Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
Get a Cloudy Nights T-Shirt Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu uh, User

Equipment Discussions >> ATM, Optics and DIY Forum

Pages: 1 | 2 | 3 | (show all)
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: MKV]
      #6124248 - 10/08/13 07:47 AM Attachment (12 downloads)

Mladen, that's clever to try to eliminate positive field lens with Mangin secondary, but the system is not flat field. It still has somewhat less of defocus (curvature) error than c14e would have due to astigmatism, but not really significantly.

And I agree with Frank that we should compare systems of similar length. Not only for the length itself, but for the performance level. An SCT with slower primary will have lower aberrations, both off axis and spherochromatism. This is what an f/3.5/12.2 14-inch Edge would put out, e,F,C lines.

Edited by wh48gs (10/08/13 07:49 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Loren Chang
member


Reged: 04/28/09

Re: OLSO model of the C14 Edge-HD ? new [Re: Dave O]
      #6124337 - 10/08/13 08:48 AM Attachment (8 downloads)

Quote:

In their 'White Paper' on the EdgeHD telescopes, Celestron states that the 14 inch EdgeHD corrector uses N-SK2 and N-BALF2 glasses. So yes, it seems to exit.




Hello Dave,

That's the problem. I tried to google N-BALF2 but found nothing. And here is C8 EHD prescription in book. The mirrors system is f/8.5 if you remove corrector. I wonder why using corrector to increase focal length.


Post Extras: Print Post   Remind Me!   Notify Moderator  
MKV
Carpal Tunnel
*****

Reged: 01/20/11

Re: OLSO model of the C14 Edge-HD ? new [Re: wh48gs]
      #6124469 - 10/08/13 09:50 AM Attachment (10 downloads)

Vla, a C14 EdgeHD with an f/3.5 primary rivals a (simulated*) field-flattened dilayte counterpart. The question remains: if an ATM were to make one of these which would be easier. I think the one with all spherical surfaces wins, even if its Mangin mirrors require greater precision. It doesn't require extra tooling.

regards,
Mladen

*simulated using a curved imaged field since OSLO.edu doesn't allow more than 10 surfaces in all


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave O
sage
*****

Reged: 12/21/11

Loc: Sri Lanka
Re: OLSO model of the C14 Edge-HD ? new [Re: MKV]
      #6124551 - 10/08/13 10:31 AM

Hello Loren,

Yes, the smaller EdgeHD scopes (8", 9.25", and 11") use N-SK2 and K10 glasses in their corrector; only the 14" uses the N-BALF2 glass per the "White Paper" put out by Celestron.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Loren Chang
member


Reged: 04/28/09

Re: OLSO model of the C14 Edge-HD ? new [Re: Dave O]
      #6124851 - 10/08/13 12:42 PM

Dave,

Vlad said location of the corrector is closer to primary in N-BALF5(longer BFL). I'd like to see if N-BALF2 will do the right job. SK2/K10 combination intruduces lateral color off-axis. It can be defeated by using N-BALF.

Edited by Loren Chang (10/08/13 12:44 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: Loren Chang]
      #6126237 - 10/09/13 01:14 AM Attachment (6 downloads)

Quote:

I tried to google N-BALF2 but found nothing. And here is C8 EHD prescription in book. The mirrors system is f/8.5 if you remove corrector. I wonder why using corrector to increase focal length.




I don't think they had complete prescription. Why tweak otherwise? Their lenses are noticeably different (thickness, radii) than what Celestron gives in its file. The closest I can come to it - with all the dimensions nearly identical as in Celestron's drawing - is if I go with 0.707 neutral zone radius (not 0.866 as in the book). No lateral color to speak of, and pretty close blur-size-wise.

With 0.866 zone there has to be more lateral color, or a slight longitudinal chromatism (and that with the corrector pulled a half inch, or so, out). Another possibility is that they go with 0.866 zone and somewhat more relaxed Schmidt radius, giving them ~0.87 zone and minimized lateral color. The secondary is also different than in the standard SCT, so they are not a perfect match for the standard SCT attachments for prime focus imaging anyway.

Vla


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: OLSO model of the C14 Edge-HD ? new [Re: wh48gs]
      #6126286 - 10/09/13 02:27 AM

They say that,
Quote:

we optimized the design for the largest possible field of good correction.




That makes me think the original design was targeted more at highest performance in the center, for planetary and visual work, while reducing the Strehl farther out. This is consistent with the white paper, which makes the point that deep sky imaging is seeing limited.

I don't think they are just talking about a choice of focus, since they say "optimized the design."

Since Smith/Ceragioli/Berry compare scopes based on Strehl across the field, a design optimized more for the center would not look as good. But for the intended usage modes of this scope, it would make sense to me. Minimal sacrifice of on-axis performance, while maintaining overall performance adequate to maintain small deep sky fwhm's across the field in long exposures.

