Lens thickness

[Little Goat]

I know that the information is out there in a dozen or more threads but I was thinking of pulling together a general thread to get it all in one. I know what you are thinking, "Who is this little Goat guy?" I've been a lurker for roughly a year now. I've been researching information on DIY dive gear and the light is one that can be done with relative ease. So onto the meat and potatoes.

What lens thickness do you recommend for what diameter lens? (For example:
52mm Dia with a thickness of 3mm.) I'll keep the recommendations posted as edits in this thread.

***FYI, the reason to start this thread was due to the fact that there was a lot of conflicting information out there on the web-tubes***

Here is what we have so far:
Stock Maglite Lens to 40m [103 ft] (42m [136 ft] was failure)
52mm [2 in] X 4mm [5/32 in] Acrylic tested to 57m [187 ft] without failure.

 

[gcbryan]

Good idea and I'd personally like to see a thread about all the various aspects of building dive lights,ie best switching methods/lens/sealing methods but so for it seems to me this forum is more about a few people building their lights and others who want to buy them.

If I knew the answer to your question regarding lens I would post the answer but unfortunately I'm looking for the same info myself!

I'd be interested in a thread discussing all aspects of designing a robust state of the art hand held light just as a continuing point of reference/ideas.

It seems like the led/battery part of the equation is the easy part and there is plenty of information there. The actual underwater container and it's technology is where there is much less info and potentially more variety in it's implementation.

 

[Packhorse]

... but so for it seems to me this forum is more about a few people building their lights and others who want to buy them..

I think that is a bit unfair.

Perhaps you need to ask the questions if you want the answers.


As for the OP question...

That all depends.
Truth is I dont know the answer. There should be information out there that will tell you if you look hard enough.
What you really need to take into account is the lens material.

I used a stock Maglite lens for a while. It failed at 42meters by going concave and pressing against a halogen MR16 front lens with enough force to smash it. It didnt leak a drop.

I then changed to a 4mm ( ?) acrylic lens. Have had it to 57 meters with out issue. I think it would be good to 100meters but I dont know.

Glass lenses probably have a lower pressure rating but maybe a toughened glass lens may out perform acrylic.

Polycarbonate may be worth looking at ( Maglite lens is PC).

My advice... Over engineer if you can.

 

[DM51]

My advice... Over engineer if you can.

Good advice, IMO. Don't worry about the light becoming too large or heavy. What seems like a big clunker out of the water is fine when diving, especially if you have to wear gloves.

 

[wquiles]

I think that is a bit unfair.

+1. I have never been in any forum in which members share so freely information as to how to build them, the technology behind them, comparisons, etc.. There are LOTS of very valuable information in this forum about any/all topics regarding flashlights an illumination, from battery chemistry, to Titanium alloys, to how to properly seal a lens for water resistance, to what is the start of the art LED about to come out, etc. - simply amazing

Back on topic ...

Javier from Barbolight stated that they tested their 2 inch diameter 5mm Polycarbonate lens at 200meters and that there was less than 0.5mm deflection at that pressure, so that and the experience from Packhorse lets me to believe that something between 4mm and 5mm (at 2 inch dia) is definitely "enough" for most recreational diving. Javier also stated that he prefered the poli lens due to its higher impact resistance, even if "suffered" in terms of how easily it is to scratch.

I have looked at ready-cut glass from flashlightlens (lens specifications) and the stock a relatively thick glass lens at 2.84mm, but I don't know if that would be "enough" even in a Mag head, specially since Borofloat would probably be a better glass to for "rough" use ( about glass types ). I also recently got a request for consideration of a diving light for a Mag in which the customer wanted a 1/4" thick glass lens (6.35mm), and he was convinced that he needed that much in terms of ensuring that the lens will work properly, so that could potentially also be considered "over-designed", but stout!.

For those familiar with the Star Trek movies, I always remember from the movie "The Voyage Home (1986)" in which they are at a plastics factory trying to "borrow" glass to contain the whales. In that dialogue, Scottie asks the plant's engineer something like "what is the thickness necessary for [some plastic] to withstand [some enormous watter pressure] and the the engineer says something like: "easy, that would be 6 (or maybe 12?) inches - we even carry it on stock". I wish it were "that" easy for us to find out what we need to build diving lights :devil:

OK, sorry about the Start Trek rant ...

Will

 

[gcbryan]

No offense was meant by that comment by the way. It was just my general first impression of this (dive lights) sub forum. I'm willing to concede if may be inaccurate.

I just meant that so far it has seemed to be more about a particular build or two rather than about in depth discussions of many different ideas related to dive lights.

I think it's a good sub forum and I'm sure people can get out of it what they want to get out of it...including me...so again no offense was meant.

I think that is a bit unfair.

Perhaps you need to ask the questions if you want the answers.

 

[Little Goat]

My advice... Over engineer if you can.

I totally agree but at the same time I want to make sure that I am not working with a 10mm thick lens if I don't have to. There is a huge price break between thicknesses of materials.


Anyone use borosilicate glass or polycarb? Composite lenses?


I had a thought last night: for the materials that are "scratch prone" would it make sense to put in a scratch resistant shield? For example, use a thin (read ~1mm) lens placed on the water side of the dive torch that would be sacrificial? Just an idea... I don't mean to hijack the thread but an idea none the less......

 

[Little Goat]

My advice... Over engineer if you can.

I agree but at the same time I don't want a canister light half the size of my tanks...

I had an idea last night. What if you put some scratch resistant sacrificial lens in front of a strong but scratch prone lens? The sacrificial one would be thin (read ~1mm) and made of a scratch resistant material (any ideas?)...

 

[gcbryan]

Also, I wonder how big a deal it really is to have a little scratch on a polycarbonate lens in a dive light application?

All my cheaper dive lights have plastic lens and it's not a problem. I think it's more important to have a robust lens.

I totally agree but at the same time I want to make sure that I am not working with a 10mm thick lens if I don't have to. There is a huge price break between thicknesses of materials.


Anyone use borosilicate glass or polycarb? Composite lenses?


I had a thought last night: for the materials that are "scratch prone" would it make sense to put in a scratch resistant shield? For example, use a thin (read ~1mm) lens placed on the water side of the dive torch that would be sacrificial? Just an idea... I don't mean to hijack the thread but an idea none the less......

 

[Packhorse]

When I say over engineer it I was referring to the lens. Sure over engineer the rest too but a maglite is over engineered for the purpose. 5mm Delrin is more than thick enough for a cannister.
Green force use 10mm thick lenses in their 50mm heads.
The W200 uses a 20mm x 6 mm lens.

I use acrylic in my lights as its cheap to replace if it gets scratched and less smash resistant than glass.

If I was to use glass I would want it to be at least 5mm thick boro glass.

 

[350xfire]

I use 3/16-1/4" thick boro glass in my can lights. Have had it presured to 265 feet equivalent with no problems.

Whatever you do, don't go buy jeweler's glass 3/16"... Had to of them crack!!!

BTW, anyone know where I can get custom cuts of boro glass. I get mine thorugh McMasters, but they onle go from 1 3/4-2"... I need like 1 7/8".

Thanks

 

[whitenoise]

For those familiar with the Star Trek movies, I always remember from the movie "The Voyage Home (1986)" in which they are at a plastics factory trying to "borrow" glass to contain the whales. In that dialogue, Scottie asks the plant's engineer something like "what is the thickness necessary for [some plastic] to withstand [some enormous watter pressure] and the the engineer says something like: "easy, that would be 6 (or maybe 12?) inches - we even carry it on stock". I wish it were "that" easy for us to find out what we need to build diving lights :devil:

Heh, I remember that film and that scene. I think it was 12 inches, and Scottie says something like "Aye, what if I could show you something that would do the same job but be only one inch thick, would that be worth something to you?". That's what you need!