# Is a glass lens actually better than a plastic one?



## iamerror (Oct 11, 2006)

The more expensive flashlights usually have a glass lens (or window, if you like that term better) instead of a plastic one. I have been thinking... maybe plastic ones are actually better? They should be more durable at withstanding falls, etc. They do however let out less light and scratch easier. If a light were to take much use and abuse would a plastic lens be more suitable? Your thoughts?


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## leukos (Oct 11, 2006)

I guess it depends what factors are more important to your uses. Except for my PT40, all my lights now have glass windows (probably in reaction to all the scratched windows of my old maglites). Sapphire is one tough window that can stand up to a lot of abuse; I would trust it over plastic.


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## Long John (Oct 11, 2006)

Yes, it depends on your uses. I had an UCL in my favour Magmod, but it was too fragil. I changed the broken glas into a hardened mineral glas from member "4Sevens", so far it's ok

The disadvantages of plastic are scratches and less transparency, but at a light with really hard abuse, it could be worth.

Best regards

____
Tom


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## Concept (Oct 12, 2006)

I agree on the scratching issue I dont know of any plastic that can stand up to the mineral glass or pyrex in regards to toughness.


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## InfidelCastro (Oct 12, 2006)

Glass lenses have nothing to do with the flashlight being expensive. There's plenty of cheapies out there that have el-cheapo glass lenses.


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## chesterqw (Oct 12, 2006)

high quality glass should help ... but high grade optical plastic should work too.

the only thing is that glass will scratch less easily. 

mineral glass is a good choice and less fragile then most 'glass'

the borofloat(did i spell it correctly?) is made of something which can withstand high heat 

pyrex is tough but more easily scratched then mineral glass.


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## adirondackdestroyer (Oct 12, 2006)

Speaking of glass lens, does anyone know where I can get a UCL for my MMLED? I think it uses a 22.6mm lens, and I can't find the UCL in that size.


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## pilou (Oct 12, 2006)

There is glass ... and then there is glass


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## Trashman (Oct 12, 2006)

I'm guessing, since the Barbolight has a plastic lens, that plastic is more suitable than glass for dive lights.


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## Biker Bear (Oct 12, 2006)

Now, if they ever manage to grow cheap diamond - that would make the ULTIMATE flashlight lens.  Until then, synthetic sapphire will probably be the best there is.


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## RCatR (Oct 12, 2006)

Plasic for my beaters, UCL for my babies


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## tebore (Oct 12, 2006)

I noticed a huge difference when my MiniMag got it's crappy lens upgraded with a Mineral Glass Lens. It's not UCL but it was still noticeable.


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## FlashKat (Oct 13, 2006)

Try this website...I am not sure the thickness you are looking for, but the left hand column has different thickness. Your size I think you are limited to 1.0mm thickness.http://www.toolsgs.com/cart/browse.asp?subcat=258&pg=2


adirondackdestroyer said:


> Speaking of glass lens, does anyone know where I can get a UCL for my MMLED? I think it uses a 22.6mm lens, and I can't find the UCL in that size.


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## Schnotts (Oct 14, 2006)

Glass is the way to go! Doesn't scratch like plastic!


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## andrewwynn (Oct 14, 2006)

I figure that i'm like 'the vast majority' who will.. instinctively clean the dirt off a window of their light (torch for most of the world) with their T-shirt or a spit-wetted thumb when needed.. it's this basicaly 'crazy behavior' that ruins a perfectly good plastic window, but i just can't help it so whenever i can i use glass.. it's worth the risk for me (drop=break risk that is).. Also many of my lights are far too powerful to use plastic, they just will melt within minutes. 

