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mcyoung

Low vis/UK waters - wide angle minimum aperture?

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Hello,

 

So, putting together a system for a Sony a7RII. Diving in the UK in cold green waters. Visibility is pretty poor. Obviously there's a limit to when you can actually take a photo, but assuming I can see a scene through my mask (let's say 5 - 10 m vis) is there a generally recommended minimum lens aperture for those conditions, to help keep exposure times (and risk of camera movement) down?

 

I assume that because large apertures (low F) increase background blur, which isn't ideal for a wide angle shot, in reality it's a compromise between setting the aperture get the DoF you want, and exposure to then get the light, but I thought I'd ask just in case...

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Are you talking about video or stills? I think generally you will just have to bring enough artificial light for cold/murky water, although backscatter can be a problem, if you're not careful. Apart from that, general rules about aperture and soft corners for wide angle lenses still apply. Quite possible that you will just have to increase ISO to get the exposure you want.

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Sorry - stills.

Yeah, I'm assuming that artificial light would be a non-starter. The water where we are tends to be quite bitty (algae, maybe?) which you can sort of tell is there but not see directly, if that makes sense? But would definitely show up under lighting.

 

I guess as the support diver it's up to me to take along some v. large lights...

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5-10m vis is pretty reasonable in much of the UK. Careful use of strobes is fine. As for aperture, well that depends on your lens/port and whether the subject matter in corners shows aberrations up badly. I tend to use f/11 as a miniumum with the Soy 20/1.8 behind a 200mm port but as I said, it depends. I also find the A7II better in terms of focus than the R. 

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Your aperture underwater is generally chosen based on depth of field (macro) or corner sharpness (wide).   It's not really going to change based on visibility very much.   Remember that wide focal lengths start with a wide depth of field, so stopping down doesn't really do much to bring in more depth of field.   But it does a lot for corner sharpness.

It's not always correct to use aperture to brighten up an underwater image - too many other effects at play.   It's much more typical to add light with strobes or increase ISO rather than open aperture for more light.   The effect on corners is just too obvious to ignore if you don't stop down to some minimal amount which may be F8.

Shooting underwater is a challenge,   

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Cool - thanks.

 

No satisfaction without a challenge - good to know not to use aperture in this way.

 

 

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