104 replies to this topic

[Neptune]

Then again, all my sites (and frequent star parties) are within platform latitude range, so anywhere else I'll leave the platform at home.

So, platforms have a latitude limit and a time limit?

[lphilpot]

Yes. Platforms are specific to a certain latitude, although depending on the design you have some margin for error north-south, a couple of degrees usually. Also they typically run for about an hour and then need to be reset. 

[stargazer193857]

It's been known to happen that my wife will hand me an eyepiece and say "Get out of the house" making it my choice of which scope to take with me.

Only good if it is a clear sky. If so, very nice.

[junomike]

or you can do what I just did..... I bought a vehicle that the Dob can be wheeled into without any dismantling..... a pair of telescopic aluminium ramps is all that is needed... 

Agreed.  I've considered a few large Dob's that came with the trailer.  Still not as good as an OB, but better than the alternative.

[stargazer193857]

You could remove the tank from a porta potty and repurpose the door into a ramp and tow that. Then it could be straight up and shorter parking space needed. I don't know if it would cost less than a regular trailer.

[cuzimthedad]

You could remove the tank from a porta potty and repurpose the door into a ramp and tow that. Then it could be straight up and shorter parking space needed. I don't know if it would cost less than a regular trailer.

I have a friend with a 20" F/5 Obsession that stores it in a converted porta potty during the winter. Wish I still had the pic he sent me as I would have posted it.

[junomike]

I have a friend with a 20" F/5 Obsession that stores it in a converted porta potty during the winter. Wish I still had the pic he sent me as I would have posted it.

So he has an obsession with an outhouse, er, wait that would be an outhouse with an Obsession......

[stargazer193857]

So he has an obsession with an outhouse, er, wait that would be an outhouse with an Obsession......

Obsession with what's stored in it.

[Sheol]

       Could be an obsession about  an Obsession? Kind of makes your head ache, but in a kind of good way. lol

        About the only downside I can think of with Dobs & since I'm totally un-biased here  is they really are not that great for astrophotography. But I do not want to get into that any way, so for me, its a non-issue. But I thought the thread was starting to move away from topic & needed to get back on track.

 

    Clear Skies,

      Matt.

[Keith Rivich]

I agree that goto / tracking adds complexity. Personally I value tracking much more than goto, but if you're talking pure alt-az, tracking pretty much implies goto in most scenarios. However, an EQ platform (and yes, there are limitations and disadvantages) is nice in that it's a separate component - You can use it, or not. If you integrate the platform into your scope, i.e., it becomes the "ground board", then the option is gone. But if you just sit your scope on top of the platform, you can have tracking when you want or not mess with it when it's not needed.

 

But I have to say, once (even roughly) aligned and running, the way an EQ platform becomes invisible -- other than resets -- is great. I've gotten very attached to having an object sit in the eyepiece while I peruse a chart, look up info in SkySafari, etc. That said, if I'm just heading out for an hour or two, I don't worry with it (I always "head out" - observing from home with my Dob is a waste of time and effort).

 

This is in no way meant to trash ServoCat or other alt-az tracking systems, since my "experience" with them is relegated to observations of a few friends with them, but... I can't tell you how many times I've seen them on their knees with a red light after dark, trying to diagnose and fix some issue in the drive system. All the while my platform purrs.   Then again, all my sites (and frequent star parties) are within platform latitude range, so anywhere else I'll leave the platform at home.

When I rebuilt my 25" I though long and hard about a drive system. I love platforms for all the stated benefits. However...I couldn't quite think through a a way to easily get the scope up onto the platform by myself. The Servo-Argo certainly has its issues at times but for the most part works just fine. 

[lphilpot]

With my 12" f/5, I just lift the rocker box on top of the platform, assemble the OTA and go from there. With the 14.5" f/4.5, I backed it up onto it using the wheelbarrow handles then assembled. In both cases, the scope just sits on top of the platform. If the platform replaces the ground board, it would certainly have to be assembled on top of the platform.

 

But, yeah, that's a consideration and certainly neither of my scopes are a 25". A friend (also from the Houston area -- You might know Walt) has a 25" f/5 Obsession and I can't imagine trying to navigate it, fully assembled, onto an EQ platform ("beam it over, Scotty!"). Assembling it while on the platform? Probably a different matter.

 

Re: ServoCat, obviously it works well or it wouldn't sell like it does. That's why I carefully worded what I wrote.   But if the limitations of a platform aren't an issue, it can be a nice solution. Like everything else, it's a matter of the right tool for the job.

[izar187]

In addition to the good advise and experiences shared by others...

The down side of dobsonian mounted reflectors is where the primary goes.

The upside is where the focuser is.

As opposed to dobsonian mounted refractors, where the primary goes on the upside, and the focuser is on the down side. 

[Neptune]

As opposed to dobsonian mounted refractors, where the primary goes on the upside, and the focuser is on the down side. 

I couldn't agree more!  The focuser was inches off the ground when pointed straight up.

[Sky_LO]

I am going to disagree--to an extent.

 

There are advantages to speed in that size:: take my 13" F/3

 

13newbase02.JPG

 

Notice that the primary is at hip height, above the dust and moisture of the ground.

Notice the assembly is so short one can hold the top and the altitude bearing at the same time, making precise altitude adjustments more precise.

 

The only downside is one needs very short FL EPs in order to operate at high power.

Mitch - Kudos to you for building the F3 dob.  I got lucky and was able to get the Zip Dob by Mel Bartels, which is also a 13.2 inch mirror at F3.   I can view and remain seated with the scope at zenith.  The weight is only 31 pounds as it is a slumped meniscus mirror.  And it folds for easy travel and storage.   It is my favorite gadget!  Large FOV capabilities.    No downsides ! 

