Lens Thickness

350xfire · Jun 29, 2010

Guys, I am playing around with some MagLites and I know I can stack 2 of the DX lenses in there. Question is, how deep have you guys taken your dual DX lens Mags? Pack, I know you will have some say on this...

What I want to do is to have some custom cut lenses that will be the thickness of 2 DX lenses out of boro glass. I want to be able to hit 300-350' without cracking and I am wondering whether a lens that is a bit larger than 1/8" will stand up to that psi.

Thanks

SmurfTacular · Jun 29, 2010

I would also like to know this.

kingofwylietx · Jun 29, 2010

If you don't get an answer, you can try to rig a test. 350' of water is about 150psi. If you can put something together that will hold the pressure (and do it safely) and adapt to the Mag head. You could even go a step further to see just how much pressure it can withstand before breaking.

Good luck

350xfire · Jun 30, 2010

kingofwylietx said:
If you don't get an answer, you can try to rig a test. 350' of water is about 150psi. If you can put something together that will hold the pressure (and do it safely) and adapt to the Mag head. You could even go a step further to see just how much pressure it can withstand before breaking.

Good luck

Working on it... Just wanted to see if anyone knew the answer before wasting my time. I will try a test with stock o-rings and see what happens. I just cut the barrel and fitted it. Just need the JB Weld to secure it and I'll be ready.

Thanks

gcbryan · Jun 30, 2010

350xfire said:
Working on it... Just wanted to see if anyone knew the answer before wasting my time. I will try a test with stock o-rings and see what happens. I just cut the barrel and fitted it. Just need the JB Weld to secure it and I'll be ready.

Thanks

Unless my math is off it's more like 171 psi (you have to include the surface pressure).

That's also just static pressure. Dynamic pressure would be greater.

You are talking about 3 mil thickness it sounds like? My guess is that it's right on the edge for a static test. I would prefer 5 mil at least for something the size (diameter) of a mag at 350 fsw.

It will probably work however if you are careful.

Packhorse · Jun 30, 2010

Whats with all the imperial measurements guys?
Time to get with the metric system I think!!!
100 meters depth is 10 bar pressure + 1 bar atmospheric.
gcbryan.....no you dont have to take into account surface pressure since the internal pressure is also 1 bar assuming it was sealed at sea level.

Now as for the DX lenses. I used 2 back to back for a little while. I think I got to 40 meters or so but I never had a great deal of confidence with it. An acrylic lens of the same thickness should be better ( in my mind at least) since it will change shape with the pressure while glass will just shatter.

I have used a stock maglite lens ( polycarbonate?) to 40 meters ( 4 bar/58psi) pressure before it went concave enough to press against a MR16 lamp and smash it. Lens remained intact.

I am currently using 3.8mm ( I think) acrylic lenses and have not had issues with any of my builds. I have had mine to 57 meters and one has been to 65 meters.

Sorry there is nothing scientific in there but it is tried and tested.
If I was building a light for 100 meter dives ( not just rated to 100 meters) I'd be looking at 8-10mm glass.

lucca brassi · Jun 30, 2010

I have only one Maglite lamp in the car ..so I don't use it for diving and of course I don't buy lens on Dx.

But If someone is interested how much load can resist these lens ( depends also from holder situation inside enclocure ) I can measure breaking point (tenssion trough load) on such machine

Packhorse · Jun 30, 2010

One more thing about doubling up glass lenses. They are not perfectly flat. When you put two together and tighten the bezel down you may notice that there is some distortion of the lens and this shows as a "rainbow effect". If you swap the lenses around and or turn one or both around this can be reduced or eliminated.
I would think that a single lens would be stringer than 2 half thickness lenses.

DaYerk · Jun 30, 2010

It`s a bit OT, but has anybody tried to use a plastic lens like the Ledil Cute 4 in direct contact with water?

I think this could work instead of a glass lens.

baywatch106 · Jun 30, 2010

so do you guys epoxy your lens to the beze or use slightly larger orings for the lens?

350xfire · Jun 30, 2010

Packhorse said:
Whats with all the imperial measurements guys?
Time to get with the metric system I think!!!
100 meters depth is 10 bar pressure + 1 bar atmospheric.
gcbryan.....no you dont have to take into account surface pressure since the internal pressure is also 1 bar assuming it was sealed at sea level.

Now as for the DX lenses. I used 2 back to back for a little while. I think I got to 40 meters or so but I never had a great deal of confidence with it. An acrylic lens of the same thickness should be better ( in my mind at least) since it will change shape with the pressure while glass will just shatter.

I have used a stock maglite lens ( polycarbonate?) to 40 meters ( 4 bar/58psi) pressure before it went concave enough to press against a MR16 lamp and smash it. Lens remained intact.

I am currently using 3.8mm ( I think) acrylic lenses and have not had issues with any of my builds. I have had mine to 57 meters and one has been to 65 meters.