That's my interpretation anyway.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: freestar8n]
      #6127025 - 10/09/13 01:40 PM Attachment (7 downloads)

Quote:

That makes me think the original design was targeted more at highest performance in the center, for planetary and visual work, while reducing the Strehl farther out. This is consistent with the white paper, which makes the point that deep sky imaging is seeing limited.




What doesn't feet in is that the paper design (according to the blurs shown) has less astigmatism and less lateral color. Thus it can only be superior to the book "optimized" variant, not the other way around (center field is not discernibly different). The book variant would have been slightly better overall if some 5mm closer to the secondary.

When compared based on their design performance, tweaked and original corrector configurations do not show significant differences in any respect, except when the original configuration is matched with 0.707 neutral zone corrector (bottom). The blur shapes then are also quite close to Celestron's. It suggests that the standard C8s are made with 0.707 neutral zone, and that the actual C8 Edge corrector is similar to this variant.

Vla


Post Extras: Print Post   Remind Me!   Notify Moderator  
BYoesle
Post Laureate
*****

Reged: 06/12/04

Loc: Goldendale, Washington USA
Re: OLSO model of the C14 Edge-HD ? new [Re: wh48gs]
      #6133180 - 10/12/13 02:23 PM

It seems activity on this thread has subsided, so at the risk of hi-jacking it, Id like to know if anyone has pursued similar improved optical performance from a standard C8 and C14?

"Telescopes, Eyepieces, Astrographs" shows significantly improved performance from the standard SCT optics via relocation of the corrector plate -- close to the Edge HD levels. But this seems it would necessitate significant mechanical modifications including some sort of spider assembly to maintain the position and alignment of the secondary.

Has anyone explored design of a lens corrector system similar tho the Edge HD for the standard Celestron SCT designs which could be located in the OEM primary baffle tube? Could these be modeled in the OSLO edu version?


Post Extras: Print Post   Remind Me!   Notify Moderator  
ch-viladrich
member


Reged: 07/14/13

Loc: France
Re: OLSO model of the C14 Edge-HD ? new [Re: BYoesle]
      #6134719 - 10/13/13 10:43 AM

Hi all,

Thanks a lot for this very interesting discussion.

I have been playing with the two OSLO models Vla derived for the C14 Edge-HD:
http://www.astrosurf.com/viladrich/astro/instrument/sensitivity/sensitivity-a...

Remember my point of view here is from high resolution imaging on large size sensors ;-)
The C14 Edge-HD seems to give lower Strelh ratio than the classic C14 over 650 nm, which is not good news for us. Maybe this is due to the corrector ?

On the blue side, they seems to be equivalent.

http://www.astrosurf.com/viladrich/astro/instrument/sensitivity/SC14-Strelh.jpg

The version with a neutral zone at 0.866 gives less change of focus with wavelenght which is nice when changing filters in LRGB imaging :
http://www.astrosurf.com/viladrich/astro/instrument/sensitivity/SC14-focus.jpg

The major drawback of these large size SC for planetary / lunar imaging is the fast degration of optical quality in blue and UV.
The CDK seems a promising alternative. Smith/Ceragioli/Berry gave the description of a 300 mm F-3-F7 optimized for deep sky imaging with a diffraction limited field of over a 1 field from 410 to 800 nm.

Of course this design with a 46% obstruction would make no sense for high resolution imaging.

So, I was wondering if it would be possible to design a CDK 350 mm F3-12 optimised for high resolution, with a 30% obstruction, and a flat diffraction limited field of say 7 arcmn in diameter, from 350 to 800 nm ?

The all spherical surfaces would be easy to manufacture and collimate(much easier than the hyperbolic secondary of a Cassegrain). While the absence of the Schmidt corrector would gives access to blue and UV with good image quality.


Post Extras: Print Post   Remind Me!   Notify Moderator  
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: ch-viladrich]
      #6135001 - 10/13/13 01:20 PM Attachment (6 downloads)

Quote:

I was wondering if it would be possible to design a CDK 350 mm F3-12 optimised for high resolution, with a 30% obstruction, and a flat diffraction limited field of say 7 arcmn in diameter, from 350 to 800 nm ?




It can be done. Since it is relatively small aperture and long focal ratio, it can't use the simplest arrangement with two plano lenses (too much higher order astigmatism), but what can be used is still within the reach of the advanced amateurs. The system pictured, 350mm f/3/11.2 is not fully optimized, but it shouldn't make appreciable difference. The 350nm diffraction limited field is about quarter of a degree, and 800nm about half a degree.

