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Home Built 10.1" f 4.5 Dobsonian Tube Weight

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#1 beertracker

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Posted 06 August 2020 - 07:22 PM

I hope this is the correct forum.  The problem is I want to convert to a equatorial mount for astro-photography. My tube is made of heavy 3/16" fiberglass. Since my tube assembly weight is 49 lbs I need a equatorial mount in the $800 price or higher range. Too much for me. So I am looking at shedding tube weight. If I can get the weight down I can buy a less expensive mount.

 

Three options come to mind; 1. reducing the tube length by 12".  2. converting to sonotube.  3. converting to truss design.  I doubt removing 12" of tube length will give the weight reduction I want.   So which weights less:  a sonotube or truss of equal length?

 

See attached photo.

 

Thanks,

bt

Attached Thumbnails

  • telescope.jpg

Edited by beertracker, 06 August 2020 - 07:24 PM.


#2 Augustus

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Posted 06 August 2020 - 07:27 PM

IMO, even with weight reduction a 10" f/4.5 is HUGE for astrophotography and will need something in the EQ6-class range at the minimum which will easily run you $1500. For astrophotography you'd be better off with an HEQ5 and small apochromatic refractor or 6" f/4 Newtonian.

 

As for reducing the weight of this for visual use, I'd convert to a truss Dob.


Edited by Augustus, 06 August 2020 - 07:27 PM.

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#3 kfiscus

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Posted 06 August 2020 - 07:38 PM

What's your budget?

My first thoughts are to keep your 10" as a visual-use dob and get a much smaller (refractor?) scope for AP.  If $800 is too much for a mount, though, I'm afraid getting into astrophotography might be a non-starter.

 

To answer your weight reduction question, a well-executed truss design can be much lighter than sonotube.  Tube stiffness is important for AP- lightening poses risks of causing flexure.  You don't need a lot of aperture for AP but you do need a solid mount.


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#4 spereira

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Posted 06 August 2020 - 07:46 PM

Moving to reflectors..

smp
 



#5 ShaulaB

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Posted 06 August 2020 - 09:06 PM

With Sonotube, you still need to flock the inside. Then you will need to coat the outside with layers of polyurethane or something because dew will degrade the cardboard over time. Unless you live someplace where dew or humidity during storage is never an issue. No location is mentioned near your avatar, so can't say for sure.

 

These things add weight.

 

Please read some of the imaging threads here to see what people doing astrophotography really use. The mount is #1 in priority.


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#6 Tom Stock

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Posted 06 August 2020 - 11:09 PM

I hope this is the correct forum.  The problem is I want to convert to a equatorial mount for astro-photography. My tube is made of heavy 3/16" fiberglass. Since my tube assembly weight is 49 lbs I need a equatorial mount in the $800 price or higher range. Too much for me. So I am looking at shedding tube weight. If I can get the weight down I can buy a less expensive mount.

 

Three options come to mind; 1. reducing the tube length by 12".  2. converting to sonotube.  3. converting to truss design.  I doubt removing 12" of tube length will give the weight reduction I want.   So which weights less:  a sonotube or truss of equal length?

 

See attached photo.

 

Thanks,

bt

Question is what TYPE of astrophotography?

 

CCD imaging of planets, and stacks of short exposures (10-15 sec) for deep sky?

 

Build an equatorial platform.  You can get some great images with little effort.

 

If you want longer exposures, buy a small refactor or SCT and an equatorial mount and be prepared to spend many many hours imaging, stacking, and processing images.  Capturing data is actually the easy part.


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#7 N3p

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Posted 06 August 2020 - 11:12 PM

I hope this is the correct forum.  The problem is I want to convert to a equatorial mount for astro-photography. My tube is made of heavy 3/16" fiberglass. Since my tube assembly weight is 49 lbs I need a equatorial mount in the $800 price or higher range. Too much for me. So I am looking at shedding tube weight. If I can get the weight down I can buy a less expensive mount.

 

Three options come to mind; 1. reducing the tube length by 12".  2. converting to sonotube.  3. converting to truss design.  I doubt removing 12" of tube length will give the weight reduction I want.   So which weights less:  a sonotube or truss of equal length?

 

See attached photo.

 

Thanks,

bt

If the tube is good, you already have a good fiber glass tube.. (which is a good thing) it's meant to be a Dobson based Newtonian.

 

I would keep it as it is and buy something else for photography.


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#8 Tony Flanders

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Posted 07 August 2020 - 05:56 AM

You could also buy or build an equatorial platform. But honest, a scope that size that isn't explicitly built for astrophotography is likely to have all manner of problems. Starting with a much smaller optical tube would almost certainly make more sense.


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#9 Pinbout

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Posted 07 August 2020 - 11:33 AM

go to home depot and hand weigh a 12" sonotube... see if its strong enough for you.  there's other cardboard tubes more structurally stable, but they weigh more.

 

you don't have to do anything to the tube except for install the hardware and optics... see what the weight difference is.

 

you only need to flock, if at all, oposite the focuser.

 

a truss will complicate everything, it could be light, but the sonotube is 1 piece, making it more stable. 

 

so I would use the sonotube 1st and then afterward if you decide to try, build a split truss.



#10 beertracker

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Posted 08 August 2020 - 08:45 PM

Thanks for all the good suggestions you guys provided.   I think I will get a smaller aperature telescope for astro-photography.   For the 10" dobsonian I like the idea of hand weighting a 12" piece of sonotube at Home Depot then deciding if the weight difference is significant compared to my 3/16" thick fiberglass tube.   The fact sonotube absorbs moisture is a factor since I live in Houston, TX.

 

I am un-decided on a truss conversion for my 10" dobsonian.  I wonder if it would be stable.

 

My 10" dobsonian fiberglass tube is 59" long and I have at least 12" of tube above the vane secondary mount that I could cut off.  It wouldn't provide much weight saving but should be easier to move around.   Plus I would have to re-balance the tube but no big problem.   For some reason I chose a tube that was longer than needed?  




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