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Equipment Discussions >> Cats & Casses

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UnderDriven
member


Reged: 04/22/13

Loc: Pennsylvania
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: jrcrilly]
      #5819665 - 04/24/13 12:20 PM

I'm no expert on the HyperStar, but it seems fair to say that it is a "crude" system in the sense that it is a improvised system--meaning that the designers of SCTs never intended that a camera should replace the secondary mirror, and therefore did not take this into account when designing the corrector plate. However, that does not mean that it doesn't work--there have been many improvised systems which have worked well, or at least well enough to accomplish the intended task. As someone else mentioned, every telescope is a compromise...

The only non-improvised system I know of which is nearly as fast as HyperStar is a Takahashi hyperbolic astrograph for $5400. But the Takahashi aperture is only 180mm and it's pretty much a one-trick-pony. Part of the appeal of HyperStar is being able to reconfigure an F/10 telescope as an F/2 astrograph as needed, while spending a lot less than $5400...

Cheers, Keith


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bilgebay
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Reged: 11/06/08

Loc: Turkiye - Istanbul and Marmari...
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Alph]
      #5819696 - 04/24/13 12:35 PM

Quote:

How about alignment? Do you expect everybody to go through the same process as you did?




I am not expecting anything Alph. I am only addressing what Mike considers as issues with this system, which, as an actual user, I know that they are not.

My effort to align the optical axis of my C11 Edge was/is an attempt to reach perfection. The system was still useable even before I aligned everything and remember, what i aligned had nothing to do with the Hyperstar lens, it was the secondary and corrector plate to the primary which is an essential parameter even for visual work.

I have bought a multipoint laser collimation tool from Hotech after discussing the possibilty to use this device to optically align all the components of a SCT+Hyperstar system with David. David is willing to invest into this area. The result will be more elegant and we will be sure of aligning the optical axis rather than having to rely on some mechanical properties to support my previous method. Of course, this laser is not cheap but still justifiable.

Lastly, i will really appreciate your sharing the wealth of knowledge you seem to have rather than hitting with negative comments and running. My shooting or not shooting with Hyperstar has no relevance in this context.


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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: jrcrilly]
      #5819950 - 04/24/13 02:42 PM

No stretch, here.

The Mt. Lemmon system is at f/2, now. The lens set for it is about 16" across. The corrector with spherical primary on an SCT already correct for spherical aberration in an SCT. That's why these literally are the same type of system. And it's not a coincidence the same guy designed all of them.

-Rich

Quote:

Quote:

The original design came from the 60" scope on Mount Lemmon. The scope was originally a cassegrain and got a new front end built to allow deep sky searches for asteroids.




To be fair, that was a classical Cass with a paraboloid mirror at F/4 or thereabouts. All that would be required to switch to prime focus would be removal of the secondary and addition of a coma corrector. Takahashi offered a convertable classical Cass/Newt for years. Converting an SCT with a spherical F/2 primary is much more of a compromise and definitely not the same design.

It's OK to like Hyperstar but let's remain realistic.




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Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: bilgebay]
      #5819989 - 04/24/13 03:01 PM

Quote:

My shooting or not shooting with Hyperstar has no relevance in this
context.



The point is that many hyperstar owners move on to other telescopes quite quickly including you . They don’t want to deal with alignment issues every single imaging session. Also the hyperstar f/2 optics has additional inherent shortcomings like vignetting, poor narrowband efficiency, focusing issues, diffraction artifacts caused by cables/camera profile and bloated stars.

Quote:

I have bought a multipoint laser collimation tool from Hotech after discussing the possibilty to use this device to optically align all the components of a SCT+Hyperstar system with David. David is willing to invest into this area. The result will be more elegant and we will be sure of aligning the optical axis rather than having to rely on some mechanical properties to support my previous method. Of course, this laser is not cheap but still justifiable.




I pointed out to David Ho few years ago that the ACT collimator could be used to align the Hyperstar. I had a number of discussions with him about it. He has been very slow in embracing the Hyperstar. I could not convince him to make a mounted mirror that could be threaded on the Hyperstar. Once I even tried to setup a meeting between Starizona and Hotech at a local show, nothing came out of it. Starizona showed very little interest. Personally, I have used the ACT collimator with a blue filter a couple of times to align my 14” HS with mixed results. Squaring the ACT collimator to the SCT is not repeatable.

I think f/2 is simply too fast for narrowband filters and micro-lenses, f/3 would be better, but that's too slow for Starizona (talked to them about it, no plans for Hyperion Hyperstar)


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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Alph]
      #5821168 - 04/25/13 01:00 AM

Micro lenses work at f/1.4. The narrowband filters work, though they can produce unusual flares on bright stars.

Actually, I wonder what the limits are for driving existing hyperstar variants with different primary mirrors. Of course, getting an f/2 parabola isn't trivial.

