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 Underwater strobes at times are not triggered by their fiber optic cable. Several types of cables are available, and to determine which one carries the most light, I tested 4 different cables.   

 Materials: The cables were one Toslink cable 4 mm o.d.,1 meter long (Fig 1 &2, upper left); two commercial 1.4 mm coiled multicore cables: one was labelled 1000 cores (bottom left), and one was labelled Multicore (upper right); the fourth cable (lower right) was a commercial 1.4mm coiled, single fiber cable. I used a piece of black foam rubber to hold the tips of four cables on a black background. The free cable ends were held together in front of a single bright light. I used a Nikon D500, 1/250 sec, variable f stop, for the photos. 

 Results: It was a bit tricky to get the photos to show differences in cable brightness, as the points of light tended to appear the same, unless I played around with the f stop.  The 3mm Toslink cable was the brightest, followed by the multi-strand cable, then the 1000 core cable, while the commercial single strand, coiled, 1.4 mm fiber cable was rather dim. 

 

 Fig. 1

Close up photo (as the notches are all on the same side of the lights, I suspect they are caused by some external artifact)..

 

 2b.thumb.jpg.6b7e58e9ecf08625eacc01a7a243629b.jpg

 About 1 meter distance. 

  Comment: These findings agree with previous Wetpixel posts that multifiber cables or 3 mm thicker Toslink cables transmit more light than single fiber coiled 1.4 mm commercial cables.  The present findings are qualitative, and quantitative photometry would be better. However, the present photos show the Toslink cable transmitted the most light, followed by the multi strand cables. 

 Conclusion: Better light transmission, toughness and low price indicate that Toslink cables, followed by multi strand cables, are a good choice to trigger UW strobes. 

Note: Toslink cables are available from Amazon, eBay and others as digital optical audio cable. 

References:
1. Erratic firing of the Backscatter Mini Flash, several excellent comments: use larger diameter f.o. cable. https://wetpixel.com/forums/index.php?/topic/66482-firing-backscatter-mini-flash/

2. Dave Hicks comment. https://wetpixel.com/forums/index.php?/topic/66482-firing-backscatter-mini-flash/&tab=comments#comment-426656

3. Bvanant (Bill VanAntwerp) on homemade 613 fiber optic cables. https://wetpixel.com/forums/index.php?/topic/66482-firing-backscatter-mini-flash/&tab=comments#comment-426543

4. FO Cable Problem with strobe and Nikon z7 II. https://wetpixel.com/forums/index.php?/topic/67509-problem-with-strobe-and-nikon-z7-ii/&tab=comments#comment-426782

5. Excellent write up on DIY fiber optic cables, with useful comments by many Wetpixel  contributors. https://wetpixel.com/forums/index.php?/topic/60564-diy-fiber-optic-writeup-with-parts/&tab=comments#comment-387130

6. Stuartv on fiber optic multi strand cables: https://wetpixel.com/forums/index.php?/topic/60564-diy-fiber-optic-writeup-with-parts/page/3/&tab=comments#comment-424488

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Edited by Kraken de Mabini
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Fascinating - thanks Elias!

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Good comparison there, the question is are all toslink cables created equal?  I imagine the type of fibre they use will vary depending on manufacturer? 

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Variation between manufacturers is a valid consideration. As Toslink cables are designed to carry music, music translated by electronics into a highly complex optical family of messages that vary greatly in intensity and rapidly with time, the Toslink cables have to be manufactured to some pretty demanding specifications. Otherwise they will not sell and the music lovers will cry out. 

In contrast, the light pulse to fire a strobe is intense and brief, about 2 milliseconds, so it is a truly simple message, just a bright flash that fires the strobe. 

I am reasonably confident that the quality of Toslink fiber optic cables will remain of high quality, thanks in part to buyer pressure, independent of manufacturer, and will remain available to flash our strobes for the foreseeable future. 

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Certainly my experience of Toslink with Inon Z240s and Retra Primes has been very good - although, of course, they are maybe the easiest strobes to trigger.

I made two cables from Toslink and the Howshot L-fittings to use with wide angle lenses and 2x 12" + 8" arms and they work like a charm and cost about $10!

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