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  #21  
Old 25-05-2011, 09:09 AM
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ZeroID (Brent)
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Rolf, a couple of questions.

Did you come up with a weight for the scope ? Asking because long term I intend to probably 'copy' your design for my own setup using again my existing 10" mirrors and spider.
Is it also still holding collimation well ? If it proves robust enough I'd possibly be modifying to also sit in a DOB base. A pair of ( removable?) quadrants on either side of the central cage might allow an easy transition. I don't have a Ob ( yet ) and this plan is over the next two years maybe.

And second: Do you sheild the primary from stray light. I thought of using a lightweight ( black card maybe ) tube inside the truss above the mirror cell. Or does the Ob installation make that unnecessary ?

Still the nicest ATM scope I have seen.

Cheers
Brent
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  #22  
Old 25-05-2011, 01:03 PM
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Originally Posted by ZeroID View Post
Rolf, a couple of questions.

Did you come up with a weight for the scope ? Asking because long term I intend to probably 'copy' your design for my own setup using again my existing 10" mirrors and spider.
Is it also still holding collimation well ? If it proves robust enough I'd possibly be modifying to also sit in a DOB base. A pair of ( removable?) quadrants on either side of the central cage might allow an easy transition. I don't have a Ob ( yet ) and this plan is over the next two years maybe.

And second: Do you sheild the primary from stray light. I thought of using a lightweight ( black card maybe ) tube inside the truss above the mirror cell. Or does the Ob installation make that unnecessary ?

Still the nicest ATM scope I have seen.

Cheers
Brent
Thanks for your kind words Brent

I haven't weighed it yet, because I didn't want to take it down and have to maybe re-collimate etc. But I'll have to do it soon because there are a few things I want to correct.
They are only minor issues such as when I want to remove the cover I made for the main mirror then it tends to get slightly stuck on the bolts that hold the bottom truss tubes, so I'll file them down a bit. I also want to experiment with installing some fans for cooling both the primary and secondary. So once I do that I'll be able to also weigh it, but I can tell you it's pretty light, less than a sonotube of similar aperture which I was surprised about.

Collimation was still spot on last time I used it which is maybe a week ago, so that's promising.

And you could certainly modify the design to fit on a DOB base, there is a very nice example of that here: http://www.cloudynights.com/item.php?item_id=2571

Regarding stray light, I have noticed it several times on image frames depending on the direction of the scope, so it's something to watch out for. I am however able to switch off all light and computer screens in the observatory while imaging and then it's completely dark here, so I have gotten around the issue so far. But when I take it down to install the fans then I think I will also look into fitting some screens in appropriate locations.

I'll post an update here once I get around to fix these small issues
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  #23  
Old 25-05-2011, 02:16 PM
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Cheers Rolf and thanks for the link, very informative and encouraging. More grist for the mill to digest.

If you need any small computer type fans give me a yell. I am looking at fitting a miniature laptop fan assembly for the small Newt primary after getting it dewed the other night. Duct it in sideways across the front surface. Run it at 5 volts when needed.
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  #24  
Old 22-06-2011, 08:46 PM
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Just a quick update for those who asked previously regarding the weight of the Serriurier truss OTA.

I took it off the mount tonight because I had to adjust a few minor things. The primary mirror cover that I made was a little difficult to take off because it was just ever so slightly larger than the available space between some protruding nuts and bolts at the bottom truss assembly. So rather than making a new cover I took out the mirror cell and filed the nuts down 1/2 mm each.
There were also a few scratches on the paintwork and on the wood stain from when I assembled it all, so I touched these up.
Other than that I've had no issues with the new scope, it's been a big success so far.

While I had the scope off the mount I weighed it and the measures are as follows:

OTA without mirror and finderscope (but with finderscope brackets): 7.85 kg
OTA incl. mirror: 11.85 kg
OTA incl. mirror and finder scope: 13.15 kg

The finder is an Antares 80mm and is fairly heavy at 1.3 kg.