Premium dobs can make the dob experience even more "primo!" 

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Edited by Sky_LO, 02 December 2020 - 05:00 PM.

[Miranda2525]

The only downside for a dob that I can see is no tracking at very high powers. Otherwise I like everything else about them.

 

Big downside to owning a refractor is when viewing at zenith, you have to kneel on the ground. Dobs have "Dobson's hole" at zenith, but waiting until the object gets just past that hole is much better than having to kneel or crouch on the ground with a refractor if you don't own a tall pier.

[stargazer32864]

Mitch - Kudos to you for building the F3 dob.  I got lucky and was able to get the Zip Dob by Mel Bartels, which is also a 13.2 inch mirror at F3.   I can view and remain seated with the scope at zenith.  The weight is only 31 pounds as it is a slumped meniscus mirror.  And it folds for easy travel and storage.   It is my favorite gadget!  Large FOV capabilities.    No downsides ! 

Premium dobs can make the dob experience even more "primo!" 

That is so cool!!! I love it!! I wish I was that gifted.

[BDS316]

David,

 

A premium Dobsonian has very few downsides.  High quality mirrors, smooth yet accurate motions, significant size and weight reduction.

 

Your absolutely right about the "boat anchor" Orion and SkyWatchers.  I've been there and the best thing I did was to get the base rebuilt by DobSTUFF.  But I don't think you need to go as fast as F/4 if your looking for a manageable size.  The F/4.6 in my old XX14g never gets high enough that I can't sit in my adjustable chair...

 

XX14g on DobSTUFF.jpg

 

If you can go without adding motors, you'll save yourself a lot of unnecessary hassles as these scopes are much easier to move manually than the mass produced ones.  Get a Nexus or something similar if you need the Push-2 (Star-hopping works just fine for me).

The biggest downside of Dobs is the particleboard base.  Congratulations on your solution.  Great looking setup.  Did you increase the size of the original altitude bearings?  

Edited by BDS316, 03 December 2020 - 04:03 PM.

[brentknight]

The biggest downside of Dobs is the particleboard base.  Congratulations on your solution.  Great looking setup.  Did you increase the size of the original altitude bearings?  

I went up to 12" diameter.  I would have liked 14", but that would have started interfering with the truss pole attachments.

[Tyson M]

Mitch - Kudos to you for building the F3 dob.  I got lucky and was able to get the Zip Dob by Mel Bartels, which is also a 13.2 inch mirror at F3.   I can view and remain seated with the scope at zenith.  The weight is only 31 pounds as it is a slumped meniscus mirror.  And it folds for easy travel and storage.   It is my favorite gadget!  Large FOV capabilities.    No downsides ! 

Premium dobs can make the dob experience even more "primo!" 

I absolutely loved this when I first saw Mel built it.  Just a unique scope all around.

 

Very cool.

[Sheol]

           Wow! That may be the coolest solution to making a Dob portable I've seen... Well, ever. It is also very attractive. While I prefer a telescope to be functional above all things, its nice looking & would be great to show off in your house.

           I doubt that has many down sides, other than maybe the lack of tracking for very high magnification. 

           I think I am in love with a scientific instrument! 

 

           Clear Skies,

             Matt.

Edited by Sheol, 04 December 2020 - 02:35 PM.

[Tank]

Downside NONE
Get a goto DOB Skywatcher amd Orion makes them

[BlueTrane2028]

The main reason I don't have a big dob is the ergonomics of viewing positions.  With a dob, I'm always kneeling, bending, crouching, hunching over and craning my neck.  After an hour or two, I'm finished. I do much better with smaller scopes on tall alt-az mounts.  I give up a few inches of aperture but enjoy the session much, much more.

I don't enjoy the tripod mounted refractor experience much at all.  Dob? I'll spend hours....  EQ mounted Newts are fine if you can rotate the tube in the rings. 

[Keith Rivich]

With my 12" f/5, I just lift the rocker box on top of the platform, assemble the OTA and go from there. With the 14.5" f/4.5, I backed it up onto it using the wheelbarrow handles then assembled. In both cases, the scope just sits on top of the platform. If the platform replaces the ground board, it would certainly have to be assembled on top of the platform.

 

But, yeah, that's a consideration and certainly neither of my scopes are a 25". A friend (also from the Houston area -- You might know Walt) has a 25" f/5 Obsession and I can't imagine trying to navigate it, fully assembled, onto an EQ platform ("beam it over, Scotty!"). Assembling it while on the platform? Probably a different matter.

 

Re: ServoCat, obviously it works well or it wouldn't sell like it does. That's why I carefully worded what I wrote.   But if the limitations of a platform aren't an issue, it can be a nice solution. Like everything else, it's a matter of the right tool for the job.

I do know Walt!

 

My 18" uses a platform for tracking. I just wheel the mirror box onto the platform using plastic ramps, such as the ones used for driving cars onto for service, center it on the peg then assemble the rest of the scope. Takes about 15 minutes total. 

 

If I get tired of the ServoCat I may switch the 25" over to a platform and mount it the same way as the 18". Not sure I want the extra height, though. 

[stargazer193857]

At a public observatory, I waited for M31 to get a bit higher out of the muck. Only once it climbed above 45 degrees did I head over to the pier mounted 110mm binoculars. They did not aim high enough, stopping at maybe 45 degrees. Fortunately the nearby 10" Newtonians showed it just fine.

[stevew]

Will an F- 3 or F-3.5 have a larger secondary mirror than an F-4.5 or F-5 ?