-awr


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## BentHeadTX (Oct 14, 2006)

andrewwynn said:


> I figure that i'm like 'the vast majority' who will.. instinctively clean the dirt off a window of their light (torch for most of the world) with their T-shirt or a spit-wetted thumb when needed.. it's this basicaly 'crazy behavior' that ruins a perfectly good plastic window, but i just can't help it so whenever i can i use glass.. it's worth the risk for me (drop=break risk that is).. Also many of my lights are far too powerful to use plastic, they just will melt within minutes.
> 
> -awr



Pretty much what Andrew states,
I use glass in all my mods since I will get better brightness with them. No scratches so it has that extra bit of class. 
I've broken glass "windows" in a modded minimag by dropping it in some gravel but had a spare so no problem. My D cell sized Mag mods run glass to keep the reflectors stabilized as plastic will bow under pressure. If I drop the Mag in gravel, I'll have the weight of the flashlight and 8 NiMH AA cells to make sure the glass gets destroyed. 
Thanks to kiu, he is making black HA-III crenulated strike bezels which will help protect the glass. The farther up the head the gravel has to go to hit the glass, the less force and chance it has to actually shatter. I have two of them on order, one for my LuxV Mag and one for my upcoming Quad XR-E Mag. 
For my EDC 2AA and AAA lights, the stock plastic lens works fine and has taken some hits. When glass breaks, it can tear up the reflector and punch a hole in the Luxeon domes. Not a good thing if your really, really need the light to work in rough situations.


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## Long John (Oct 14, 2006)

BentHeadTX said:


> Pretty much what Andrew states,
> I use glass in all my mods since I will get better brightness with them. No scratches so it has that extra bit of class.
> I've broken glass "windows" in a modded minimag by dropping it in some gravel but had a spare so no problem. My D cell sized Mag mods run glass to keep the reflectors stabilized as plastic will bow under pressure. If I drop the Mag in gravel, I'll have the weight of the flashlight and 8 NiMH AA cells to make sure the glass gets destroyed.
> Thanks to kiu, he is making black HA-III crenulated strike bezels which will help protect the glass. The farther up the head the gravel has to go to hit the glass, the less force and chance it has to actually shatter. I have two of them on order, one for my LuxV Mag and one for my upcoming Quad XR-E Mag.
> For my EDC 2AA and AAA lights, the stock plastic lens works fine and has taken some hits. When glass breaks, it can tear up the reflector and punch a hole in the Luxeon domes. Not a good thing if your really, really need the light to work in rough situations.



BentHeadTX

I had an UCL in my Trilux-D-Mag mod with Kiu's bezel ring. I don't know if you plan an UCL or hardened mineral glas, but my UCL shattered after a *little *hit of the bezel ring at a door frame. It's extremly fragil, since the UCL should not be hardened.
So my advice is, go with the mineral glas. I can't see a difference in output with my pure eyes, but the advantage of more thoughness is it worth.

Best regards

____
Tom


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## andrewwynn (Oct 14, 2006)

i've killed 3-4 UCL just from heat alone.. they are quite fragile.. but here's the problem.. most likely you had your bezel tigher than necessary, introducing some pre-loaded stress.. glass is nearly impossible to crack until it has some initial crack.. but the UCL glass has little chips all around (as will all cut to circle glass that is not polished afterwards).. when tightening the bezel 'full tight' rather than just a big snug it pre-stresses the thin glass and a small tap can break it pretty easy. 

I like the UCL for the anti-reflective properties in lights w/o extreme power.. Long John is 100% correct about 'cant see the difference'.. you won't be able to, except that with anti-reflective windows, there is an elegance to them when they are off and handled.. not getting that glare off the lens brings them to 'another level up' in elegance even if the difference in output is small.

-awr


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## soapy (Oct 14, 2006)

I'd always go coated optics if you are running a hot light. The extra 2% or so you get from the coated optics means less heat build-up.

Hard coated AR polycarbonate is probably the best, unless you go for the synthetic sapphire windows.

Thoughts?


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## Bozzlite (Oct 14, 2006)

adirondackdestroyer said:


> Speaking of glass lens, does anyone know where I can get a UCL for my MMLED? I think it uses a 22.6mm lens, and I can't find the UCL in that size.


 
Try flashlight-lens.com Thats where I got mine. Sometimes he is out of stock, just keep trying.


