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New Moon mirror cell

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#1 pao

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Posted 20 July 2019 - 12:59 PM

It seems to me that New Moon Dobsonians are really wonderful instruments and, using a premium mirror, they can be very desirable.

My only concern is the flotation mirror cell produced in house. It seems a little bit “light” (mostly the 9 points) looking at the pictures available on the web, in particular the are some very thin springs connecting the various supports of the cell. They seem quite fragile to me and can break easily. 

But obviously the appearance can be deceiving, therefore what are the experiences of those who own these cells? Performance? Any concern?

Thank you



#2 spencerj

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Posted 21 July 2019 - 09:46 AM

I certainly have zero experience with mirror cell design, but I have never had an issue with the mirror cell on my 12.5” NMT. The wire sling edge support works well. Primary mirror collimation is easy and very stable. I have never seen anything in the focused or unfocused image that would indicate any kind of support issue.

The thin springs you mentioned only seem to keep the orientation of the plates when the mirror is not installed. They don’t support anything and seem fine for their intended application. Overall, the cell is well made and perfectly integrated into the scope.
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#3 tomykay12

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Posted 21 July 2019 - 12:22 PM

can we see a picture?



#4 berkleystg

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Posted 21 July 2019 - 12:52 PM

The mirror cell works great. Never had issue with those springs. I attached a picture of the back of the mirror cell.

 

 

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#5 a__l

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Posted 21 July 2019 - 08:15 PM

What's the meaning to make a mirror cell from high-priced aluminum, if you then add a heavy weight for balance?


Edited by a__l, 21 July 2019 - 08:18 PM.


#6 Kunama

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Posted 21 July 2019 - 08:46 PM

What's the meaning to make a mirror cell from high-priced aluminum, if you then add a heavy weight for balance?

Not every scope will require the counterweight, it really depends on what the owner wants to use as finder and eyepieces as well as adding SIPS etc...

I doubt that the price of those triangles will be any higher in aluminium or steel...


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#7 The Ardent

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Posted 21 July 2019 - 08:50 PM

Counterweight ...... Finder

"Cause and Effect" Says the Merovingian

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#8 stargazer193857

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Posted 21 July 2019 - 08:57 PM

What's the meaning to make a mirror cell from high-priced aluminum, if you then add a heavy weight for balance?


Weights can be changed out to balance a different finder.

#9 George N

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Posted 21 July 2019 - 09:04 PM

What's the meaning to make a mirror cell from high-priced aluminum, if you then add a heavy weight for balance?

"Heavy" counterweight???

I don't own a NMT telescope, but several friends do. There is nothing 'heavy' about the latest NMT design. I've used Ryan's personal 20-inch F/3.2 on several nights - and it was an outstanding performer.

 

On his own scope the counterweight is a standard (cheap) 3.5 lb barbell weight of the type sold in most sporting-goods stores -- hardly "heavy".

 

Ryan parked his vehicle on the other side of my pickup truck & cargo trailer. He carried the entire tail end of the 20-inch scope - including mirror, around my vehicle - and then another 20 yards before plunking it down. Second trip he brought the truss poles and UTA ring - 3 minutes later the scope was assembled and ready to collimate. The only thing easier would be if the scope set itself up!


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#10 George N

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Posted 21 July 2019 - 09:18 PM

At this Flickr link (https://www.flickr.c...4171502/sizes/l) is a photo I took of Ryan's personal 20-inch at Black Forest Star Party in 2017. Select the size you want and down-load it.

 

As can be seen here - the springs only hold the plates in the proper place if the mirror is removed. They don't appear to have any mirror support function. You could probably buy a dozen of them for $2 if you are worried about one breaking.

 

The rest of my Black Forest 2017 album has more photos of Ryan's 20-inch, my Obsession 20, another friend's 36-inch ATM scope: https://www.flickr.c...157686894730370

 

The best part of Ryan's scope -- I have to bend down a little to look thru the eyepiece with the scope pointed at the Zenith - while with my Obsession 20 F/5 I have to climb 3 steps up a ladder to do that. Over 3 nights the two scopes provided near identical views of many deep sky objects.

