ISO settings

Just wondering what ISO other people tend to use for their underwater photos....I hadn't thought much about this and believe mine is always set at ISO 200, but have no idea why or what it should be!

Thanks and as always Happy Diving!

E

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Nikon D100, L&M Titan Housing, 16mm, 12-24mm, 60mm, 105mm

I think the general consensus is that you should use the lowest ISO that your camera supports to optimize for the lowest noise. Low iso values reduce the grainy effect of film or sensor and give smooth tones (blue backgrounds without any speckling).

For Nikon users that would be 200, for Canon and Fuji ISO 100.

Usually you can get enough light for the exposure even at small apertures (needed for good depth of field) with strobe power and you want to try to underexpose the background a bit for the deep blue feel. If the iso value is used to lighten the foreground, then it brightens up the whole picture and there isn't as much contrast between the bright foreground and darker background. The best way to do this is with the strobe.

Generally, you want to use the lowest possible ISO, because it provides the best image quality - lowest noise, etc, for each camera.

Only use higher ISO if you must, due to light levels, or strobe limitations.

Don

I agree with the comments above. That is why I often think the discussions we have here comparing the high ISO noise performance of cameras is a bit irrelevant to their UW performance. (Of course I realise that lots of UW photographers do take pictures on land).

Alex

My 2 cents and some C-5050 and D70 sample shots at different ISO settings.

http://www.splashdowndivers.com/photo_gall...ettings_iso.htm

Now if only the wind would stop blowing I could get out and shoot some ISO 200 pics.

I never use high ISO underwater. The issue is not the performance at high ISO but the underlying noise that caused the image to be unacceptable when amplified to high ISO. The difference between low ISO and high ISO is just the amplification between the sensor and the A/D converter.

For example, when shooting into a bright sunball, the first prority is to not over expose the sunball. That may imply that shadow areas not lit up by the strobe may be too dark. These shadows can be brighten with curves in photoshop, an operation that is roughly equivalent to increasing the ISO just for the shadows. Think of this as exposing the sun at ISO100 and smoothly increasing the ISO for darker parts of the scene until you're at ISO 800 for the darkest shadows. A camera that has better high ISO performance will render cleaner shadow details in this situation.

I agree with the comments above. That is why I often think the discussions we have here comparing the high ISO noise performance of cameras is a bit irrelevant to their UW performance. (Of course I realise that lots of UW photographers do take pictures on land).

Alex

I agree and I'm puzzled by how many people hail the superb noise performance of the 20D. Yes, its high ISO performance is remarkable but its low ISO noise is worse than the 10D and 1DMk2. Not saying the 20D is bad (quite the opposite), but its not a lower noise camera than the 10D for underwater shooting (and a stop noisier than the 1DMk2 if I interpret Phil's data correctly). We need to concern ourselves with the noise levels at the base ISO.

I agree and I'm puzzled by how many people hail the superb noise performance of the 20D.  Yes, its high ISO performance is remarkable but its low ISO noise is worse than the 10D and 1DMk2.  Not saying the 20D is bad (quite the opposite), but its not a lower noise camera than the 10D for underwater shooting (and a stop noisier than the 1DMk2 if I interpret Phil's data correctly).  We need to concern ourselves with the noise levels at the base ISO.

The only place I've seen detailed comparasion is here:

http://www.imaging-resource.com/PRODS/E20D/E20DA12.HTM

It looks like you are right about higher noise in 20D vs 10D but it's small enough to be within the resolution of the test. The sensor size is about 30% smaller so if they didn't improve the process the expected noise curve would be 1/3 stop to the left of the 10D curve.

Pattern dependent image processing aside, signal-to-noise of regions 3 stops down from the brightest highlight in a photo exposed at ISO 100 is the same as the signal-to-noise of the brightest highlight of a photo shot at ISO 800.

DPreview has a noise comparison here. It shows that the 20D has somewhat higher noise at ISO 100 but better noise performance at higher ISO's. I don't think you can compare zones in ISO 100 and ISO 800 images just because they would be equivalent in light levels. There is noise processing and analog amplifiers that are involved.

I would say that Canon has improved their high ISO noise suppression in the 20D but that its fundamental noise levels are higher than the 10D. That makes intuitive sense as well.

In a separate review, Phil shows that the 1DMk2 has better base ISO noise performance than the 10D. Because of the two tests I conclude that the 1DMk2 has better noise performance, perhaps as much as 1 stop, at ISO 100 than the 20D does. There's no shame in that considering the pixel site size, yet the typical dpreview forum member doesn't agree. The 20D is a nice improvement but you'd expect the 1DMk2 to have better noise and DR and I'm confident that it does.

I haven't followed dpreview chat, but twice the area and 1 stop better noise as it's commonly measured is how the thing should scale. You're right about image processing confusing some of the issues. That's why I qualified my comments. It's probably fair to say that what you see at ISO 800 at a given brightness represent a upper limit to signal-to-noise of things 3 stops lower at ISO 100, otherwise you can underexpose everything 3 stops and push it back up in photoshop and get a better image compared to changing from ISO 100 to ISO 800.

Right, I understand now.

Phil's noise tests are a little hard to follow (being unitless and all). I think you can't compare his graphs between different reviews, either, since the numbers tend to change.

UWphotoNewbie or anybody, re"If the iso value is used to lighten the foreground, then it brightens up the whole picture and there isn't as much contrast between the bright foreground and darker background. The best way to do this is with the strobe."

