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what to look for in used 10 inch Parks Dob

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#1 cordite33

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Posted 19 February 2013 - 05:17 PM

Hi, first post here. I'm looking to get back into astronomy after many years away. What a great site this is. I've learned a lot by just searching and reading.

I have a chance to go look at at 10 inch Parks Dob this weekend that is for sale. Its one of those deals where the seller inherited it and doesn't know much about it other than it is valuable because they have the original receipt!
From my searches here it appears that Parks is well respected from a quality optics standpoint. Is there anything in particular I should look at to determine the telescopes value. It has some sort of custom base and only one eyepiece. Thanks in advance for any guidance you can give me.

#2 nirvanix

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Posted 19 February 2013 - 05:31 PM

Are the movements of the scope (up and down and sideways) reasonably smooth? Do the two mirrors appear to be undamaged? No cracks, scratches, gouges, silver coating falling away? Don't worry about a bit of dust or dried dew spots - they can be cleaned with care. Because it's an unknown I wouldn't offer too much because you can buy a used Orion, Zhumell, etc 10" dob for about 300$ and you'll know from the owner that it works.

#3 GeneT

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Posted 19 February 2013 - 07:03 PM

I have a chance to go look at at 10 inch Parks Dob this weekend


This is the key--to personally look over and test a telescope when buying used.

#4 KerryR

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Posted 19 February 2013 - 07:37 PM

I'm not sure, but I don't think Parks ever offered Dobsonain mounts.

So, the tube and/or mirror(s) may be Parks, and the Dobsonian mount is probably made by someone else.

Parks sold both tubes and mirrors by themselves, so you'd want to be sure what parts are actually Parks and what parts aren't. Parks tubes are all fiberglass, I believe, and easily recognizable as such. The primary will likely be labeled on the back with a serial number, hopefully a Parks logo, and some other information, probably depends on how old it is.

Parks mirrors have a solid reputation for being very good.

Parks fiberglass tubes are excellent-- excellent thermal characteristics, rigid but soft enough to help reduce vibrations, and nicely over-sized; both these things reduce tube currents far more effectively than the comparatively narrow metal ota's common to mass-market Dobs. Both these things are now nearly impossible/expensive to get, so this may be a pretty good score. Don't underestimate the value of non-thermally conductive tube materials.

Mirrors can be cleaned or re-coated if necessary, but you don't want to see ANY chips or scratches.

What's the asking price?

#5 cordite33

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Posted 19 February 2013 - 09:03 PM

He is asking $550

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#6 cordite33

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Posted 19 February 2013 - 09:06 PM

It has some sort of location or tracking built into the mount as you can see the keypad. The owner was not at home when we talked so he couldn't give me any more details at the time.

#7 nirvanix

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Posted 19 February 2013 - 10:03 PM

A Parks tube and optics with a custom base. The locator adds some value, maybe an extra $100. It looks like it was well cared for but check the mirrors for any damage. I'd be offering more like $400 for what I see if the optics are ok and the locator is working. These days used dobs are going for half price or less.

#8 azure1961p

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Posted 19 February 2013 - 10:19 PM

Take it.

I had a PARKS F5 and I prefer the views through my PARKS 8" F/9 as its small secondary simply provides a look on everything I prefer. But my scope WAS at least good. The ronchi like for my 8" they made later on was ruler straight - completely. Too, another 10" f/5 by PARKS was reviewed by sky and tel as so good it would produce essentially perfect star images. They based it on the ronchi. Other mirrors tested in that article failed behind the parks, notibly MEADE. I forgot the others but recall the PARKS ten beat them all - hence my PARKS purchases.

If you don't mind the f/5 and most folks don't, it may be the best ten you'll ever look through. At the price its going at - you've got a bargain sitting there.

Pete

#9 Jon Isaacs

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Posted 19 February 2013 - 10:34 PM

It has some sort of location or tracking built into the mount as you can see the keypad. The owner was not at home when we talked so he couldn't give me any more details at the time.


