Beinnger help! Sony RX100ii focusing issues

[Blenny84]

Hi guys,

So I bought my first compact kit from ebay and tried it all in the pool yesterday but something is not quite right and can't figure out what it is.

Setup:
Meikon RX100ii housing
Sony RX100ii - setup for underwater use only following this guide Underwater Settings for Sony RX100 II & III & IV
Camdive Fish eye wet dome lens
ISO Auto 160-800
AF off

Issue: The object (a weight) I was filming got out of focus as soon as I zoomed in a little or got a bit closer to it (1 feet +-) on video mode. Also the image was getting darker overall but more pronounced around the edge of the frame - no vignetting though, it was as if someone suddenly switched off the main light.
Bigger objects like other divers doing some training seemed to be in focus all the time.
I only do video with the camera and the dial was setup on A mode. I just pressed the movie button to start filming and was fiddling with the zoom a bit to test.

There was a message on screen all the time that said 'Tracking focus' I have no idea if this is related or not.
There was a layer of water between the house port and the dome lens (as it is supposed to be?) so the lens was working fine at providing wide angle.
I changed the focus area from flexible spot to center but did not make any difference.

Does anyone know what this could be? I hope there is nothing wrong with the focusing on the camera...

Cheers

 

[Blenny84]

This is the clip that shows the actual issue - 00008
As I zoom out it gets in focus and when zooming in again out of focus.

 

[outofofficebrb]

How close are you to the subject? Do you have a dive light? If you shined light on the weight, does it help you focus any bit?

(I have a RX100 but in a different housing and have never run into this issue.)

 

[Blenny84]

I was about a feet away and was not using any dive light. Having said that this was and indoor pool and light conditions were not great.

How much of a difference does a dive light make in terms of helping the camera focus? I have seen really high quality videos made with the same camera with natural light.

I did some more testing at home in low light with limited ISO 160-800 first and the results were identical to underwater. As soon as I zoom in a bit the image gets really dark. I then changed the ISO to 32000, 1/50 f1.8 and it got much better and allowed me to zoom in much more before it got darker.

Does this mean it was purely due to the fact that there wasn't enough natural light in the pool?

 

[Andrew Donn]

Autofocus systems have historically not worked very well in underwater videography. The systems get confused by stuff floating in the water column or by tiny bubbles on the outside surface of the lens causing the system to "hunt" back and forth trying to find the correct focus. Most recommendations are to turn of the autofocus system altogether and just use a manual focus or to allow the camera to autofocus but then lock the focus with an "AF Lock" feature if so equipped. Unfortunately for the situation you described this does not work because as soon as you zoom your focus setting changes. If the AF is locked the subject will go blurry. Although it sounds pretty basic it has not been until very recently that digital cameras have been able to maintain focus while zooming in video mode. Adding a light may help the situation because you will be increasing the contrast in the image which is what the camera is using to set the focus. One technique might be to shoot at one zoom setting with the AF off or locked, pause your recording, zoom and unlock the AF and allow the camera to refocus, lock the AF again, then continue to record. Another is to avoid using the zoom and leaving the AF system turned off. It will probably work fine under the right conditions, clear water, bright light, etc.