MWB issues with Sony A1

WB works by adjusting the gain on RGB. When you have strong GB, the contrast is lost. Putting the filter on increases the contrast which is why the camera managed to WB. As I said, MWB is a function of enough light and contrast with a background that allows the WB to find what it thinks is neutral.

I don't think I understand what you are saying here. If you are talking about contract within a color channel, then adding a red filter would lower the levels of the green and blue channels, but I don't think it would change the contrast in the green and blue channels (unless the lower levels were getting clipped at zero, which would reduce the contrast, not increase it). If you are talking about contrast between channels (which would make more sense), then adding a red filter would reduce the contrast between the red and blue/green channels, not increase it. Or, am I completely missing the point you are trying to make?

Thanks,

--Mark

Mark...if you are shooting medium or close ups, I would think your lights would be mandatory and would necessitate a new white balance.

Steve B)

Pakman

Why don't you WB to the lights? Your background will automatically look blue if you do that and no more red foreground subjects. The video by Peter Lombar is a good example.

Either due to my inexperience or possible shortcomings in the HC-7's WB'ing capabilities, when I WB to my lights (HIDs), I get nasty greens in the areas outside the light coverage.

edit: Not to further hijack this A1 thread, wonder if someone could summarize (maybe make it a sticky) general guidelines for MWB'ing with or w/o lights and red filters for general consumer cams?

Or, am I completely missing the point you are trying to make?

In simplest form, check your underwater image with and without filter. Which has more color contrast? That should explain it.

Mark...if you are shooting medium or close ups, I would think your lights would be mandatory and would necessitate a new white balance.

Steve B)

Sure. In my previous post, I was just talking about reverse engineering the white balance feature of the A1. If I am reasonably shallow, I don't bother with the lights, and white balance with sun light. If I want to do some close-up work at depth, then I use lights as the camera isn't all that good in low light situations.

--Mark

In simplest form, check your underwater image with and without filter. Which has more color contrast? That should explain it.

I still don't follow you. The definition of color contrast that I am familiar with is: "the perceptual effect of the juxtaposition of very different colors". However, since the camera doesn't work the same way that our brain works, "perceptual" effects are not relevant.

I would say that all other factors being held constant (manual exposure for example), the image with no filter has more color contrast because there is a lot of blue information, and very little red information. Hence, the amount of information in one channel has a high contrast to the amount of information in the other channel. But, this goes against my observation that I can white balance with the filter, and cannot without it.

--Mark

Lets see if this helps..

The filter doesn't actually add red, it more along the lines of cuts down on the overwhelming blue and green.

Therefore allowing the reds and oranges to come through stronger resulting in a more even spread of colours and therefore more contrast due to better colour representation..

One thing I did notice with my A1 was that sometimes pressing the assign button (set to MWB) would cause it to go into Expanded Focus. This is with the Ikelite image reverser plugged into the lanc port.

HAHAH, I have the exact same problem with my L&M housing with my A1 camera. I pulled it out of the housing, and couldnt replicate the problem. Put it back in the housing and got it to do it about every 4 or 5th time underwater. Sent the whole thing back to L&M and they couldnt figure it out either. The replaced some stuff but the problem is still there. To be honest, I think its a problem with the camera, not the housing. Its just that the housing brings the problem to light.