It looks like a Parks tube on a custom mount. It looks big, long and heavy. A major virtue of the Asian 10 inch F/5 Dobsonians is that they were carefully designed to be compact, they fit in smaller cars and are of a reasonable weight. This one looks like a handful.

The mount is also an unknown. It looks to be a one-off design that did not follow common practice, it might work great, it might not. I don't recognize the electronics, maybe someone does...

A new 10 inch F/5 from Apertura, Astronomics or Zhumell is right at $500 shipped to your door. My gut feeling is that this Parks tube on a Dob mount is a bit clunky, something of a project.

Would this be your first scope? Where are you located?

Jon

#10 azure1961p

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Posted 19 February 2013 - 10:56 PM

I'd laugh if that was the OTA I sold in New Hampshire. I too built a dob mount for it but ended up jus selling the tube.

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#11 Mirzam

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Posted 20 February 2013 - 08:23 AM

The bearings on the mount are on the small side. Perhaps they have some sort of tension adjustment? This would aid in maintaining balance when using eyepieces of different weights. It is nice to also have the tube rings though.

If the coatings on the primary are bright and undamaged then the price is not too bad. The fiberglass tube will be heavy but is an upgrade from the typical steel tubes offered by the Chinese makers. If you have to have the mirrors recoated figure on about $100 unless you live close to a coating facility (to eliminate shipping costs). Obviously the recoating cost should influence the price.

If the scope comes with any decent eyepieces that would also be a plus.

JimC

#12 Mirzam

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Posted 20 February 2013 - 08:25 AM

You mentioned the receipt. If the coatings are more than 15 years old I would absolutely want a recoat.

JimC

#13 KerryR

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Posted 20 February 2013 - 10:00 AM

Looks well built.

One nice feature is the use of tube rings-- this will allow you to put the eyepiece where you want it, and allow you to balance the scope easily, without counterweights, should you change things out on the front end.

Parks tubes weigh a LOT more than the steel Asian variety. This can help make the movements smoother-- seems to take a certain heft before Dob bearings enter the truly butter-smooth realm. This only applies if the bearings are done correctly, but it should be pretty easy to tell-- when you push the tube there should be no stick-jerk action. It's alright if they the movements feel stiff, as long as they are smooth. You shouldn't feel that you have to apply a lot pressure to start the movement, but then far less as soon as it begins to move.

As I mentioned earlier, there's much to recommend to the thermal characteristics of over-sized fiberglass tubes, so I see that as a plus for the scope. But, it does you no good if you can't easily get the thing out the door!

It's nice that the tube has dust covers for both ends. You don't see that very often.

If everything fits in your car, I can't see much reason not to go for it, as long as the movements feel super-smooth to you. I think the asking price is quite fair, but no reason not to haggle.

#14 The Planetman

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Posted 20 February 2013 - 10:42 AM

I'm not sure, but I don't think Parks ever offered Dobsonain mounts...


Yes, Parks offered dobs back in the late '80's/early 90's. But this is not the mount that they used. It is definitely an aftermarket.

I had a 10" f/5 Z-Scope -who remembers those scopes?- and it was built with Parks optics. It was a killer scope! Optics were great! But like any telescope/optics manufacturer, they can make a really great one or a not so really great one....

Check to see if the mirror has "Parks" etched on the back. Also, check to see if the optician signed it. I've had three mirrors, one 8" and two 10", that were made by George Clements and they were all nice.

#15 Jon Isaacs

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Posted 20 February 2013 - 10:50 AM

This only applies if the bearings are done correctly, but it should be pretty easy to tell-- when you push the tube there should be no stick-jerk action. It's alright if they the movements feel stiff, as long as they are smooth. You shouldn't feel that you have to apply a lot pressure to start the movement, but then far less as soon as it begins to move.



In my experience, it is very difficult to judge the action of a Dobsonian mount unless one is out under the stars. A mount can seem nice and smooth to the touch, most do, but looking a target at higher magnifications, small imperfections are highly magnified. Stiction results in overshoot, vibration, it only takes a tiny fraction of a millimeter to mess things up.

Jon

#16 dpwoos

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Posted 20 February 2013 - 11:11 AM

I agree - the only way to know the worth is to observe with the scope. If the seller isn't interested in facilitating that then I would pass.