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## BentHeadTX (Oct 14, 2006)

Long John said:


> I had an UCL in my Trilux-D-Mag mod with Kiu's bezel ring. I don't know if you plan an UCL or hardened mineral glas, but my UCL shattered after a *little *hit of the bezel ring at a door frame. It's extremly fragil, since the UCL should not be hardened.
> So my advice is, go with the mineral glas. I can't see a difference in output with my pure eyes, but the advantage of more thoughness is it worth.



Thanks for the heads-up Tom and Andrew,
As I am gathering parts to build my XR-E Quad Mag, I've been thinking about the "window" that can handle the stress of holding four McR19 Flood aluminum reflectors. The UCLs seem to be fragile so I guess I'll go with the mineral glass. The light's primary use is a frame mounted bike light so toughness is necessary. 
Already sent my order to 4sevens for a three-pack of the mineral lens...thanks for the tip!


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## Long John (Oct 14, 2006)

BentHeadTX said:


> Already sent my order to *4sevens* for a three-pack of the mineral lens...thanks for the tip!



This was a very good decision*:thumbsup:*

You're welcome BentHead

Best regards

____
Tom


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## Theatre Booth Guy (Oct 14, 2006)

iamerror said:


> The more expensive flashlights usually have a glass lens (or window, if you like that term better) instead of a plastic one. I have been thinking... maybe plastic ones are actually better? They should be more durable at withstanding falls, etc. They do however let out less light and scratch easier. If a light were to take much use and abuse would a plastic lens be more suitable? Your thoughts?


 
I used to strongly favor glass until a very short drop of my HDS EDC took a chip out of the lens. Switched to the plastic one (with anti-scratch coating) and managed to put several scratches in it by wiping dust off. While I don't like the ease of scratching plastic, it seems more up to being dropped.

On a positive note, my E2e got dropped at the very wrong angle and it took a chunk out of the floor with just a tiny bit of damage to the anodizing! Their very thick pyrex lens' seem much tougher.


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## Lee1959 (Oct 14, 2006)

I am in the minority, plastic works every bit as good as glass to me. In fact it is in some aspects preferable for durablity. Scratches in plastic can be fairly easily polished out too, but scratch a sapphire or glass and it has to be replaced. Then again I dont freak out about artifacts in the beam, or the tint of the LED either.


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## chevrofreak (Oct 14, 2006)

I prefer glass, as long as it is mineral or borofloat/pyrex. I tested some 1mm thick mineral glass I had by smacking them with a hammer. They dented before they broke, which took quite a few smacks to accomplish.

The 52.1x2mm mineral glass windows I had made (that 4sevens now sells) are very tough and I have heard no reports of them breaking. They have beveled edges which prevents them from catching on threading and chipping.

Some glass chips very easily. I had a UCL chip just by setting it into the bezel ring of my Pelican M6. I'd rather have something stronger than something that transmits 5% more light.

I think antireflective coated mineral glass is the way to go if you want every last bit of light to make its way out.


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## Anglepoise (Oct 14, 2006)

chevrofreak said:


> I prefer glass, as long as it is mineral or borofloat/pyrex. I tested some 1mm thick mineral glass I had by smacking them with a hammer. They dented before they broke, which took quite a few smacks to accomplish.
> 
> The 52.1x2mm mineral glass windows I had made (that 4sevens now sells) are very tough and I have heard no reports of them breaking. They have beveled edges which prevents them from catching on threading and chipping.
> 
> ...



I agree. I have just looked at UCL and it chips.

Do you have a recommended supplier of coated mineral glass in sizes around 16mm to 22 mm??


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## chevrofreak (Oct 14, 2006)

Anglepoise said:


> I agree. I have just looked at UCL and it chips.
> 
> Do you have a recommended supplier of coated mineral glass in sizes around 16mm to 22 mm??


 
I don't know of anyone that sells them aftermarket. 

Inova uses coated mineral glass in their lights though.


