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18" Obsession, wheelbarrow handles and other ???s

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#1 Kevdog

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Posted 27 July 2013 - 11:10 AM

I just bought a used (1997) 18" Obsession last night. The guy was very helpful and showed me everything (EVERYTHING) he had done to the scope, so I was confident he'd taken care of it. It's in great shape for 16 years old. The mirror was recoated last year and it had been refigured by Swazee (sp?) optics back in 2000.

One thing he mentioned was not to use the wheelbarrow handles while the scope is assembled as it will tip over. Now I know many many people here have it assembled in their garage and just roll it out to view, then roll it back in. Do you do something special to do that? It seems like maybe some cords/rope to keep the scope from tilting while moving it? Wanted to check here before doing anything like that.

Also I have a decent slope coming out of my garage and then I have a semi-level area where I can set it. Any problems having it tilted a bit while using it?

Any other hints/tips before my first night out. That may be a while as its monsoon and even though it looks fairly clear now the storms roll in during the afternoon.

Thanks!

#2 cloudmagnet

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Posted 27 July 2013 - 12:51 PM

I have a 14" Obsession clone that I built and use the wheelbarrow handles all the time with it fully assembled. What you need is some device to hold the mirror box/truss assembly from rotating in the altitude axis. It could be any number hooks, luggage catches, bungee cords, etc. that secure it to the rocker box. Even a simple pin/rod inserted into a matching hole drilled through both the mirror and rocker boxes.

#3 johnnyha

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Posted 27 July 2013 - 02:55 PM

You can use a bungee cord between the wheelbarrow handle and truss tube, just make sure it's on the proper side.

#4 Jon Isaacs

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Posted 27 July 2013 - 06:20 PM

Now I know many many people here have it assembled in their garage and just roll it out to view, then roll it back in. Do you do something special to do that?



This is my experience:

My 25 inch F/5 is stored in a garage. The door is the typical height and there is a drop off of maybe 3-4 inches between the garage door and the ground outside.

To get the upper cage under the door, the scope has to be at a very low elevation, it is low enough that the bump from going over the drop off is enough to slide the scope forward out of the bearings.

So, I just make sure someone helps me, they guide the upper cage under the door and the raise the scope up somewhat before I guide it over the drop off.

In the photo, you can see the rather low angle of the scope under the rafters. To the right, you can just see a glimpse of the garage door which is quite a bit lower, the scope really has be low to clear the door.

Jon

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#5 cpr1

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Posted 27 July 2013 - 07:15 PM

I have a Astro sky 16. James makes a small wooden C channel to fit between the mirror box and back rocker cross member to keep it from moving. Of course it will be at zenith, but it should be very easy to make. THX.

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#6 Kevdog

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Posted 28 July 2013 - 07:14 AM

Got first light tonight with mixed results.

1. It pulls in a LOT of light. Stars just pop into view.

2. I am terrible at starhopping. Some clouds and a 1/2 moon didn't help. Also being out much later than I have been recently meant everything I was used to had moved. I am getting used to the Telrad and probably need to use the 9x50 finder as well.

3. Since Uranus is close to the moon I actually found that, which was pretty cool!

4. Went to the moon for a final view. Super sharp in the ES82 18mm. Went to put in my 7-22.5 Zoom so I could really dial it in (and add in our 1.25" moon filter). Then couldn't get the scope to focus. THe focuser runs out of indward travel just a little bit before focus. Which leads me to my main question at the end of the day.

5. What do I do to fix the lack of inward focus travel. The previous owner already shortened the tubes to make room for the larger dual speed focuser he put in. Since it's close I'm betting I can just loosen all 3 collimation screws so the mirror sits lower in the rocker box right? I'm sure I can gain a 1/2" or so that way. And both times I collimate it I did tighten them (habit from my SCT).

Anything else I can do for that?

The moon was super sharp though in the 18mm. I even saw a crack right in the lunar surface that I'd never seen before. Very cool.

#7 JimMo

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Posted 28 July 2013 - 10:37 AM

Since it's close I'm betting I can just loosen all 3 collimation screws so the mirror sits lower in the rocker box right? I'm sure I can gain a 1/2" or so that way. And both times I collimate it I did tighten them (habit from my SCT).


If you lower the mirror you'll need even more in-focus. You'd have to raise it. Cutting the truss tube length in effect raises the mirror, or shortens the distance between the secondary and primary.

There are 2" to 1.25" adapters available that will lower the eyepiece into the focuser which would probably be the easiest fix.

To keep the mirror in the same place, once you fix your in focus problem, you can lock down one the the collimation bolts and collimate using only the other two.

#8 Kevdog

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Posted 28 July 2013 - 02:32 PM

Yes, duh.... of course the mirror needs to be closer!

I'll look for a in focus adapter as well.

Thanks for the tips!

#9 WOBentley

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Posted 28 July 2013 - 03:34 PM

I had the same in focus problem and asked the Obsession users group. Recommendation was to cut down the poles...in 1/4" increments that is also recommended in the instructions that came with my scope (20" f5) . I actually removed 1/2" initially and it is perfect. All my eyepieces come to focus. The only thing I need to do is to use the Ethos eyepieces that are set up for both 2" and 1 1/4 inch finders with the adapter for 1 1/4" and all is well. Likely you just need to take a bit more off of your tube length...but check that the poles are all full seated on the bottom end first. Sets of poles are reportedly available from Dave if needed (you old ask first) in case you get over zealous! I used a tubing cutter from Home Depot...did it during the day at the Golden State Star Party.
Good luck, you have an awesome instrument that should give you a lifetime of enjoyment.

#10 auriga

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Posted 28 July 2013 - 09:23 PM

I just bought a used (1997) 18" Obsession last night. The guy was very helpful and showed me everything (EVERYTHING) he had done to the scope, so I was confident he'd taken care of it. It's in great shape for 16 years old. The mirror was recoated last year and it had been refigured by Swazee (sp?) optics back in 2000.

One thing he mentioned was not to use the wheelbarrow handles while the scope is assembled as it will tip over. Now I know many many people here have it assembled in their garage and just roll it out to view, then roll it back in. Do you do something special to do that? It seems like maybe some cords/rope to keep the scope from tilting while moving it? Wanted to check here before doing anything like that.

Also I have a decent slope coming out of my garage and then I have a semi-level area where I can set it. Any problems having it tilted a bit while using it?

Any other hints/tips before my first night out. That may be a while as its monsoon and even though it looks fairly clear now the storms roll in during the afternoon.

Thanks!


Hi,
The jp astrocraft web site shows photos of the Sweet Sixteen f/4 with integral wheels, so that it can simply be tipped and rolled out of a garage, no danger of tipping.

For loading into a van or truck, using ramps, wheelbarrow handles can be used. The photo on the jp astrocraft web site of a 25" Dob shows the wheelbarrow handles using the integral wheels as the wheels for the handles. So you could conveniently use both integral wheels and wheelbarrow handles on the same scope.

Hope this helps,
Bill






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