Aspheric lenses - 52mm/37mm fl - 52mm/33mm fl - 50mm/35mm fl - 50mm/38.5mm fl ~ Best?

[wintermute]

So, I am looking into building an asperical mag light next (putting my 3xCree Mag on the back burner for now). Of these asperical lenses which are available...which one is the best for the Mag light and most throw??

52mm diameter w/ 37mm focal length
52mm diameter w/ 33mm focal length
50mm diameter w/ 35mm focal length
50mm diameter w/ 38.5mm focal length

I know that some have started to make due with the 50mm lenses, but if I remember correct the 52mm diameter lenses fit the best.

I am not familiar with optics off the top of my head, although I could sit down and figure it out using all of my physics books and such...but which one would be recommended for the best throw.

Also, bare emitter on hotlips (no reflector at all), bare reflector on hotlips w/large reflector, or LED on some type of pedestal that allows the use of either stock mag reflector or some other replacement reflector (like the Malkoff drop-ins)?

Those more familiar with the optics could really help in deciding which lens and configuration. Mosts posts around here are just builds, not info on different lenses, reflectors, etc.

Last, but not least, we need some more of these bezels. Everyone interested in an asperical mag...post in there to see if we can get another group buy going.

 

[wintermute]

How far is the distance (in mm) from the back of an asperic lens to the LED mounted on a heatsink. This would be the ideal focal length without using any reflector I think.

 

[MrMimizu]

I tried to get a 52/37mm from surplus shed but they ran out. Shipped me a 50/35mm instead.


In this thread, the led is mounted on a hotlips with the pedestal cut off. That's a 52/37mm lens though. I'll have to measure it when I get my hotlips, but possibly it won't be necessary to remove the pedestal for a 50/35mm lens.

I've noted in the Kiu bezel thread that I'd like one already. Not sure if it'll happen but if it does, I'm definitely in for one or two.

 

[wintermute]

I tried to get a 52/37mm from surplus shed but they ran out. Shipped me a 50/35mm instead.


In this thread, the led is mounted on a hotlips with the pedestal cut off. That's a 52/37mm lens though. I'll have to measure it when I get my hotlips, but possibly it won't be necessary to remove the pedestal for a 50/35mm lens.

I've noted in the Kiu bezel thread that I'd like one already. Not sure if it'll happen but if it does, I'm definitely in for one or two.

There are other places to get the aspherical lenses - just cost 3x as much. But, when it comes to the total build cost - it's pretty minor. That's why I can get all 4 of those lenses. Just wondering what the distance is from the back of the lens to the emitter on a normal hotlips heatsink (and hence the ideal focal length).

 

[MrMimizu]

Well, I have a hotlips with a lux III on it right now.
I'm seeing about 27mm from where the bottom of the lens would be to the top of my LUX III. That is with the lens ON the pedestal of the hotlips and the mag about 3/4 twisted to the top. I can't guarantee the accuracy but it looks around there.

Would you mind letting me know where you are getting your lenses from?
I haven't been particularly successful while trying to google myself a lens.
For my 1C aspherical mag, I'll end up spending just over $300 I think.
custom mag body, AW C Li-ions and the charger for em are the bulk of it.

There are other places to get the aspherical lenses - just cost 3x as much. But, when it comes to the total build cost - it's pretty minor. That's why I can get all 4 of those lenses. Just wondering what the distance is from the back of the lens to the emitter on a normal hotlips heatsink (and hence the ideal focal length).

 

[OhMyGosh]

http://www.surplusshed.com/ has several aspheres. Very reasonable prices.

As for focal length, a lower F ratio (focal length/lens diameter) will capture more light from the emitter. A longer focal length will make a smaller spot. I have some of these to play with but haven't experimented much yet. You might consider trying 2 lenses, one 'collimator' to capture most of the light, and one 'focuser' to change the spot size. A big problem with these is that they are not anti-reflection coated. That is OK for close to right angles, but as the angle increases you lose more and more light from reflection. Uncoated glass loses ~4% for each surface, ~8% per lens. But at oblique angles the loss is much higher.

Remember these are lenses - think overhead projector. They will make a 'picture' of the LED chip as a spot. some kind of diffuser close in front of the LED may give a better, more even spot.