-Rich


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mmalik
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Reged: 01/13/12

Loc: USA
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: rmollise]
      #5821215 - 04/25/13 02:09 AM Attachment (14 downloads)

Quote:

No idea what "fastness or short circuiting" means... sorry.




Good discussion everyone (I am using Rod's comments for elaboration for all); I would like to use this fastness aspect to get a consensus here.

So most of you DO understand what I meant by short circuiting? Simple... regular SCT has three folds of light path, in HyperStar last one gets clipped. Consensus I would like to have is that HyperStar is condensing light of the last fold (in other words converging or bringing to focus) onto the sensor hence giving the appearance of fastness with some loss of resolution/image detail for a given sensor. Do you all agree? If yes, then we are all on the same page with this (whether it is good or bad is a different story).

Now with that said, hypothetically speaking, why not apply this last 1/3 convergence principle to all optics, refractors and all [e.g., imagine clipping last 1/3 of the light cone of a refractor with a "hypothetical" HyperStar for a refractor]; that would be BAD or considered counter productive, correct? If you can understand what I mean then I think I have made my point.


To sum up, then what heck the rest of the astrophotography community is doing with slower, non-HyperStar systems, exposing for long hours... they are getting more resolution than HyperStar would get. That's all; if that's sophistication then one would be justified in calling HyperStar with the 'C' letter word, especially in its current incarnation with SCTs. Regards


Elaboration of last fold condensing/converging by HyperStar:
•Image circle C11: 42mm
•Image circle C11 + HyperStar: 27mm

Edited by mmalik (04/25/13 11:38 AM)


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frolinmod
Carpal Tunnel


Reged: 08/06/10

Loc: Southern California
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: mmalik]
      #5821258 - 04/25/13 02:53 AM

mmalik, there's nothing wrong with a lower effective focal length so long as one has small pixels in his camera as well. Your analogy appears to be flawed.

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Phil Hosey
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Reged: 10/29/08

Loc: LaGrange, GA
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: mmalik]
      #5821392 - 04/25/13 07:22 AM

Wait a minute.. The SCT's primary is already at f/2, the Hyperstar isn't condensing anything. Your analogy doesn't seem to make sense to me. You are comparing a refractor being reduced to f/2 to a system that is natively f/2. Maybe I'm missing something in your argument. I need a more thorough explanation.

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rmollise
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Reged: 07/06/07

Re: Why do some consider Hyperstar a 'crude' platform? new [Re: mmalik]
      #5821459 - 04/25/13 08:33 AM

Quote:



So most of you DO understand what I meant by short circuiting? Simple... regular SCT has three folds of light path, in HyperStar last one gets clipped. Consensus I would like to have is that HyperStar is condensing light of the last fold onto the sensor hence giving the appearance of fastness with some loss of resolution/image detail for a given sensor. Do you all agree? If yes, then we are all on the same page with this (whether it is good or bad is a different story).




Sorry Malik... This is not correct. There is no "condensing of light" (whatever that might be). The bottom line is that the primary mirror of the SCT is being used at its normal, native focal ratio, about f/2. No unfolding or magic at all, you see.

Edited by rmollise (04/25/13 09:55 AM)


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Phil Hosey
Carpal Tunnel
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Reged: 10/29/08

Loc: LaGrange, GA
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: rmollise]
      #5821621 - 04/25/13 09:37 AM

Rod,
I thought the SCT corrector plate is what is correcting for the spherical mirror and that the Hyperstar lens is correcting for other abberations such as coma and flattening the field. I don't think the Hyperstar is correcting spherical abberation.


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rmollise
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Reged: 07/06/07

Re: Why do some consider Hyperstar a 'crude' platform? [Re: Phil Hosey]
      #5821673 - 04/25/13 09:54 AM

Quote:

Rod,
I thought the SCT corrector plate is what is correcting for the spherical mirror and that the Hyperstar lens is correcting for other abberations such as coma and flattening the field. I don't think the Hyperstar is correcting spherical abberation.




You are right, Phillip...I got carried away.


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ghataa
professor emeritus


Reged: 06/20/11

Loc: Central, NJ
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: rmollise]
      #5821824 - 04/25/13 11:22 AM

For me, sometimes you just have to look at the data. There are so many incredible images taken with the Hyperstar approach that it seems like a nice addition to an imager's toolbox. Like a lot of things in life, it's a choice. I don't own a Hyperstar but would love to have such a system!

Best,

George


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J. Barnes
super member


Reged: 04/11/09

Loc: Kalispell, Montana
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: ghataa]
      #5822177 - 04/25/13 01:32 PM

I really love the short exposure times, especially on a borderline adequate Ultima fork mount. Without a permanent pier or observatory, and Polar alignment that is so-so, it makes imaging for beginners like me easy and satisfying. I haven't used it for video yet, but I hear it does rather well in that regard. That being said, the $800 HS and $300 conversion is a tough pill to swallow. I would feel more justified if I could figure out a way to Barlow it to F/4. That would make a lot more objects available.

