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Does EdgeHD have an edge with Hyperstar?

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#1 Dom543

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Posted 06 January 2013 - 02:56 AM

Hi All,

I see many proud astrophotographers using an EdgeHD+Hyperstar configuration.

Since an EdgeHD costs significantly more than a traditional (non-Edge) SCT, I am asking the following question. When used with Hyperstar, does the EdgeHD offer any significant benefit over a non-Edge SCT? By "significant" I mean more than bragging rights and some incremental improvement due to more careful or up-to-date manufacturing execution.

If I understand it correctly, the Edge scopes still have f/2 spherical mirrors and the Schmidt corrector that goes with it. These are the only components that matter when used with a Hyperstar.

That mirror can have a better coating, be polished to higher precision or ride on a smoother focusing mechanism but these are what I consider better manufacturing. The corrector/flattener optics in the draw tube that distinguishes the EdgeHD is not in play when Hyperstar is used.

Please explain me what I am missing here!

Thank you,
--Dom

#2 GlennLeDrew

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Posted 06 January 2013 - 08:11 AM

As I understand it, other things being equal, from the Hyperstar standpoint there is no difference between the old 'classic' SCT and the Edge variant. In other words, the only difference lies in the field corrector optics near the rear end of the primary baffle tube.

#3 rmollise

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Posted 06 January 2013 - 10:40 AM

Hi All,

I see many proud astrophotographers using an EdgeHD+Hyperstar configuration.

Since an EdgeHD costs significantly more than a traditional (non-Edge) SCT, I am asking the following question. When used with Hyperstar, does the EdgeHD offer any significant benefit over a non-Edge SCT? By "significant" I mean more than bragging rights and some incremental improvement due to more careful or up-to-date manufacturing execution.

If I understand it correctly, the Edge scopes still have f/2 spherical mirrors and the Schmidt corrector that goes with it. These are the only components that matter when used with a Hyperstar.

That mirror can have a better coating, be polished to higher precision or ride on a smoother focusing mechanism but these are what I consider better manufacturing. The corrector/flattener optics in the draw tube that distinguishes the EdgeHD is not in play when Hyperstar is used.

Please explain me what I am missing here!

Thank you,
--Dom


There is no difference. As you note, the only component being used in the Hyperstar setup is the primary, which is the same as that in the standard scopes. Celestron is not producing special "better" primaries for the Edge. Back in the day, the top of the line Ultima 8 had a primary no different from that in the C8 Classic or PowerStar.

#4 Alph

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Posted 06 January 2013 - 01:25 PM

When used with Hyperstar, does the EdgeHD offer any significant benefit over a non-Edge SCT?


How do you define a significant benefit?
Proper alignment of all optical components is critical for Hyperstar performance. The EdgeHD OTAs are assembled to higher standards required by their design. You can download an article from Celestron website which explains that. You will have a better luck with the EdgeHD Hyperstar.

#5 rmollise

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Posted 06 January 2013 - 02:37 PM

Maybe, maybe not, and the Hyperstar is collimateable and will likely have to be collimated no matter which scope you use it on.

#6 dobsoscope

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Posted 07 January 2013 - 10:38 AM

As an aside, note also that Celestron never refers to the EdgeHD as an SCT.. but as an AS (aplanatic Schmidt).

#7 freestar8n

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Posted 07 January 2013 - 11:06 AM

I'm not sure what range of things they call it - but they do often call it an aplanatic Schmidt as you say, and that is unfortunate because aplanatic only refers to the coma reduction and not the flat field. So it should really be called a flat field aplanatic SCT. Although the field isn't perfectly flat - nor is any aplanatic telescope truly coma free, but the key is that additional lenses have been added to correct the Petzval curvature inherent in the sct design - and that correction is on top of the aplanatic aspect, which is reduction of coma also taken care of by the corrector lenses.

This thread makes some reference to Edge only being different from the normal design in the added lenses - but it's clear from the celestron documents there is at least a spacing change between the primary and secondary, and possibly a change in the curvature of the secondary. This is why Edge requires a special adapter for hyperstar. I believe the corrector and primary are still the same and that is key to hyperstar still working - but other aspects of the OTA are different.

Frank

#8 Alph

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Posted 07 January 2013 - 12:25 PM

Maybe, maybe not, and the Hyperstar is collimateable and will likely have to be collimated no matter which scope you use it on.

The Hyperstar on the EdgeHD might not need any collimation at all as some owners have reported to my surprise. I must say I was quite skeptical about it until I read the cited documented. All optical components in the EdgeHD are carefully aligned and squared to the optical axis. This is exactly what the Hyperstar needs.

#9 Peter in Reno

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Posted 07 January 2013 - 12:35 PM

All EdgeHD correctors are supported by four set screws at the front cell. The set screws help to accurately center the lens corrector. No more cork or paper shims.

http://www.celestron...se&_a=viewar...

Peter

#10 bilgebay

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Posted 07 January 2013 - 12:57 PM

After aligning the corrector and the secondary holder to the primary, and getting rid of all the play on the Hyperstar unit itself, I am no more using any of the collimation screws.

Please see this thread for the modifications I have done to the Hyperstar unit.

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#11 Alph

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Posted 07 January 2013 - 02:26 PM

After aligning the corrector and the secondary holder to the primary, and getting rid of all the play on the Hyperstar unit itself, I am no more using any of the collimation screws.


:( This isn't exactly what I wanted to hear. Your experience implies that the cited Celestron document might be wrong and the EdgeHD scopes are not that well aligned as Celestron claims.

#12 bilgebay

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Posted 07 January 2013 - 03:12 PM

I am sorry to disappoint you Alph :( But mine was either not centered at the factory or got screwed up later when the secondary holder started rotating within the corrector. I guess, it is the latter. All the details are in the thread I referred to above :)

Oh, my C11 Edge is one of the earliest deliveries... this might have a role in my problem as well.

But now, I love my C11 Edge :)






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