ICEINSPACE
Moon Phase
CURRENT MOON
Waning Crescent 29.5%
|
|
01-11-2013, 01:38 PM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
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?
|
01-11-2013, 02:11 PM
|
|
Registered User
|
|
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,918
|
|
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 02:25 PM.
|
01-11-2013, 02:20 PM
|
Politically incorrect.
|
|
Join Date: Apr 2009
Location: Tasmania (South end)
Posts: 2,315
|
|
Quote:
Originally Posted by alpal
|
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.
|
01-11-2013, 02:25 PM
|
|
No More Infinities
|
|
Join Date: Apr 2008
Location: Townsville
Posts: 9,698
|
|
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......
|
01-11-2013, 06:43 PM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
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 07:12 PM.
|
01-11-2013, 07:02 PM
|
|
Narrowfield rules!
|
|
Join Date: Nov 2006
Location: Torquay
Posts: 5,065
|
|
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.
|
01-11-2013, 07:14 PM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
Quote:
Originally Posted by Bassnut
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!
|
01-11-2013, 07:58 PM
|
|
Narrowfield rules!
|
|
Join Date: Nov 2006
Location: Torquay
Posts: 5,065
|
|
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.
|
01-11-2013, 09:25 PM
|
|
PI rules
|
|
Join Date: Jul 2006
Location: Sydney
Posts: 2,631
|
|
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
|
02-11-2013, 09:55 AM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
Quote:
Originally Posted by ghsmith45
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.
|
05-11-2013, 10:22 PM
|
|
PI cult recruiter
|
|
Join Date: Apr 2010
Location: Brisbane
Posts: 10,584
|
|
Spot diagrams don't tell you a lot. I want to see ray-fan plots!
|
06-11-2013, 10:35 AM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
Quote:
Originally Posted by RickS
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.
|
13-11-2013, 06:48 PM
|
|
Narrowfield rules!
|
|
Join Date: Nov 2006
Location: Torquay
Posts: 5,065
|
|
Quote:
Originally Posted by alpal
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?.
|
13-11-2013, 10:51 PM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
Quote:
Originally Posted by Bassnut
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 F ocusMax & 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.
|
14-11-2013, 05:38 PM
|
|
Narrowfield rules!
|
|
Join Date: Nov 2006
Location: Torquay
Posts: 5,065
|
|
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.
|
14-11-2013, 05:59 PM
|
|
Registered User
|
|
Join Date: Feb 2006
Location: Sydney
Posts: 18,002
|
|
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.
|
14-11-2013, 06:09 PM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
Quote:
Originally Posted by Bassnut
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?
|
14-11-2013, 06:14 PM
|
|
Registered User
|
|
Join Date: Jan 2012
Location: Melbourne
Posts: 3,689
|
|
Quote:
Originally Posted by gregbradley
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?
|
14-11-2013, 06:23 PM
|
|
Registered User
|
|
Join Date: Feb 2006
Location: Sydney
Posts: 18,002
|
|
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.
|
14-11-2013, 06:59 PM
|
|
Narrowfield rules!
|
|
Join Date: Nov 2006
Location: Torquay
Posts: 5,065
|
|
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.
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT +10. The time is now 06:03 AM.
|
|