#101  
Old 12-01-2014, 05:28 PM
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Originally Posted by clive milne View Post
the merit function of quartz optics installed in carbon fibre tubes.

carbon fibre truss tubes and quartz optics ?

You carefully always connect your comments on the value of CF with quartz optics, whys that ?. Is there something about quartz optics that makes CF tubes of lesser value?.
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  #102  
Old 12-01-2014, 06:10 PM
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Got up and close with the RC 12" a few weeks back.... (promo shot attached...what a co-incidence...it's on a really nice mount )

Nicely finished, but I have no idea on the optical quality.

The first thing I tried was the focuser. With just a few pounds of pressure it easily deflected 2-3 mm...hence large format camera owners (STX, STXL, Proline, Apogee) would be entering a world of hurt if they kept the native focuser in place.

Others have suggested adding Atlas focusers etc. I quickly tallied up what the suggest "upgrades" might cost...you wouldn't get much change from $5000....

Franky I don't get the logic.

I'd need to see the Top Gear lap first ...as I wouldn't buy a car thinking, well, gee, if I change the engine and suspension it could be really good....

Yet if I get the Ferrari 458 while it won't be cheap, I know it will perform brilliantly. Caveat emptor!
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  #103  
Old 12-01-2014, 10:54 PM
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Originally Posted by Peter Ward View Post
Got up and close with the RC 12" a few weeks back.... (promo shot attached...what a co-incidence...it's on a really nice mount )

Nicely finished, but I have no idea on the optical quality.

The first thing I tried was the focuser. With just a few pounds of pressure it easily deflected 2-3 mm...hence large format camera owners (STX, STXL, Proline, Apogee) would be entering a world of hurt if they kept the native focuser in place.

Others have suggested adding Atlas focusers etc. I quickly tallied up what the suggest "upgrades" might cost...you wouldn't get much change from $5000....

Franky I don't get the logic.

I'd need to see the Top Gear lap first ...as I wouldn't buy a car thinking, well, gee, if I change the engine and suspension it could be really good....

Yet if I get the Ferrari 458 while it won't be cheap, I know it will perform brilliantly. Caveat emptor!

2 - 3mm.
That's ridiculous - why sell a focuser that is not fit
for the purpose for which it's intended?
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  #104  
Old 13-01-2014, 09:02 AM
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Originally Posted by alpal View Post
2 - 3mm.
That's ridiculous - why sell a focuser that is not fit
for the purpose for which it's intended?
Probably because it's adequate for most people who will never put in the time an effort to exploit what an instrument may truly be capable of and that involves a lot more than tuning the focuser - like mounting the scope adequately for a start . It all comes down to $ and price point .

GSO would factor in the cost benefit of every cent that goes into these instruments and are very successful at that . They know that the small proportion of buyers who are really serious enough to find the focuser a problem will buy an after market focuser .
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  #105  
Old 13-01-2014, 10:48 PM
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Quote:
Originally Posted by Bassnut View Post
You carefully always connect your comments on the value of CF with quartz optics, whys that ?. Is there something about quartz optics that makes CF tubes of lesser value?.
Fred, I was just pointing out that the marketing spiel on the Astronomics website was specious at best. The claim that you need CF truss tubes and quartz optics to preserve focus (or image scale) is meaningless in the context of the OTA under discussion. They would have been better off supplying a welded steel truss and pyrex optics and including a mechanically adequate ascom compliant rotating focuser with the money saved. A properly engineered steel truss would also be lighter and stronger than what we see with these OTA's. GSO missed a trick here.

That is not to suggest that the OTA is fundamentally flawed (I think it looks reasonably good) just that money was spent were it isn't really needed.
My hope is that future iterations will address the mechanical requirements of an imaging OTA rather than just trying to replicate the cosmetic appeal of Planewave et al.

In saying all that, if the only issue with these telescopes is the focuser, then they are without doubt a fundamental game changer. I have my fingers crossed that this is the case. I also think it is time they supplied a field corrector to go with them too.

c
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  #106  
Old 16-01-2014, 02:33 PM
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Originally Posted by alpal View Post
2 - 3mm.
That's ridiculous - why sell a focuser that is not fit
for the purpose for which it's intended?
Just about all OTA makers outside the really high-end ship with ****ty focusers for heavy camera use, that is why there are so many after-market ones around.
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  #107  
Old 16-01-2014, 04:33 PM
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Just about all OTA makers outside the really high-end ship with ****ty focusers for heavy camera use, that is why there are so many after-market ones around.

OK fair enough - a dose of reality for me.

It makes you wonder why the camera makers don't try
their best to make the lightest possible cameras?

The sensor chip only weighs a few grams but the camera etc can weigh 5Kgs.
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  #108  
Old 16-01-2014, 08:42 PM
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Originally Posted by alpal View Post
OK fair enough - a dose of reality for me.

It makes you wonder why the camera makers don't try
their best to make the lightest possible cameras?

The sensor chip only weighs a few grams but the camera etc can weigh 5Kgs.
Some of the camera manufacturers do make fairly small, lightweight cameras. Starlight Xpress and QHY are examples I'm familiar with but there are probably others. However, if you want a big sensor and deep, well regulated cooling then you need a larger camera with multi-stage Peltier, fans and heatsinks. Then you need large filters to minimize vignetting (at least 7 of them) and a rigid filterwheel to avoid tilt. That all comes at a cost in weight.

