On 10/11/2025 at 2:48 PM, CaolIla said:

  On 10/11/2025 at 2:33 PM, Luko said:

  On 10/11/2025 at 1:13 PM, CaolIla said:

The idea is putting some reduction in the tube and why not some extension with lens in it.
BUT there is a BUT with a lens when the distance is the focus length the light is like a donut because the tube of the retra a circular.
I need to but a diffusor on the retra side...

More than a diffusor that you need but rather a fresnel lens of something equivalent, the problem without any converging lens is that all the power will be lost. (That's what happens with the crappy Scubalamp snoot which is only equiped with a diffusor device, used it on one trip, never again, back to Retra snoot now) .This is why the Retra snoot is for me the most efficient one : you see for instance there is a sweet spot according to the distance you aim at your subject, the "halo" of the snoot will get sharper whenever you're on the ideal distance.

Diffusor or fresnel lens it is more or less the same... I'm using a fresnel on my other snoot.

Hi @Luko

I made a test to explain the donut

No lens no difusor only a small output

14 hours ago, CaolIla said:

No lens no difusor only a small output

Disclaimer : I am replying to you but am afraid that we are completely out of the OP topic, sorry for that.

So far I can notice you have 2 problems : one is the black hole inside the light which I guess is the signature of the circular bulb, the other one is that you have a light "fall off" spilling outside of the snoot hole (the outer ring of subdued light around the main light).

For me, it's due to the absence of a condenser lens that would both diffuse the circular light into a flat light and make the light converge to a focus point this avoiding spill off. We (my guide and myself) usually take continuous torch lights when we do macro, that we use when I need precise lighting other than the main snoot light or when two snooted lights are needed.

All of these small torches are equiped first with a lens like this one https://www.uwcamerastore.com/weefine-optical-collector-with-m52-for-smart-focus-6000?gad_source=1&gad_campaignid=21961101493&gbraid=0AAAAAD6tS_h9daR4-OxoqiVVd9_zdO1Lf&gclid=CjwKCAjwr8LHBhBKEiwAy47uUpyg-mpCh6yNn1-WSBCsL9CNJP9mI_UhLEkk2WRtWjKc90Kuc_xbshoCXKoQAvD_BwE

then screwed onto the condenser a plain metallic black funnel to reduce the light spot. However it wouldn't work without the condenser, which is the most important piece.

Just to show you the difference, I snapped 4 images of my mousepad with a tirch light, the condenser and a funnel.

A= full mousepad image lit by the torchlight, B= condenser on, the beam is reduced and condensed, C= condenser and funnel on, exactly what you expect from a snoot, even though I was not aiming at the sweet spot distance, not much light loss, same distance as withe condenser only D= funnel but NO condenser, I had to put the light much closer because of the loss of light, light spills outside of the main focus point, you cannot clearly see it but when I put the light close there are distinctly patterns of the LED light inside the main focus point.

@Luko


With a torchlight it is easy to visualize the result... and it is easy to achieve the goal: have a small spot

It works also good with the LED in the center of the Retra strobes... but a flash from the circular light is not as easier.

1) the need of a longer tube is necessary

2) a lens /fresnel or a concentrator as you name it is important to concentrate the light

3) with a lens with circular or only a LED you will have good "picture" of the light sources when you are at the focal length... that is the main problem. With a circular flash light you will have a bright disk with the dark center.

I made several test "Difussor" with frosted glas or such glasses

I made folowing construct
Light/strobe -> Diffussor --> 1 or more lenses with different focal --> tube with special internal shape to avoid the parasite reflexion --> and why not a lens for a last light concentration

It is not easy to make a compact solution I still exploring in different direction.
Target: Light, easy to (re)build, compact and not expensive.

In the tube a try with good results this shape

important printed with a black mat filament to avoid a maximum of the reflexion and have a nice boundery beetween the black and white zone on the picture.

Small update of my test.

The idea is to have a snoot where the water can go in --> no problems with water coming in ... it is build for that.
Perhaps in an other step I'll try to have air in the snoot but it is not the subject now

The bottom part will be "fix" and the top can be print again and again to try different size length and/or diameter of the opening in the top.

It is also possible to try different type of glas, lens, fresnel to test the result

In the midle it is possible to insert some additional lense to focus the light an put some part in to avoid the reflexion.

