Metering the Blue

So, I have finally been able to get consistently relatively decent blue backgrounds in my shots using the tried and true "metering the blue" technique. My problem is that when I actually use the setting that the camera tells me to use it is always overexposed.

On a recent Aggressor trip I tried to get to the bottom of it, dive after dive. Then I had a couple of well known photo pros with me on a few dives with the same results. As long as I under expose by a stop and a half the picture looks fine. http://www.flickr.com/photos/abbpics/sets/72157618582242195/

I shoot a D300 with 2 DS 125's. This happens in Shutter or Aperture Priority, and it's not because I'm not pointing the camera into the blue properly.

Why would this be?

Why would this be?

Hi Andy,

Which metering control are you using, Matrix, Center-weighted Average, or Spot? It's a pretty common issue. A bunch of folks shoot manual mode so they have the control they want.

Steve

Don't shoot in an auto mode. Use manual exposure.

If you need to shoot in an auto mode than you need to use your exposure compensation to get the right blue. Also you have to measure your blue background and then hold down your exposure lock.

When you say it is "always overexposed," that is in your judgement. Not the camera's. The camera meters to achieve a certain "middle of the road" exposure (18% gray or actually 12% gray equivalent), based on what the camera's engineers believe an exposure should be for any scene. In your case, the exposure you desire is a stop and a half below the camera's preference. In my case, it is about 1 stop below. I dial in -1 EV compensation for wide angle. I shoot Canon cameras.

Take a look at this article on Camerea Metering and Exposure. Looking at the 18% blue tone you might think it is over-exposed.

Also this article on 18 percent gray.

Thanks for the replies. Glad to know it's a common issue.

I do shoot in manual and use spot metering when shooting cfwa, When I say it's overexposed I mean that in manual mode, if I take the shot based on the reading the meter gives me it will be overexposed. At that point I have the option to adjust speed or aperture and I do.

Yes, in auto mode I would use -1.5EV and hold down the lock but I try to get my manual groove on whenever I can hoping to make it second nature to me.

So, basically, what I'm hearing is that I should just keep doing what I'm doing and adjust for that stop and a half?

If you expose for your blue background it should be correct. You may have to adjust your settings or EV exposure.

If you are shooting CFWA you then have to adjust your strobe out put so that the close subject is properly exposed. If you are trying to meter your close subject then your background will not be properly expose. You need to expose the background and your subject separately.

Usually you adjust your background settings with ISO, aperture, and f stop. You adjust the subject exposure with your strobe settings.

If you expose for your blue background it should be correct. You may have to adjust your settings or EV exposure.

 

If you are shooting CFWA you then have to adjust your strobe out put so that the close subject is properly exposed. If you are trying to meter your close subject then your background will not be properly expose. You need to expose the background and your subject separately.

 

Usually you adjust your background settings with ISO, aperture, and f stop. You adjust the subject exposure with your strobe settings.

Actually, that is exactly what I do. Meter for the blue and adjust strobes for the close focus. Although it would be nice to have a little easier way to control the output of my DS 125's like the Ikelite guys do.

My issue was why a supposedly "correct" and properly exposed meter reading gave me an overexposed background. Now that I realize that all I need to do is allow for that and all should be honky dory.

Is there a device that would allow me to dial the output of the ds125's without having to manually do it on the strobes?

Usually you adjust your background settings with ISO, aperture, and f stop. You adjust the subject exposure with your strobe settings.

that's not entirely accurate. the only setting to independently control background exposure is shutter speed. Aperture & ISO affect your strobe/foreground exposure also. I often like the simplicity of presetting a aperture/strobe power combo for expected subject distance and adjusting the shutter speed in the 1/30th-1/400th range (yes you can beat the sync speed limits to a degree) to compensate for the changing background exposure on the fly.

My issue was why a supposedly "correct" and properly exposed meter reading gave me an overexposed background. Now that I realize that all I need to do is allow for that and all should be honky dory.