 

The lady seen in these photos - a long time friend - ended up buying a 16-inch NMT after her experience with using Ryan's. She remains very happy with her NMT 16.


Edited by George N, 21 July 2019 - 09:19 PM.

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#11 spencerj

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Posted 22 July 2019 - 08:15 AM

Looked through pictures and didn't find a lot for the mirror cell.  I found a couple I got from Ryan during the build and one from the scope set up in my yard that shows how clean the scope looks from the back. My mirror is 12.5" and is supported by a 9-point cell.  Looks like the 16" above has an 18-point cell.  

 

 

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  • cell 3.jpg

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#12 peleuba

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Posted 22 July 2019 - 09:38 AM

What's the meaning to make a mirror cell from high-priced aluminum, if you then add a heavy weight for balance?

 

Aluminum is used because its easiest to machine to exacting standards.  

 

The addition of a counterweight is a per telescope decision.  Not every NM dob needs a counterweight.  


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#13 pao

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Posted 22 July 2019 - 10:10 AM

Thanks guys, now everything is clearer to me. So beautiful dobs, hope to own one in the future!



#14 Starman1

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Posted 25 July 2019 - 07:39 PM

Lighter mirror = better cooling.

Lighter mirror cell (providing it is adequately engineered) = less thermal inertia in the vicinity of the mirror.

Lighter mirror cell (with removable weight = easier transport and in/out of vehicle.

So adding a weight isn't a bad idea.

 

I used one for a while on my own dob, but went to a "virtual" counterweight instead (a bungee cord that stretches as the scope points lower).

So far, it works with all my eyepieces from 45° down to ~10°.  Above 45°, I don't need a counterweight.

 

But I can see the value of the weight--especially if it is toward the bottom of the mirror box when the scope points low, to keep the COG in the altitude axis.


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#15 Jon Isaacs

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Posted 26 July 2019 - 02:13 PM

Lighter mirror cell (providing it is adequately engineered) = less thermal inertia in the vicinity of the mirror.

 

 

The cell is thin wall tube.  Both steel and aluminum have much better conductivities than even Pyrex or quartz.  The cell should cool much faster than the much thicker mirror.

 

Jon



#16 a__l

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Posted 09 August 2019 - 03:18 AM

"Heavy" counterweight???

I don't own a NMT telescope, but several friends do. There is nothing 'heavy' about the latest NMT design. I've used Ryan's personal 20-inch F/3.2 on several nights - and it was an outstanding performer.

 

On his own scope the counterweight is a standard (cheap) 3.5 lb barbell weight of the type sold in most sporting-goods stores -- hardly "heavy".

 

Ryan parked his vehicle on the other side of my pickup truck & cargo trailer. He carried the entire tail end of the 20-inch scope - including mirror, around my vehicle - and then another 20 yards before plunking it down. Second trip he brought the truss poles and UTA ring - 3 minutes later the scope was assembled and ready to collimate. The only thing easier would be if the scope set itself up!

Rules of good form in design require a well-balanced design without additional steel (?) ingot (red arrow).
Curiously, is there a need to increase the height of the rocker because of it?
Aluminum is not only triangles. But also the design of the frame. Argon welding (?) Price aluminum frame?
Perhaps replacing the frame from aluminum to steel abolished the need for additional ingot, reduced the height of the rocker and ultimately reduced the weight of the entire telescope.

 

I will add. Is there a ServoCat down there? How does it all fit together with a ingot.....

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  • Mirror Cell_.jpg

Edited by a__l, 09 August 2019 - 04:14 AM.


#17 a__l

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Posted 09 August 2019 - 04:43 AM

Examples of my 14.5 "(ZOC) and 18" (Santel). Everything is pretty tight there.

 

ZOC - lightweight mirror (8 kg). Steel mirror cell (photo 3)

Santel - heavy mirror (18 kg) - aluminum mirror cell (photo 4)
All home made. All telescopes are perfectly balanced. No extra weights.