Edited October 27Oct 27 by CaolIla

a first picture 

You see, no you don't see the donut... I reach the target.

It is not with the "big aperture" but I hold a small cap with a small hole of 9 mm

The idea is to make some cap with different hole size and change it during the dive, Probably printed in TPU

Edited October 27Oct 27 by CaolIla

Did you use a fresnel lens?

23 minutes ago, Davide DB said:

Did you use a fresnel lens?

no in this example only a matte glass (like you can find on the Retra snoot.

I have some fresnel lenses from different diameter and focal length. I will probably combine different lenses.

My ultime idea, (result of my precedent test) is to have a part I can put on the top of more or less this solution, with a diaphragme in it.

Why on the end of the snoot... because if the diaphragme is on the begining to much light is lost. I I can focus a maximum of light on a small point (in my case with the smal diaphragme I have from Aliexpress, 25 mm diameter)

The hole will be possible to be adjust from 2 on 25 mm and that with a maximum of power light comming out.

2mm is probaly not usefull but will be possible. (if the guide is good and understand what the photograph want... why not. but this no the scope of the model I show you today

Have you tried this snoot in water? I did similar snoot with couple glasses and didn't seal the tube to allow water coming in, even with support by GPT to setup the right focal length with multiple glasses to reduce the light output angle, it could be only 8mm spot at 10cm distance from the snoot, considering the impact of sea water. Everything looks perfect in the air but when I tried it in the real dive, it didn't work as expected, the spot is much bigger and the brightness was also much more lower as what I tested in air.

@flowdesign

Thanks for your remark. Yes I know under water it is different.
That is exactly the reason I want to optimize the light coming out of the strobe.
My past experience wasn't like I imagined it...
I want to have near 100% of the light output from the strobe coming out on the top.

This time I'll make a "lowtec" snoot (I haven't enough time to do a complex solution.)
I change the design of this snoot.. but at the end I want to seal it to have air in it.

After the coming trip I'll make changes to adapt this solution and I'll make some dive with a modified version of it. (if i'm happy of the base design)

It is allways the same problem not enough time to test before the trip.

a point more is to have a light snoot for travelling I'm at the limite... with the weight.


a big problem I had in the past was the sealing of the lenses to avoiding water coming in the snoot. I'm planing to test some construction without silicon sealing but with TPU

I also want to be able to open it and close it again and again to make some changes in the parts in the snoot.

Change lenses, focal length also type of lense.
Add some fresnel or normal lenses ..

When I found the good combination (the one I like) I'll build a lighter snoot optimized for the lens combination/position/number I chose

The fundamental problem you are dealing with is that you have a strobe beam that is between 90 and 130-150deg wide and you are trying to cram this into a small tube,. Optically this is kind of like a fisheye lens in reverse. There was a thread on the relatively low output from the Rreta LSD when used on their strobes some time back and I think the Inon strobe had less power loss. This purely down to geometry, I did a calculation on this that showed only a small percentage of the beam actually entered into lens on the LSD. So if you use a fresnel to capture the beam it needs to be as big as the strobe front dia, any light that doesn't make it into the fresnel is lost. Then once you capture all that light it needs to be turned into a more parallel beam.

Hi @Chris Ross

You are right you describe the main problem of the retra, and probably the problem of mainly all new strobe with the circular flash light.

That I didn't have engouth time before the the hollidays I only make a light version, but It work well (on air). I'll give you some feedback after using it underwater.

The main opening at the bottom (strobe side) is larger as the lamp. I putted a frosted glass AND direct over a fresnel with a focal length of 80mm. The idea is to bring a maximum of the light in the good direction. OK they will be some loss but it seems to be ok (I repeat on land)
The first problem is solve no more light in form of a donut.

In the first version, watreproof with air inside, I used fresnel of 70 mm diameter. But the problem is the tightness at the junction between the glass and the PETG. Need to make some new experiment.

I really want to have a version I can open for changing the lenses and the possition of it in the tube.
Different focal and number. The idea is to have a concentrate beam of light and on the top where light come out a more or less paralell beam to be able to have a smal disk of light.

I finished yesterday the light (weight) and short snoot I'll take with me end of the week to Malapascu & Sogod... probably more wide angle as macro...
Really happy of the solution... hope it will work (not to bad) during the next trip.
The light output is really good, no dark point in the middle, boundary sharp and working distance not to short.

