S90 exposing - slightly underexpose?

[browncd81]

Hi,

I was advised to slightly underexpose the images. From my understanding, the S90 combines the 3 channels into a composite histogram. The composite comes from averaging the 3 channels.

So, what happens is the blue channel is to the right of the composite, so underexposing prevents the image from being too washed out.

Is this accurate? Also - I'm not quite sure then how much to underexpose. I can look afterwards at a 3 channel histogram or just how the picture looks and be able to tell. But during the dive, is there any kind of thumbrule? Also, does my 'underexpose to account for blue channel brightness' concept change due to depth, lighting conditions, etc?

Thanks, I'll hang up and listen

 

[Warmwater Wank]

B--Are you shooting in RAW? You should be if you are serious enough about exposure to be paying attention to histograms (more people should pay attention to them but that's a whole other argument). What you'll find is there can be almost a 2 stop latitude for underexposure in RAW but very liitle latitude for over-exposure. I'm not arguing for a 2 stop under correction, just that that is where RAW can really help--with underexposed shots. Use the exposure compensating dial (if you aren't shooting in Manual) and run a test. I'm usually around 2/3's of a stop under but this changes for some situations, like dark scenes I can't throw enough light into. Then I tend to not compensate.

You don't mention if you are using an external strobe, which would certainly matter when you are asking about changing exposure with depth. If you are shooting w/ an external strobe it will govern exposure w/in a 4-5 foot range, which would not change all that much with depth.

Shallow dives in bright sun with white sand below etc. make an even bigger argument for under-exposure, especially if you aren't using a strobe. I think you will get by if you learn to judge things in a quick review on the LCD display. If you aren't shooting jpegs you will find exposure becomes less problematic. I'm not arguing for being imprecise just because you shoot RAW but given it's latitude you can pay more atention to important things. Like composition, diving safety etc.

Getting good exposure uw is critical but so are good post-production techniques. Be as accurate as you can with exposure uw but not so fanatical you miss shooting opportunities or create an unsafe diving situation. You can take plenty of time later, above water, correcting decent expoures in Photoshop, or your image editing software of choice. Don't short change that aspect (or use it as a crutch for bad technique!). RAW is not a magic bullet, it just gives you much more ability to correct and adjust images--if you learn how to. // ww

 

[browncd81]

WW - thanks - great advice. Actually just what I was looking for. And timely too because I'm off to Bermuda tomorrow.

I do shoot RAW, manual, and I use two external strobes. I'm right now starting to learn Photoshop. So I've got a bunch of RAW files ready to go through my workflow - once I figure that part out

Big bummer that I accidentally lost almost all of my RAWs from a trip to the Philippines last summer, especially after hearing what you were saying about recovering the underexposed RAW shots.

 

[Nemrod]

I usually underexpose by 1 stop or more with the S90. I also generally shoot RAW.

N

 

[Cumbo]

If you underexpose the images, is there going to be more noise in the darker areas once you increase the exposure in Lightroom (more grainy etc.) compared to if you expose correctly when taking the photo?

 

[Warmwater Wank]

Eventually there would be noise in underexposed areas that are lightened too much, but not in the range we're talking about (2/3's-1 stop under). It was one apparent reason Canon went to 10mb in the G-11 compared to the 14mb in the G-10--it's less noisy. That same 10mb sensor is in the S-95.

I find I have much less trouble bringing up shadow detail w/ a moderately underexposed area compared to getting any detail that doesn't look faked in overblown highlights. If any noise is present it is fairly easily dealt with (well, at least in Photoshop anyway). It also helps to not be shooting above ISO100. // ww

 

[browncd81]

Thanks guys. Good info.. keep it coming

For setting the amount you underexpose - specifying 1 stop or 2/3 stop etc as opposed to me saying "slightly" - is it possible to be this precise in manual mode? I know for the other modes you just adjust the EV, but for manual are you looking at the histogram in real time and just going off your experience that a certain amount of slightly left is X stops, or are you going off the shade of the blue background color in the LCD (either in real time or reviewing after shots).