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Edited by a__l, 09 August 2019 - 06:05 AM.


#18 Lenard

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Posted 09 August 2019 - 11:15 AM

I have an 18" New Moon Hybrid. It uses no weights as it was balanced with heavy eypieces, pc2, binoviewer's, raci, in mind. If you pull out the pc2 and Ethos it will rise slightly but that is to be expected. When any eyepiece is in you can let it go and it does not move. I think that one reason for aluminum is that it does not rust. The bearings used on the 18" are the same size as on the 20" and 22". Maybe this also helps?



#19 Pinbout

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Posted 09 August 2019 - 12:23 PM

 

Rules of good form in design require a well-balanced design without additional steel (?) ingot (red arrow).

that's for a traditional dob.

 

Ryan is making a hybrid design, between trad and ultralight.

 

even teeter puts a counter weights on the backside of his mirror boxes...



#20 Starman1

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Posted 09 August 2019 - 12:26 PM

I have an 18" New Moon Hybrid. It uses no weights as it was balanced with heavy eypieces, pc2, binoviewer's, raci, in mind. If you pull out the pc2 and Ethos it will rise slightly but that is to be expected. When any eyepiece is in you can let it go and it does not move. I think that one reason for aluminum is that it does not rust. The bearings used on the 18" are the same size as on the 20" and 22". Maybe this also helps?

That would make the 18" less sensitive to imbalance.

The usual rule is for the altitude trunnion to be 1.5x the diameter of the mirror (i.e. 27" on an 18" scope) for the right feel of "stiff enough to

stay in place when an eyepiece is changed, but smooth enough to track without too much effort".

That also means much less rebalancing is necessary when the scope points low.

 

Having an extra weight on the mirror box is useful to keep the side panels of the rocker box short.

Short rocker boxes are stiffer, and lighter.

They usually entail short mirror boxes as well, which helps keep the overall scope lighter.

So whatever weights are added to the mirror box, they need to be removable easily for transport.


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#21 Pinbout

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Posted 09 August 2019 - 12:28 PM

they are easier to put in the backseat of the car...tongue2.gif grin.gif



#22 Kunama

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Posted 09 August 2019 - 03:17 PM

.......

All home made. All telescopes are perfectly balanced. No extra weights.

but at the price of much deeper rocker boxes.... every design has compromises. There are no right or wrong ways, just different approaches... flowerred.gif


Edited by Kunama, 09 August 2019 - 07:01 PM.

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#23 spencerj

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Posted 10 August 2019 - 09:58 AM

Had to look up ingot. That just holds the removeable counter weight in place. The counter weight can even slide a bit to dial in balance. Overall it just barely protrudes deeper than the collimating knobs into the rocket box. On an F4 or F4.5 mirror the counter weight is probably not needed. It is needed for the F5 truss poles I have on my scope. I also have a Rigel quickfinder SV50 finder use a Paracorr 2 and heavy eyepieces.

I don’t have a servo cat system, but is a common add on for NMT. There is room in there. I keep my battery for my dew controller in there without an issue.

#24 CrazyPanda

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Posted 10 August 2019 - 08:30 PM

Lighter mirror = better cooling.

Lighter mirror cell (providing it is adequately engineered) = less thermal inertia in the vicinity of the mirror.

Lighter mirror cell (with removable weight = easier transport and in/out of vehicle.

So adding a weight isn't a bad idea.

 

I used one for a while on my own dob, but went to a "virtual" counterweight instead (a bungee cord that stretches as the scope points lower).

So far, it works with all my eyepieces from 45° down to ~10°.  Above 45°, I don't need a counterweight.

 

But I can see the value of the weight--especially if it is toward the bottom of the mirror box when the scope points low, to keep the COG in the altitude axis.

The fact that the weight is on a vertical track is clever.


Edited by CrazyPanda, 10 August 2019 - 08:33 PM.



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