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## LuxLuthor (Oct 14, 2006)

I have not had any breaks with Borofloat lenses, but two UCL broke easily, and I will never buy them again. I need the glass over plastic for the heat demands. Where are these 4Sevens one at?


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## adirondackdestroyer (Oct 14, 2006)

Can the lens on a Surefire G2 be changed to a nice UCL glass lens? I noticed on flashlightlens.com they have an application chart and all the sizes for various lights. The G2 is listed as having a 28.8mm lens, and flashlightlens.com carries the UCL in the 28.8mm size, so I figured it was for modding a G2. Can anyone comfirm this? Does the lens on the G2 pop right out, or does it take some serious convinving to get it out of there. I hate how the G2 has a plastic lens but I really like everything else about it.


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## chevrofreak (Oct 15, 2006)

LuxLuthor said:


> Where are these 4Sevens one at?


 
http://fenix-store.com/index.php?cPath=25_26&osCsid=bd65d9b4515be28c2879d41ee5b94764


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## andrewwynn (Oct 15, 2006)

I'm going to be buying these exact lenses soon. very nice I love the finished edges!
-awr


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## NewBie (Oct 15, 2006)

soapy said:


> I'd always go coated optics if you are running a hot light. The extra 2% or so you get from the coated optics means less heat build-up.
> 
> Hard coated AR polycarbonate is probably the best, unless you go for the synthetic sapphire windows.
> 
> Thoughts?




The problem with standard (no AR) mineral glass or sapphire, is that it's losses are extremely high, due to it's high index of refraction.

You can loose an extra 13-20% of your light, just from using a standard mineral glass or sapphire windows. The proper coatings on them will put them within 1% of AR glass lenses.


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## 4sevens (Oct 15, 2006)

Here is an analysis done by burnt_retinas in AU.
He use a spectrum analysis on a UCL, Mineral glass lens, and the stock mag
polycarb lens.







Optical performance, obviously the UCL wins.
1. UCL
2. Mineral Glass
3. Polycarb

Scratch resistance:
1. Mineral Glass
2. UCL
3. Polycarb

Impact resistance:
1. Polycarb
2. Mineral Glass
3. UCL

I ship my mineral lens without any packaging  And they are unconditionally
guaranteed for a year. I've sold hundereds and have yet to have one return 
to me


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## NewBie (Oct 15, 2006)

That curve for the glass looks exaggerated. But I don't know the specific coatings and glass that is used in the UCL.

Typically, even for low cost AR coated glass, the transmission curves look like this, NOTE the SCALE on the side:






More info here:
http://www.uqgoptics.com/materials_commercial_ARCoatedGlass.asp


Normally mineral glass is worse than what was shown:






I suspect there may be some errors in the measurement setup?

.


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## Sub_Umbra (Oct 15, 2006)

Plastic windows may also be more adversely affected by corrosive chemicals or atmospheres.

AR coatings and some plastics may attenuate UV.


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## NewBie (Oct 15, 2006)

That is very true, Polycarbonate crazes when exposed to quite a number of chemicals.

When the data is layed over each other, and scaled properly, this is the result:


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## Burnt_Retinas (Oct 17, 2006)

Newbie,

The coated lens data you posted shows a peak around ~500nm as being ~99.35%. A further hump ending at 420nm is ~99.6%. My data had those two points at 97.8% and 97.09% respectively and the graph represents those values. I don’t understand how you conclude they are exaggerated results I got? They show the UCL as being worse!

The mineral glass I tested showed better results than the graph you showed. Same equipment, same test method, same baseline cal and check with no lens before getting data. Is the data for the mineral glass you posted from the manufacturer of the mineral glass I tested from 4-7’s? If not, it’s not worth even thinking about. If it is then I may re-test.

Would you like the data I gained from the equipment? It’s a lot better than the back-yard hack of overlaying of pictures and scaling them, then purporting them as fact. Just PM me with email, I don’t bite.

Chris


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## Bertrik (Oct 17, 2006)

I wonder if all the light reflected by the "lens" is actually lost. It is sent back into the flashlight reflector after all, so part of the light reflected by the lens gets another chance to get out (although I think part of the reflected light gets focused back onto the emitter).


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## GarageBoy (Oct 17, 2006)

On the G2, you need to remove the retainer ring with somesort of tool (improvise)


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## soapy (Oct 17, 2006)

Bertrik, yes, most will be lost as heat. The majority of the amount that gets bounced back will be reflected again (as your reflector is about 98%), but it will go back to the bulb, and probably turn to heat there. The fraction that is absorbed will turn to heat with very little exception.

Anyone know the refractive index of the glasses/plastics we are talking about here? It's probably about 1.5 to 1.66 for mineral glass (from 1.4890 for Albite, up to 1.89 for full lead), and polycarbonate (plexiglass) is 1.5, whilst Sapphire is 1.76.

Glass typically has about 4% reflection from each surface (interface), so about 8% will come back to the bulb without being converted to heat. At 540nm (green) we can see from the chart above that there is about 16% loss, so half the unpassed light is heat in the lense, and the other half gets bounced back to the bulb, where probably most is lost as heat.

Someone mentioned diamond. The refractive index of uncoated diamond is 2.417, so any light hitting at beyond 25 degrees will be Totally Internally Reflected back. This might mean you have some real issues with a diamond lense! However, it is very clear at IR wavelengths, so cooling will be far better. The beam would be tighter, too, with less side spill.


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## Slaro (Oct 17, 2006)

andrewwynn said:


> i've killed 3-4 UCL just from heat alone.. they are quite fragile..
> -awr



OK, I have a question. 

I want to use the UCL in the Mag85. Do you mean that this lens can just burst from the heat? Or are you talking about more heat than that? If so, I'm switching to the Borofloat lens. I've put a UCL lens in my MagCharger60 2 years ago and so far so good. No cracks. It runs perfect.


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## iamerror (Oct 17, 2006)

The Mag85 is close to the limit the UCL can handle. Most likely, using a UCL for this will be no problem. Much higher than this can be damaging.


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## Slaro (Oct 17, 2006)

Thanks iamerror. I was just wondering because I see that alot of people here put the UCL in the Mag85, but I wasn't sure. It could be a scary if the Lens blew out on me.


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## NewBie (Oct 18, 2006)

Burnt_Retinas said:


> Newbie,
> 
> The coated lens data you posted shows a peak around ~500nm as being ~99.35%. A further hump ending at 420nm is ~99.6%. My data had those two points at 97.8% and 97.09% respectively and the graph represents those values. I don’t understand how you conclude they are exaggerated results I got? They show the UCL as being worse!
> 
> ...




I'm just looking at some typical data of different materials from some manufacturer's datasheets and your results on the stuff you measured and wondering why there is so much difference.

If one zooms in on the picture, your hums on the 2 side AR glass are even backwards as compared to some 2 sided AR glass.

If things were only off a little, I would have expected similar curves for the 2 sided AR glass, just offset, or possibly exaggerated. Not curves that have nearly exactly opposite bumps in them.

I am just wondering why...chill man!









Typical data for 2 sided AR glass:







The manufacturer's source data is found here:
http://www.uqgoptics.com/materials_commercial_ARCoatedGlass.asp


During Gransee's calibrated integrating sphere tests at the lab he went to,
this was further borne out, when the lens of a HDS LED flashlight was replaced with mineral glass, during Gransee's calibrated integrating sphere tests. It was found that the mineral glass alone caused an additional 13% of loss.

Dunno, just wondering why the differences. Maybe I should just order some of the actual lenses and have them tested.


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## Slaro (Oct 18, 2006)

NewBie, Keep up the good work. You always have valuable information for us. I read your information page on Lithiums. WOW Thanks!


