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Upgrades for Orion ST-90

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#1 SteveG

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Posted 18 August 2010 - 02:45 PM

My friend has an ST-90 that I had a chance to view through on a recent dark-site visit. I set it up along side my 10" reflector and was quite surprised by how good the views were. We mostly used it as a wide-field low-power scope.
He has a Pentax XL 21mm, which was excellent with this scope. In the works is the Baader zoom.


We plan on getting a new diagonal, but the focuser has a little sag and is not that smooth. Is there anything special I need to know about this rack & pinion focuser?


I have read about a tune-up for these scopes, which involves adjusting the lenses. Can someone advise me where to find more on this?

V-Block filter - Is Orion's good for this, or is there another?

That's about it - we're going to replace the finder with a RDF, but the optics of this scope are quite good.

#2 eric_zeiner

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Posted 19 August 2010 - 09:07 AM

I have been looking for one of these scopes for a while but they are scarce. What I would do as I have done with all of my other refractors is to install a dual speed Crayford and upgrade the diagonal to a 2" dielectric. GSO makes a focuser that will fit this scope for about $140.00 and I recently picked up a very nice 2" dielectric diagonal from Adorama for $80.00. It is sold under the brand of Pro Optic and it is the exact same one that Orion sells for $130. With these improvements the scope will really start to perform.

#3 eric_zeiner

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Posted 19 August 2010 - 09:08 AM

Oh, and as for the V-Block, I would go with the Baader Semi Apo filter. Agena has these as well as the GSO focuser I mentioned.

#4 Photobud

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Posted 01 February 2013 - 10:28 PM

Wondering if anyone has upgraded Orion's ST-90 like this and whether it is worth the effort and expense?

I have been looking for one of these scopes for a while but they are scarce. What I would do as I have done with all of my other refractors is to install a dual speed Crayford and upgrade the diagonal to a 2" dielectric. GSO makes a focuser that will fit this scope for about $140.00 and I recently picked up a very nice 2" dielectric diagonal from Adorama for $80.00. It is sold under the brand of Pro Optic and it is the exact same one that Orion sells for $130. With these improvements the scope will really start to perform.



#5 Scott Beith

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Posted 01 February 2013 - 11:45 PM

I agree with Eric. A few well chosen accessories will go a long way.

#6 Photobud

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Posted 02 February 2013 - 09:32 PM

I guess I was hoping that some people would give some advice about whether it is worth upgrading this telescope or just leave it as is. I know that a new focuser could be added, and a new finder scope added, I just don't know if the telescope itself is worth the cost of doing so.I paid $500 for the scope and EQ2 mount back in 2000 and bought the solar filter for $70.

#7 Jon Isaacs

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Posted 03 February 2013 - 12:11 AM

I guess I was hoping that some people would give some advice about whether it is worth upgrading this telescope or just leave it as is. I know that a new focuser could be added, and a new finder scope added, I just don't know if the telescope itself is worth the cost of doing so.I paid $500 for the scope and EQ2 mount back in 2000 and bought the solar filter for $70.


If you have some 2 inch eyepieces, a 2 inch focuser and diagonal would be a nice addition. The problem is the cost, you might end up sinking more than $200 in to just those two items and when ED-80s show up used for $300, it's hard to justify, at least in my mind.

What's the tube diameter of the ST-90? It's possible that an ED-80/ED-100 focuser might fit, add a used 2 inch diagonal and you might be in business for $100 or so..

Jon

#8 Photobud

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Posted 03 February 2013 - 09:49 AM

Thanks, Jon. That's the kind of evaluation I was trying to get. It also reaffirms what I thought might be the case (unfortunately).

#9 Jon Isaacs

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Posted 03 February 2013 - 10:15 AM

Thanks, Jon. That's the kind of evaluation I was trying to get. It also reaffirms what I thought might be the case (unfortunately).


What is the tube diameter? If you can fit a standard focuser, even a rack and pinion from maybe an ST-120, it should be a real treat, particularly from dark skies.

Jon

#10 hottr6

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Posted 03 February 2013 - 10:42 AM

I had a ST90 around 1996, and unlike your experience, it was awful! The only 'scopes I have encountered worse CA have been Gallilean and sub f/3.5 achros. Not all ST90s are good.

#11 KWB

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Posted 03 February 2013 - 12:43 PM

An excellent,informative thread. :waytogo:

I can see both sides as to upgrading or not. If it were me,I'd use the scope as is. A used Synta ED80 isn't much more expensive than what the upgrades to this telescope are probably going to cost in reality. The ED80 is in another league optically.

#12 Photobud

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Posted 03 February 2013 - 03:15 PM

Thanks to everyone for the comments. I think I'll use it as it is and maybe pick up a used refractor in the future and pass this one on to grandkids.

#13 Jon Isaacs

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Posted 03 February 2013 - 05:45 PM

An excellent,informative thread. :waytogo:

I can see both sides as to upgrading or not. If it were me,I'd use the scope as is. A used Synta ED80 isn't much more expensive than what the upgrades to this telescope are probably going to cost in reality. The ED80 is in another league optically.


I think it depends on how creative one is, on the particulars of the scope and how lucky one is. Also, a $300 ED-80 is unlikely to include a 2 inch diagonal so that would represent a necessary investment either way. My story:

A few months ago I was able to figure out how to mate a 2 inch William Optics focuser from my parts box to an ST-80 with nothing more than a thin strip of plastic. I then advertised on Astromart of a 2 inch diagonal and ended up with a Meade dielectric for under $40.

Even though I have a very nice William Optics 80mm apo and a nice 101mm apo, I am very much enjoying this ST-80 because of it's ultra widefield capabilities, it offers a binocular like 6 degree TFoV and is quite amazing with an O-III filter.

If Photobud were able upgrade the ST-90 in a similar manner, maybe an ED-80 focuser from Astromart or something like that, I think it would be a very worthwhile investment. Ungrading with a new focuser, that would be too much... Knowing the OD of the tube would go a long way in determining whether such a simple upgrade were possible.

Jon

#14 SteveG

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Posted 03 February 2013 - 06:47 PM

My friend ended up selling the ST-90. He just wasn't using it enough. We spent some time tweaking the focuser and cleaning up the optics. Someone got a very good deal on the scope / mount package, including the Pentax low-power eyepiece.


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