen and stopped at- rigid mounting makes any scope perform better, to the point that the mount is almost as important as the glass.

 

I use a older GP mount and it does fine with both scopes.  The SW120ED Pro is pushing it for the GP.



#16 JIMZ7

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Posted 06 November 2019 - 06:47 PM

It's a Synta constructed scope. My friend had an Orion version (Short Tube 90) that I spent some time with. Very cheap construction, poor focuser, but good light grasp in a very lightweight tube. Best suited for low powers only.

The Orion ST90 I have is made in Taiwan all metal construction with metal lens cell & the focuser is smooth as it can be. Probably made by GSO. Much better in my opinion of the China version Orion ST8O or Meade 80 Adventure a clone of Orion. I believe It's the mid-90s version but need verification of that from someone else. Only using 21x so far & of course no CA.

Jim


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#17 Wildetelescope

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Posted 06 November 2019 - 08:31 PM

I always factor money into it.  I have too many scopes as it is and never know what scope i should use on any nite  Just looking at M42 the WO blows the 90st out of the water. I do notice some color on Venus with the WO.  I need to thin them down some and for the price the ST90 is not bad for a grab and go.  Not like i would ever look at planets with the ST90 when i got much better scopes for that.

But  you have already bought and paid for BOTH scopes.  Why wouldn't you keep the one with the better optics?  I can see making the price/performance estimation BEFORE buying a scope, but after I have already bought it?   Not sure I follow that logic. On the other hand, this is a hobby and supposed to make you happy.  I know some of my own choices seem counter intuitive to others, so pick the scope that makes you happy, and sell the other one.   Enjoy yourself, as life is way too short.  

 

Cheers!

 

JMD


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#18 Sarkikos

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Posted 09 November 2019 - 11:26 AM

Yep.  Keep what works better for you.   Don't even factor in how much you paid for them or how much you can sell them for.  You probably couldn't get much for either one, especially if the buyer expects you to pay for the shipping.

 

Mike


Edited by Sarkikos, 09 November 2019 - 11:28 AM.


#19 Sarkikos

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Posted 09 November 2019 - 11:31 AM

Field curvature is an identical problem for APOs... No difference there unless the scope is corrected for field curvature, quite rare.

 

I'd keep them both or sell the ST-90 and replace it with an ST-80 with a 2 inch focuser.  I have an ST-80 with a 2 inch focuser for the widest possible views plus an AT-80 LE which is an 80mm F/6 FPL-53 doublet which provides up to 5.5 degrees with very good color correction, slightly wider than is possible with the ST-90 with a 2 inch focuser.  

 

And then there's more.  If you really like ultra wide field sweeping and dislike field curvature, one the TeleVue Modified Petzvals would do the trick. The older ones have some false color, the newest, none.  The NP-101 has a 540mm focal length, only 40mm longer than the ST-90 but a flat field and excellent color correction.  These will do 4.9 degrees with a 41mm Panoptic, 4.45 degrees with a 31mm Nagler.

 

Jon

 

Another option is to buy a field flattener.  The TSFLAT2 works well to flatten the field in several of my achros and APO/ED's.  It can make sense economically if you have several refractors.

 

Mike




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