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Its a bit indefinable Mike. Light scatter is quantifiable, colour correction is too much in the hands of other factors I suspect to be definitely quantifiable.
Its certainly not a large effect. But there was a definite change between FSQ106N and 106ED. It may not be the glass but perhaps the coatings.
The 106N has 2 X fluorite lenses and the 106ED 2 X FPL53 lenses.
However the 106 suffered from several other shortcomings like vignetting on bright perimeter stars (the dreaded black bar through bright perimeter stars) and a lack of backfocus. The 106ED has better colour correction so in that case it shows lens design also is a huge factor.
I have also read visual reports comparing a fluorite and non fluorite same model and they claim they can notice differences. Very subjective though.
One of the best visual scopes I have had was the Tak FS152. Stunning. That was a fluorite doublet.
Yuri is quite sure there is a gain, Roland Christen not so.
The main advantage of fluorite is more for the optician in that they can make colourfree lenses more easily with faster f-ratios. But fluorite definitely has less light scatter as the laser test shows clearly. But it would be very subtle. Perhaps more of an issue for visual users who want that last little bit of detail. So faster f-ratios with superior colour correction and knowing every last little bit of light is getting through with current technology is what its giving. FPL53 also is superb of course.
Also for example Berts 300mm Canon. That has a fluorite or several fluorite elements. His images seem superior to normal 300mm lenses,
Pentax 67 300mm EDIF excepted. It has superior colour correction for a camera lens.
TEC180FL F7 versus AP180 F7. The only images I have seen of AP180 are not impressive at all unlike AP155 or your AP152 or my AP140 which are super scopes. Perhaps its the fluorite that makes the TEC better in that specific instance. They are both oiled triplets. Again, very subjective as it could be easily argued its really the astrophotographer's skill, imaging location, camera etc etc.
So its a subtle thing. But then again a lot of these scope differences are often small improvements at large expense to achieve it.
I guess I will know for sure in a week or two!
Greg.
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