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Discussion on exposure


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#1 divegypsy

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Posted 20 May 2012 - 04:15 PM

Adam, Again you've provided us with some shots that very nicely show the D800's ability to render the sun nicely. The pictures as posted are small, and they aren't of the same subject, but to me the Sigma 15mm shot looks sharper, crisper, than the shot taken with the Tokina 10-17mm lens. Thank you.

Paul, I agree with you concerning using the matrix metering. I think Canon used to, and maybe still does, call their equivalent metering "evaluative metering". I don't use matrix much because Nikon says "matrix" is based on algorithms derived from "thousands" of pictures. But all these thousands of pictures are almost certainly topside pictures. And since I don't know the thinking Nikon used, I cannot predict what the camera might do consistently enough to really count on it in my underwater photography.

I do use center-weighted metering. A lot. Especially when photographing a subject, like a fish, that is moving around in the water column. Because of this movement, the color of the water behind the fish varies continuously. In this type of situation, I find it almost impossible to keep changing the camera exposure settings (aperture or shutter speed) based a manual spot meter setting which would keep the water color consistent. And still keep my attention on composition and focus. If the fish moves 15 degrees to up or down in the water column, the water color brightness behind the fish can change by at least a full aperture. If the fish moves 90 degrees or more to either side, the angle relative to the sun changes dramatically and the water color change can be two or three apertures. In this type of situation I find that using the center-weight metering in combination with shutter-priority auto-exposure gives me a much more consistent "background" exposure. And TTL flash allows the fill flash to be about right and compensates as the fish moves closer or farther away. This technique also has the advantage of maintaining a good ambient light exposure component if a cloud passes in front of the sun and the overall light level drops. The camera just opens the aperture setting to compensate. And TTL flash adjusts to the wider aperture. This technique has worked so well that I now use it on virtually all of my shots where water color is important in the picture. My thinking on this is that if I can delegate this technical aspect, exposure, to the camera, I can give more of my attention to focus and framing the subject.

I will attach a few shots from earlier this month in Bali where I used this shutter-priority exposure technique.

If I've done it right, there will be five pictures. There are two pairs of shots - a sweetlips with butterflyfish and a cleaning station with surgeonfish. The camera settings on both pairs of shots were the about same. If you look at the sweetlips shots, you will see that one shot is virtually head-on while the other is angling upward from below. If I had used manual spot metering, I would have had to manually readjust the shutter speed or aperture to keep the water color such a consistent blue. Shutter-priorityauto exposure did it for me. The shots of the surgeonfish cleaning station are from totally different angles. And in one I am much closer. But the proportion of blue water in both is about the same, so auto-exposure kept the overall scene very similar and the TTL flash compensated for the difference in distance. My white balance in the two surgeonfish shots did change noticably because in the closer shot, the flash had been filtered by less water and was warmer when it got to the fish. But that would also have been the case if you were shooting everything on manual. The fifth shot is just a crinoid shot I liked, again shot on shutter priority with TTL flash.

Paul, I guess we will always disagree on whether housing color makes a difference. All I can say it that topside wildlife photographers use camou clothing, and even camou tape on their tripods and lenses to get closer to their subjects. Should we believe that marine creatures are so unobservant and so unwary that it wouldn't make a difference with them, also? I believe it does and so I try to minimize bright things that can grab their attention. I believe a darker, less reflective color is better than a bright color. And believe that a camou or disruptive color pattern is still better.

Fred

Attached Images

  • Surgeonfish_2.jpg
  • Surgeonfish_Unicornfish.jpg
  • Sweetlips___Butterflfish__V2.jpg
  • Sweetlips___Butterflfish__V1.jpg
  • Crinoid_on_Sponge.jpg

Edited by divegypsy, 20 May 2012 - 05:23 PM.


#2 divegypsy

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Posted 20 May 2012 - 05:00 PM

Oops! I just realized that the five pictures I posted are "processed" and I've gone from the RAW to a jpg after adjusting the white balance and exposures slightly. I'll try to locate some consecutive shots from the sweetlips session, which was in shallow water and on a dive that lasted almost three hours. And post those. Perhaps this should be in a new topic thread, not the D800 thread. Maybe I could call it "P&S D700". P&S an abbreviation for "point and shoot".

Perhaps still another thread, which might be called "Does housing color matter?" might also be worthwhile? Is anyone interested in either of these topics?

Adam. I've seen that you are able to label your attached pictures individually. How can I do this so I don't just have a bunch of pictures after all the written explanation? If I write a paragraph or sentence and then attach one picture. And then write some more and attach another picture, will that do it? Or do I need to to it a different way. Your help on this would be appreciated. Thank you.

Fred

Edited by divegypsy, 20 May 2012 - 05:03 PM.


