Setting White Balance

Having just purchased some of Alex's Magic Filters I now understand the need to set the white balance at the depth that I'm taking the image. Reading through this forum too has emphasised the need to do this.

Now, having spent some time with my nose buried in my D100 users manual I think I undrstand the steps to go through on the camera. However, I have read differing opinions on what to use as my 'datum':

white slate,

grey slate,

sand,

my hand,

even the subject itself (unless blue)!

But how can all these items give the 'right result'???

I would be grateful for an explanation or advice on this esp. as I'm off on a red sea liveaboard next week-but please, in easy to understand terms as I was unsure whether to post here or in the Beginners Forum!!!

Thanks.

Ralphy,

I think Alex Mustard (one of the inventors of the Magic Filter) recommends filling the frame with the subject prominent in your foreground (coral, anemone, etc.) as your ""Custom" white balance reference pic.

I shot a photo of the sand / coral rubble at the depth I was taking photos. Seemed to work pretty well for me.

Check out the galleries at www.magic-filters.com .

dhaas

Yep, filling the frame with the subject you are going to shoot, and of course at the angle you are going to shoot, will work great.

Just think of it as taking two photos of the same subject.

OK, thanks for the above replies.

I don't doubt that what you say works, but I'm still puzzled by this!

Presumably, I am telling the camera 'THIS is white, now go and caclulate accordingly'. But if my subject isn't white (say it's a turtle for example), then how does the camera calculate correctly?

OK, thanks for the above replies.

 

I don't doubt that what you say works, but I'm still puzzled by this!

 

Presumably, I am telling the camera 'THIS is white, now go and caclulate accordingly'.  But if my subject isn't white (say it's a turtle for example), then how does the camera calculate correctly?

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Well I think you're rightfully puzzled. If you do a white balance on a purple frame-filling sponge the WB-corrected image will have a grey sponge. You are telling the camera that your reference image should have equivalent values for red-blue-green so it must be a shade of grey to work perfectly.

The reason you can get away with a shot of sand or a hand, the latter especially in cold water , is that you don't need to be perfect to get a major benefit. The red-light imbalance is so big that most corrections will be improvements. Still you should be aiming for something resembling white or gray.

I read somewhere that the Nikon D200 can store something like 5 WB reference settings. If that is the case you may be able to take proper WB shots of a gray card at different depths and then later during a real photoshoot select the most appropriate one for the depth you're at. If the WB reference doesn't have to be perfect then having 5 at conveniently spaced depths stored in the camera may be all you need. That might also be of interest to our Greek, freediving, natural light shooting, Nikkon lover, whose name suddenly escapes me B) .

Bart

Lambis

Lambis

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???

I spent New Year in the Maldives. It was a shame my case full of my flash equipment went to Thailand. However, carrying my housed camera as hand-luggage, it gave me the chance to experiment taking pictures by natural light.

Without any Magic filter, I resorted to cranking up the film-speed to 400ASA and firing away on aperture-priority setting with the White Balance set to Auto. I shot in in RAW.

I then downloaded my pics and took them into the CS RAW converter after adjusting both colour-temperature and tint controls.

The result? Down to 20m deep the pictures turned out remarkably well!

The camera was a Fuji S2Pro.

John,

Are you advocating not bothering with filters and manual white balance and sorting everything out in in a RAW converter later?

Using any 'red 'type of filter adjusts the colour of the light recorded by the camera - by blocking bluer light and increasing the red component of light reaching the sensor. If you are using RAW files then the white balance remains irrelevant as this can be adjusted afterwards.

If you are working below the depth at which red light has been filtered out by the sea (nominally ~10m) then shooting RAW will allow as much adjustment whether or not a filter has been used as the red component of the light reaching the sensor is so minimal anyway. Using a 'red' filter in shallower water allows white balancing in RAW after shooting without altering the data as severely as shooting without it.

I haven't tried the Magic Filters (yet) and don't know their spectral absorption, but the above comment will broadly apply whatever filter system you adopt.

No. I am by no means an expert. I simply report what I did and it seemed to work. I had no Magic filter because I did not anticipate losing my flashguns!

I used to use a Wratten cc30r on the back of my Nikonos 15mm lens but it demanded 400ASA film because it reduced the light passing through the lens so much. I upped the equivalent ISO setting on my S2 Pro because there was not so much light down at 20m for a fast shutter speed (1/180) and small lens opening (f./11). The pic shown was taken with the 12-24mm Zoom at 13mm.

Shooting in RAW does allow you to make some crucial decisions back at your PC when you have time to experiment. I have never needed to use the tint adjustment before so I learn something new (every day!).