 

[KingGlamis]

I ordered the 50/35 yesterday. When it arrives I will surely post beam shots.

 

[KrisP]

I got the 50mm x 35mm from Surplus Shed too. It's ok, but i'd like to buy a 52mm x 37mm if anyone knows another source as SS is out and not getting anoymore in stock.

 

[wintermute]

Anti-reflective coating on these lenses costs ~$40 I think...so that drives up the price a bit. But some people may find it worth it.

 

[KrisP]

There are other places to get the aspherical lenses - just cost 3x as much.

Where are these places?

Thanks.

From the other threads i've read on here, the 52mm x 37mm has the best throw.

 

[wintermute]

Melles Griot Asperic Lenses.

52mm with 37mm focal length is here.

This is why I wanted to know the distance from the emitter to the back of the aspheric lens:

See, Fb is 21.9mm - so the pest possible placement of the LED from the back of the aspheric lens would be 21.9mm. MrMimzu found the distance to be 27mm, so moving the emitter slightly closer to the back of the lens should provide more throw.

The 52mm w/ 33mm focal length, the Fb is only 16mm - which would be bad.

Conversely, the 50mm w/38.5mm focal length, the Fb is 24.3mm - so if the emitter placement is indeed 27mm, then the 50mm w/38.5mm focal length should throw better.

The moral here is for maximum throw, the LED should be Fb distance from the back of the asperic lens for best throw. Having the emitter at the exact focal point of the lens should focus the most rays straight ahead - of course the focal point is measured from the middle of the lens, so we have to look at the Fb number.

Optimal distances from back of asperic lens to emitter:
52mm w/33mm fl = ~16mm
52mm w/37mm fl = ~22mm
50mm w/35mm fl = ~23mm
50mm w/38.5mm fl = ~24mm

So, considering the Fb for the 52/37 and the 50/35 are only 1mm apart - I would be surprised if they threw that much different.

You can get a magnesium fluoride AR coating on the 50mm lenses for $20 and on the 52mm lenses for $40.

 

[wintermute]

Who's gonna take the thrower they have, and order a 50mm with 38.5mm focal length with MgF2 AR coating to see how it does.

At the very least, those with the throwers already built should try moving the emitter to a distance Fb from the back of the lens to see if you get more throw.

 

[cryhavok]

So, considering the Fb for the 52/37 and the 50/35 are only 1mm apart - I would be surprised if they threw that much different.

Check out this thread of mine a while back that kicked off the whole aspheric lens/Xr-E combo in a maglite.

The light above is a 50x35mm lens from surplus shed. Then on a whim, I ordered the 52mm lens. My new aspheric lens host is regulated at 1.5A and just by switching the lens, my lux @ 1 meter readings rise about 15,000 lux@ 1 meter - a significant improvement. With my current setup, my light produces about 70,000 lux@ 1 meter.

You can see a comparison between the 50 and 52mm lenses here

At the very least, those with the throwers already built should try moving the emitter to a distance Fb from the back of the lens to see if you get more throw.

Most everyone does...Remember that the maglite head is able to be unscrewed and screwed in quite a bit, most people find the optimal length very easy...just screw in or unscrew until you get a nice tight spot.

 

[WadeF]

Will the 52/37 drop right into a Mag's head? Or do you have to customize the head?

 

[wintermute]

Check out this thread of mine a while back that kicked off the whole aspheric lens/Xr-E combo in a maglite.

The light above is a 50x35mm lens from surplus shed. Then on a whim, I ordered the 52mm lens. My new aspheric lens host is regulated at 1.5A and just by switching the lens, my lux @ 1 meter readings rise about 15,000 lux@ 1 meter - a significant improvement. With my current setup, my light produces about 70,000 lux@ 1 meter.

You can see a comparison between the 50 and 52mm lenses here

Cryhavok, what do you think caused the significant increase in lux readings at 1 meter between the 50mm/35mm fl and the 52mm/37mm fl lenses? What do you think the 50mm/38.5mm lens would do in the same host(AR coating on the 50mm lens is only $20)? The longer focal length of the 50mm/38.5mm lens with the shorter Fb might make it the best lens. You would be the best one to test this obviously. Also, the F-number of the 52mm/37mm fl is 0.71 while the 50mm/38.5mm fl is 0.77. Might be worth a try.

 

[cryhavok]

Will the 52/37 drop right into a Mag's head? Or do you have to customize the head?

It has to sit on top of the bezel and you need to remove a bit of the bezel lip so the bezel ring can be screwed down a bit more.

Cryhavok, what do you think caused the significant increase in lux readings at 1 meter between the 50mm/35mm fl and the 52mm/37mm fl lenses? What do you think the 50mm/38.5mm lens would do in the same host(AR coating on the 50mm lens is only $20)? The longer focal length of the 50mm/38.5mm lens with the shorter Fb might make it the best lens. You would be the best one to test this obviously. Also, the F-number of the 52mm/37mm fl is 0.71 while the 50mm/38.5mm fl is 0.77. Might be worth a try.

If you looked at the thread with the pictures comparing the two lens, you can see that the 52mm lens is significantly larger in height/depth. I also have a few other lenses and it seems that the ones that have the larger height/depth will focus better.

I believe I read somewhere that you can focus the 52mm setup better because the LED die is further away and more of a point source.

 

[wintermute]

If you looked at the thread with the pictures comparing the two lens, you can see that the 52mm lens is significantly larger in height/depth. I also have a few other lenses and it seems that the ones that have the larger height/depth will focus better.

I believe I read somewhere that you can focus the 52mm setup better because the LED die is further away and more of a point source.

I'm not sure if the larger diameter will help focus better, but the longer focal length might. That's why I tried to recommend the 50mm with thr 38.5mm focal length. The Fb would be 24mm, which could allow a better focus of the emitter, and you would not have to remove any of the stock bezel, ergo easier builds.

I'd be willing to pitch in $5 (by PayPal) to you to order this lens to try with your throwers. If a few other people did the same, you could test this last lens to see which one is best and have it not cost you a thing. I don't have the hosts to compare, so it makes no sense for me to order it, your experience with this stuff so far makes you the best tester. It's the only asperic lens in this size which hasn't been tried - and it has the longest focal length and highest F-number (0.77 vs. 0.71). Is anyone else willing to pitch in 5 bucks to order this lens if cryhavok is willing to test it?? (Although, don't forget - the AR coating on a 50mm lens is only $20 and that could improve light output by as much as ~8%!!).

I have to say cryhavok - I really respect you for doing this whole aspheric lens thing first! :bow: - :thumbsup:

 

[shiftd]

just FYI, newbie (who is the first one to make a cree throw) has posted some beamshots in his old thread here

 

[KingGlamis]

So when measuring Fb, what is the exact point of F*? Do you measure to the tip of the emitter? The middle? The base?

With my Mag 4D with Mag LED emitter the max Fb I can get is 21mm, when measured from the tip of the emitter.

Edit: I can easily get 24mm by unscrewing the bezel and still have good thread engagement for the bezel.

 

[cryhavok]

Yep, as far as I can remember, NewBie was the first to try a lens with the XR-E :thumbsup:

The only problem with the 50mm lens is that it actually fits inside the maglight head, so there is no way to have it rest at the front of the light by itself. When I used the 50mm x 35mm lens, I had to put a UCL between the lens and the head so the lens would have something to sit on. Alternatively, you could just use the reflector to create a platform.

With the 52mm lens, it sits on top of the head like the window. Some of the top threads had to be removed so that the bezel ring would screw down completely (you can screw down the bezel without doing this step, but it doesn't go down far enough to cover the O-ring).

I'm not sure if the 50mm/38.5 fl lens would be a good choice. I believe what makes the lens a really good thrower has to do with the center thickness. I have another lens that is in the 60mm+ diameter, with a relatively short fl, but it's center thickness is not much. It does focus the light, but not to the really tight projection like my current 52x37 fl lens.

I just measured my 52x37mm lens and it has a center thickness of 23mm. The 50x38.5mm lens has a center thickness of 20mm. The only lens that seems to have a better center thickness is the 52 x 33mm lens, which is 25mm.

I'd love to order and try them both, but I don't know what I'd do with them if they don't work out :shrug: I appreicate your offer, though :wave: