# H51/H51w mod: flip-away diffuser



## tedh (Jan 29, 2011)

I thought I had a simple need: I wanted a small, neutral white, regulated, single AA headlamp which could easily be switched between flood and spot. The Zebralight H51w seemed nearly perfect, except for needing to buy two lights, one for flood, one for spot. So, I built a diffuser:
































Construction notes: 



The diffuser is a Fenix AD401. I cut off 5.4 mm of the diffuser collar, on the side away from the hinge. By sliding the collar snugly against the lens mount of the H51w, the diffuser is centered on the H51w lens, as can be seen in the following photo. When in use, the diffuser is rotated 270 degrees away from what would be its normal diffusing position on a typical flashlight. 










Note the diffuser did not sit flat against the outer flange of the H51 lens. To prevent glare from this gap, I glued a piece of thin cord around the outer circumference of the diffuser. I further reduced glare by painting the clear plastic edge of the diffuser. 



So far, it's working very well. No problems with glare. The diffuser fits snugly against the lens when in use, but also lies flush against the H51 body when not in use. 



Beamshots:

















The diffusion pattern has more artifacts than are visible in the photograph, but nothing distracting in normal use. 



Next steps:



1. The optical quality of the diffuser is only fair. It was also inexpensive, so I didn''t expect stunning quality. I plan to drill out the plastic in the center of the diffuser and glue in a higher-quality diffusing lens, perhaps something from flashlightlens. Can anyone suggest a good source for ground-glass discs? 



2. I thought the the diffuser might tend to swing away from the H51 lens, but so far it has been staying in place. Nonetheless, I will probably install some small magnets to hold the diffuser snugly against the lens. 



The headband mount, visible in a few pictures, deserves a brief explanation. I removed the elastic headband from the silicone holder, and replaced it with the string retractor portion of a Petzl Zipka headlamp. It's not as comfortable as the elastic band, but it's easier to carry in a pocket. Doesn't bounce as much as the stock version, either. 



I'm quite happy with the outcome, and it should be an easy mod for anyone who can't decide between the flood and normal versions of the H51. 



Ted


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## foxx (Mar 22, 2011)

Hi there!
Unfortunately the original thread was lost.
Any updates/ideas to the zebra diffuser?


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## tedh (Mar 23, 2011)

The thread was lost, but now it's back! Thanks to whoever did that...or was it just lurking deep in the list of threads? 

Anyways, no, I haven't done much more with the project. I've been using the headlamp, flipping the diffuser back and forth as necessary, and I'm pleased with the results. It definitely adds utility. 

I did order a few more Fenix diffusers, and the design has changed since the version you see above. The collar to attach the diffuser to the light is now black plastic, and thinner. I would have to tear the current diffuser off the light to be sure, but I think the diffuser will fit flush against the light without the blue string "gasket". I'll probably give it a shot down the road. It's a case of finding the time. 

I also want to try putting a similar diffuser on the Spark ST5. 

Ted


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## StandardBattery (Jul 8, 2011)

Great Idea. Until they can make some electronicly controlled lens for diffusion of clear, the best EDC is to have a light with some throw incase you need it outside, and a diffuser for indoors. The problem is most add on diffusers don't look so great, come completly off so they can get lost, or are on the large size like the Surefire flip away ones. You're mod turned out very nice and is quite compact. Great Job!

Are you aware of the DC Fix diffusion film being sold on the marketplace. All reports are is it is very high quality with minimal light loss. You might consider a clear lens with this diffusion film.


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## gcbryan (Jul 8, 2011)

StandardBattery said:


> Great Idea. Until they can make some electronicly controlled lens for diffusion of clear, the best EDC is to have a light with some throw incase you need it outside, and a diffuser for indoors. The problem is most add on diffusers don't look so great, come completly off so they can get lost, or are on the large size like the Surefire flip away ones. You're mod turned out very nice and is quite compact. Great Job!
> 
> Are you aware of the DC Fix diffusion film being sold on the marketplace. All reports are is it is very high quality with minimal light loss. You might consider a clear lens with this diffusion film.


 
Have you ever used any? I've thought about something like that but you still have the issue of taking it on and off...not convenient.


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## StandardBattery (Jul 9, 2011)

gcbryan said:


> Have you ever used any? I've thought about something like that but you still have the issue of taking it on and off...not convenient.


 
I've just bought some for some tests on some lights that really need it. The first couple will be permanent mods, but some one used transparancy film then the difiuser appled, so you can put it on and off quickly on some lights that have enough of a ridge on the bezel.

I was really refering to the OP though since he has solved the removable problem with his swing out lens set up.


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## tedh (Jul 10, 2011)

Thanks for your comments, glad you like the mod. I had some fun doing it, and it definitely works. Yes, I've heard of DC Fix, and I've been thinking about getting some, thanks for the suggestion. It seems pretty thin, and would probably have to be combined with a clear lens. I also considered other frosted lenses (for example, from Edmund Scientific). Even better, it now seems Spark is making their frosted lenses available as a spare part. By any chance have you compared the Spark frosted lens to DC fix? I may post that question as a separate thread, in case anyone else has done the comparison. 

Ted


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## gcbryan (Jul 10, 2011)

I read somewhere where someone found that the wrapper from Kraft Singles (cheese wrapper) was perfect...diffused a bit while still allowing a hot spot with throw.

Maybe I can get everyone on CPF buying cheese wrappers from me


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## tedh (Jul 10, 2011)

Ye Olde CPF Marketplace and Sandwich Shoppe?!? Cheese wrappers will also probably give a nice warm tint!

Ted


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## StandardBattery (Jul 10, 2011)

tedh said:


> Thanks for your comments, glad you like the mod. I had some fun doing it, and it definitely works. Yes, I've heard of DC Fix, and I've been thinking about getting some, thanks for the suggestion. It seems pretty thin, and would probably have to be combined with a clear lens. I also considered other frosted lenses (for example, from Edmund Scientific). Even better, it now seems Spark is making their frosted lenses available as a spare part. By any chance have you compared the Spark frosted lens to DC fix? I may post that question as a separate thread, in case anyone else has done the comparison.
> 
> Ted


I'm still waiting for my DC fix, but if you read the sales thread you will see some interesting applications, and everyone is happy with it. Someone there compared it to the ZebraLight frosted lens which might be close to the Spark. I would post your question to that thread and see if you get a response. If the frosted lens is good though, using that would be pretty nice and then you would not need to get a clear lens. Maybe frosted lens and DC Fix...

*Update:* I see you got your question answered in a thread here; maybe that is what I saw in the sales thread...


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## tedh (Jul 10, 2011)

Thanks, StandardBattery. I'll look at the sales thread for additional info, good suggestion. 

Ted


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## gcbryan (Jul 10, 2011)

I think I'm figuring out what the DCfix vs Scotch tape argument is all about...different people are looking for different things.

Every time I mention my good luck with Scotch tape someone mentions how great DCfix is. They say it lets more light through. I look at Scotch tape and don't see how that is possible.

Now I see that DCfix diffuses as much as a frosted lens. That's great if that was what someone was looking for. When I use Scotch tape on a light for hiking I want it somewhat diffused but I still want a narrower directed beam with some throw. To do this you need less diffusion than frosted glass therefore DCfix would not be the right material (for me).

I already have the H51f so DCfix would not apply as I already have a frosted lens. I've wondered what it would be like to have the H51 and lightly diffuse it so it still has some throw. DCfix would not be the right material for this. Scotch tape would still leave a directed beam. However I'd rather have the modification on the other side of the glass and this isn't possible with Zebralight since you can't take it apart.

So, it would be more accurate I'm finding out to consider that DCfix produces more diffusion than Scotch tape and Scotch tape works better when you still want a directed beam.

I don't get the attraction of Press and Seal. I have some and have experimented with it extensively and it doesn't diffuse evenly. It results in a diffusion that is more vertical (or horizontal depending on how you are holding the light). To me Press and Seal is not a solution for anything other than the fact that it isn't as sticky as Scotch Tape but it also doesn't work as well as Scotch tape.


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## robostudent5000 (Jul 11, 2011)

i think that there are two different factors involved in diffusion, at least as it is being discussed here. there's dispersion and there's opacity. there are diffusers that work by letting maximum light through the material but disperse the output light at a wide angle. there are diffusers that are opague and achieve diffusion through blocking a good chunk of light output. 

i haven't tried DC Fix, but based on everything i've seen and read, it seems to be better at dispersing light than other opaque materials. this may account for it's ability to test at high transmission rates and still produce a minimal hotspot by scattering the light that gets through and changing it's pattern. 

scotch tape, i know from personal experience, causes a lot of light loss but doesn't seem to disperse the light that much as the beam pattern seems to stay closer to the original. this may account for it's ability to maintain a hotspot (albeit muted) while having poor transmission rates.

i'm not sure where Press'n Seal falls in that spectrum. i know people have issues with it, but it actually works great for certain applications. You need two layers applied at right angles to each other and it causes a healthy loss of output. but the fact that it's big and cheap can come in handy. i use it to diffuse my DIY LED floor lamps and i can't think of another material that would work as well as cost effectively. 

Press'n Seal does leave a sticky persistent residue that i've only been able to remove with acetone, so it should not be used on plastics.


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## gcbryan (Jul 11, 2011)

robostudent5000 said:


> i think that there are two different factors involved in diffusion, at least as it is being discussed here. there's dispersion and there's opacity. there are diffusers that work by letting maximum light through the material but disperse the output light at a wide angle. there are diffusers that are opague and achieve diffusion through blocking a good chunk of light output.
> 
> i haven't tried DC Fix, but based on everything i've seen and read, it seems to be better at dispersing light than other opaque materials. this may account for it's ability to test at high transmission rates and still produce a minimal hotspot by scattering the light that gets through and changing it's pattern.
> 
> ...



I don't think Scotch tape reduces the light output like Press n Seal. I don't have any personal experience with DCfix but unless it sticks as well as tape it's not appropriate for many applications anyway (is it sticky like tape)?

With a flashlight I can take the bezel off and rather than Scotch tape I generally use some diffusion material that I happen to have. With my headlamps I can't get behind the lens so Scotch tape has the effect I want to stay put better than most of the other methods. If done right it's also invisible. No one would know that I had it on my Storm. I've also tried up the Storm with and without the tape and I can't see a lot of difference in turns of reduced output or reduced throw. There is some of course but the throw is because of the diffusion obviously. When you diffuse something it's hard to tell if the output was reduced because the beam was redirected.

I just find it hard to believe that DCfix has magical properties that no other diffusion material has.


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## robostudent5000 (Jul 11, 2011)

DC Fix is adhesive backed. i was thinking of getting some for my bathroom windows, which is actually their intended use. it's supposed to stick on and peel off cleanly and it's also UV resistant according to the dealer (Berlin Wallpaper, not Phaserburn).

i remember there was a thread where selfbuilt did some tests on a bunch of diffusion material... let me see if i can find it.

found it. i'm not sure if that's the original thread, but it has the test results there. i'll quote the relevant part:



> Test result from selfbuilt, done with Olight M20
> 
> Clear glass: 84.2 (reference)
> d-c-fix: 81.5 (3.2% loss)
> ...



i don't know what kind of frosted scotch tape he used, and i'm pretty sure that different brands of frosted tape have varying diffusion properties (e.g. i have some tape right now that has a mildly prismatic effect similar to Press'n Seal). so i don't know if your experiences with frosted tape will mesh with selfbuilt's test results. but based on his results, DC Fix doesn't seem that bad.


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## gcbryan (Jul 11, 2011)

robostudent5000 said:


> DC Fix is adhesive backed. i was thinking of getting some for my bathroom windows, which is actually their intended use. it's supposed to stick on and peel off cleanly and it's also UV resistant according to the dealer (Berlin Wallpaper, not Phaserburn).
> 
> i remember there was a thread where selfbuilt did some tests on a bunch of diffusion material... let me see if i can find it.
> 
> ...



Thanks for the info. It doesn't seem that bad and if I'm looking for another alternative to some diffusion material I have I might consider it. When I'm using Scotch tape however I'm not going for the effect that DCfix offers (frosting). I use it when I still want throw but can live with less throw and a nicer beam. If I'm going for the flood look then I generally don't use Scotch tape but rather use some of my very limited supply of diffusion material. I did use two pieces of tape on the EOS to eliminate the tunnel effect so I might as well have used DCfix and would if I'd had any.


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## tedh (Jul 11, 2011)

rs5k, nice find on the post, that's helpful. I'm surprised the Olight diffuser had such a high loss rate. A bit disappointing. 

Ted


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## gcbryan (Jul 13, 2011)

Hey Ted, I just received my diffuser (with the black plastic collar) and I'm playing around with my H51f. The H51f doesn't need another diffuser but I also have the H51 coming at the end of the week.

Anyway. It looks like a nice idea but I'll have to work with it a bit. What did you do to make the collar fit the H51 body tube? The collar is larger than the tube. I guess the choices are to build up the tube under the collar or break the collar, take some material out, and try to glue it back together.

Yours looks a bit different than mine (in additional to the blue paint).


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## tedh (Jul 14, 2011)

Yes, Fenix changed the design of their diffuser. On mine, the collar was clear plastic; as you noted, they have now switched to a thinner black plastic. I have not yet figured out a way to get the new collar to fit, but that's primarily because I'm still using the older collar design. I cut the black collar to see how it might fit, and it looks like it could work. I'll be curious to see what your experiments yield. I'm still obsessing on the right diffuser material. 

Ted


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## gcbryan (Jul 14, 2011)

Yeah, since the diffuser material isn't great I'm not going to do anything permanent or that would potentially mess up my light.

I may decide that I don't need a diffuser since I'll have both the H51 and the H51f.

However I did cut out a few mm out of the collar on the side (obviously) opposite the hinge. Instead of worrying about trying to glue it back together I decided to take out more than necessary thus making it more like a clip. I'm going to wrap a bit of pipe fitting tape to protect the body of the light and then put the collar on and then when its tight use a long strip of (thin) electrician's tape to hold the collar together. If I need to do something with the gap between the diffuser and the light head (where you glued string) I'll glue on an o-ring.

If doing any of this is going to make the light not fit correct (and rotate) in the silicone holder on the headband or if having the diffuser loosely on the light is going to make the light less rugged in my pack I'll just not use it.

I've played around a bit with the H51f which doesn't need it of course. The H51 doesn't arrive until Thursday or Friday.

The diffuser was cheap (shipping was free) so I got it just to play with in case it turned out to be useful.


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## turboslug (Jul 14, 2011)

This is pretty neat. Very ingenuitive! This gives me a great idea for one of my lights. I just might have to steel your idea. I think you should consider developing a prototype for remarketing commercially. I am sure it would sell, I would buy one. Thank you for posting.


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## gcbryan (Jul 14, 2011)

Ted, one more questions...what is that white stuff between the collar and the headlamp head? Is that caulk to fit the collar to the head?


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## tedh (Jul 14, 2011)

gcbryan, one of the advantages to the new Fenix design, with its thinner collar, is you may not need a "gasket" (blue cord in my prototype) like I did. I suspect a the right number of turns of electrical tape around the body of the light will provide an exact fit, so the diffuser lies flat on the bezel. I didn't have any trouble putting the light in the silicone holder, it wasn't an issue at all. The white stuff is 3M Ultra Flex. It's a two part urethane adhesive. You mix it like epoxy, but it dries flexible. It's basically used for what you said, caulk to hold the collar in the right position relative to the head. 

Turboslug, go for it! And post a picture of what you did, I'll be curious how your diffuser comes out!

Ted


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## gcbryan (Jul 15, 2011)

I got my H51 today. I haven't had a chance to use it at night yet but I'm pleased so far. It has a hot spot (of course) but isn't harsh looking...good OP reflector I guess.

I rigged up something with the flip diffuser. I am not sure at all that I want to leave it on as everything I did can be undone without messing up the finish on the headlamp. The diffusion effect could be smoother.

I used an o-ring around the body just next to the head as a spacer and then clipped the collar on and held it in place with thin strips of electrical tape. I used plumbers pipe fitting tape on this portion of the body tube as protection and to build it up a bit since there is a ridge there.

I can still slide or position the diffuser to get to the proper spot. It seems the diffuser is slightly too small and I get a bit of light coming out due to size. I also can't get it flat and didn't glue anything on to the diffuser so when wearing it I get glare. Gluing an o-ring onto the diffuser would probably fix the glare issue.

Since I like this beam and don't see needing to use diffusion while hiking the diffuser would only be for later in camp. I have a H51f for that so I may take the diffuser off just to keep things simple.

If this were my only light then I would probably stay with the diffuser. It's a nice idea and a good call on your part. It would have been nice for Zebralight to have designed a sturdy form fitting clip-on diffuser for this model.

Anyway, for anyone who wants to try this diffuser out without going to too much trouble it can be fitted with just tape. Ted, I can also see why you are thinking about drilling some of the diffuser material out and replacing it with something smoother.


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## johnmeyer (Aug 11, 2011)

I purchased the Fenix AD401 diffuser, but found that it has indeed changed from what was described in the OP. I decided that to make it work that I would shim one side of the diffuser's mounting ring. I looked around the house and found some Felt Gard pads that are designed to go on the bottom of furniture legs to keep the furniture from leaving marks on hardwood floors. Here's what it looks like:







I cut a small strip off this material and then used an Exacto knife and also a small set of dykes that I use to cut small electrical wires to make the material conform somewhat to the ridge that goes around the flashlight near the lens. The diffuser collar fit over this very nicely, but still felt like it might slip or move if the flashlight were bumped or handled roughly. Since I am not planning to remove the diffuser, I used a little hot glue to keep the collar from slipping. This is what the result looks like:







This obviously doesn't look too professional, so I wrapped a little electrical tape around everything, and then mounted the flashlight in the headband holder. I might eventually replace the electricians tape with heatshrink tubing. Here's the final result:


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## gcbryan (Aug 12, 2011)

Does the diffuser lay flat against the light and have you tried using it outside yet and is there any glare?


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## johnmeyer (Aug 12, 2011)

gcbryan said:


> Does the diffuser lay flat against the light and have you tried using it outside yet and is there any glare?


No, it does not lay flat against the light's lens, and I don't think that is possible. But, it really doesn't make any difference. I checked before I did the mounting to see what difference in diffusion, intensity, etc. that I got with the diffuser slightly away from the lens, compared to having it flush against the lens. It didn't make any difference. This shows the "fit:"






However, one problem with this diffuser is that the edges of the diffuser itself are made of the same clear material as the diffuser and as a result, this edge gets very bright, and this bright light is directly at the top of my field of vision when I wear the headlamp. Today I plan to take a Sharpie pen and paint the bottom edge of the diffuser black in order to get rid of this problem.






If the light leaking from the gap is still an issue (it is a small fraction of the amount of light conducted to the edge of the lens that I'm going to block by painting with the Sharpie), I'll attach a small rubber washer.


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## gcbryan (Aug 12, 2011)

When I tried something similar I had glare that was bothersome to me when I was outside and it was totally dark. It wasn't so much an issue when using it with some ambient light.


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## michman (Nov 12, 2011)

This is a great mod!


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