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Wilki
super member


Reged: 03/15/10

Loc: California (recently moved)
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: J. Barnes]
      #5822357 - 04/25/13 02:54 PM Attachment (40 downloads)

I have to put my two cents in. I have the system, due to work/deployments and crummy German weather, I've only been able to use it once since I bought it a year ago. Here is my first image, the only processing was done with the nightscape astro fx software. I am a total amateur with no other imaging experience. It's easy to use and it works, and in my opinion relatively inexpensive. Oh, and don't forget, it's tons of fun.

I'm moving to norther California soon, I can't wait to get out to some dark skies, away from the clouds and light pollution here, and try my hand at some more imaging.


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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Wilki]
      #5822440 - 04/25/13 03:38 PM

MMalik, I think the misunderstanding here goes all the way back to what the telescope does in the first place.

I'm thinking we should maybe start by discussing what a SCT is, and then we can move on to what hyperstar does differently.

The original device in the series was something called a Schmidt camera, which had a camera facing a primary mirror with a corrector in front of the entire assembly. This was in the film days, and the telescope was made to stretch the film to curve it into the shape of the focal plane.

The Schmidt telescope was a modification of this concept where a secondary mirror was added to make a multi-purpose telescope.

An SCT has a corrector matched to an f/2 primary mirror (on most, f/2.3 on a C9.25). This paired set produces a short light cone going to the secondary, again at f/2.

The curved secondary mirror acts as an f/5 barlow and stretches the light cone out to an f/10 cone, although there is still coma present due to the curvature at the focal plane.

Now, looking at this, it is apparent a complete telescope is possible by mounting a camera at the focus of the primary.

In fact, this design is simply reverting to the original Schmidt camera, but the main problem it had is the film needed to be stretched to match the curved focus surface.

The fastar device appeared as a flattener to allow a flat chip to take the image from the Schmidt optics and focus it on a flat surfaced imager.

Now, Hyperstar is an expansion of that concept to support larger sensors.

So, saying hyperstar is a crude platform is really missing much of the point behind it.

Now, in the world of modern telescope versions, the Celestron Edge was purposey designed to be compatible with hyperstar. That was one reason for putting the flattening optics into the baffle tube- so the telescope could revert to being a Schmidt camera.

The Meade ACF was not designed to be compatible with hyperstar, and the change to the prescription broke the commonality with a Schmidt camera which allowed a flattener to take the place of the secondary. This is why Meade Hyperstar variants have disappeared.

Anyway, as I hope you can now appreciate, the hyperstar setup is actually a very elegant solution to a difficult problem, and offers remarkable performance with modern cameras.

-Rich


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jrcrillyAdministrator
Refractor wienie no more
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Reged: 04/30/03

Loc: NE Ohio
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Starhawk]
      #5822455 - 04/25/13 03:49 PM

Quote:

The Schmidt telescope was a modification of this concept where a secondary mirror was added to make a multi-purpose telescope.




...and the corrector was relocated to about 1/2 the ideal distance from the primary. That's where SCT coma comes from.


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J. Barnes
super member


Reged: 04/11/09

Loc: Kalispell, Montana
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Wilki]
      #5822482 - 04/25/13 04:09 PM Attachment (39 downloads)

Quote:

I am a total amateur with no other imaging experience. It's easy to use and it works, and in my opinion relatively inexpensive. Oh, and don't forget, it's tons of fun.

I'm moving to norther California soon, I can't wait to get out to some dark skies, away from the clouds and light pollution here, and try my hand at some more imaging.



I'm with you there. I shot this single 30 sec. exposure through a brief "sucker hole" that opened up the other night.
Collimation on? Doesn't look like it.
Polar aligned? Sort of. (I saw Polaris for about 20 seconds)
Stange abberation?
Better than eyepeice projection a year ago?
In a couple of years my response?


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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: jrcrilly]
      #5822896 - 04/25/13 07:38 PM

You are correct, of course, and there are telescopes originally configured as Schmidt cameras which now have an internal flattener and CCD installed to turn them into astrographs. The 30" scope on Mount Bigelow matches this description.

-Rich

Quote:

Quote:

The Schmidt telescope was a modification of this concept where a secondary mirror was added to make a multi-purpose telescope.




...and the corrector was relocated to about 1/2 the ideal distance from the primary. That's where SCT coma comes from.




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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Starhawk]
      #5822918 - 04/25/13 07:49 PM Attachment (44 downloads)

Here is an Orion Nebula I did with the Pentax K-5 on C-11 hyperstar.

-Rich


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Starhawk
Space Ranger
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Reged: 09/16/08

Loc: Tucson, Arizona
Re: Why do some consider Hyperstar a 'crude' platform? new [Re: Starhawk]
      #5822923 - 04/25/13 07:50 PM Attachment (39 downloads)

Here is the upper left hand corner.

-Rich


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