Sorry there is nothing scientific in there but it is tried and tested.
If I was building a light for 100 meter dives ( not just rated to 100 meters) I'd be looking at 8-10mm glass.

Hey I'm in the USA!! The land of Imperial measurements. Still one of the very few that use it.

Looks like 4-5 mm is the biggest that can fit in a Mag, unless someone knows of a way to fit 8mm in there.
Thanks

350xfire · Jun 30, 2010

baywatch106 said:
so do you guys epoxy your lens to the beze or use slightly larger orings for the lens?

Don;t epoxy, I have not had good results with it. At least the normal store stuff is not water proof. You may need to get some special type of epoxy. I have had good luck with the black RTV silicone.

kingofwylietx · Jun 30, 2010

gcbryan said:
Unless my math is off it's more like 171 psi (you have to include the surface pressure).

That's also just static pressure. Dynamic pressure would be greater.

You are talking about 3 mil thickness it sounds like? My guess is that it's right on the edge for a static test. I would prefer 5 mil at least for something the size (diameter) of a mag at 350 fsw.

It will probably work however if you are careful.

Good call about adding surface pressure, I was only focusing on the water depth.

350xfire · Jun 30, 2010

kingofwylietx said:
Good call about adding surface pressure, I was only focusing on the water depth.

Actually, not a good call. Like Pack said, the surface pressure is equalized on both sides of the lens at the surface (assuming the light was assembled at the surface) so not necessary to add it.

kingofwylietx · Jun 30, 2010

350xfire said:
Actually, not a good call. Like Pack said, the surface pressure is equalized on both sides of the lens at the surface (assuming the light was assembled at the surface) so not necessary to add it.

Very true. Another thing to consider as a safety margin is that if the light seals before you complete the assembly (assumed threaded housing), you may get a positive pressure inside the housing. This pressure will increase as heat is generated, which will offset some outside pressure.

SUBjohan · Jun 30, 2010

kingofwylietx said:
This pressure will increase as heat is generated, which will offset some outside pressure.

No the outside pressure will not be changed, only the pressure differance changes.

Greetz Johan

gcbryan · Jun 30, 2010

Yeah, I wasn't paying attention on that one.

The W200 at 30 mm has a 6 mm lens and I think it would handle 350 feet (the lens anyway).

On another board an engineer did a rough calc for glass thickness for a 50 mm lens and came up with 5 mm for the 250 fsw range.

Otherwise, I haven't seen any numbers. I know 1mm will work for a 30mm lens at 100 fsw if you don't bump into the lens but it's not optimal and I know 3 mil will work at 200 fsw with the same caveats. This is just from experience. Thicker is always better however.

Regarding epoxy, I haven't used epoxy to hold in the front glass but I have used it (marine grade epoxy) to seal a hole in the tail cap and it is waterproof in that application.

Packhorse · Jun 30, 2010

kingofwylietx said:
Very true. Another thing to consider as a safety margin is that if the light seals before you complete the assembly (assumed threaded housing), you may get a positive pressure inside the housing. This pressure will increase as heat is generated, which will offset some outside pressure.

True. If you manage to heat the interior of the light to 270 deg C you can get an extra 10 meters depth rating! While screwing in the head and compressing the internal gas may get you another meter or so!

kingofwylietx · Jun 30, 2010

Packhorse said:
True. If you manage to heat the interior of the light to 270 deg C you can get an extra 10 meters depth rating! While screwing in the head and compressing the internal gas may get you another meter or so!

LOL....that's why I said 'some' and not 'a lot'.

Klem · Jul 1, 2010

A dive buddy last year bounced to 105Mts recently with a modified Maglite using a 6mm Perspex lens, and the torch did not leak.

No O rings in the head section; 6mm Lens is glued to the bezel with 2-part epoxy putty (Selleys, Aqua Knead-it), then bezel screwed onto Maglite head waterproofed with silicone liquid gasket sealant (Silastic). A 6 mm Lens is too thick to use an O ring as the bezel when tight does not extend past the threads to cover an O ring. The Silastic seals in the threads so the bezel can sit prouder than an O ring will allow.

If you still wanted to use an O ring to seal you can still use a thick lens, by stepping it. Cut a 52mm disk for the lens, then spin it in a lathe and cut a 47mm step, say 2mm thick (leaving 4mm for lathe jaws to grip). That way some of your lens can extend forward of the bezel by a couple of millimeters. You can then fill the forward wedge gap created with more glue for added strength and seal. A 6mm lens will then be 4mm inside the bezel and protrude 2mm to the front of it.

Lens Thickness

Flashlight Enthusiast

Enlightened

Enlightened

Flashlight Enthusiast

Flashlight Enthusiast

Flashlight Enthusiast

Enlightened

Flashlight Enthusiast

Newly Enlightened

Newly Enlightened

Flashlight Enthusiast

Flashlight Enthusiast

Enlightened

Flashlight Enthusiast

Enlightened

Newly Enlightened

Flashlight Enthusiast

Flashlight Enthusiast

Enlightened

Enlightened

Similar threads