With 13.15 kg all up this OTA is easy to carry for the G-11, and I'm very happy with that.
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  #25  
Old 22-06-2011, 09:02 PM
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If you need any small computer type fans give me a yell. I am looking at fitting a miniature laptop fan assembly for the small Newt primary after getting it dewed the other night. Duct it in sideways across the front surface. Run it at 5 volts when needed.
Thanks Brent. I've temporarily fitted a large 120mm fan next to the secondary. I have it running fairly slow, but due to its size it pushes quite a large volume of air over the secondary. Judging from 1 nights use it does seem to eliminate dew forming on the secondary, but I need some more clear nights for testing beforee I decide to mount it permanently. It's mounted with rubber bands at the moment to eliminate vibrations, and when viewing the Moon though a 5x Powermate I couldn't see any induced vibration at all so it's very promising.
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  #26  
Old 23-06-2011, 09:59 AM
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Excellent Rolf, thanks for the weight information. My build has started as well. Spent up on a router and some 17mm ply. Routers make a hell of a mess !! I'm placing my mirror inside the truss frame rather than hang it off the back as you have. No welding to the centre cage. Instead a ply diaphragm/baffle brace will make it all rigid and as it will be also visual possibly a rotating UTA assembly so the focusser can be accessible. Spent very little other than the router ( useful anyway ), the ply and some aluminium square and strip. I have picked up a lot of useful stuff from work after they had a big chuckout. Photos will come when there is more to see.
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  #27  
Old 23-06-2011, 06:30 PM
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Thanks very much for the weights. Light enough for an EQ6 also, well done...
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  #28  
Old 01-08-2011, 11:55 AM
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I just wanted to add something I observed last night.
This Serrurier truss structure is really amazingly rigid. I haven't used the scope for a couple of weeks, then last night I popped the camera in and grabbed some frames in the Sagittarius area. I was ready to start focusing when the first test frames showed up on the monitor, but to my surprise the focus was absolutely spot on straight away with no adjustment required. Yes it hasn't changed at all since I last used it, despite daily temperature and humidity changes over 2 weeks...
I don't know how that compares to other scopes, but I'm certainly very happy with that. The performance of this design is just beyond what I could ever have imagined.

Now I just need some new optics to match, my mirrors hasn't been coated in 16 years
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  #29  
Old 01-08-2011, 09:25 PM
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..... Now I just need some new optics to match, my mirrors hasn't been coated in 16 years
I got a bit of silver spray paint if that would help ...
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  #30  
Old 02-08-2011, 11:08 AM
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I got a bit of silver spray paint if that would help ...
Hehe, that might actually be an improvement!
From looking at the mirror last time I cleaned it I think I'm losing maybe 20-25% of the light. I can see through it in many places, there are clear pits all over without any coating left, and if I hold it up against a light source I can clearly see some of the light making it through also where the coating is still in place. It must be very thin now.
The secondary is in a similar state, so effectively I might be losing maybe 35-40% of the total light at the moment. Scary!
I'm thinking of getting a set of RF Royce mirrors, or similar quality. The conical Royce mirrors have the added benefit of being much lighter and easier to cool.

Actually I'd prefer to just have them re-coated, but I'm not aware of any places in NZ that offer this service? With the cost of safe packaging and shipping overseas and back I might just as well get a whole new set.

But the focus at the moment is to upgrade my camera to a 'real' one, most likely QSI. That will give me the biggest boost by far and is also the more expensive item so I prefer to get that purchase done first.
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  #31  
Old 03-08-2011, 01:08 PM
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I have heard of a place down in Wellington that does them. Might have been mentioned in the EQMOD group. Price was quite reasonable as well. I 'may' have saved the post. I'll check when I get home or do a back search.

On the matter of guiding how are you doing it at present ? I bought back a Shoestring GPUSB and ST4 cable from Australia but haven't had a chance to play with it yet or figure out how to configure and run it all. There seems to be a number of options and they are all confusing.
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  #32  
Old 03-08-2011, 01:49 PM
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Thanks Brent, that would be awesome if you know of a place that can do coatings!

Re guiding I don't do any. I'm using short subs only, but once I get a better cam then I'll definitely be guiding. So there is a bit of a learning curve there waiting for me too
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