Focus mode

Hi there. I am a pretty seasoned UW photographer with a point-and-shoot (Canon A710IS in a Canon housing). I just moved up to a 30D in an Ikelite housing with a DS-160 strobe.

I took the rig out for its initial saltwater wet test yesterday -- La Jolla Shores in San Diego. Visibility was not great but I was able to get some good shots in. This rig is going to take some getting used to!

In any case, I was wondering what focus mode you guys use. I was using AI-Servo (continuous focus) but got quite a few shots out of focus because I drifted off target just as I pushed the shutter.

I was wondering if single-shot autofocus would be preferred -- just wondering about your collective experiences.

Thanks,

Dan

You'll likely get different answers from different people, but I for one do use single-AF. Reason one, my Oly is a bit older and only has 3 focus zones, which I deactivate to only the center anyway. Then if I want my focused subject to be off-center, I focus where I want with a half-press and reframe before completing the shutter operation. If I tried that in continuous mode, as soon as I moved for the reframe I'd lose my selected focus element, thus ruining shots like this:

Of course, I didn't get much DOF variation in that shot anyway, so its an even bet whether you think that shot is 'ruint' to begin with.

The other reason is related to the Oly focus being a little slow sometimes, even with a focus lamp. If I was on continuous AF I'd run the risk of it running in and out the whole range, vs. just doing it once and then I have to re-press to have it try again. I probably lose shots but prefer the sensation of being a little more in control of the hunt. Not sure how either of these ideas would apply to either your shooting style or camera.

As to drifting as you push, that's probably a matter of technique improvement as well, kind of along there with breathe control to hold steady, or stretching/compressing your body to compensate for drift direction a little (as best you can when using a viewfinder) if you know you'd still gliding a little at the time you're shooting. Don't let the first try get you down too bad, especially if your prior experience was using the PnS in 'liveview' like mode at arms length with the screen, holding a rig up to your eye will take different 'muscles' so to speak.

Thanks. This is an amazing photograph. Do you have the EXIF for this shot, just out of curiosity (lens and aperture is what I am after).

Regards,

Dan

In any case, I was wondering what focus mode you guys use. I was wondering if single-shot autofocus would be preferred -- just wondering about your collective experiences.

Hi Dan,

In my own experience I've used single-shot autofocus. That way I'm assured that the shot will be in focus. I had too many experiences using continuous focus topside with my D70 to trust it underwater!

I just attended a Niikonians workshop on the D300 camera where the instructor suggested a technique of separating the determining correct exposure task with the focusing task. Depending on whether my housing allows control of the buttons on the camera that separately control these functions, I may try the new technique on my next dive trip.

I know that some uw photographers use continuous focus but I haven't been one of them.

Ellen

Thanks. This is an amazing photograph. Do you have the EXIF for this shot, just out of curiosity (lens and aperture is what I am after).

 

Regards,

Dan

Click on the photo and it takes you to the page on Flickr directly (according to Flickr TOS that's the way you're supposed to use images shared from there), then there's a "more properties" link for the EXIF down toward the bottom right. But for brevity, I did a cut and paste:

Exposure: 0.01 sec (1/100)

Aperture: f/8

Focal Length: 54 mm

ISO Speed: 100

Exposure Bias: -2 EV

Lens was a Zuiko 14-54, which is pretty sharp from wide open at the wide end, so at the 'long' end and f/8 wasn't going to be at much risk. But note I'm on Olympus 4:3 system so my DOF for a given aperture and focal length will differ from yours.

Thanks for the comment. That's one of my favorites too, although I do confess I cropped it more than a wee bit to get that final framing. I still debate with myself everytime I look at it if I should go for more of a portrait orientation to get that diagonal line from the moray's "chin" up to his dorsal fin where it meets the sponge as the main diagonal of the framing, but then I'm always dissatisfied about losing that dark contrasty shadow. But that's a topic for a different thread (C&C).