#3 Don in Colorado

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Posted 20 May 2012 - 09:27 PM

Sorry to go off topic here, but

Fred,

That is the best explanation on the "proper way to expose an underwater photograph" that I have ever read. Thank you! If you ever write a book or booklet on proper underwater technique, I'll buy it.

Don

Edited by Don in Colorado, 20 May 2012 - 09:28 PM.


#4 adamhanlon

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Posted 20 May 2012 - 11:07 PM

Hi all,

I have moved these posts from the discussion about the new Nikon D800 as I feel that these definitely warrant a topic on their own, and they are not related to the D800 at all.

The original thread is here:

http://wetpixel.com/...t...46334&st=60

@Fred, I embed my images from my Smugmug site-they actually provide the bb code to do so. If you click on the images you will open in bigger size. There are comprehensive instructions on embedding from other sites here:

http://wetpixel.com/...p?showtopic=904

and here:

http://wetpixel.com/...showtopic=15473

Adam

Adam Hanlon-underwater photographer and videographer
Editor-wetpixel
web | Flickr | twitter | Linkedin | Facebook


#5 divegypsy

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Posted 21 May 2012 - 02:20 AM

Hi Adam - I think you were right to move my post to a new topic thread. I try not to spend a lot of time on the internet and don't go to lots of other websites. Don't know what smugmug is. Didn't get a mobile phone until four years ago. Guess I'm just a DAD - Digital Age Dinosaur. It looks like I'm out of luck on matching pictures and caption info. I don't have a website yet.

Don - Thank you for the nice very compliment about my explanation on why I'm using center-weight metering in combination with shutter-priority auto exposure so much these days. I could also use aperture priority, but too often then, the camera would drop the shutter speed so slow that the fish would blur. And I don't want that to happen unless I do it intentionally. My D700's, are my first digital cameras for underwater use and have opened a lot of shooting possibilities that weren't there with film and the film cameras I used before. One of the reasons I waited so long to make the switch was that I wanted to continue using the same Nikon lenses I had been using with film. And have them perform with the same angle of coverage and same working distance from camera to subject. And Nikon took much longer than Canon to introduce a full-frame DSLR. The best example of those "special" lenses is my 70-180mm Micro-nikkkor zoom, the lens I shot the sweetlips and butterflyfish pictures with. The 2.5:1 zoom feature lets you find a good shooting position and vary the framing to shoot different "views" without moving, which often requires you to change strobe positions as well. And by not moving a lot, you disturb the critters less.

Because I came to digital from the film era, and the film era prior to TTL flash, I had to learn how to do a lot of things manually. And really value all the automatic capabilities of today's camera's and flashes. None of my film cameras had a separate control for flash compensation. So if you tried to use an auto-exposure mode for the ambient light, the TTL flash also got lighter and darker proportionately. With a separate flash compensation capability, you can now vary the ambient light in an auto-exposure mode using the normal compensation control (which I call "global compensation because it also affects the flash) and then make the flash lighter and darker as you want to using the flash compensation, which adds to or subtracts from the "global" compensation. As you get familiar with this idea and making it work with your camera and housing, your number of good "first shots" will increase. Maybe considerably. Accessing these controls easily, is why I've spent a lot of time and money making modifications to my housings.

Certainly manual exposure has its place. And is the best option in certain situations. But with any shooting technique, it is important that you run a series of "tests" to program yourself so that you can predict what the camera will deliver with particular settings. This was all the more important in the film era because you had to wait until you got home to have the film processed. Digital is great for speeding up the learning process.

One of the "tests" you can do very easily is to shoot a whole series of pictures of just the water. Have something so dark it will remain black in all of the pictures if possible. Use it as a reference when you view the pictures on your computer. Set your camera to the manual exposure mode and on spot metering as a start. (Later you can try the different auto-exposure modes and different metering patterns.) Shoot a series of shots up and down the ambient light metering scale that is in the camera's viewfinder. With my D700, this scale runs from -2.0 to + 2.0 in thirds of an f-stop. When you do this a couple times, you will start seeing that when the water is exposed at -.7 on the analogue metering scale, it comes out the same dark blue again and again. At +.3 you will get a lighter blue. The same thing is true for each rendering of the blue water relative to where on the analogue exposure scale you shot it. Later, when you're shooting a real subject, meter the water color and expose the water to give you the shade of blue you want for the background of your subject. You may want a dark blue for a light or bright subject. Or to make your picture look like it was taken late in the day. Conversely, you may want a lighter blue to silhouette something against when shooting upwards towards the surface. Once you set the ambient light exposure to get the background color you want, then add the amount of flash you need to complete your picture as you envisioned it.

Think about what you want for your result before you push the camera trigger. Don't just take a picture. Make a picture. And make it YOUR picture.

Fred

Edited by divegypsy, 21 May 2012 - 03:37 AM.