I plan to make some more experiment when I'll be back. I have some paint spray to make mirror The idea is to make a mirror/ deflector before the fresnel to puch a maximum of the light in the tube... you can see I have a lot of idea/experiment in reserve in my mind 🤪

Edited Sunday at 08:58 AM4 days by CaolIla

I made some picture

Snoot mounted on the Retra Pro Max II (you can also see the new bumper)

I made the choice to fix all together with bungee

Edited Sunday at 08:59 AM4 days by CaolIla

I can't loose anything and it is very fast and easy to change the ending part to have different diameter the smallest is 9 mm

TPU (red) to make the make the part holding together

With the lamp (not the flash) picture taked with a smartphone

Edited Sunday at 09:00 AM4 days by CaolIla

The three size

Oh wow... nice design!

Could be an object out of a Super Mario Kart videogame. (I don't how it would be used though : snoot Bowser at full power and you get 100 additional golden coins? )

10 minutes ago, Luko said:

Oh wow... nice design!

Could be an object out of a Super Mario Kart videogame. (I don't how it would be used though : snoot Bowser at full power and you get 100 additional golden coins? )

Don't know how to interpret this post ?????

48 minutes ago, CaolIla said:

Don't know how to interpret this post ?????

First with a tint of humour (which never hurts btw).

If you think at it, the videogame industry has always been on the edge of design novelty.

Seriiously I think it's really a nice piece of design which changes from usual underwater stuff, or reminding of the rounded earlier Hugyfot aesthetics.

I understanded it was humor... but in english... I was not sure.

The design is made to hold the snoot easier and turn it on place on the Retra.
It important with dry gloves ;) than I want to train tu usage of the snoot in cold water ;)

Really cool design regardless of its use 😁

What parameters have to be held in account for the fresnel lens?

Focal distance... ok but is there a specific distance from the light source?

9 hours ago, Davide DB said:

Focal distance... ok but is there a specific distance from the light source?

The frostet glas is there to made the light source more diffus.. the light go out on the other side did not have a direction but got more or less in 180 ° direction.
The fresnel lens in this construction is directly putted after the frosted glas and the frostest glas is beetween 5 and 10 mm from the front of the strobe glas. As near as possible.
It the final version I'll made 2 mm
I'll didn't try with only the fresnel prehaps it is ok... but I have a doubt. I'll try it to show if the light is uniformfly coming out... I'm really not sure my fear is that there will be a "dark" zone in the middle.

I'm not an optic specialist I need to study a little bit more the principle of lenses and find a software capable to make some calculation. to avoid to many "Try and error" loops.
A problem is the change/or not of material on the glass interface..water didn't react same as air. The lense are build and giving focal distance etc in air not in water.

I repeat the idea is to build a snoot with

1) as light as possible (for travelling)

2) as short as possible

3) suitable for ring strobelight, like the Retra

4) As less as possible lost of light,--> pilot light brighter
5) in the high end version an option for a diaphragme to smoothly change the size of the spot light.

The fresnel is basically a large lens and it will form an image at its focal point. In this case you have the frosted glass in front so it will try to form and image of that, but it needs enough room to form the image. The problem you have is that it makes a cone of light that is smallest at the focus point and then gets larger beyond the focus point. so getting the light to travel down the tube without hitting the walls and being absorbed is the issue.

You could take your frosted glass and place it in a cardboard mask and have a light source behind it then take the fresnel and move it back and forth to see what size spot it forms. to get the light into the tube you want a spot the same diameter as the tube. This you c coul use to determine how far to place the fresnel from the tube.

If the light goes into the tube the cone is still going to try to expand so maybe paintin the inside white so it bounces around in there might help? Otherwise you would be looking at building a collimator to get parallel light rays in your beam.

You could look into raytracing software but I think it's a fairly steep learning curve setting up software to model what you are trying to correctly.

One example of what you are trying to do is the "better beamer" strobe attachment for bird photos it narrows the strobe beam from something covering the field of a 100-200mm lens to something covering a 300-400mm lens it quoted as increasing strobe light by 2 stops or so. See this link:

Shutter Muse

Better Beamer Flash Extender Review

The Better Beamer Flash Extender is used by many wildlife photographers to extend the range of a standard hot shoe flash. But is it any good?

If you can concentrate the beam enough just sampling from this beam using a tube up front may be enough?