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Borg 90FL - Ultimate optics in small form factor?

refractor equipment observing
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#301 Peter Besenbruch

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Posted 02 April 2018 - 12:46 PM

FYI I have the Borg 55FL which has even more FC. I fitted it recently with a TS flattener and now I don't have to refocus to see nice stars center or edge. This model flattener screwed directly on a 1.25" to 2" adapter in front of the T2 Baader Amici diagonal.

Interesting. I use the same flattener with a GSO diagonal in a 600mm refractor. How does the Amici diagonal handle the steep light cone?


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#302 moshen

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Posted 02 April 2018 - 01:11 PM

Moshen,

 

FYI I have the Borg 55FL which has even more FC. I fitted it recently with a TS flattener and now I don't have to refocus to see nice stars center or edge. This model flattener screwed directly on a 1.25" to 2" adapter in front of the T2 Baader Amici diagonal.

 

I use mine as a finderscope with a Pan 24 and now from FC rearing its ugly head 50% out of the center, it appears at 90%+ out of the center. I am sure if I play with it a bit in terms of spacing I will get it right, but my eye now accommodates FC to such an extend that I think I will hold off.

Very interesting Nick, not too pricey and maybe a good solution for those who have issues with the field curvature. Nice to know it works well visually.



#303 moshen

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Posted 02 April 2018 - 01:30 PM

Got it! Would love to hear about your tests and how well the mod3 works with them.

The mod3 works great with the 90FL. I was up late last night and was viewing a fully resolved-to-the-core M13. I did use a barlow to get some image scale but it looked really nice.


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#304 nicknacknock

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Posted 02 April 2018 - 11:43 PM

Anthony, I use the astronomical Amici prism which is better than the garden variety one and since it is mated to the flattener, it performs brilliantly.

 

For such a fast light cone on a doublet refractor, a mirror is definitely preferred, but the Borg is my RACI finder so yeah, Amici for me :)


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#305 nicknacknock

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Posted 02 April 2018 - 11:44 PM

Peter, really pleased with its performance. I have not "finalized" the spacing between the flattener yet now I can easily accommodate the little remaining field curvature. I'll try to fix the spacing next time I am out but even as is, it is perfect for my intended use!


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#306 Anthony236J

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Posted 03 April 2018 - 09:19 AM

Anthony, I use the astronomical Amici prism which is better than the garden variety one and since it is mated to the flattener, it performs brilliantly.

 

For such a fast light cone on a doublet refractor, a mirror is definitely preferred, but the Borg is my RACI finder so yeah, Amici for me smile.gif

 

Hey Nick, I'm glad that worked out! I would not have expected that a 1x flattener would affect the light cone in a way that could be beneficial to the prism diagonal.



#307 jay.i

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Posted 03 April 2018 - 10:17 AM

Hey Nick, I'm glad that worked out! I would not have expected that a 1x flattener would affect the light cone in a way that could be beneficial to the prism diagonal.

I don't think Nick is saying the prism diagonal is beneficial, he's just saying because he wants it to be a RACI finder, he has to use the Amici prism, despite the shortcomings of prism diagonals with fast focal ratios.


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#308 Anthony236J

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Posted 03 April 2018 - 10:36 AM

I agree with you in the use case of the amici prism, but that was not my comment. My comment was that I did not expect the flattener to positively affect the performance of the prism diagonal since the focal ratio remains essentially unchanged.



#309 nicknacknock

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Posted 03 April 2018 - 11:02 PM

I don't think Nick is saying the prism diagonal is beneficial, he's just saying because he wants it to be a RACI finder, he has to use the Amici prism, despite the shortcomings of prism diagonals with fast focal ratios.

 

Correct. A prism is not the best option for fast focal ratios and I did try it. Better results with a mirror diagonal. But I want RACI for myself so Amici prism for me.

 

At the low magnification I work (x10) and using it as a finderscope, the only aberration I care about is FC. The flattener took care of that.


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