Strobes

Here is some data from our local pool. Not quite the way the Backscatter boys did it. Put a bright white screen against the wall (about 11 feet deep). Put the strobe on a tripod parallel to the screen (PITA). Shot the strobe 20 times, averaged the shots using an image processing tool in Matlab. Also put a strip of photodiodes along the screen at the axis of the strobe light. Here is data from the photodiodes. I can post the error bars, but all shots were within 5% or so except one shot with the S2000. Note this is all from a single example of each strobe so YMMV. The intensity scale is completely arbitrary, my waterproof flash meter was in fact not so waterproof so I have only intensity measurement.

strobe.pdf

Hey Bill

This is cool, where can we find the stuff that backscatter did that you reference?

Bill

Here is some data from our local pool. Not quite the way the Backscatter boys did it. Put a bright white screen against the wall (about 11 feet deep). Put the strobe on a tripod parallel to the screen (PITA). Shot the strobe 20 times, averaged the shots using an image processing tool in Matlab. Also put a strip of photodiodes along the screen at the axis of the strobe light. Here is data from the photodiodes. I can post the error bars, but all shots were within 5% or so except one shot with the S2000. Note this is all from a single example of each strobe so YMMV. The intensity scale is completely arbitrary, my waterproof flash meter was in fact not so waterproof so I have only intensity measurement.

 

strobe.pdf

You can really see that the effect of the diffuser is to flatten the light really strongly

The Inon -0.3 is much more close to -1 The Sea and Sea strobe holds really well

Bill L: On the backscatter website there is a strobe report but done on land. One thing I don't get, if you are trying to measure light at 90 degrees isn't that at infinity?

Bill

Again, remember this is for a single strobe of each flavor, if anyone wants to send me 20 or so I will test them all.

Bill

90 deg is achievable but not on a flat screen that would be measured 1m out to the side of the flash. Because they are using a flash meter they are effectively testing the illumination of a spherical surface if in fact they have the flash meter 1m from the strobe at all times.

This seems a bit odd as the coverage angle of the strobes is 80-120 deg so 40-60 deg away from the centreline each side. perhaps the 90 deg is 45 deg away from the centreline?? 1m directly to the side would not get much light apart from light reflected back from the walls of the testing room - which does not occur UW.

If you are testing on a flat screen the distance will vary at each point as the strobe unit is closest to the screen directly in front and is further away at the various angles, not an issue on land but more significant underwater.

Bill V

It is my understanding that light behaves differently in water than it does in air. The light from the strobe travels a distance altho short before it reaches the diffuser and then after it goes threw the diffuser it is back in the water. Therefore comparing a strobe performance in the air is somewhat irrelevant to how it will preform underwater and then adding the diffuser in the mix really makes it irrelevant.

Bill V

 

It is my understanding that light behaves differently in water than it does in air. The light from the strobe travels a distance altho short before it reaches the diffuser and then after it goes threw the diffuser it is back in the water. Therefore comparing a strobe performance in the air is somewhat irrelevant to how it will preform underwater and then adding the diffuser in the mix really makes it irrelevant.

Actually looking at Bill data is very similar to the test in land even if there is a flat surface

If the water of the pool is very clear and there are no suspended particles there should not be much difference at short range

Also to consider the theory of magnification in water assumes one of the surfaces to be the eye that is not exactly the same size of a strobe reflector so the change of the incident angle may be much smaller

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Well done Bill, your brightness values seem to mimic the guide number values published by the manufactures, with Inon rating the Z-330 at GN33 and Sea & Sea rating the D2J at GN-32.

At the same time the brightness values are hardly apples to apples. The over 400 value for the S&S is for the strobe which has a beam angle of 80 X 80 degrees while the Z330 has a 110 X 110 beam angle. When the 110 degree diffuser is added to the S&S the brightness value drops to under 150. Using this logic it would stand to reason that if you reduced the beam angle of the Z330 strobes to 80 degrees the brightness value would jumpy 250 or close to 700.

Regarding diffusers the S&S 100 and 110 diffusers are designed to widen the beam angle. The Inon strobe dome filters are not designed to widen the beam they are designed for two reasons, to reduce the out put of light by up to four stops and too change the color temperature of the light output.

So again if you compare the S&S with the 110 diffuser for 110 beam angle and the Inon -0.3 dome filter with the same 110 beam angle the brightness value for the Inon Z330 is 100 points higher.

I am pointing these issues out not because I have an issue with the work Bill has put in I am very well aware of how time consuming doing these tests can be. I just think it needs to be pointed out because these two strobes are in the same price ranged but not comparable apples to apples.

Well done Bill, your brightness values seem to mimic the guide number values published by the manufactures, with Inon rating the Z-330 at GN33 and Sea & Sea rating the D2J at GN-32.

 

At the same time the brightness values are hardly apples to apples. The over 400 value for the S&S is for the strobe which has a beam angle of 80 X 80 degrees while the Z330 has a 110 X 110 beam angle. When the 110 degree diffuser is added to the S&S the brightness value drops to under 150. Using this logic it would stand to reason that if you reduced the beam angle of the Z330 strobes to 80 degrees the brightness value would jumpy 250 or close to 700.