Cheers,
Rick.
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  #109  
Old 16-01-2014, 09:51 PM
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Originally Posted by RickS View Post
Some of the camera manufacturers do make fairly small, lightweight cameras. Starlight Xpress and QHY are examples I'm familiar with but there are probably others. However, if you want a big sensor and deep, well regulated cooling then you need a larger camera with multi-stage Peltier, fans and heatsinks. Then you need large filters to minimize vignetting (at least 7 of them) and a rigid filterwheel to avoid tilt. That all comes at a cost in weight.

Cheers,
Rick.


Hi Rick,
Sure - it's difficult to reduce weight in large format cameras.

Maybe we'll see a new generation of light but large format cameras?

I think we'll see more of these ideas in the future & some are already here:

(1) Drill out the heatsink with enough holes to halve it's weight.

(2) Use lighter materials such as magnesium in as many parts as possible.

(3) Using unmounted filters to create a super light filter wheel.

(4) design everything as thin as possible.

(5) place the CCD sensor as close as possible to the outside of the housing - reduce back focus - to reduce the size of the housing & lower leverage.

(6) Place 4 little fans on the outside of the heatsink instead of one big heavy one at the rear - lowering the leverage.


Numbers 1 & 6 could be done by the camera owner.


The fact is that any weight suspended from a "lever" is going to cause flexure forces -
weight versus angle of flexure is what people need to know.
Do any telescope manufacturers provide such graphs for their focusers?

Another good idea is what Bert has done with his RH200 -
breaking new ground by mechanically removing all sideways force on the focuser.


cheers
Allan
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  #110  
Old 16-01-2014, 10:03 PM
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Allan,

I agree there is certainly stuff that could be done to reduce camera weight further. Whether the camera manufacturers find it economical to do so we'll have to wait and see. In the meantime I'll just run an Atlas focuser.

Interesting comment on the economics of our hobby: http://tleaves.com/wp-archive/2011/0...ars/index.html

Cheers,
Rick.
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  #111  
Old 16-01-2014, 10:24 PM
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Originally Posted by RickS View Post
Allan,

I agree there is certainly stuff that could be done to reduce camera weight further.
Whether the camera manufacturers find it economical to do so we'll have to wait and see.
In the meantime I'll just run an Atlas focuser.

Interesting comment on the economics of our hobby: http://tleaves.com/wp-archive/2011/0...ars/index.html

Cheers,
Rick.
Hi Rick,
very funny but I'm sure there are $millions to be made from sales in this hobby.

I am surprised you needed an Atlas focuser.
as per here:
http://www.ceravolo.com/ceravolo_focuser.html


Quote:
This heavy duty focuser will easily carry the weight of a large CCD camera and filter wheel.
cheers
Allan
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  #112  
Old 16-01-2014, 10:32 PM
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I am surprised you needed an Atlas focuser.
as per here:
http://www.ceravolo.com/ceravolo_focuser.html
Allan,

The standard (Optec TCF-S3) focuser on the Ceravolo is pretty good but I like the Atlas because I can use the same image train on my other scopes, the step size is tiny allowing very precise focusing and it also gives me the extra backfocus needed to incorporate more gadgets (at f/4.9 I don't think there is even room for an OAG with the std focuser).

Cheers,
Rick.
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  #113  
Old 16-01-2014, 10:44 PM
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Originally Posted by RickS View Post
Allan,

The standard (Optec TCF-S3) focuser on the Ceravolo is pretty good but I like the Atlas because I can use the same image train on my other scopes, the step size is tiny allowing very precise focusing and it also gives me the extra backfocus needed to incorporate more gadgets (at f/4.9 I don't think there is even room for an OAG with the std focuser).

Cheers,
Rick.
OK Rick - thanks -
the same old story - never enough back focus.

Still the GSO 16" will be interesting to follow.
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  #114  
Old 16-01-2014, 11:18 PM
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I used to use the Atlas with a 10" GSO RC. I'm sure it would work great with the 16" as well.
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  #115  
Old 17-01-2014, 09:28 AM
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I've never really understood why scopes designed to carry a heavy camera use crayford focussers rather than a rack and pinion +/- a focus motor as the standard. They certainly exist. see
http://starlightinstruments.com/stor...&product_id=61
The crayford is lovely and smooth and an eyepiece slips in beautifully but I like a solid attachment for my camera that doesn't use a nosepiece adaptor on the front.
The R & P focusser on my vixen scope is much more reliable than the expensive Moolight crayford on my refractor and is easier to lock down.
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  #116  
Old 17-01-2014, 01:59 PM
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Are the 12 inch carbon fibre truss RCs available now or is it a future release?

Same with the 16inch?

Greg.
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  #117  
Old 17-01-2014, 02:24 PM
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Late Feb was the last I heard
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  #118  
Old 17-01-2014, 04:06 PM
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I've heard that the 12" hits Oz in the next few weeks - currently en route from Asia - while the 16" pre-production model is doing the rounds in the northern hemisphere to iron out any kinks before full scale production begins. The same was done for the 12".
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  #119  
Old 17-01-2014, 05:23 PM
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Thanks. It could be quite a scope for the money.

Greg.
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  #120  
Old 18-01-2014, 01:19 PM
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I've heard that the 12" hits Oz in the next few weeks - currently en route from Asia - while the 16" pre-production model is doing the rounds in the northern hemisphere to iron out any kinks before full scale production begins. The same was done for the 12".
Yep there is a truss for my mirrors on the way to me in one of those shipments. Looking forward to seeing the new truss and then not so looking forward to installing the mirrors.
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