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CFWA and depth of field


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#1 adamhanlon

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Posted 19 March 2010 - 05:25 AM

Hi all,

You may be aware that I have been doing quite a lot of experimenting with CFWA.

I'm using a Tokina 10-17, a Kenko 1.4 x teleconverter, and a Zen 100mm dome.

With larger subjects, like the sturgeon below, in green water and low light, I seem to be struggling to get the DOF sorted. To my eye, the snout is out of focus (and a little over exposed) Settings were 1/50th at f5, 200 ISO.

Posted Image

I want to expose for the background, which means an open aperture (and slow shutter speed) - which gives me a relatively shallow DOF. In this case, the Sturgeon's snout was almost on my dome!

Any ideas/feedback?

Many thanks

Adam

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#2 JDeighton

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Posted 19 March 2010 - 05:55 AM

Unless you have a better way than I do to bend the rules of physics, you still need a smaller aperture to get the greater DoF.

If you want the background to be the shade you have here, you'd need to keep the shutter open for longer to balance the smaller aperture...

The strobes should still be able to freeze the fish, as they should be the major contributor to the lighting on the foreground subject.

Or you could ask the Sturgeon to hold still while you take the picture. :-)

#3 MikeVeitch

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Posted 19 March 2010 - 06:04 AM

I would bump up the ISO to 400 and then you can use f8 to achieve the same exposure and also be able to speed up your shutter a little.

Or as JDeighton said, its the shutter that will control your background exposure more than the fstop. So feel free to go to f8 and 1/30 on iso 200.

How fast do the sturgeon move?

1/30 is not a problem for camera shake underwater on a wide lens, its just the speed of the subject that will matter.

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#4 PRC

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Posted 19 March 2010 - 09:21 AM

Jump the ISO.

Suspect the sturgeon look like they move slow but like sharks do not.

BTW - can't stay off of the band waggon - just ordered a Zen 100mm dome...

Sturgeon shot looks good to me - there is not an abundance of these shots around - not like say clownfish or something!


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Edited by PRC, 19 March 2010 - 09:24 AM.

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#5 Alex_Mustard

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Posted 19 March 2010 - 09:23 AM

I wouldn't take the D2x to ISO 400. But you need to close the aperture a bit. So it looks like longer exposures or wait for brighter conditions. Alex

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#6 yahsemtough

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Posted 19 March 2010 - 09:23 AM

I agree with Mike, try bumping the iso and adjusting the stop for DOF. I would also look to raise the strobes a hair. Looks like a little more light higher on the subject would be a little more pleasing.

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#7 bmyates

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Posted 19 March 2010 - 10:59 AM

I hesitate to (ever!) disagree with Alex, but I agree with others that I'd bump the ISO. The slight noise you might get should be far less noticeable/distracting than having the subject out of focus...and if you use Noise Ninja, you could make the noise scarcely noticeable at all.

In that light, unless you use your strobes to light the fish more, you've got limited ways to get enough light to get it exposed, sufficient DoF AND in sharp focus. I like the shot, but immediately noticed the blur...it could have been a great shot if it was more in focus.

Edited by bmyates, 19 March 2010 - 11:01 AM.

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#8 adamhanlon

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Posted 19 March 2010 - 12:15 PM

Thanks for all the comments guys!

My results with the D2Xs on ISO's much greater than 200 have not been great. I have used 400 for some magic filter shots, and the noise does get pretty out of hand. Bring on a D700x!

By adding more strobe I think you negate the CFWA idea (in this instance) It would light the fish, but not the background-I guess I could probably get a similar result with a macro lens!

Posted Image

Wait for a brighter day!

Adam

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#9 MikeVeitch

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Posted 19 March 2010 - 05:21 PM

Adam, what was your shutter on the second photo? looks like it was far faster than the first shot. You need to concentrate on the shutter speed more for the background as opposed to the fstop. Raise the fstop to f8-11 for more DOF and lower the shutter speed for the background exposure.

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#10 AndyC

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Posted 24 March 2010 - 05:16 AM

Just a thought Adam.
Maybe another approach would be to put the Sturgeons snout and the eye in the same image plane, that way the most important parts of the photo would be sharp.
I believe Martin Edge calls it "paralleling the subject" in his book. Though he mentions it in connection with a flat port, I'm sure its the image plane that matters with regard to DOF.

Cheers

Andy.

#11 adamhanlon

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Posted 24 March 2010 - 09:19 AM

Hi guys,

Thanks for all the input.

The second image is 1/60th at f7.1. It was taken on a particularly gloomy day! Lovely British weather!

The point about paralleling the subject is a good one-in this instance though, and given the distance between the snout of the sturgeon and it's eye-unless you want a side on image, you are forced I think to try and increase DOF. The problem with CFWA is that the snout of the sturgeon is almost on the port in the first picture!

I do think that maybe working on placing the focus point may help. I must admit that I wasn't really concentrating on where it was.

Adam

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