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GM8 weight capacity...

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#1 relee

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Posted 06 July 2020 - 05:53 PM

Hi All! New to this forum and just getting back into observational astronomy.  I would like to tap into the mega-years of experience available to validate or change some of the ideas I have for new equipment I would like to acquire.  I started with a Tasco telescope in my youth and have been in and out the hobby for many years.  I currently have a Discovery 10" F6 Dobsonian and a small refractor (90mm) on an equatorial mount.  I have thought all my life how great it would be to have top notch equipment to observe with.  My current circumstances make that possible.  I have read great reviews on the Takahashi 130NS and it seems perfect for what I want.  I need a mount, preferably an equatorial with drive motors but no go-to.  I have always admired the Losmandy products for their look and function. Would a GM8 which is capable of handling 30lbs. be sufficient for mounting the TAK-130?  The OTA weighs 22 lbs. or so and I would be adding a RA finder scope only.  I have no interest in photography although I certainly appreciate those who do and the fantastic images they capture. I will be pairing it with the Berlebach Planet wood tripod for Losmandy mounts.  Kinda old school but I remember going thru the Unitron catalog as a kid and dreaming...  If you can give feedback on this  combination I would greatly appreciate it!  Thanks, Bob  


Edited by relee, 06 July 2020 - 06:59 PM.


#2 rkaufmann87

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Posted 06 July 2020 - 08:03 PM

For visual only it would be okay, Losmandy rates it at 30-40lbs for AP work so for visual it should be fine. If you are considering AP at any point in the future, I'd recommend getting the GM811G which is rated at 50lbs so it gives you some head room. I'd also recommend joining the Losmandy user group at https://groups.io/g/Losmandy_users that is where most of the really experienced Losmandy owners hang out. 


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#3 macdonjh

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Posted 07 July 2020 - 07:18 AM

I think it will work also.  I use my GM-8 with two scopes: an ATM classical Cassegrain (appx 25 lb) and a GSO Newtonian (I'll bet it weighs close to thirty pounds, it seems heavy).  

 

20190411_164931 small.jpg

 

13 Finished.JPG

 

Replacing the stock Losmandy lightweight tripod with a Berlebach tripod will make your GM-8 more stable.  I have a project in my queue to replace the stock legs of my tripod with wood legs from a Takahashi tripod.  I also use the digital drive, but I've got encoders and an old Sky Commander computer for my mount.  I need to shim my scopes to minimize cone error.  I hope that will improve the accuracy of the Sky Commander.



#4 relee

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Posted 07 July 2020 - 08:23 AM

I think it will work also.  I use my GM-8 with two scopes: an ATM classical Cassegrain (appx 25 lb) and a GSO Newtonian (I'll bet it weighs close to thirty pounds, it seems heavy).  

 

attachicon.gif20190411_164931 small.jpg

 

attachicon.gif13 Finished.JPG

 

Replacing the stock Losmandy lightweight tripod with a Berlebach tripod will make your GM-8 more stable.  I have a project in my queue to replace the stock legs of my tripod with wood legs from a Takahashi tripod.  I also use the digital drive, but I've got encoders and an old Sky Commander computer for my mount.  I need to shim my scopes to minimize cone error.  I hope that will improve the accuracy of the Sky Commander.

Thanks for the reply...  The weight included with the GM8 is 7lbs.  As my load will be about what you have could you tell me the size of weight you are using?  It looks to be more than 7lbs... Thanks!



#5 SonnyE

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Posted 07 July 2020 - 10:35 AM

Last February I bought my Losmandy GM811G HD. It is the last mount for me.

Truly my Lifetime Mount. It replaces a defunct Celestron AVX.

 

I do imaging as a rule. But I of course began by doing Observation to learn how to run everything and to learn the night skies from my location. One of the biggest thrills was when I was showing my new equipment to my Step-Son and we got Saturn in the telescope full view by stacking up two Barlow's and dialing in my Celestron variable eyepiece. That sold my skeptical wife on my endeavors.

 

I'll help you drool, and to research your new mount. http://www.losmandy.com/eq-mounts.html

 

To me, my GM811G is considerably overboard for my currant use, with a 50 pound Photographic instrument weight rating. My present imaging telescope, et all, now tips the scales at 15.4 pounds. (~7 Kg).

I don't plan on changing that, but I do dream of bigger telescopes, and "piggy backing" observational and imaging on my mount.

 

Scott Losmandy recently added a new video about how he has now made his mounts convertible as well. https://youtu.be/rvm2bgx_DJA



#6 macdonjh

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Posted 08 July 2020 - 10:31 AM

Thanks for the reply...  The weight included with the GM8 is 7lbs.  As my load will be about what you have could you tell me the size of weight you are using?  It looks to be more than 7lbs... Thanks!

The large gray/ silver weight is a Losmandy 11 lb, the black weight (in the photo of the red Newtonian) is a 5 lb weight a friend made for me several years ago.



