AF assist on or off?

[Jetwrench]

I have the A95 and will be shooting manual mode with auto focus on.
One thing I'm not sure of is whether to keep the AF assist beam on or turn it off. Anyone out there notice a difference with the camera's ability to focus u/w with it turned off? I'm guessing distance and normal vs macro mode may play a part as well.
I don't want to scare away the critters if I can help it. Thanks for any help!

Jet

 

[RiotNrrd]

Hey Jetwrench,

I don't know if this is just because I was diving at a popular dive area, but I was quite surprised at how little the fish up a the quarry where I dive paid attention to my flash. They seemed to ignore it completely. My inital thought would be that its no big deal to leave your auto-focus beam on (in fact, I'm prety sure it is an invisible IR beam - I don't think fish see wavelenghts different from ours, but I'm not sure).

All: is this lack of fear of a strobe common among fish? Or does it vary from fish to fish, location to location? I know temprament to divers is often by species, but I'm curious if in general their brains don't see a flash as a scary thing. Any comments?

RiotNrrd

I have the A95 and will be shooting manual mode with auto focus on.
One thing I'm not sure of is whether to keep the AF assist beam on or turn it off. Anyone out there notice a difference with the camera's ability to focus u/w with it turned off? I'm guessing distance and normal vs macro mode may play a part as well.
I don't want to scare away the critters if I can help it. Thanks for any help!

Jet

 

[bobf]

One thing I'm not sure of is whether to keep the AF assist beam on or turn it off. Anyone out there notice a difference with the camera's ability to focus u/w with it turned off?

Curious if there's a diffuser on your housing blocking (actually diffusing) the onboard flash that may also be blocking (diffusing) the af assist lamp.....if so, is the assist lamp still strong enough to offer any influence?

If not, might a separate aiming light aid your camera's ability to capture focus lock in low light situations?

You may be able to conduct tests in a very dimly lit room, camera in housing, to determine if the af assist lamp is of value in your situation...........

hth,
b

 

[Spoon]

wow i never thought of that, il test it out later, i always ahve used the af beam on

 

[Jetwrench]

Curious if there's a diffuser on your housing blocking (actually diffusing) the onboard flash that may also be blocking (diffusing) the af assist lamp.....if so, is the assist lamp still strong enough to offer any influence?

hth,
b

Bob, good question! Yes, the beam will be blocked by the diffuser. I have since tested the camera in several different light levels and I can't see any difference in the focus control. I have mixed feedback on this from other quality shooters on the board, but the results so far say turn it off. I'll bet Canon doesn't even take in to account one may be shooting u/w. I haven't seen any hunting of the lense, so I think the AF beam may be just a waste of power. My trip coming up should reap some reward on this subject. I'll let you know what I find.

Jet

 

[Uncle Pug]

The Fuji housing for the F10 point and shoot has a clear circle in the diffuser so that the focus assist lamp can *shine forth and illuminate*. However, what I found was that the focus assist lamp (visible green) illuminated *stuff* in the water between the camera and the intended subject... and the camera would then focus on the *stuff*. I have some excellent pics of *stuff* taken using the assist lamp.

Don't know if this carries over to the Canon but my suggestion is to turn off the assist lamp for U/W photography.

 

[bobf]

A technique that has worked for me is to set the camera to spot focus. On my camera that means that the camera will only be interested in the area between the two brackets [ ] found on the LCD when searching for what to focus it's attention on.

In low light situations, if I then use an aiming light such as a mini q 40 and target it to that specific location, it allows the user specific control as to which area of the scene the camera will deem important. I lock in focus with a half-press shutter technique. One focus is locked in ( a green light located next to the optical viewfinder on my digicam will stop blinking and remain in on position), I can then recompose the composition if desired prior to full press on the shutter button.

When using an aiming light to assist focus, be sure to choose a shutter speed that will diminish the capture of ambient light. I recommend a minimum of 1/125 sec to avoid the "hot spot".

hth,
b

 

[malaysia-islands]

I did make a few mistakes by turning on my A70's flash when diving recently. Some of my photos were rendered useless because of the excessive backscatter. My WP-DC700 does have a diffuser but still the "stuff" snowy effect was too strong.

In fact, at this one spot, I managed to expriment with and without flash on the same subject. The non-flash was considerably darker but brilliantly correct through Photoshop's Auto Level. The flash shot, while the raw image looks nice, but a close-up looks reveals too much particles.