#17 rflinn68

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Posted 20 February 2013 - 11:37 AM

It has some sort of location or tracking built into the mount as you can see the keypad.


I don't recognize the electronics, maybe someone does...A new 10 inch F/5 from Apertura, Astronomics or Zhumell is right at $500 shipped to your door.


It looks exactly like the Hand Controller that came with my Orion XT10i. The 10" Apertura, Astronomics, Zhumell dobs for $500 new do not include the hand controller. Those cost about $750. My guess is it is a Push-To object locator and does not have a tracking motor. These are still nice to have if they work right. You just need to know a couple stars then you find and center them in the eyepiece and you are ready to go. It will show you up and down (ALT) and side to side (AZ) arrows with a set of numbers that will count down (or up if you're going the wrong way) as you move the scope to the object you are wanting to observe. If this scope has a nice mirror made by Parks I'm sure it would be worth the asking price assuming everything is in good working order. Looks nice to me.

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#18 KerryR

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Posted 20 February 2013 - 11:40 AM

This only applies if the bearings are done correctly, but it should be pretty easy to tell-- when you push the tube there should be no stick-jerk action. It's alright if they the movements feel stiff, as long as they are smooth. You shouldn't feel that you have to apply a lot pressure to start the movement, but then far less as soon as it begins to move.



In my experience, it is very difficult to judge the action of a Dobsonian mount unless one is out under the stars. A mount can seem nice and smooth to the touch, most do, but looking a target at higher magnifications, small imperfections are highly magnified. Stiction results in overshoot, vibration, it only takes a tiny fraction of a millimeter to mess things up.

Jon


Agreed.

But it's not always possible to do so, so the OP may have to do it by feel as best he can.

It's pretty easy to recognize truly bad bearings-- the differential between the force required to initiate movement and that needed to continue the movement can be pretty obvious, and if it is, it suggests a problem.

Another 'error' that can be easy to detect is a significant difference between alt and az friction, most obvious with Dobs with (un-tuned) lazy-susan az bearings.

It is, of course, much more difficult to recognize the subtle 'over shoot' of close-but-not-actually-good bearings without actually looking through the scope at high power.

Really bad movement might suggest the need for heavier duty mods that the OP might want to avoid, such as having to re-do the laminate on a bearing surface.

Close-to-good bearings often respond well to movement of bearing pads, cleaning bearing pads, sanding bearing pads, wax, Sailcoat, etc.; things the OP might not mind trying.

Point is, definitely give the scope a push or two and look for glaring errors, and take the results of a pass with a grain of salt if not actually looking through the scope.

Failing stars, a daylight trial on a distant target at high powers would help.

#19 Binojunky

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Posted 20 February 2013 - 12:51 PM

To be honest if your getting back into the hobby and thinking of spending around $550 or so, I would be inclined to go with a new scope,a 8 or 10 inch dob would be ideal.
With new you have recourse if their are problems, the mirror coatings would be new, the Parks scopes though good in their day are heavy, some came with only 1.25" focusers etc,you may be buying a pile of problems, JMTCW,DA.

#20 KerryR

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Posted 20 February 2013 - 01:15 PM

I bet the focuser is 2".

It sure doesn't LOOK like a hack-job mount. It looks like someone took a bit of time and care to build the mount and retrofit the locator. 'Course, what can I actually tell from a photo?

Parks mirrors are usually quite good. So are many of the current Asian mirrors, but it's always a gamble. I'd gamble on the Parks mirror before I gambled on an Asian mirror.

New scopes in a similar price range typically take some work to get their motions butter-smooth anyway, and their narrow metal tubes are a thermal drag, though commercial inserts and/or fans help reduce much of the issue.

Parks currently (I thought they were out of business??) lists their 10" f5's at $1,500 ota only. This makes the $550 mounted scope with push-to look pretty darn good to me. There'd have to be something pretty wrong with it for it to be a bad deal, assuming it fits in the OP's car.

OP: Let us know what the Receipt says (cost, date, etc.).

