Low light focusing

Hi there

Newby to digital and DSRL

Probably a commen newby question:

When taking pictures of marine mammals in low light conditions, low contrast

with a Canon 10-22 in Subal housing 8'' dome etc....

HOw do you obtain a decent focus, as autofocus will be searching , contrast is low so

it doesnt fix and the animals are fast moving.

Regards

Anton

If your strobes have modelling lights, switch them on. This should help.

If your strobes do not have modelling light, you can add a focus light to the top of your housing. There have been some discussions on which models to use recently...

Thanks for the reply Matt

I recently spend a week in Norwawy-- Had to use 1600 ASA setting to obtain an f-stop of 5.6 and

a shutter speed of 125 , because of the low light conditions in the Arctic at this time of te year. Managed a few shots of some Orcas with freediving.

Strobes was not a option--due to the nature of the subject and freediving and my unfit ass .

Wow!! I hope you are going to show us some of these.

Hope this works

Very nice. I'd love to swim with those guys one day...

Now that I understand your problem better, I suggest you look up another thread on wetpixel that talks about hyperfocal distances. Basically, you could set your camera to manual focus, preset the focus to the hyperfocal distances, and this would ensure your subject's in focus. This way you can focus on lighting and composition.

Hi!

Please be aware that top side hyperfocal distances are not transferrable to UW hyperfocal distances when you use a WA behinde a dome.

The dome itself is a negative diopter so UW infinity is somewhere around 50cm (depending on the dome radius).

Keeping this in mind you could try to focus under good light conditions and remember the so gathered settings for manual focus settings under bad light conditions. Sure, there's a way doing it by maths but it's a bit complicated if you don't know the exact dome diameter etc.

Helge ;-)=)

In low light, low contrast conditions where you are shooting big subjects I'd suggest that your best bet is to prefocus on a something at a similar distance away as the subject that you want, then lock focus (I'm sure that you can do this on your camera) and use this setting for the dive.

Another alternative is to use a manual focus gear and manually focus not relying on the autofocus at all - but with short zooms this may not be an available option - check with Steve at Ocean Optics - he will know if Subal support manual focus on the 10~22 Canon lens. If Subal don't, and you are happy to use the lens at a fixed focal length then there are one or two people in BSOUP who will be able to produce a custom manual focus gear for you. There are no other solutions as your autofocus sytem relies on contrast and large creatures in dull conditins may simply never produce sufficient contrast for any AF system to work with.

Paul's suggestion is probably the best. The problem comes from both low light, and lack of contrast between your subject and the background. Therefore, pre-focusing (whether manual or autofocus on another subject) is the best all round solution.

Another (potentially costly) suggestion is to use a faster lens. Just looked up the 10-22, which is a F3.5 max lens. Not sure about Canon lenses, but there may be a better, faster wide angle lens (say F2.8 or better). With one or more stop of light, the camera should focus better.