Don’t use reddit, sorry.
But guys did it wrong, sanding will make it better but not properly focused. You need to add thickness for perfect corona free tight hotspot.
You don’t need a reddit account to see the thread.
The issue is that “perfect” and “corona free” are mutually exclusive–a corona is an inevitable byproduct of the geometry of a parabolic reflector.
If there is no corona, it means the focus is off and you’re not getting as much intensity as you could.
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Yeah well that is debatable, since i swapped from incan hotwire Maglites to LED, that is neverending theme…
And of course i can see post on reddit, but don’t care about checking it daily just to find something.
A lot of drama there, like in olight groups 
Where do we buy the 90 CRI SFT25r?
KD had some of them at some point, but not anymore since they were just engineering samples or something like that.
maybe Kaidomain will restock.. I missed the first two batches, they sold out really fast.. I have not emailed them to ask.
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Could you pls clarify - from this slide, isn’t corona a result of the LED not being a point source? Nothing to do with the reflector?
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Still waiting for the 4000K SFT-40 to come back
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Happy to! BTW, would you share the entire slideshow with me? I am interested because I recently worked on making a comprehensive mathematical model of a reflector beam, which required coming up with precise definitions of what the hotspot and corona are. It seems that the slides and I have independently arrived at the same definitions!
Incidentally, the claim that apparent angle is maximized 60 degrees off-axis is not strictly correct–the true angle is always a bit bigger, and the 60 degrees is achieved by taking the limit as emitter size goes to 0.
Yes, this is a great observation. Since real-world emitters are not point sources, a corona would always be present with proper focus. In fact, the angular size of the corona can be predicted from just reflector and LED dimensions. The only way to eliminate/reduce the corona is to move the LED away from the focal point of the reflector, which I regard as suboptimal.
Different types of secondary optics produce different beam shapes. Someone used to aspheric zoomies or certain types of TIRs might expect all beams to have just a hotspot, with no corona and no spill, and thus regard the corona as an abnormality rather than something to be expected.
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Looks like it is the below presentation from 2011. There’s a download button if you’re interested.
The LEDs listed are out of date, of course, but it looks like a reasonable overview of optics (reflectors and lenses).
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Thanks - see above. I posted a few screen shots in the more appropriate thread on beam shape.
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