Vla


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alph
Carpal Tunnel


Reged: 11/23/06

Loc: Melmac
Re: OLSO model of the C14 Edge-HD ? new [Re: ch-viladrich]
      #6135021 - 10/13/13 01:31 PM

Quote:

I have been playing with the two OSLO models Vla derived for the C14 Edge-HD:



I haven't found any C14 Edge-HD OSLO files there.


Post Extras: Print Post   Remind Me!   Notify Moderator  
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: BYoesle]
      #6135045 - 10/13/13 01:42 PM Attachment (2 downloads)

Quote:

Has anyone explored design of a lens corrector system similar tho the Edge HD for the standard Celestron SCT designs which could be located in the OEM primary baffle tube? Could these be modeled in the OSLO edu version?





The problem here is that inducing coma in simple correctors always comes with some undercorrection, so if a corrector is to be used in otherwise well corrected system, that is a price to pay. In this example corrector cuts coma nearly in half, but induces some 1/10 wave of undercrrection. More coma corrected, more undercorrection. For an SCT with 1/4 wave of overcorrection this would, however, work perfectly, correcting both, coma and residual spherical (rear lens is deliberately made thicker to allow possible use of two thin plano lenses).

Vla


Post Extras: Print Post   Remind Me!   Notify Moderator  
ch-viladrich
member


Reged: 07/14/13

Loc: France
Re: OLSO model of the C14 Edge-HD ? new [Re: wh48gs]
      #6135111 - 10/13/13 02:09 PM

Many thanks a lot Vla :-)
I'll have a look it.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ch-viladrich
member


Reged: 07/14/13

Loc: France
Re: OLSO model of the C14 Edge-HD ? new [Re: ch-viladrich]
      #6135306 - 10/13/13 04:03 PM

Hi Vla,
You've find an amazing design :-)
- Strelh ratio on axis is 0.99 at 300 nm, then 1 from 350 to 1000 nm !!
- the focal shift from 350 nm to 1000 nm is a mere 0.01 mm !!
With a F/3 primary ratio, the optical tube will be arround 100 - 110 cm, which is still nice.
You've just designed the perfect large and still portable planet/ moon killer :-)


Post Extras: Print Post   Remind Me!   Notify Moderator  
BYoesle
Post Laureate
*****

Reged: 06/12/04

Loc: Goldendale, Washington USA
Re: OLSO model of the C14 Edge-HD ? new [Re: wh48gs]
      #6135318 - 10/13/13 04:08 PM

Thank you very much Vla - it will be fun to explore the possibilities...



Post Extras: Print Post   Remind Me!   Notify Moderator  
MitchAlsup
Pooh-Bah


Reged: 08/31/09

Re: OLSO model of the C14 Edge-HD ? new [Re: wh48gs]
      #6135330 - 10/13/13 04:17 PM

Quote:

Vla




Looking at the spot diagrams closely, I see some similarities between the book figure and the corrector 5mm closer, and some similarities between book and 0.866 null zone.

The 5mm closer overcorrects blue <spots> wrt book and undercorrects red.
The 0.866 corrector null undercorrects the blue <spots>

What would happen it fyou split the difference and tried 0.80 null zone and 2.5mm corrector spacing?

http://www.cloudynights.com/ubbthreads/attachments/6127025-edg.PNG


Post Extras: Print Post   Remind Me!   Notify Moderator  
ch-viladrich
member


Reged: 07/14/13

Loc: France
Re: OLSO model of the C14 Edge-HD ? new [Re: MitchAlsup]
      #6135353 - 10/13/13 04:29 PM

BTW, is there a way to display the Strelh ratio accross the field with OSLO-LT ?

Post Extras: Print Post   Remind Me!   Notify Moderator  
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: MitchAlsup]
      #6135469 - 10/13/13 05:40 PM

Quote:

The 5mm closer overcorrects blue <spots> wrt book and undercorrects red.
The 0.866 corrector null undercorrects the blue <spots>





It only appears so. They are all overcorrected in the blue. Look at the lateral color graphs at right. It would take a zone below 0.7 to get them together. In effect, it is inducing some longitudinal color error in order to minimize lateral - can't have both with this glass combination.

Vla


Post Extras: Print Post   Remind Me!   Notify Moderator  
wh48gs
Carpal Tunnel
*****

Reged: 03/02/07

Re: OLSO model of the C14 Edge-HD ? new [Re: ch-viladrich]
      #6135485 - 10/13/13 05:46 PM

Hi -

Quote:

is there a way to display the Strelh ratio accross the field with OSLO-LT ?




Not that I know. But it should have the RMS OPD under Spot diagram>>Spot size and OPD vs. field. Just as good for monitoring diffraction limited field.

Vla


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
14 registered and 28 anonymous users are browsing this forum.

Moderator:  ausastronomer, richard7, Starman81 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1639

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics