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Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

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  #1  
Old 01-11-2013, 12:38 PM
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8 times better than a Ritchey-Chretien ?

Hi Guys,
Hypergraph's are excellent telescopes but
have a look at this link:

http://www.astrooptik.com/Komplettge...ph_frame_e.htm

Quote:
Optical performance without equal
The spot size on the plane field of the Hypergraph is more than 20 times smaller compared to a conventional Schmidt-Cassegrain,
about 10 times smaller compared to a classical Cassegrain and

about 8 times smaller compared to a Ritchey-Chretien telescope.

Tight specifications guarantee,
that the theoretical performance is also reached in the manufacturing process.

Could this be business puffery or true?
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  #2  
Old 01-11-2013, 01:11 PM
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it could be true but meaningless. The spot size (with diffraction) only has to be less than about half the atmospheric blur disk to get close to the maximum possible resolution - after that it becomes immaterial how much better it is. In Australian conditions, better than about 1 arc sec is probably good enough in most locations, so anything from a reasonably well made 150mm scope on upwards will be as good as it gets.

Looks like this is a hyperbolic system with a Ross or Rosin 2 element corrector. It will be pretty good, but the extravagant claims really are hyperbole.
http://www.telescope-optics.net/sub_..._corrector.htm is worth a read for the general idea.

Last edited by Shiraz; 01-11-2013 at 01:25 PM.
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  #3  
Old 01-11-2013, 01:20 PM
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Quote:
Originally Posted by alpal View Post
Hi Guys,
Hypergraph's are excellent telescopes but
have a look at this link:

http://www.astrooptik.com/Komplettge...ph_frame_e.htm




Could this be business puffery or true?
When a supplier wont list prices, there's usually a good reason; greed, guilt etc. Maybe I'm expecting to much but if I don't see a price I look else where.
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  #4  
Old 01-11-2013, 01:25 PM
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renormalised (Carl)
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Those quoted spot sizes and such are usually from lab tests. Real life performance will vary and sometimes substantially. As Ray said, it might be true, but then again......
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  #5  
Old 01-11-2013, 05:43 PM
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Thanks guys for your replies.

Have a look at the pics on this page:
many of them are taken with a Hypergraph 16” f8
from the Tivoli farm - high altitude dark site in Namibia Africa.

http://astrofotografia.com.pl/galeria.htm

They are incredible pictures.

However:

The only better pics I can find are from this site from Chile:

http://www.chart32.de/index.php/nebulae-n

32” Astro Optik Philipp Keller 80cm robotic classical Cassegrain with 3-Lens corrector.


Notice that it’s a much larger telescope so you’d expect better but it’s a Cassegrain

so how come it’s better?
According to the Hypergraph site it should only be a 10th as good.

Last edited by alpal; 01-11-2013 at 06:12 PM.
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  #6  
Old 01-11-2013, 06:02 PM
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It's funny, I've often wondered about these spot diagrams. Manufacturers of CDK, cassegrain,RC,and "corrected" anything all quote spot diagrams better than the others. I was swayed by "all serious OBS use RC", what do I know sounds good to me . It's all marketing BS IMO, horses for courses.
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  #7  
Old 01-11-2013, 06:14 PM
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Quote:
Originally Posted by Bassnut View Post
It's funny, I've often wondered about these spot diagrams. Manufacturers of CDK, cassegrain,RC,and "corrected" anything all quote spot diagrams better than the others. I was swayed by "all serious OBS use RC", what do I know sounds good to me . It's all marketing BS IMO, horses for courses.

I would have thought that the RCOS ion milled telescopes were the best
but as you can see - at the Chilean advanced Robotic Telescope
they have chosen a Cassegrain design - & wow - look at the results!
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  #8  
Old 01-11-2013, 06:58 PM
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Well, how wrong could I be, I got done in right there. The Chilean advanced Robotic Telescope?.... what a name, cant beat that . Dunno about the images on the astrooptik gear site though, dont look that flash at all .

RCOS is dead now anyway, must be crap.
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  #9  
Old 01-11-2013, 08:25 PM
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Any spot size that is smaller than the diffraction disc is meaningless, even with perfect seeing, since it is using ray optics and ignoring the wave nature of light. I don't have the actual data, but reporting a spot size 20x smaller than some quality telescope is probably reporting a spot size smaller than the diffraction disc, so in real life the pic you get from it would be limited by the wave nature of light in perfect seeing (never going to happen) or, more realistically, by the seeing conditions.
Geoff
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  #10  
Old 02-11-2013, 08:55 AM
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Quote:
Originally Posted by ghsmith45 View Post
Any spot size that is smaller than the diffraction disc is meaningless, even with perfect seeing, since it is using ray optics and ignoring the wave nature of light. I don't have the actual data, but reporting a spot size 20x smaller than some quality telescope is probably reporting a spot size smaller than the diffraction disc, so in real life the pic you get from it would be limited by the wave nature of light in perfect seeing (never going to happen) or, more realistically, by the seeing conditions.
Geoff
Still - the debate gets complicated when manufacturers make such claims.