Whether to use single servo AF or continuous servo AF depends on camera/lens combination. I shot AF-S with my D70 because AF-C seemed a bit slow to track. Since I upgraded to D300 I've been using AF-C because the response is much faster. YMMV

Exposure: 0.01 sec (1/100)

Aperture: f/8

Focal Length: 54 mm

ISO Speed: 100

Exposure Bias: -2 EV

 

Lens was a Zuiko 14-54, which is pretty sharp from wide open at the wide end, so at the 'long' end and f/8 wasn't going to be at much risk. But note I'm on Olympus 4:3 system so my DOF for a given aperture and focal length will differ from yours.

Was this shot from behind a dome? The reason that I ask is that I am getting a really shallow DOF at f/8 -- much less than this! I think it's because of the close-up filter that I am using -- going to do some experimentation with that.

Regards,

Dan

Dan,

The focus mode on your Canon will also depend on the subject your shooting. On slow moving or staionary subject I like to use one shot AF mode triggered by the button on the back of the body. Then I can recompose and shoot. For moving targets like sharks, dolphins, fish schools etc. I'd use AI Servo. Same idea holds for macro.

Have fun,

Steve

Was this shot from behind a dome? The reason that I ask is that I am getting a really shallow DOF at f/8 -- much less than this! I think it's because of the close-up filter that I am using -- going to do some experimentation with that.

 

Regards,

Dan

Yes, I have an 8" (dia) dome port, and this lens does not use a diopter with the proper dome and extension (close focus is to a bit under 9 inches). But again the 4:3rds system already has higher DOF for the same aperture/focal length than either FF or cropped sensor CaNikons (which is perhaps a strength for instances like this, but considered a weakness by many who want extremely narrow-range DOF slice images, which are much harder to get with Oly). Another difference might be that I wasn't as 'close' to the subject as I like to be. I don't recall the shooting distance here (3' from dome to nostrils?) but remember that DOF is bigger for wide angle than narrow, and for smaller apertures than larger, but also bigger for long distances to subject than short. If I was good enough to get really close, and be focusing much closer to the dome face, the DOF would drop.

Sorry, we've kind of hijacked your original topic of focus mode? I don't want to turn this into an Oly vs. the others thread, because I always lose. I do see it's related - increasing DOF can make the effort/technique involved in getting the focus where you want a bit less - but not quite fully on your original question. And the downside of too much DOF is you 'lose' subjects in too clear and busy a background, which is criticism I hear on a lot of my shots (and agree with - the above-linked shot in particular would've been more powerful IMO with a blurrier background).

If you can get your technique right to put the focus where you want, then I wouldn't sweat a narrower DOF. Although from the other discussions in parallel threads you started it does sound like you might be able to ditch the 4x you're using and that would help out a bit but I really thought that was more a factor on CA and corner sharpness, but I guess it makes sense that magnification also sacrifices DOF. Back on the OT, Steve's got a good point about the subject of the shot mattering, and using continuous AF for faster-moving larger beasts. I wish I was fast enough on settings to be able to swap out when I was shooting reef and got the 'shark' gesture and a point over my head from my dive buddy.

I nearly always use AI Servo (or APS-C as it is called on my D300). In your post you said you drifted off target before pressing the shutter. I don't think using Single will help that. Single will help if your lens is continually changing its focus from one object to another (focus hunting). I find I don't have a problem with hunting if I use a focus light and single area focus. Camera movement due to breathing, currents, surge, or other factors are always an issue with Macro. For the smallest subjects, I make the final focus adjustments by way of physically moving myself inches closer or further from the subject and anticipating precisely when it will be in focus. Here is an example when I needed to physically move and anticipate the shutter release because I couldn't stay exactly still for long enough to stay focused on the narrow DOF.

I also think you will find that F8 has plenty of DOF if you are at least a few feet away from your subject. For macro work, you will need smaller apertures (eg F16-F36).

The first several dives being new to a U/W DSLR you are bound to have some of focus shots (I had a ton of them), take your time and practice and you will figure it out soon enough.

Thanks everyone for your replies. I am well on my way. I need a lot more practice! I have a lot of stuff to try out. Unfortunately, due to a 15-month-old running about, my diving opportunities are very limited, but I look forward to a lot more in the coming years.

Kindest regards,

Dan