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Bandula

WB method for Magic Filter

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I did some testing with the new Magic Filter on my 12-24 yesterday.

Mod' vis', sometimes cloudy sky and the sun almost up and down have not really been good conditions, but good enough for testing.

I wanted to find out which one is the best method for presetting the WB.

I did 2 comparable shots on the same szene. The first one with pre-WB done on the subject, and the second one with pre-WP performed with a Grey Chart.

All pics resized JPG basic straight from the camera.

 

Please check out the pics and choose your favorite WB method....

 

post-3594-1127061904_thumb.jpg post-3594-1127061004_thumb.jpg

post-3594-1127061386_thumb.jpg post-3594-1127061958_thumb.jpg

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I think the 1st ones are best - WB on subject. It's hard to make a good assessment with such small images though.

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Yes, it is obvious that the ones with WB on Grey Chart are too red.

Unfortunately I do not understand why? I thought WB with Grey Chart is the "perfect" method?

@ Alex: Do you have an explanation for this? What is the best method for you?

 

@ Larry: Sorry for the small pics, but the space for attachments is limited.

I don't have a website, so I can't link it.

 

 

Thilo

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I have to say that I am surprised by how different they are. In my tests I have found a much smaller difference. Did you ensure that the grey card is illuminated by the light when taking the reading. If it is in shadow then it is illuminated by upwelled instead of direct light and this would result in an over correction because of the longer light path? But I am surprised by the difference too.

 

Testing the Magci Filter in Bali (my first time with the production version) I found that the filter worked well in less than perfect blue water and also in cloudy conditions.

 

Alex

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Alex,

 

I tried to hold camera with grey chart in front exactly in the direction of the subject, but the chart was very close in front of the lens. This might be the reason for the huge amount of red. The chart produced too much shadow.

So it must be a compromize between the chart filling the frame and still being well illuminated. Which method do you recommend?

This was my first time with the filter and need more practice.

 

Thilo

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I think that the reason for that is that the grey card is much closer to the camera than the subject, What was the distance from the subjects here?

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The distance to the subject was approx. 1m and the Grey Chart can be hold an armlength away from myself. To fill the frame it must be a few cm in front of the port.

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It won't be this. If you think of the light paths the difference is very small. Say you ar at 10m, then light path to reef is 11m and light path to grey card is 10.5m - only a 5% difference so not significant.

 

Generally I just WB on the subject or some sand/rubble nearby these days - and my images have a much better WB straight from the camera. But anyway, you can always finetune the WB in the RAW converter later.

 

Alex

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Hi Bandula

 

Looks to me like your grey card is not a perfect grey, at least not underwater. When I use filters on the back of my fisheye, I WB off a white dive slate, which is easier to check for neutrality. I'm not saying its definitely this, but its hard to think of anything else.

 

One question, how are you presetting the WB off the scene? Obviously it can be quite critical what falls into the white balance zone. In my D60 and 20D this zone is the partial metering circle. Obviously if you are presetting WB off a more red part fo the subject, then you'll get the cooler balance that we see in the first set of pictures.

 

For my 2p, I'd recommend getting WB off a white target. If you get enough of the frame covered by it, then it'll be rendered as grey anyway, due to autoexposure.

 

HTH,

 

Martyn

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Hi Martyn,

 

Maybe you are right and my chart is too grey uw, but I thought that a neutral grey chart with 18% reflexion would be perfect, even uw.

I don't now the exact zone the camera uses for WB. It uses the main sensor and the 1005-RGB-Metering-sensor. So I presume it uses the whole frame.

It is also possible to make a custom WB of the light by use of the Ambient Sensor, but that is not possible UW with my housing because no control for the FUNC-button.

It looks a like I wasted the money for the waterproof grey chart and better to WB on the scene or I might try with a laminated white paper.

 

 

Thilo

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Hi Martyn,

 

Maybe you are right and my chart is too grey uw, but I thought that a neutral grey chart with 18% reflexion would be perfect, even uw.

I don't now the exact zone the camera uses for WB. It uses the main sensor and the 1005-RGB-Metering-sensor. So I presume it uses the whole frame.

It is also possible to make a custom WB of the light by use of the Ambient Sensor, but that is not possible UW with my housing because no control for the FUNC-button.

It looks a like I wasted the money for the waterproof grey chart and better to WB on the scene or I might try with a laminated white paper.

Thilo

 

Which card are you using? I ask because not all 18% grey cards are neutral. They're really designed for exposure calibration, not white balance (clue's in the name B) )

 

The Auto WB on the D2X is reputed to be pretty fantastic, so if you're shooting RAW, then it's a great place to start, plus you can always tweak in Photoshop CS Camera RAW, or your own fave converter. Plus you can pull detail back out of the highlights for sunbursts and the like.

 

Martyn

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The Auto WB on the D2X is reputed to be pretty fantastic, so if you're shooting RAW, then it's a great place to start, plus you can always tweak in Photoshop CS Camera RAW, or your own fave converter. Plus you can pull detail back out of the highlights for sunbursts and the like.

 

That's correct and exactly what I do when taking "normal" pics.

The Magic Filter does only work with preset WB.

 

Thilo

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Fair enough Thilo,

 

Looking back at your images again, I'm coming down on Alex's side. The angle of the card may be very important.

 

If the card is pointed upwards, it will be lit mostly by light that has taken a simple path from the durface, just like the primary illumination on the reef. This light will be blueish, but not overly so.

 

As the card is pointed more downwards, the illumination becomes more from light that has passed through much more water, i.e. the deep blue of the ocean you see when looking out from the reef. I think this is what Alex meant by "upwelled". Simply tipping the card too much will cause this. The WB will then be based on this much bluer light, and will look like the card-WB images you posted.

 

So try a white card, and try orienting it so that it is not in shadow and is pointed towards the sun.

 

Hope that helps,

 

 

Martyn

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The Magic Filter does only work with preset WB.

 

AUTO white balance is much more conservative than preset WB and won't produce the unusal WB values required for filter photography! This is why we need to use Preset WB.

 

You can see the effect at home. AUTO WB will not do a particularly good job of correcting the tungsten or fluorescent lighting. It is too conservative. So you need to use preset (or the specific modes) to deal with these usual colour temperatures of light.

 

When setting the white balance in the water make sure that neutral coloured reef fills most of the frame (like the sample image in the Magic Instructions) and you will get a good reading. Just make sure it is evenly illuminated and at a similar depth to your main subject.

 

Obviously if there is not time to do this - with a skittish subject for example - then shoot first and sort out the WB in the RAW converter!

 

Alex

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