#21 Jon Isaacs

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Posted 20 February 2013 - 02:11 PM

It's pretty easy to recognize truly bad bearings-- the differential between the force required to initiate movement and that needed to continue the movement can be pretty obvious, and if it is, it suggests a problem.



My concern is that the base is a non-standard design and for an OTA that heavy, it does look a bit undersized and with small altitude bearings.

My gut feeling is that this scope will be a project, the OTA probably weighs about what a 12 inch F/5 does, from what I can see in the photo, the OTA is long...

Jon

#22 KerryR

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Posted 20 February 2013 - 03:18 PM


It's pretty easy to recognize truly bad bearings-- the differential between the force required to initiate movement and that needed to continue the movement can be pretty obvious, and if it is, it suggests a problem.



My concern is that the base is a non-standard design and for an OTA that heavy, it does look a bit undersized and with small altitude bearings.

My gut feeling is that this scope will be a project, the OTA probably weighs about what a 12 inch F/5 does, from what I can see in the photo, the OTA is long...

Jon


You could certainly be right.

The open design of the base actually looks pretty similar to the Skyquest XT12i (similar ota weight), but with an additional vertical stablilizer on the sides not present on the Orion XTi. The apparently 5-6ish" diameter alt bearings probably are a little small for ensuring best motions, but their pretty close to, if not bigger than, Orion's 12i alt bearing diameter . Plus they look like they have laminate on them, while most Asian dobs are glossy plastic on teflon.

The ota is heavy-- 42# according to Parks's website vs. 29# for the Orion 10i ota. I could certainly see potential for focus wiggles given the weight. But, the plywood might dampen more quickly as well as be more rigid in the first place, so it might not be any worse than the Orion despite the additional weight. If the base is glued and screwed, there's potential for it to be nice and solid. A lot would depend on things we can't see in the image.

The Parks is 52" (according to their website), vs. 48" for the Orion. I don't think this would prevent the ota from fitting in a car, though it certainly adds to the clunk factor.

I could see how it COULD end up being a project scope (I'd venture to say most Dobs are, commercial or otherwise), but probably not more so than an Orion equivalent. It's obviously impossible to know from a photo for sure, but the construction sure LOOKS well thought out and executed if maybe a little 'wispy' (but also lighter-- maybe a good thing).

Hopefully, the OP will get a chance to take a peek through it, either at stars or a daytime target. That would answer the questions.

#23 azure1961p

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Posted 20 February 2013 - 10:45 PM

At $550 I wouldn't care about the recoat. It's still a deal on what probably a great scope. I would take it over a new dob by anyone else for the same aperture and f ratio.

Pete

#24 Pinbout

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Posted 21 February 2013 - 09:14 AM

I would take it over a new dob by anyone else for the same aperture and f ratio.



Even Teeter's new 10in travel dob?

#25 Jon Isaacs

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Posted 21 February 2013 - 09:46 AM

At $550 I wouldn't care about the recoat. It's still a deal on what probably a great scope. I would take it over a new dob by anyone else for the same aperture and f ratio.

Pete


I have had my 10 inch F/5 Generic Asian Dob for about 10 years, it's been a good scope, solid optics and has required a minimum of tweaks, most of which are now standard. I have some scopes with fancier names but this GSO is a good scope and I wouldn't be trading it for this Parks unless I knew more about the Parks.

I am looking at the photo of this Parks Dob, the base design is what concerns me the most. It's not clear to me how the altitude bearings work, to my eye, the one bearing I can see does not appear to be the standard trunion design. It could be that it works great, it could be that it needs a complete rebuild.

To Kerry's points, the difference between a 48 inch long OTA and a 52 inch long OTA can be quite critical when it comes to fitting the scope into a car. I know my 10 inch F/5 fits nicely across the back seat of our 1999 Honda Accord, the Parks might fit but probably would require some shenanigans.

My thinking goes like this: Over the years I have purchased a fair number of second hand Dobsonians. With customs scopes, I have had some surprises that required major rebuilds. If the Original Poster, Cordite33, is ready to take on what might be a project scope, it's probably a reasonable choice.

Jon






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