#7 vahe

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Posted 08 July 2020 - 12:23 PM

Someone asked Roland a similar question, something along the lines if a certain refractor would stress a certain Astro-Physics mount.

His reply pretty much applies to all mounts including the one under discussion here.

 

"For visual, the rule of thumb for refractors was that the mount's worm wheel diameter be same size as the scopes lens aperture. Smaller worms take longer to settle than larger worms.

That was the rule of thumb back last century"

.

Vahe


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#8 Yasuhiko

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Posted 08 July 2020 - 09:57 PM

Does Tak-130 mean TOA-130?  If so, the GM8 can also be used even for high magnification visual observations. Attached you can find a photo when I had a planetary observation session with TOA-130 on GM8 (about 15 years ago).  If you're planning to take Astro Photos with TOA-130, you'll need a slightly larger mount.

Attached Thumbnails

  • TOA130 GM8 ext.jpeg

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#9 Nippon

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Posted 09 July 2020 - 09:41 AM

Someone asked Roland a similar question, something along the lines if a certain refractor would stress a certain Astro-Physics mount.

His reply pretty much applies to all mounts including the one under discussion here.

 

"For visual, the rule of thumb for refractors was that the mount's worm wheel diameter be same size as the scopes lens aperture. Smaller worms take longer to settle than larger worms.

That was the rule of thumb back last century"

.

Vahe

Gee that puts the GM8 as suitable for a 3" refractor. I'll file that with the "rule of thumb" that suggests if you need more counterweight than what's supplied with the mount you are overloading it. 


Edited by Nippon, 09 July 2020 - 09:46 AM.


#10 honyi

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Posted 09 July 2020 - 01:33 PM

Gee that puts the GM8 as suitable for a 3" refractor. I'll file that with the "rule of thumb" that suggests if you need more counterweight than what's supplied with the mount you are overloading it. 

That rule of thumb may not be accurate these days given that some mount companies only supply a light c/w with the mount, and offer a full range of c/w of various weights for optional purchase.

The GM8G comes default with only a 7lb counterweight, which would have difficulty balancing even a 10-12lb payload. Losmandy does offer 11lb and 21lb c/w for sale too.

Another example would be iOptron's cem25p and cem40. Both come with 4.5kg c/w, but have vastly different capacity.



#11 vahe

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Posted 09 July 2020 - 03:11 PM

Gee that puts the GM8 as suitable for a 3" refractor. 

The “rule of thumb” as discussed by Roland is more of an Astro-Physics design philosophy when it comes to mount capacity, AP typically stated considerably more conservative payload capacity when it comes to mounts that they offer.
(I have a G11, its payload capacity is listed at 60 pounds, while Astro-Physics Mach1, a considerably larger mount than G11, initially listed its capacity at 45 pounds).

.

Also, the “rule of thumb” mentioned by Roland is not a limit on payload capacity, it is a recommendation for a mount/refractor combination that is very stable and does not take a very long time to settle.

.

As for GM8 being only good for a 3” refractor, no, that is not what the rule of thumb is saying, what it is saying is that a 3” refractor on GM8 achieves maximum stability and settles very quickly, you can focus the 3” scope at high powers and the image will not shake at all, lightly bump on scope and resulting vibrations dies down instantly.

.

Vahe



#12 Nippon

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Posted 09 July 2020 - 04:47 PM

Yeah I know guys just making fun of how the ideal and the real world ain't exactly ever similar.



#13 Wildetelescope

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Posted 09 July 2020 - 08:21 PM

Hi All! New to this forum and just getting back into observational astronomy.  I would like to tap into the mega-years of experience available to validate or change some of the ideas I have for new equipment I would like to acquire.  I started with a Tasco telescope in my youth and have been in and out the hobby for many years.  I currently have a Discovery 10" F6 Dobsonian and a small refractor (90mm) on an equatorial mount.  I have thought all my life how great it would be to have top notch equipment to observe with.  My current circumstances make that possible.  I have read great reviews on the Takahashi 130NS and it seems perfect for what I want.  I need a mount, preferably an equatorial with drive motors but no go-to.  I have always admired the Losmandy products for their look and function. Would a GM8 which is capable of handling 30lbs. be sufficient for mounting the TAK-130?  The OTA weighs 22 lbs. or so and I would be adding a RA finder scope only.  I have no interest in photography although I certainly appreciate those who do and the fantastic images they capture. I will be pairing it with the Berlebach Planet wood tripod for Losmandy mounts.  Kinda old school but I remember going thru the Unitron catalog as a kid and dreaming...  If you can give feedback on this  combination I would greatly appreciate it!  Thanks, Bob  

I have used my gm8 on an HD tripod with my f8 AP triplet for visual with good results. Did not notice much wiggle when focusing.   The berlbach tripod will be a good match.  

 

Jmd 




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