Dale, I have some experience with lens and double lens lights and would be happy to try to help if you wanted to run something by me.
Thanks EasyB, this all started when a friend saw a deal on ebay and shared a link… apparently a large company had ordered quite a few 200mm condenser lenses turned down to 7”, then didn’t use quite all of em. I got this $150 lens for $30. It’s got a 16” back focus so part of what I was counting on was help determining what lens to use in front of an emitter to focus the light into this big condenser. I have formally not been very fond of aspheric lights, so this is way outside my ball park.
Loosely holding the big 7” lens out front of a de-domed XP-G2 it does indeed make a super small hot spot, so it should have some seriously monster throw, maybe even exceeding 1Mcd, possibly, done right, even exceeding 2Mcd! How cool would it be to dial in a 2 mile thrower? That’s what got me started here.
I’ve purchased an 8” tube, 4’ long, I’ve got some aluminum stock I can make a base holder for the emitter and driver and I have some material I can probably fashion into a carrier plate for the big optic, pretty sure I even have it figured out how to affix it. This is a combination of a 1/2” thick plate of FR plate and 1/8” Kydex. So I’ll still need the back side 8” plate, threaded for focus ability, and probably a threaded on mount for the secondary lens. Which lens, that’s my problem. I look at the Edmunds catalog and there seems to be quite a few things that could possibly work, figuring I’ve got it narrowed down to one I’d like to try, but don’t want to start dropping $35 on lenses that aren’t quite right for the job at hand, if that makes any sense.
I’ve even got a second aspheric that goes in the Jax Z1 aspheric, not sure if that one might work just as well, longer back focus probably than is desirable as I’m thinking this secondary should be practically right on top of the emitter.
I know enough to know there’s trade-offs. I can gain lumens by using the double glass, but the overall throw is better with the single primary. So it’s going to come to a point that I’m going to have to build it as a single with concession applied towards an additional lens, see how it goes.
For a little perspective… I have an SBT-70 in my Jax Z1, if I focus it on the wall across my room the hot spot is about 9-10” in diameter. If I remove the aspheric and focus it through this condenser lens, the hot spot is about 3/8” in diameter and looks like it’s going to start a fire! And that’s from the big SBT-70!
subscribed and intrigued
That looks like a high quality lens. Here are my thoughts and suggestions. I actually think the Z1 lens might work well as a precollimator lens. For high light collection efficiency you want to maximize the lens diameter to focal length ratio, but it’s hard to get this ratio much larger than 1 and still have good lens quality (from what I’ve seen). I think the Z1 lens has a ratio probably around 1 and I’ve heard it is good quality.
Here is how I would choose the location for the precollimator lens. Rig up the large lens so that it is in place, 16” from the LED. Then hold the Z1 lens and start very close to the LED. As you move the Z1 lens farther away from the LED, you should see the cone of light coming from the Z1 lens start to narrow. Keep moving it away until the light cone narrows so that it’s overfilling the 7” lens by 1 to 3”. Around this configuration is where you are going to maximize the light collection efficiency. This should approximately double the beam area and hopefully not drop the lux by more than 10%. Fine tune the 7” lens position to get focus because adding the Z1 lens will change this distance slightly.
See here for a picture and more discussion.
That’s about what I was thinking but was worried about the Z1 lens having that 2.75-3” back focus. It’s pretty far. I build a precollimator set up for the Z1 and while it did improve lumens at zoom it also made a larger hot spot by a good margin. (the secondary was pretty cheap)
I just simulated that by leaving the aspheric on the Z1 and focusing it through the condenser lens. This virtually eliminated all spill but kept the hot spot the same diamter. So I will gain overall output lumens by utilizing the Z1 secondary lens, gain throw by keeping only one lens.
Might it be that a 2 lens “secondary” could be the answer to maintaining as much lumens output as possible while keeping the tight hot spot for throw?
The motivation for using a precollimator lens is to increase beam lumens while keeping the beam intensity the same. The extra lumens manifest themselves as a larger hotspot.
Dale, have you tried a zoom position between spot and flood? I was thinking, if your big lens has a focal distance of 16”, then maybe set the Z1 to a zoom setting that just covers the back of the big lens at about that distance. From there, move the ‘zoom’ position of one/both lenses just enough to get a good focus while also trying to keep the back of the big lens completely lit.
I don’t know if this is anything like plausible, just popped in my head. 
Trying something. Just bought a broken camera lens off ebay for parts. I’ll disassemble it and try to make use of some of the 21 optics inside. 
It’ll be fun taking it completely apart at the very least, I’ve used this particular lens before and had one during two different periods so I’m pretty familiar with it. There’s an aspheric inside as well as multiple condenser type combination optics. We’ll see next week if any of it will be useful to this project or not.
Damn, sounds amazing. Did you post a deal alert for the us for the rest of these awesome sounding $30 lenses? Are they still available?
There was 4 when my friend saw em, he bought one for a job he was working on and I bought one… he went back and only one was left so he snagged it.
Looking forward to seeing what you do with this big boy. 
That lens is impressive, can’t wait to see the finished light.
I got the Canon lens I ordered off ebay. Took it completely apart, there are two optics that can work, the largest one is the top outermost element from the lens and probably the one I’ll use. It focuses cleaner and from a bit further thatn the Z1 optic, gives a pretty tight hot spot in combination with the 7” lens and as expected, virtually eliminates spill. The hot spot with the 7” lens alone is just insanely small so throw would be absolute without the second lens, using a second lens to collimate light into the larger lens will give more output, brighter hot spot albeit larger and with less overall throw. Will have to do the build and compare the two options to see what would be the best way to set it up.
Dale, forgive me if I’m telling you something you already know, but when you add a precollimator lens, the beam lux doesn’t necessarily go down significantly when the beam size increases. For example, below are my measurements from the thread I linked above, for a UF-1504 with XPL HI V2 1A.
Stock light without pre collimator lens.
11,800 lux at 6.05m: 432,000 cd
approximate beam size: 20cm x 20cm
With pre collimator lens
11,340 lux at 6.05m: 415,000cd
approximate beam size: 29cm x 29cm
While that might seem relatively insignificant, you ARE talking about a difference of 20cm to 29 cm. The way this one is looking, it will be a much more drastic difference than that.
What if that difference was from 29cm to 0.5cm?
At any rate, I’ll have to get busy and make the lens mount plate before I can really start figuring any of this out. It won’t be all that difficult to make an attachment to allow the pre-collimator lens to be added or subtracted. Well, I’ll plan on it going in. lol
One thing that might be happening is that when you put in the pre collimator lens it changes the apparent position of the LED, so the big lens becomes out of focus.