 

Is there a device that would allow me to dial the output of the ds125's without having to manually do it on the strobes?

You're not getting an overexposed background, its properly exposed. However, if you fully expose a scene with the ambient light then add more light with a strobe, the subject will be overexposed and the background properly exposed at 18% grey or however it is the camera measures it (of course "properly exposed" can be quite subjective, as in this case). You want the subject underexposed so that you can expose it primarily with your strobes, and that underexposure produces the most pleasing natural looking blues.

ikelite does have a strobe power controller which is also a slave sensor that attaches between the strobe & camera. it has more power settings too i believe. Cheers,

Chris

Also worth noting that newer Nikon cameras have a very different blue water metering than older ones. For example cameras like the D100, D200, D2X and F5 and F100 usually need significant under exposure to produce a pleasing blue water colour.

For example, using matrix-metering and aperture priority (or another auto exposure mode) you will generally need between -1.7 and -1.3 EV exposure compensation to produce a rich blue water colour. Because, as others have pointed out, a rich blue water requires under-exposure relative to the 18% grey the camera is looking for.

However, the newer Nikon SLRs (I have not tried them all) e.g. D700 and D3/D3x will give this rich blue using matrix-metering and aperture priority, with only a marginal under exposure of -0.3 EV. (Not shot the D300 on an Auto mode, so not sure which camp it falls in to).

I am not sure why this is. My guess is that maybe Nikon has included some underwater scenes in Scene Recognition aspect of the exposure evaluation (possibly linked with the fact that white balance evaluation, the camera can tell it is underwater, also feeds into the exposure evaluation).

Anyway, whatever the reason the D3 series and D700 (and possibly other new Nikons) are significantly different from the older Nikon Film and Digital SLRs in this regard.

Alex

Alex,

thats really interesting, i had no idea. very cool. i'm awaiting a housing for my D700 set to replace my D200 for UW work. I'll have to test this out before i sell my D200 rig. I could also borrow a housing for my D300, maybe i'll do a comparison within the next couple weeks. Has anyone done this yet? I'd be interested to see how this translates to open ocean ambient light work, as i've sometimes had trouble getting a 'correct' exposure with my D200 in these scenarios. Cheers,

Chris

It is interesting - but most of us shoot manual most of the time (as you say above) - so it is not that significant. Alex

For example, using matrix-metering and aperture priority (or another auto exposure mode) you will generally need between -1.7 and -1.3 EV exposure compensation to produce a rich blue water colour. Because, as others have pointed out, a rich blue water requires under-exposure relative to the 18% grey the camera is looking for.

 

Alex

Thanks Dr. Mustard. For some reason I was under the impression that the camera would meter the blue "correctly". All is well with he world now. This combined with the response I got from Ikelite about using the in-camera flash compensation with the DS 125's and the TTL adapter in TTL mode to control flash output instead of keeping them in manual and adjusting output from the strobes should help a lot. The whole point was to not have to keep taking the camera away from my face and reaching up and turning the dial on 2 strobes. The Manta is usually gone by then.

I've been using the camera and strobes in pure manual mode with spot metering and adjusting the "blue" with shutter speed. I guess I'll try Aperture mode and matrix metering. Plus now with more control over the strobe output the close focus part should be easier to control too.

You find you have better results with matrix vs spot metering?

Andy

Alez wrote:

"Not shot the D300 on an Auto mode, so not sure which camp it falls in to."

Aperture priority setting ont he D300 usually means I dial down by -0.3EV or even -0.7 depending on the location.

Your mileage may vary.

Michel

PS: And yes... we mostly shoot manual mode anyway.

PS2: Resorted to "A" mode when my last vintage Sekonic MMII died three years ago... sob..

If you use a Sekonic Marine meter you can set it to provide your basic exposure and then set your camera TTB (Through The Brain). Incident meters work best but the old Sekonic will do the job.

My Sekonic still works, but I never use it (maybe that is why!).