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what does Celestron's 0.7 reducer do to an edge hd?

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#1 Benni123456

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Posted 22 August 2019 - 01:42 PM

Hi,

 

I have an edge hd 800. Even if I try to collimate the scope with reducer perfectly, I see color dependent distortions at the edges (i.e. different filters show different star shapes). Without the reducer, this is not the case and it is not a problem of the filters, since my refractor does not show this.

 

 

So I wonder what the reducer does to the edge hd optically?

 

Since there are people here who have put their telescopes into interferometers, I wonder whether there are people here who have tested the scts with reducer and can tell what it does to the optics, and whether there are ways to optimize image quality in the field (different corrector rotation, different distances, different focus positions for the filters etc.).

 

 

Best regards


Edited by Benni123456, 22 August 2019 - 01:42 PM.


#2 John Miele

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Posted 27 August 2019 - 04:50 PM

Dunno benni but I and many others have seen this problem. The .7 reducer is quite disappointing in this regard. I need a heavy crop to remove the bad corner stars. Celestron should be embarrassed by this lateral color smear...

#3 freestar8n

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Posted 27 August 2019 - 05:44 PM

I wouldn't expect any add-on reducer not to need some tweaking of collimation after attachment.  The tolerances are very tight and it is no big deal anyway.  You should always collimate for the actual system you are using - and there is no need to collimate first at f/10 and then at f/7 - if all you intend to use is f/7.

 

The EdgeHD8 reducer appears to have challenges compared to the other sizes.  It's not trivial to take a well corrected and flat field and reduce it down - that's why they are expensive and have large lenses.  Try it at different spacings and perhaps you will find improvement.

 

But the challenges people seem to have with the 8" reducer don't seem to be a factor for the larger sizes.

 

I have used EdgeHD8 at f/10 but not with the reducer - so I have no experience with it.  I use EdgeHD11 with reducer and it takes some care to get the field corrected well - but I have good results with 8300 ccd and asi1600.  And that is without any special changes to a stock OTA.  There are others with EdgeHD14 and reducer who get similar results with larger sensors - and no realignment of the internal optics or corrector.

 

Frank


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#4 Astrojedi

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Posted 27 August 2019 - 10:59 PM

Hi,

 

I have an edge hd 800. Even if I try to collimate the scope with reducer perfectly, I see color dependent distortions at the edges (i.e. different filters show different star shapes). Without the reducer, this is not the case and it is not a problem of the filters, since my refractor does not show this.

 

 

So I wonder what the reducer does to the edge hd optically?

 

Since there are people here who have put their telescopes into interferometers, I wonder whether there are people here who have tested the scts with reducer and can tell what it does to the optics, and whether there are ways to optimize image quality in the field (different corrector rotation, different distances, different focus positions for the filters etc.).

 

 

Best regards

Did you not start another thread on exactly the same topic? I remember having the same conversation with you there. You really don’t seem happy with your EdgeHD 8. As I mentioned these scopes are made to a price point, if you are seeking perfection you need to spend a bit more.



#5 Sarkikos

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Posted 28 August 2019 - 09:09 AM

The EdgeHD 8" is fine by me.  Well-corrected flat field. 

 

The 0.7x reducer is just that.  A reducer.  It gives you more options for your eyepieces.  The EdgeHD 8" is already corrected for coma and has a flat field, so don't expect the reducer to do anything else but reduce.

 

I see no optical problems induced by the 0.7x reducer.  But then I'm 100% visual.  I don't do AP.  The only sensors I use are my retinas.

 

Mike


Edited by Sarkikos, 28 August 2019 - 09:10 AM.

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