Two Naive Flash Questions

[dlwalke]

1) In WPB a week ago, I had the opportunity to take a closeup pic of a large Nurse Shark. The instructor touched the fin and it swam off before I had a good shot ready. Got me wondering though, if a charging flash can disturb a shark or ray given their very sensitive lateeral line.

2) I also noticed that on some occasions I was ready to take a shot, pressed the button down, but then had to wait a couple of seconds before the shutter opened. I believe this was because the flash was charging (I am really new to this sort of thing). With an external flash, would this not be a problem. As I was taking pictures in a bit of a current, the delay was a bit of a problem since I was being pulled away from the spot where the focus and metering was taking place.

Thanks,
Dave

 

[Gilligan]

Please tell us what kind of camera you are using so that we may respond. External strobes are slave strobes. Some of them are activated by the cameras flash. If you are using a digital camera you are likely experiencing "shutter lag". This is inherent to most point and shoot digital cameras. Taking the camera off full time auto focus will help because the lens will not be "hunting" all the time. Use the method of pushing the shutter half way down to focus then all the way down to take the photo.

 

[alcina]

1) In WPB a week ago, I had the opportunity to take a closeup pic of a large Nurse Shark. The instructor touched the fin and it swam off before I had a good shot ready. Got me wondering though, if a charging flash can disturb a shark or ray given their very sensitive lateeral line.
Dave

Can't speak for every place out there, but the white tips, black tips, grey reefies, wobbies & leopards we get here don't seem the slightest bit disturbed by photographers. Same goes for the variety of rays we get.

Have seen creatures swim off as you try to approach, but haven't seen any get startled by the flash nor act wonky after the strobe fires...

 

[dlwalke]

Please tell us what kind of camera you are using so that we may respond. External strobes are slave strobes. Some of them are activated by the cameras flash. If you are using a digital camera you are likely experiencing "shutter lag". This is inherent to most point and shoot digital cameras. Taking the camera off full time auto focus will help because the lens will not be "hunting" all the time. Use the method of pushing the shutter half way down to focus then all the way down to take the photo.

Thanks Gilligan. I have an Olypus C5050. I did have it on autofocus but the delay occured even after I had depressed the shutter halfway down, waited, and then tried to shoot. It is possible, however, that I did not really have it pressed halfway down as I was doing this through a PT015 case and it is a bit hard for me to judge exactly how far down it is being pushed.

 

[alcina]

Thanks Gilligan. I have an Olypus C5050. I did have it on autofocus but the delay occured even after I had depressed the shutter halfway down, waited, and then tried to shoot. It is possible, however, that I did not really have it pressed halfway down as I was doing this through a PT015 case and it is a bit hard for me to judge exactly how far down it is being pushed.

OK...I have had this problem. First thing to check is to see if the little lights are flashing anywhere on the back of the camera. If the ones by the viewfinder are flashing, you are waiting for your flash to recharge and get ready. The camera should still fire but you'll get a very dark image. Getting better batteries or changing every other dive (YMMV) will help.

If the red one is flashing, you are waiting for the data to write to your card. Only real fix for this is a faster card - which is what I am saving pennies for!

I finally got very frustrated with it all and that is one of the reasons I switched to shooting RAW...figured if I had to wait anyway, I might as well be able to watch the little bar on the screen count down the wait time and might as well get the best image quality I could!!

Oops, also check to make sure your continual autofocus is off...your autofocus when you push the shutter will still be on in this case but the camera won't be constantly hunting.

 

[dlwalke]

Getting better batteries or changing every other dive (YMMV) will help.

If the red one is flashing, you are waiting for the data to write to your card. Only real fix for this is a faster card - which is what I am saving pennies for!QUOTE]

OK. I think it was a battery problem because I believe that this was hapening towards the end of the pictures that I got with that charge. As for the card...what cards are fast and what cards are slow. I'm getting reading to order a 512 MB Sandisk Compactflash card. Currently have a 256 MB Olympus XDpicture card.

Thanks,
Dave

 

[alcina]

I'm getting reading to order a 512 MB Sandisk Compactflash card. Currently have a 256 MB Olympus XDpicture card.

Thanks,
Dave

Scan Disk makes a few...in the stats of the card before you buy read the write speed. I wouldn't buy anything less than 40x...52x would be great...

 

[PapaBob]

We used to have a couple of resident Blacktips on a reef called Finks in Dr. Ray's dive location book (off Highland Beach, Florida). They always seemed to show up after I popped my strobe. A local operator used to show them nearby so I think the strobe was like a dinner bell. I never got a negative reaction from them.

I got to be one of the first divers to enjoy the Walkers cay shark rodeo and have enjoyed the dive several times over the years. I have some real close shots of nurses, blacktips and reef sharks. They never seemed to mind or react one way or another to the strobe.

My evidence is anecdotal, but I don't think strobes have much affect on sharks or rays. Just my $.02.

---Bob

 

[miketsp]

Inside a strobe there is a switched mode power supply (SMPS) which converts the voltage from the low battery voltage (6 - 12V) to the hundreds of volts with which the output capacitor is charged. Older strobes used lower switching frequencies down in the 10kHz range due to efficiency considerations of the switching devices and components. Nowadays designers have no problems working up at 100kHz+. Some SMPS work right up into the MHz range.
And of course since users want ever shorter charge times, these SMPSes are ever more powerful.
So to answer the original question, one would have to know what is being emitted acoustically and electromagnetically by the strobe and what is the fish sensitive to.
Under water, the higher the frequency, the shorter the propagation, both in terms of sound waves (vibrations) and electromagnetic waves.
So my feeling is that older strobe units working at lower frequencies would be detected by some fish but the newer ones, even though more powerful, would not.

 

[ChrisM]

Can't be as specific as Mike, but sharks read electrical signals, so anything -- strobe, camera, hoseless computer -- that emits an electrical signal will be read by a shark. I have seen video of a tiger shark bumping a diver's hoseless wrist computer. During a shark feed, I had several sharks nose and bump my strobes.

I don't think it's as much a case of "disturbing" them as they "sense" it, much as we hear or see a car going down the street.

Chris