I'm starting to drift away from Manual mode when shooting wide angle anyway and just use Av. Am I being lazy and taking a shortcut, or am I finally figuring out what most of you guys have figured out works best? For macro, I still do Manual, unless it's a drift dive or I'm in a fast moving group

 

[Nemrod]

Thanks guys. Good info.. keep it coming

For setting the amount you underexpose - specifying 1 stop or 2/3 stop etc as opposed to me saying "slightly" - is it possible to be this precise in manual mode? I know for the other modes you just adjust the EV, but for manual are you looking at the histogram in real time and just going off your experience that a certain amount of slightly left is X stops, or are you going off the shade of the blue background color in the LCD (either in real time or reviewing after shots).

I'm starting to drift away from Manual mode when shooting wide angle anyway and just use Av. Am I being lazy and taking a shortcut, or am I finally figuring out what most of you guys have figured out works best? For macro, I still do Manual, unless it's a drift dive or I'm in a fast moving group

Yes, 1 stop is doubling or halving the shutter speed such as 1/30 to 1/60 is one stop. Then from 1/60 to 1/125 is another stop or two full stops over the original 1/30. It is ALWAYS this way for all cameras and all lenses.

For aperture it is :

1/ 1.4 / 2 / 2.8 / 4 / 5.6 / 8 / 11 / 16 / 22 / 32 / 45 / 64 .

Each of the above is one full stop. Obviously you can change both shutter speed and aperture to effect your exposure.

Example, 1/60 and f5.6 is the same exposure as 1/125 and f4.0. Yep, it is true and it is ALWAYS true.

N

 

[Warmwater Wank]

Sure you can be "that precise, in Manual, Av, Tv etc. You know those tiny marks between the f/stop numbers or the ones between the shutter speeds? Those are 1/3 of a stop increments. Nemrod just explained full stops, this is just a way to slice things thinner--if you want. Doesn't matter (for the sake of just exposure) if you are using Av, Tv, Manual or using the exposure compensation setting; you are lightening or darkening the exposure by thirds when you use the marks betwen any numbers. (Obviously it would matter which control you adjusted if you were trying to stop action or affect depth of field but that's not the point here.) BTW, it's considered varying the exposure in "stops" whether you change f/stops or shutter speeds, "stops" being sort of a catch all term when referencing exposure changes. There's not too much visual difference between 1/3rd of a stop changes, hard for some folks to see even when results are side by side.

About the screen biz for judging exposure: NO, just use the Review (2 sec. is plenty), not "real time". Reason being, your strobes! The screen shows you how the scene looks, up until you actually press the shutter release and those 2 strobes of yours dump a big bucket of light onto the scene. Since you are using dual strobes, but don't mention what kind, you could also possibly be able to adjust exposure using any strobe output adjustments you may have. Sea & Sea strobes are marked in 1/3rd stop increments on their output controls, other brands are too. I use Review for a quick judgement and just sort of got used to how I liked things to look while UW. It's a ball park thing, given my viewing angle to the screen, glare etc.

Best to figure out what works for you with all this. I'm in Manual most of the time but I work in close a lot. When I do shoot distance shots I tend to go to Tv--but not always! I like deciding what a scene needs, not just always using the same mode and method. (Not that plenty of my casual shots don't just get "taken" vs "made"!)

Well, that's just what one guy does--other gals/guys may vary... // ww

 

[browncd81]

Thanks guys. It's incredible how much my photography has improved since buying the S90, shooting in manual a lot, and then trying to learn as much as possible. Here's a few I'm particularly proud of.

The last one, the "IMG_3926", the coral head, is one I'm not so happy about. It looks extremely blurry. Anyone get this a lot? Current was light today (I'm in Bermuda rt now) and I held it steady. I shot in Av, Macro focus mode, UWL-04 dome, TTL w/ two S2000 strobes, large aperture, ISO about 400.

A little history.. I had a thread last October seeking help for right side blurriness. Thanks to Nemrod's help, I found it was due to an S90 that was defective. That made a big improvement. But I'm still getting general blurriness issues with the UWL-04.

Also had something strange happen today. My right side strobe was firing bright but my left was hardly firing. Test shot on the boat beforehand was okay. My optical cable edges are fine - it is not that. Afterwards, I tried it indoors against a couch. The right was way more prominent. My optical cables go into a cylinder with four holes. Then I rotated the cylinder 180 degrees, the left strobe became the strong one - because it's cable was now where the right one's was. And when I lined it up so that one cable was up and the other was down, the firing was even on both sides. Last picture shows the vertical arrangement in case you were like what the heck is he talking about?