Can't this problem be addressed by simply increasing the speed for the background e.g. ISO 200 -> 400, F 5.6 -> F 8, and Speed 1/100 -> 1/200 with strobe power constant.

Seems to me that in this example I get the additional depth of field advantage of F 8 with no penalty other than amplified sensor noise.

Can't this problem be addressed by simply increasing the speed for the background e.g. ISO 200 -> 400, F 5.6 -> F 8, and Speed 1/100 -> 1/200 with strobe power constant.

I'm fairly new to this but I'll give a try. Please chime in if others have other ideas. This gets complicated for me when you add the fourth variable of ISO.

1) I think in your example, assuming that the base settings (ISO200, F5.6, 1/100) give you proper exposure but no royal blue background, you would be 1 stop underexposed in the background with (ISO 400, F8 1/200).

ISO 200 -> ISO 400 gain 1 stop of light

F5.6 -> F8 loose 1 stop of light

1/100 -> 1/200 loose 1 stop of light in the background

Strobe constant No change foreground bg unaffected

So now your background is underexposed by one stop. You gained some DOF, used less strobe power and you gained noise.

Alternately if the goal is to increase DOF while decreasing the exposure in the background you could add DOF by decreasing aperture F5.6 -> F8 and compensate in the foreground by increasing strobe power. This should decrease the BG light and give you more shadowing, range and no noise increase.

Of course once you get pushed up against a limit, strobe power, aperture, shutter speed you have to do something and that is where the fourth variable is handy--and its nice to be able to change it midroll while underwater.

Your math is right. But, for the sake of argument, assume the background is properly exposed in the base case.

Then it's

Foreground

ISO 200 -> ISO 400 gain 1 stop of light

F5.6 -> F8 loose 1 stop of light

Strobe constant No change foreground

Net - No change in foreground exposure

Background

ISO 200 -> ISO 400 gain 1 stop of light

1/100 -> 1/200 loose 1 stop of light in the background

Strobe constant bg unaffected

Net - No change in bg exposure

And what I've gained is depth of field at the expense of noise. Besides noise, have I lost anything?

Note: For people new to photography who may be reading this thread, see the following URL for the basics of f stop math.

http://www.splashdowndivers.com/photo_gall...gs_exposure.htm

for the sake of argument, assume the background is properly exposed in the base case.

Actually, I debated about this myself when formulating my response. I actually started with this assumption but discarded it because in this case your background is now underexposed. You missed something in your example:

Foreground

ISO 200 -> ISO 400 gain 1 stop of light

F5.6 -> F8 loose 1 stop of light

1/100 -> 1/200 no change in foreground because strobe dominates

Strobe constant No change foreground

Net - No change in foreground exposure

Background

ISO 200 -> ISO 400 gain 1 stop of light

F5.6 -> F8 loose 1 stop of light

1/100 -> 1/200 loose 1 stop of light in the background

Strobe constant bg unaffected

Net - 1 stop underexposed

What you have gained is depth of field at the expense of noise. If you wanted the background perfectly exposed as before you should just leave the shutter at 1/100. If you wanted it darker go with the faster speed.

My only point is that in normal ranges where you aren't pushed up against any stops, its better to use more strobe power because then the only compromise is less strobe shots on a charge. With the DS125 (and better yet duel DS125s) you have the power you need and pleanty of shots for a day of diving. Most of the time you are not at full even at ISO 200 so you can even use continious mode as well.

So I think we agree. Your way works and so does mine. It just comes down to how much tolerance you have for noise. My opinion is, get the lowest noise and simplify by forgetting about this variable.

My suggestion is: (and I'm just learning this so Alex and James please feel free to instruct me here)

1. Set the aperture you want for DOF (try to leave it there)

2. Set the shutter speed you want for the right color blue water background

3. Adjust the strobe power for foreground exposure.

This should work for most subjects. The only exception is to adjust the aperture bigger for more blurred BG or smaller for black BG.

Oops. You are right. I forgot the F stop effect on the background i.e.

F5.6 -> F8 loose 1 stop of light .

As to the rest of it, I agree with the math. But, the wind is still blowing so I'm mulling the strategy part.

I'll probably go for lowest noise and take what I get for depth of field. But I hate to pass up an opportunity to rethink what I'm doing now that I have a new rig.

The other thing that keeps running around in my head is that I rarely have ISO 200 water to shoot in. Lately, after the storms, it's more like ISO 1600 water. Point being, I want to see the noise on some of my real shots ... not just on my test patterns ... where theory and reality collide.

This is where I envy you. Living in Colorado I get to dive maybe 2 weeks out of the year so not much time to gain practical experience.

Too many hobbies too little time. Spreading by energy between mountain sports and diving--no time for work.

I look forward to your testing. Please keep us posted and post your results. That way I can learn from your mistakes and maximize my success when I do get a chance to get wet.

While there is no question about the noise issue I think it worth pointing out that the ability to change ASA underwater is a fantastically useful thing.

I recently shot a series of natural light pictures on the stern of the Coolidge. It was cloudy on the surface and pretty gloomy down there. Most of these shots were taken at ASA1600. I used the 10.5 fisheye at f2.8 with shutter speeds between 1/5 and 1/10.

As I moved back up the wreck towards the surface I wound the ASA back to 200. Now you can't do that with film!

http://www.users.on.net/~abowie/VWindex.html

I'll have to try that on my wreck shots, particularly the way back ones.

FYI here is a before and after of one of your shots using Paint Shop Pro 9.0 Digital Camera Noise Removal set at the default settings. I never used this feature before but it looks like it has promise.

Before

After