Why underexposed?

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Postby John H. Moore » Thu Jun 24, 2010 12:35 pm

I was out at the Marine Room Canyon (La Jolla) yesterday afternoon in really silty water, trying to shoot fried egg jellyfish. Rig: Nikon D200 in Sea & Sea housing, dual YS110 strobes, TTL III converter, 60mm macro lens.

If I got up close, I could get decent shots, such as:

Image

But if I backed up some to try to frame the entire bell, my shots were horridly underexposed. Here's one as it came out of the camera:

Image

or, somewhat exposure corrected:

Image

both of which are obviously crap.

I'm guessing that the YS110's are in fact powerful enough to shoot the maybe 5-6 feet that I was backed up off the jelly. Correct?

So why are they so underexposed?

- the YS110's don't have the reach?
- the TTL III converter is messing up (go get the TTL IV instead)?
- I'm doing something wrong... what?

Or maybe when I back off in murky water, I need to open up the lens some? The strobes might have the power at that distance, just not at f/22?

Thanks!
======
John H. Moore
San Diego, California, USA
Nikon D200, Sea & Sea housing, Dual YS-110 strobes with TTL III converter
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Postby maggieD » Thu Jun 24, 2010 1:05 pm

Hi John,

God knows, I'm not an expert and Todd or Bill or Scott will probably chime in but here is my take: 5 or 6 feet is a lot of water for your strobes to punch thru. You don't say if you opened up your aperture and slowed down your shutter speed, so did you do those things? Also my understanding of WA photography is that ttl doesn't work very well with wide angle shots so maybe you could go manual on your strobes too. A higher iso would also help. I guess what I'm trying to say is that you can't expect the same exposure to work for close up and wide angle.

Margaret
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Postby seekncritters » Thu Jun 24, 2010 3:06 pm

Looks like for both photos they were ISO 200, 1/250s, F22.

Where were the strobes pointed? Same strobe position both photos? Maybe it's a simple explanation like they just weren't pointed at or in the direction of the subject when 5 ft away???

-Dana
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Postby smb2 » Thu Jun 24, 2010 3:35 pm

I like the first shot.
With a 60mm lens, by the time you get far enough away to fit the whole jelly, I doubt you can cast enough flash on the subject. Certainly not at f22. You would need to open up to f8 at least or more depending on the depth, ambient light and the size of the subject (if you have to be further away to get the whole jelly). If your flash was aimed for the macro shot
you would also have to get them out a bit from the camera.
Hope you took more of the true macros as it looks like a cool subject.

The well lit jellies that you see are mostly taken with a wide angle or a fisheye lens so the subject is probably less than a foot from the dome (and most likely in pretty clear water).
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Postby John H. Moore » Thu Jun 24, 2010 4:06 pm

The strobes were in the same position in both photos. As I'm thinking about this, I'm guessing that I should have opened up the aperture a whole bunch, but while I was in the water I only got as far in my thought process as "crap, that didn't work!" ;-) Not to mention that the water was really dirty, so there was a whole lot of gunk between me and the jelly. Need to find one of these guys in more clear water and try playing with the settings. But... do the YS-110's have enough power to cover that distance even with more light allowed to the sensor (f/stop, shutter, ISO)? And is this also an issue with the TTL converter?
======
John H. Moore
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Nikon D200, Sea & Sea housing, Dual YS-110 strobes with TTL III converter
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Postby jlyle » Thu Jun 24, 2010 7:01 pm

John,

Don't forget, the light has to travel both ways. If the subject is five feet from the camera, the strobe light has to reach ten feet.

Jim
DSDO (dive safely, dive often),
Jim

Olympus E-330, Ikelite housing with dual Ike DS-125s
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Postby scottg » Thu Jun 24, 2010 7:45 pm

hey John

Welcome to the UWPG forums.

Like everyone else said, the issue is the aperture, not the TTL converter.

5ft away at F22? Not in any of our wildest dreams. :) Not even at F11. In silty california water, you'll have to "dial down" to F7 or 5.6, based on my experiences with the YS-110's. All this is assuming ISO 200

Nice closeup of the jelly. We're looking forward to seeing more of your photos.

Scott Gietler Owner/Editor, Underwater Photography Guide & Bluewater Photo http://www.uwphotographyguide.com http://www.bluewaterphotostore.com

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Postby bvanant » Fri Jun 25, 2010 4:49 pm

John: The YS110 strobes have an underwater GN of 10 or so. The formula for Guide Number is GN=Distance x f stop. If your distance was 2 meter or so (6 feet) then you need to shoot at f5 or more open to get the pic at ISO 100. At ISO 200 you get to shoot at f6 or so but at f22 there simply isn't enough light for you to get the pic and that is assuming perfectly clear swimming pool water. In murky highly scattering water you might have to get to f4 or even more open. BUT I don't understand why when you saw the pic after you took it you didn't just put the strobes in manual mode and shoot at various fstops til you got the correct exposure. My guess is that the TTL system is fine, but I thought that there was some kind of signal on the strobes or converter that showed that they weren't capable of getting the shot, but I am not a Nikon guy (God forbid).

:D
Bill

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Postby John H. Moore » Fri Jun 25, 2010 5:23 pm

bvanant wrote:BUT I don't understand why when you saw the pic after you took it you didn't just put the strobes in manual mode and shoot at various fstops til you got the correct exposure.


Answer: general inexperience! :-)

Am new to shooting underwater. Have literally shot the thing eight times now (eight dives). Am pretty experienced above-water, but now learning how below-water changes things. I've been really focused on strobe placement & back-scatter and essentially leaving the settings untouched during the dive--which was obviously a mistake here! So now I just need the swell to come back down and go find some more fried egg jellyfish, while they're still in town, hopefully in less murky water... and play with the aperture (and maybe also shutter speed?) to see if I can get these guys well lit at some distance.

Question: at 5-6 feet away, shooting these jellyfish, put the strobes as far out from the camera as the arms will go?

Thanks all!
======
John H. Moore
San Diego, California, USA
Nikon D200, Sea & Sea housing, Dual YS-110 strobes with TTL III converter
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Postby smb2 » Sat Jun 26, 2010 5:17 am

If you have the 60mm on then do you have a shorter set of arms on the rig for macro?
In that case the answer is probably yes.
If you go back out just to take the jellies then why not take the wide angle?

Also as above try a session with everything manual checking the LCD/histogram frequently for exposure. I am usually set on the RGB (D2x) screen to see any areas of overexposure as a quick reference.
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