Did you check out the Hypergraph 16 f8 pics?
It's hard to find better.
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  #11  
Old 05-11-2013, 09:22 PM
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Spot diagrams don't tell you a lot. I want to see ray-fan plots!
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  #12  
Old 06-11-2013, 09:35 AM
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Quote:
Originally Posted by RickS View Post
Spot diagrams don't tell you a lot. I want to see ray-fan plots!
We can only compare the results that manufacturers claim.

Still - I wonder if RC designs have been superseded?

No matter what system you buy it always needs a corrector
which is just extra glass that will introduce it's own aberrations -
especially halos on bright stars.
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  #13  
Old 13-11-2013, 05:48 PM
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Quote:
Originally Posted by alpal View Post
We can only compare the results that manufacturers claim.

Still - I wonder if RC designs have been superseded?

No matter what system you buy it always needs a corrector
which is just extra glass that will introduce it's own aberrations -
especially halos on bright stars.
I sort of agree RC designs have been "superseded" in that similar performance can be obtained on "corrected" designs for way less money eg CDK.

But "No matter what system you buy it always needs a corrector" is not quite correct really. My RC set up has no glass at all, mirrors only. A flattener (glass) is recommended for larger sensors on my RC, but I get away without one. Assuming your correct that glass introduces aberrations, then thats one problem I dont have, so that must be an advantage on an RC not available on other designs I guess.

I dont know if not having glass makes any other difference. I focus every 2 weeks or so, does glass itself cause focus change with temperature?.
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  #14  
Old 13-11-2013, 09:51 PM
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Quote:
Originally Posted by Bassnut View Post
I sort of agree RC designs have been "superseded" in that similar performance can be obtained on "corrected" designs for way less money eg CDK.

But "No matter what system you buy it always needs a corrector" is not quite correct really. My RC set up has no glass at all, mirrors only. A flattener (glass) is recommended for larger sensors on my RC, but I get away without one. Assuming your correct that glass introduces aberrations, then thats one problem I dont have, so that must be an advantage on an RC not available on other designs I guess.

I dont know if not having glass makes any other difference. I focus every 2 weeks or so, does glass itself cause focus change with temperature?.

I wonder if a flattener would give you even sharper images
especially off axis?

Focus every 2 weeks?
I thought some people were using FocusMax & changing focus with
every filter & sometimes between frames?
Those electric focusers can have steps smaller than 5 microns.

I don't know about focus with a flattener & other glass versus temperatures.
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  #15  
Old 14-11-2013, 04:38 PM
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Yes, a flattener would give better images but it's VERY expensive.

Focusing every 2 weeks is just lazy, but it doesn't make much difference, and with megadata, decon/sharpening makes small changes irrelavent anyway.

RCOS RCs are over engineered and expensive, that's why they went broke (I got mine S/H). Holding focus that well is uneccessary and not required for the amature market.
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  #16  
Old 14-11-2013, 04:59 PM
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M CDK17 tends to hold focus for some time. It does change focus somewhat with significantly different ambient temps but otherwise in focus one night is likely to be in focus the next more often than not.

The joys of carbon fibre.

Greg.
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  #17  
Old 14-11-2013, 05:09 PM
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Quote:
Originally Posted by Bassnut View Post
Yes, a flattener would give better images but it's VERY expensive.

Focusing every 2 weeks is just lazy, but it doesn't make much difference, and with megadata, decon/sharpening makes small changes irrelavent anyway.

RCOS RCs are over engineered and expensive, that's why they went broke (I got mine S/H). Holding focus that well is uneccessary and not required for the amature market.

I suppose too that at long f ratios focus is less of a problem.
I believe that bad seeing actually takes the target in & out of focus anyway.

Pity that RCOS went down - some telescope versions had ion milled mirrors.
I suppose you'd need sub arc second seeing for it to make any difference?
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  #18  
Old 14-11-2013, 05:14 PM
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Quote:
Originally Posted by gregbradley View Post
M CDK17 tends to hold focus for some time. It does change focus somewhat with significantly different ambient temps but otherwise in focus one night is likely to be in focus the next more often than not.

The joys of carbon fibre.

Greg.

I use Maxim DL to check the last frame for FWHM while I'm waiting for the next frame.
I can then find out if the seeing & or focus is getting better or worse.
My limitation is the atrocious Melbourne weather -
it's been nearly 6 months without setting up my system.
I can't be bothered with even occasional clouds -
I want an all clear night forecast before setting up.


Still - this topic of RC telescopes being outdone by other designs is interesting.
Is it business puffery or not?
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  #19  
Old 14-11-2013, 05:23 PM
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Hard to tell if true or not. I believe he would be achieving better spot sizes. Phillip Keller is very good at optics.

There is an astrophotographer up at Cairns who got one of his large scopes.

Greg.
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  #20  
Old 14-11-2013, 05:59 PM
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I think RC is a bit of puffery these days, was the best in days gone by, but corrected designs are so good these days it's not worth the extra money IMO. But, There's always the placebo effect and "bugger the money I want the best" there's ALWAYS a market for that. Look at Marcus's Stella officiana RC, it's just amazing and utterly drool worthy, that can seriously make the ownership/imagining experience well worth the extra bucks. This is a hobby, how you feel about it alone can make ALL the difference.
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