Since I just couldn't pass up the low price for a 28mm aspherical lens from DX, I decided to put some info together for those (few) of you that like flood lights. This should give you some idea of what is required to make use of such a lens.
1st let me tell you that in this optic's case, size does matter. I put a 23mm lens through this and I was not impressed... not like this one.
The tests were done at 1M from the wall. This was the contraption for the tests.
To the best of my knowledge, this is an XR-E R2-WS; the one recently mod'd with a new driver. All tests were done in low @ <30ma.
A couple of grabbers, cables, and the trusty 18650 wired battery box... and a ruler, of course.
I like this shot better: almost avatar worthy, wouldn't you say 
Anyway, all the shots were done in relative darkness... Measurements are backside of lens to the pill which is approximately the face of the emitter. We start at 20mm which is where the emitter focuses at 1 meter.
All beamshots were done with manual mode at f3.5, 1/2 second exposure, ISO160
1st is the candlestick mode for the ambient output at max dispersion:
Now for full focus on the emitter... 20mm from the lens. If I pull back from here, I also see the flaws in the emitter's dome.
Next, 15mm from the lens. Classic hot spot and little spill.
Next, 10mm and a well defined hailo. Matched to an appropriate "lens", you should be able to remove the hailo. This is where the flange of the lens is.
For the last shot, we go to 5mm. THis puts the dome of the XR-E ~2mm from the lens.
Still a lot brighter than ambient and at 1 meter, the diameter of the bright beam is nearly 1 meter as well. This makes the light angle (full angle) approximtely 50 degrees... an easy 45 degrees for the purposes of calculations.
A quick comparison between full spread and ambient candlestick:
DX has a lot of different aspherical lenses available. Just know that they do little good with a standard reflector. In theory, because I got a perfect focus of the emitter at 20mm, the spherical diameter is probably 40mm. This is something you want to know if you are engineering a flood.
I have yet one other favorite image from this shoot:
And that's all I got for this sitting 
