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Sharpstar 61EDPHII (and derivatives/rebrands) CA Issue

Imaging Equipment Astrophotography
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#1 FixieRider

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Posted 21 October 2021 - 07:45 PM

There have been threads in the past from various CN users about these scopes' chromatic aberration. It appears that Sharpstar has recently started replacing consumer's primary objectives which resolves the out-of-spec CA they were seeing.

I own a Radian 61, which was my first imaging OTA, and I love it -- but holy smokes is the CA bad on it. Huge violet halos all the way around the stars, even in the very center of the frame. At first, primarily because of replies I read on this forum and others, I thought that I was just going to have to deal with it in post, because "it's a fast refractor, CA's going to be bad."

Cuiv, the Lazy Geek, on YouTube did a video recently on his Sharpstar, showcasing the CA he was seeing; and just today, released a video with a replacement primary optical assembly that put the scope much closer to how it is advertised on the spot diagrams.  The CA Cuiv shows in his images from before the replacement are nearly identical to what I'm seeing out of my Radian 61.

Because the Radian 61 is the same scope, just rebranded, I reached out to OPT asking if they could assist me in getting corrected optics to fix the CA problem. They were fairly quick with a reply, and I think it might be of interest to the other CN users who own either of these scopes. OPT's reply is as follows:
 

"We are aware of the chromatic aberration issues some users are experiencing with the Radian 61, and we are currently in the middle of testing upgraded versions to verify they will be good for replacement. It will take some time for us to verify this and then receive the upgraded Radian 61s, so please bear with us in the meantime. You can try writing in again in 4-6 weeks or so and we should have a better update to provide then."

 

Hope others who might be considering purchasing this scope, or who currently own it and have been seeing the same issues find this helpful, and I hope OPT can deliver on a fix for us. I really do love the scope in every other regard -- I just really hope they can make it right.


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#2 andysea

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Posted 21 October 2021 - 09:11 PM

Good luck! I hope they fix it for you.
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#3 terrypaula

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Posted 21 October 2021 - 09:43 PM

I don't know if it's wrong to say this but if I would have bought this scope without the CA being disclosed beforehand I'd be returning it to the manufacturer for a refund. 


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#4 FixieRider

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Posted 21 October 2021 - 10:03 PM

I don't know if it's wrong to say this but if I would have bought this scope without the CA being disclosed beforehand I'd be returning it to the manufacturer for a refund. 

There's more to it than that.  There's going to be CA present on a fast refractor like this at this price point. And to the untrained/inexperienced eye (i.e. me), I just thought I was getting what everyone gets and that I'd have to deal with it in post. It wasn't until I saw Cuiv's videos and the comparison between the original primary objective and the replacement that I realized that what I'm seeing is much worse than it was supposed to be.

So, you're not wrong, but it's also too late for a return for me. But it's also why I felt it necessary to post here, as OPT straight up says it's still a known issue with the Radian 61. So I'm holding out hope that they'll make things right by replacing the objective like Sharpstar is doing for their OTA's.



#5 rockstarbill

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Posted 22 October 2021 - 08:05 AM

I don't know if it's wrong to say this but if I would have bought this scope without the CA being disclosed beforehand I'd be returning it to the manufacturer for a refund.


Absolutely agree. As with other mind boggling things imagers are accepting today as "okay" that aren't, I really don't understand why a portion of the community is willing to take this.

In the first example Cuiv showed, horrendous and completely unacceptable CA. I would have thrown that telescope in a lake. The second example was still not good, but was improved. If these imagers are willing to accept CA, go buy a nice Takahashi 60mm Doublet. You'll get less CA (not zero though), better stars, less excuses needed and better optics.
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#6 gzljh96

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Posted 23 October 2021 - 03:51 AM

Absolutely agree. As with other mind boggling things imagers are accepting today as "okay" that aren't, I really don't understand why a portion of the community is willing to take this.

In the first example Cuiv showed, horrendous and completely unacceptable CA. I would have thrown that telescope in a lake. The second example was still not good, but was improved. If these imagers are willing to accept CA, go buy a nice Takahashi 60mm Doublet. You'll get less CA (not zero though), better stars, less excuses needed and better optics.


I think the bigger issue is selling a rebranded scope with little changes for $300 more.
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#7 awong101

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Posted 23 October 2021 - 04:38 AM

I made a video of my first impressions of the Radian 61. Here, I went to a dark(ish) site of about bortle 5 and did a test without using any filter to check for CA. Well, the raw unedited individual file speaks for itself.

 

Check out my video here:

 

https://youtu.be/c_EDmeeJj6U


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