 

Regarding diffusers the S&S 100 and 110 diffusers are designed to widen the beam angle. The Inon strobe dome filters are not designed to widen the beam they are designed for two reasons, to reduce the out put of light by up to four stops and too change the color temperature of the light output.

 

So again if you compare the S&S with the 110 diffuser for 110 beam angle and the Inon -0.3 dome filter with the same 110 beam angle the brightness value for the Inon Z330 is 100 points higher.

 

I am pointing these issues out not because I have an issue with the work Bill has put in I am very well aware of how time consuming doing these tests can be. I just think it needs to be pointed out because these two strobes are in the same price ranged but not comparable apples to apples.

I think that the test from Bill and also those done by the Retra guys and by backscatter confirm that actually the YS-D2 and the Z330 drop equally with angle without diffusers and that with diffuser the sea and sea is better distributed

So I guess 80x80 is as incorrect as 110x110. Furthermore the Inon two bulbs clearly show a cross shape so a diffuser is essential as it is to the square of the sea and sea

From all the measurements I ca see that the loss of light of the Inon at centre is more like 0.5EV and not 0.3EV the diffuser is clearly required for any strobe with a linear tube even if you put two like the inon you see the cross with the shape of the two tubes

I would actually argue that the distribution of the Sea and Sea is actually better and that the strobe with the nominal 100 degree diffuser is wider than the Inon declared 110

In terms of power at the centre the YS-D2 appears around 1/3 of a stop weaker at centre with the diffuser on but the gap close at 60 degree off centre

If I had to purely look at Bill and backscatter tests without reading the specifications of the strobe I would conclude that the Sea and Sea has a more even light distribution at the edges and that the older Z240 and S2000 although less powerful have a nice distribution too

I think having this information with tests done in water just confirms that there is a lot more than land specifications to a strobe

It would be really interesting to understand how circular tubes behave in water

Now you have me wondering how to improve the data. I could theoretically build a circular set of photodiodes and put the strobe at the center, but keeping it round is going to be tricky. I know that the distances involved increase with angle but for my purposes I was trying to compare strobes rather than try to calculate f-stops. I will also try to get my UW light meter repaired, that would make it simpler to do.

Cheers

Bill

The Backscatter review:

https://www.backscatter.com/reviews/post/Best-Underwater-Strobe-Flash

Great study Bill. You should figure out a way to slave them all at once and see what all 8 measure to. You could light up the Yukon wreck.

Now you have me wondering how to improve the data. I could theoretically build a circular set of photodiodes and put the strobe at the center, but keeping it round is going to be tricky. I know that the distances involved increase with angle but for my purposes I was trying to compare strobes rather than try to calculate f-stops. I will also try to get my UW light meter repaired, that would make it simpler to do.

Cheers

Bill

Fstops can be calculated from linear data as they are relative. So to me any scale is good. Can you get your hands on a seacam or ikelite strobe would love to check those out

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I can easily get an Ike. Seacam are not thick on the ground here in LA.

Bill

New to WetPixel here. Was wondering whats the difference between a strobe and video light?

New to WetPixel here. Was wondering whats the difference between a strobe and video light?

One is continuous (like a regular light bulb) whereas the other one flashes.

With regard to the image above showing the dispersion pattern, I am wondering if the pattern in air is similar to what one would get under water? In particular should one expect a non-diffused Z330 to have such a pronounced cross shape in actual use?

I find myself wondering if the strobe manufactures should not offer some sort of clear diffuser that would not reduce output so much. Maybe a clear diffuser with a fresnel or pebbled texture? On the other hand, you guys seem much more knowledgeable about this than I am and that may be a silly thought.

Also a bit confused about the image of the retra. I thought the "pro" was substantially more powerful than the "prime" but the image shown suggests they are the same since it is listed a pro/prime. I suppose no one has used these yet so it is somewhat theoretical at this point.

With regard to the image above showing the dispersion pattern, I am wondering if the pattern in air is similar to what one would get under water? In particular should one expect a non-diffused Z330 to have such a pronounced cross shape in actual use?

 

I find myself wondering if the strobe manufactures should not offer some sort of clear diffuser that would not reduce output so much. Maybe a clear diffuser with a fresnel or pebbled texture? On the other hand, you guys seem much more knowledgeable about this than I am and that may be a silly thought.

 

Also a bit confused about the image of the retra. I thought the "pro" was substantially more powerful than the "prime" but the image shown suggests they are the same since it is listed a pro/prime. I suppose no one has used these yet so it is somewhat theoretical at this point.

Bill test is in water not in air while backscatter is in air and so is Retra

Bill and Retra measure a flat surface while backscatter at fixed distance and different angle

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I was referring to the image from retra. That is the only one of these that really addressed the shape of the light output.

I was referring to the image from retra. That is the only one of these that really addressed the shape of the light output.

The difference will only be in power which means the circle will look smaller even if the angle is the same in theory because at some point you will consider it dark

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I am not sure what you are saying, but my curiosity was whether the shape or pattern of the light output would change underwater. It is really an academic question, I suppose. I am not sure it could realistically be tested. I was not really talking about the power of the flash.