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Difficult exposure conditions.....


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#1 chrism

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Posted 16 August 2004 - 09:49 PM

Your mission, should you choose to accept it.......

Essentially open Pacific Ocean water underneath an oil rig, fairly shallow (30 ft) but limited viz, maybe 40 feet, and under the rig, so no sunlight. Fast moving sea lions coming in and out of strobe range. Huuuuuge school of silvery sardines to flash back any strobes, being chased by said sea lions for lunch.........

That's where I was Saturday with te DigiReb, A300 housing and Sigma 15mm FE lens. THird trip with camera since coming from 5050 land. I always thought that the aperture values on the prosumer models were not equal to those of a DSLR.... So that a 5050 f6.3 was more wide open than a 300D f6.3......not so, eh? I think my stinking thinking ruined some shots yesterday. ISO 100

As I am sitting here, I am thinking I could have upped the ISO.... but didn't........

What settings would you have used for these conditions? Looking back, the sea lions I did get were a little soft, so maybe opening up the aperture to 2 something and getting more shutter speed?

And, when I start shooting RAW, I can gain two stops as well after, correct (although my constant goal is to get correct exposure out of the camera)?

Other thoughts re: shooting ambient with lo light?

Ideas I have received - shoot 400 ISO; shoot shutter priority.....others? Thoughts, ideas, magic potions and mantras accepted.....

This pic was ISO 100, f6.3 and 1/100.....

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another example

f8.0 (I know.... :roll: ) 1/80.....

shoulda been f2.8? doh!

Damn, all that extra available light......

Posted Image

Was able to get a couple decent shots, although still dark.....

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Posted Image

Chris
Canon 300D, Aquatica A300, Dual YS90-DXs, Canon 18-55 mm, Sigma 15 mm FE, Canon 50 mm Macro

#2 herbko

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Posted 16 August 2004 - 10:00 PM

Chris, It's hard to say without been there, but I often go down to 1/30 or lower at Monterey. With a moving Sealion, I may up it to 1/60 or higher. Looks like a wider aperture would have helped. I rarely move my ISO up, and choose to do it in the raw conversion instead. There's no noticeable difference between shooting ISO 100 and exposure compensate +1 in the raw conversion and shooting ISO 200 and exposing all the way to the right.
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#3 MikeVeitch

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Posted 16 August 2004 - 11:27 PM

Looking at the background exposure, 60 shutter would be better.
As for lighting up your sealions, open aperture up, 2.8 probably too much but somewhere between 4 to 5.6 would have helped.
Also you didn't mention strobes. Did you have them on full?
Having a sealion at 3-4 feet away needs full strobe, that dark fur really sucks in the light.
The second sealion shot is well exposed for the natural, background light ie shutter speed. More strobe or more open aperture would have made it a winner.
Great shot of the one with his mouth open. Great composition throughout and am sure you appreciated the lack of shutter lag for the fast moving sealions eh?.

Chalk it up to learning the new rig and get out there again!

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#4 james

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Posted 17 August 2004 - 06:04 AM

Hi Chris,

I agree with what Herb and Mike have said so far.

The way I see it, you were photographing in very difficult conditions. Just looking at the background exposure (of the water and the rig legs) I would go down to a very low aperture. Even set at f2.8 or f3.5, you will get HUGE depth of field when using the fisheye. So I would have set the fstop at f3.5 let's say. I would recon that with that lens and dome, you would get DOF from 3 feet to 20 feet - which is essentially infinity...

This will have two effects, it would give you 2 1/2 more stops of background exposure, but it would also make your strobes a LOT more powerful. Look at the strobe chart/guide numbers on your strobe for a 2 1/2 stop aperture difference.

Next, you can go with a low shutterspeed with sea-lions if you are willing to accept some motion blur. If you use second-curtain sync, you can get some killer "speed effects" shooting at 1/30th. If you don't want the blur, you could have probably gotten a decent exposure at f3.5 @ 16oth or 1/90th.

Unlike Herb, I set the ISO underater, because I can then see the exposure on the little LCD and make corrections to the foreground lighting (strobe). You can go to ISO 200 and even 400 with the Drebel and you still get almost no noise. It's cool! Something you just can't do with a consumer digicam.

So after all that, you get 2 1/2 stops exposure from the lens/shutter and another 2 stops from the ISO setting. I think you could have gotten some good shots that way, and look at it this way - you have something to aim for next time.

About the focusing question you had. With your DOF from 3 feet to infinity, you could have probably set the MF at 1 foot on the lens (remember, it's focusing on a virtual image) and left it there, and gotten some more shots that way.

Cheers
James
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#5 Craig Ruaux

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Posted 17 August 2004 - 07:22 AM

Photoshop (CS) has a nice "Highlights and shadows" filter/adjustment that may be able to help here.

I have made a roll-over of one of the shots that you can see here...

Roll your mouse over the image to see the change.....

You'd be able to do a better job with the original file, avoiding the jpeg artifacts and softening.

This is the result of increasing the exposure in the shadows only by 30%, then adding back a bit of blue in the highlights.

Just shoot it, then fix it in post :D :D
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#6 chrism

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Posted 17 August 2004 - 05:54 PM

Thanx all, some basic things to think about that honestly I wasn't thinking about........And tips to use for next time

Mike, yes, using dual YS90s full power......

Chris
Canon 300D, Aquatica A300, Dual YS90-DXs, Canon 18-55 mm, Sigma 15 mm FE, Canon 50 mm Macro