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## chevrofreak (Oct 18, 2006)

Definately not very precise, but I held a flashlight infront of my light meter and took a measurement, then put one of these Mag C/D sized mineral glass windows infront of the light and it only dropped in output by about 8%

I hope there are some more scientific tests done on these. I'd try it myself with my home made integrating sphere, but the opening isn't big enough for a Mag C/D head to fit in.


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## Lit Up (Oct 19, 2006)

Plastic is good if the light is gonna get beat up, but there's definitely a life span on them.

For instance:
I recently convinced a (non-flashaholic) co-worker to try out the MagLED drop-in. He bought one and handed me his 3D Maglite; it was a red and silver one (because of all the adnodizing chipped off) He proceeded to tell me that he bought it around 1990. 

Without really checking it out I flicked the switch and upon pointing it around, I immediately thought that it looked rather dim compared to mine and others I've seen. Especially since the 3D is supposed to be the brightest of the bunch. My 2D would've even beat it. So I turned it off and happened to look at the lens... Oh my God! It was the original lens too. Looked like cats have been taking tap dancing lessons on it for the past decade. It was so scarred up you could barely see the LED in it.

I told him I'd get him another lens next time I make a flashlight purchase.


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## adirondackdestroyer (Oct 19, 2006)

Lit Up said:


> . Looked like cats have been taking tap dancing lessons on it for the past decade. It was so scarred up you could barely see the LED in it.


 


:laughing: :laughing: Pretty funny stuff, but I know exactly what you mean. I've seen some old Mags that have lens scratched so badly it makes me sick. 
Why don't you hook your friend up with a Mineral Glass lens from fenix-store.com. They are 3 for $12, so you can give him one and have one for yourself and an extra. He will be very impressed with the upgrade in output and the fact that it won't scratch like his old one.


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## Luna (Oct 19, 2006)

chevrofreak said:


> Definately not very precise, but I held a flashlight infront of my light meter and took a measurement, then put one of these Mag C/D sized mineral glass windows infront of the light and it only dropped in output by about 8%.




I don't see why that would not be precise as the loss should be the same.



On this note, and thinking aloud, is it possible that a semireflective window causes the IS to register more. Kinda like the reflective nature of a cat's eye.


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## etc (Nov 16, 2006)

Is that a leading question? 

I like lenses from 4Sevens, I got 3 MagLites which have them. 

I don't know that they are _the_ best but in that price range, certainly. (For the best you have to go for photo lenses as has been pointed out, probably an order of magnitude higher cost)


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## tron3 (Nov 17, 2006)

http://www.flashlightlens.com/

Nothing like glass, period. Even soda tastes better from a glass bottle, than plastic, or a can.

If it's not glass, it won't pass.


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## chesterqw (Nov 18, 2006)

so from what i see in the graphs posted, mineral glass doesn't let as much light pass through as ar coated lens(around 15% less?)

but it is stronger then those ar coated lens and less fragile too right?
and i heard those AR coating are so fragile that it will be damaged by just wiping them?


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## AzN1337c0d3r (Sep 2, 2008)

etc said:


> Is that a leading question?
> 
> I like lenses from 4Sevens, I got 3 MagLites which have them.
> 
> I don't know that they are _the_ best but in that price range, certainly. (For the best you have to go for photo lenses as has been pointed out, probably an order of magnitude higher cost)



Photo lenses probably do not do well against the heat of a hotwire bulb.


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## 4sevens (Sep 2, 2008)

AzN1337c0d3r said:


> Photo lenses probably do not do well against the heat of a hotwire bulb.


Wow a thread resurrected after almost two years!
The lenses I sold were mineral glass lenses. They were not photo lenses.
I even had a guarantee that if anyone broke theirs I'd replace them.
I have yet to have one come back. thousands were sold.


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## Illum (Sep 2, 2008)

AzN1337c0d3r said:


> Photo lenses probably do not do well against the heat of a hotwire bulb.



anything higher than 30Ws I'm pretty sure the answer of that will become very obvious


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## [email protected] (Sep 2, 2008)

Outdated thread... :sleepy:


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