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Bench Test of a StellarVue SVX180 Apochromat

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#1201 CHASLX200



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Posted 19 March 2023 - 04:14 PM

Same here.  As much as I'm tempted by a 180mm apo, I don't think one could outperform my Zambuto-powered scopes, though the pristine view without diffraction spikes on planets and bright stars would sure be nice. Quality aperture is hard to beat.  

For pure raw images of in your face planets at crazy powers on my dead still nites all of my higher end Dobs from 11 to 18" always win out. I know that a 6" to 8" APO can have that cleaner and more snappy image , but they run out of light with powers over 600x vs what a 12.5" or bigger Newt can show. I never had a fract over 6" other than the 7" Meade ED that was a total flop and i got three 2 sec looks thru it the three times it came back from Meade to only have it out of center, so can't count it.


#1202 Ihtegla Sar

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Posted 19 March 2023 - 04:17 PM

I tried and inexpensive ADC and it lessened the colors but it would not totally eliminate them. 

If an inexpensive ADC improved the colors, then it likely was dispersion. I have a ZWO and a Gutekunst.  Quite frankly the inexpensive ADCs like the ZWO don't cut the mustard when you are trying to eliminate all dispersion for visual observation in a large apo. You need something like the Gutekunst. 


The types of simple prisms in an inexpensive ADC aren't the same quality as what Gutekunst uses and you can't fine tune an inexpensive ADC very well using the levers while the image is shifting up and down. The Gutekunst is optically excellent and the image doesn't shift as you turn the single dial that operates as smoothly as the fine focus knob on a good focuser. So you can eliminate very small amounts of dispersion that can't really be addressed with an inexpensive ADC. 


#1203 900SL


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Posted 19 March 2023 - 04:18 PM

I was curious too, so I did a quick model of a 152 F8 triplet using FPL-53, changing the matching glass to Ohara's version of Schott BK-7, and reducing the airgaps to something more normal (0.2mm), and letting R5 vary from the other internal radii. It's actually quite good, even allowing for it having best correction in red. At best focus in red, it has a strehl of .995, blue .856, and green .958. And since it's slower and smaller than the 180, I don't think an asphere would be needed. I'll attach the Oslo file. This was a bit hurried, I'm doing this on a quick work break..later I'll see how it does in violet light and compute the (theoretical) polychromatic strehl, my hunch though is it will be close to .95.

I think this is quite an important post. It may be that the SV180 is an outlier (for whatever reason.. still to be determined, but possibly design scaling?) and the other SV scopes may well meet acceptable 'Specification'.


I don't have a  cake in this bunfight, I don't own an SV, but I do think that SV deserve a fair hearing, rather than this somewhat vindictive dogpile that seems to be firmly rooted in past histories with several contributors.


We are, after all, talking about the potential failure of a US Company here as a result of the negative image now associated with ALL SV telescopes as a result of the test of the SV180, and ongoing mud slinging. You may have your own reasons for disliking SV's approach to marketing but I'm sure you wouldn't want to celebrate the loss of a home grown manufacturer ( and spare me the 'we are only helping SV improve their quality' arguments, gents. Crocodile tears don't wash hands clean)


#1204 Rick Runcie

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Posted 19 March 2023 - 04:18 PM

Scott, you are very welcome. We all say at times, "things happen for a reason" and I believe this was one of those instances.

Like I said I feel indebted to Paul, but I also have to give accolades to Vic because when I brought these issues to his attention his response and actions were like I would hope all business owners would be, receptive courteous and professional. He did all I could have hoped for and I'm very satisfied for the end results.

Best regards, Richard

#1205 Scott in NC

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Posted 19 March 2023 - 04:35 PM

It seems as though this would be an appropriate point to close this thread, but I'll leave it to the discretion of the Refractors forum moderators.  Unless there's more information to present, we could go on gabbing about this forever, and as one recent poster hinted at, letting this thread go on forever could do more damage to SV's reputation than any of us actually intend.


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