Holy Hot Spot Batman, 824kcd! (Formerly, 100mm Aspheric Lens at Fasttech)

By the way, that's an actual quote from the series. The below picture is an dedomed XM-L2 U2 1A at about 7 amps. Mouse over is dedomed MT-G2 (probably around 5 amps). The beam is aimed at a tree that is about 250 feet away and 70 feet tall. The light hitting the tree to the right is from the glow of the PVC head.

The lens I asked about originally in this thread was waiting for me when I got home. Big, low-profile honker. It was packed with an Allen wrench against it. Bad form FT. Just for S's and G's, I decided to hold it up in front of my latest DST build (with the reflector portion of the head off) and aim it at my lux meter from 10 feet. Got frickin 790kcd!. Tried the same thing with a dedomed MT-G2 at about 6 amps. Got 399kcd! No wavien collar or anything. Just held in mid air by hand. The die image is very small. At ten feet it barely covered the light meter sensor dome.

EDIT: Redneck engineered a quick light to go have some fun with it. Now measures 824kcd. I'm sure it can be adjusted higher, but had to get out and try it out in the wild.

The beam is so tight fully focused, that it only seems to make sense to use this lens in a zoomie. It floods beautiful and wide. Wider than any other lens I have ever used. Image of die seems to have a slight shadow, but it could be the white PVC I used to fab a temporary head. There are some pics of the funny temp light at post 25. I estimate the focal length to be about 4.75" to 4.875".

Hmm . . . what's your intentions for its use? You have a light that takes a 100mm lens?


Redneck thrower at first. I noticed this weekend that 1 1/2" PVC can be force threaded onto a DST. So need a 1 1/2" to 2" bushing. Than a 2" to 4" Adapter. Dedomed xpg2. Boom! 100mm Aspheric! That's what I'm talking about!

Of course, my luck the lens will suck. But if it does, at least I can take one of the PVC parts back for a refund. I'll still be out $8+ plus the cost of the bushing.

I ordered, but still have a window to cancel. Anyone used this lens yet?

Ah, should have figured!

And I should have put 2 and 2 together (link to post#238)!


might throw a bit that eh?

Hmmm.... I don't know optics so I may be totally off base with this but:

That low profile lens looks like it may have a long focal length. Long distance from the emitter would mean more light lost off to the side and less light focused out through the lens?

DrJones? Anyone?

LOL. Love it Garry. I like that better than the most common last heard words from a redneck, "Hey y'all, watch this!".

I'm hoping, Stockton-Rob. I need to start playing with upside down reflectors to see if I can approximate a Waven Collar. There will be some room to play around with this setup. Something tells me the lens may be a let down given it's cost though.

That makes sense Keltex78. If I understand what Djoss told me once, longer focal length means tighter hot spot. Hopefully, the bigger diameter makes up some for the longer focal length. Let's just hope it's not too long.

Yes, throw with an aspheric is trade-off: if the diameter is the same the thicker lens will catch more light and puts it in a bigger hotspot, the thinner lens will not catch a lot of light (the rest is lost), but puts that little bit into a smaller hotspot. So throw will not be too far off in the two cases, but I prefer the efficiency of a thicker lens with large hotspot.

Thank you Djozz (Sorry for misspelling your screen name above). This lens appears to have an convex curve (Not sure this is the right word, but the glass curves away from emitter going towards the center) on the inside face too. I know it would just be an educated guess without knowing the specifics, but do you have any thoughts on how that may impact the beam?

I do not see that, in the FT pictures the underside looks flat to me.

One could experiment with two of these directly on top of each other. You will loose some light from the extra reflections off the extra surfaces, but it will more or less act like one thicker lens :-)

I just ordered this a few hours ago. Going to resurrect an old old build. It's actually a perfect fit.

I don't think sandwiching two is the best idea, the amount you lose at the interface between the two lenses can be exemplified by cracked glass.

Yeah, this is how I understand it, assuming everything else is the same,
100mm lens with low convex profile - long focal length, project smaller spot (lesser light captured)
100mm lens with higher convex profile - shorter focal length, project larger spot (more light captured)

But they both have the same light intensity in the spot.

You may use dual-lens system to ‘shorten’ the the focal length of the 100mm lens - resulting a larger projected spot with still the same intensity.

(I might not use the correct technical terms here.)

Maybe focal length is 140mm same as I got 2 from DX.


I ordered one of their smaller lenses but don’t have it yet.

It adds a couple extra reflective surfaces but back to back, the focal point should be closer and capture more light. Bridging that thin gap with optically clear silicone could eliminate or at least drastically reduce those reflections.

Very clean. No I haven’t tried it yet. I thank you for showing us this lens. It might come in handy if I need some lens-changing in the future.

I have no doubts that that lens would make one hell of a thrower. That’s obvious because its close to frisbee sized.


Way to go Ramblings. Now lets see what we can do with these bad boys (Well, I hope they kick ass).