Nikon D200 5 WB reference settings.

Bart you make my day :-)

Becauce i have not time while freediving to take a"Custom" white balance reference pic this feature will help me a lot.

I only hope that with the d200 is esay to go trough those 5 stored WB settings. Not a 3-8 buttons compinations :-)

Lambis, a Greek, freediving, natural light shooting, Nikkon lover -)

so I learn something new

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Did you see that!?!? The sky just fell!!! I swear!!!!!

Ha, ha and he thinks I'm the joker

Dive safe

DeanB

I just looked in a drawer at a stock of Wratten filters that I used when I was a real photographer (prior to 1989) and found I have a lot of unopened Wratten 85. These were primarily used for shooting A type reversal film in D type conditions, something I rarely needed to do.

They look suspiciously like Magic Filters so next week when I am in the Sudan I will give it a go and let you know how I get on shooting through a Wratten 85 with natural light and sunshine. The last is a component I was very short of during the couple of dives I did in the Maldives at New Year. I was not able to dive much because it was a family holiday although we had our own liveaboard - (Thanks Sea Queen and MST!)

Using any 'red 'type of filter adjusts the colour of the light recorded by the camera - by blocking bluer light and increasing the red component of light reaching the sensor. If you are using RAW files then the white balance remains irrelevant as this can be adjusted afterwards.

<{POST_SNAPBACK}>

Some clever Linux folks have figured out how to read the proprietary RAW formats. If I start shooting with magick filters I may try to see if I can write a program to read the image and provide a slider bar where you can dial in your "water column distance" (depth + distance to subject). Instead of tweaking individual colours you can then just manipulate one parameter or, if there is a whole bunch of images taken at the same depth you could process them all with one command. Unfortunately I already have a hard time to find time to dive, so don't hold your breath.

If you are working below the depth at which red light has been filtered out by the sea (nominally ~10m) then shooting RAW will allow as much adjustment whether or not a filter has been used as the red component of the light reaching the sensor is so minimal anyway. Using a 'red' filter in shallower water allows white balancing in RAW after shooting without altering the data as severely as shooting without it.

<{POST_SNAPBACK}>

Life doesn't come in red, green, and blue, but in a continuous spectrum of which our eyes can handle something like 350 to 700 nm. The red pixels of your camera are sensitive to a range of colours, let's say 600-700, and at 10 m the long wavelength end of the red may be gone but nearer 600 you still have signal to considerable depth. Think of light absorption in F-stops. If for red you loose 50% of signal for every meter then you need to double either ISO, exposure time, or go down one F-stop to compensate for each meter of depth. A fast prime lens could allow you to go 2 or 3 meters deeper and if you normally shoot at ISO100 you could gain 3 or 4 F stops there by going to 800 or 1600 ISO respectively. Going to slower shutter speed gives you even more light to work with. Without magick filters this approach would horribly overexpose the blue and green so the real function of the filter is to be able to boost the exposure signal of red while keeping blue and green in check. In clear water on a sunny location you probably can boost exposures by 5 to 8 F stops compared to no filters.

Finally you don't have to get red, green and blue perfectly in balance. There are 12 bits for each colour (a 0 to 4096 dynamic range) whereas the eye can see only 32 to 64 shades of grey (and I expect the same applies to colour). So I guess you can loose something like 6 bits of colour information and still have a 0 to 64 dynamic range left that you can blow up in photoshop without being too horrendous to the human eye. Loosing 6 bits corresponds to another 6 F stops. If my guesses are not too far of then we're talking a 11 to 14 F stop drop in red light signal that we can overcome. I'd love to stick a magick filter in the UV spectrophotometer in the lab and do some RGB histogram data analysis of images of grey cards with and without filter and at different depths to see by experiment how the numbers pan out. With that information we may find out how deep we can push these filters. But as said, need to get time for a dive trip first, which currently looks like early May.

Bart

P.S. If anybody has already got some RGB histogram data, or knows the wavelength transmission spectra for the red, green and blue pixels of the sensor then I'd be interested to hear.

That is a fascinating theory BUt in practice I think that you will find amongst other problems, that:

Noise will be a real problem when boosting a very low 'signal',

The eye/brain system is far more discriminating that it may seem to be on paper, and

If it was a 'straightforward as this, then it would be easy enough for software manufacturers to be selling us 'underwater colour correction' software.

However, I'd love to be proved wrong!

I have tried using just an 85 warm up filter underwater as part of the development of the Magic Filter and the results leave a lot to be desired (the results are far too yellowy-green).

Just for clarification the Magic Filter is a combination of three off the shelf filters (none of which is an 85!), which is designed to work with the manual WB of the camera to allow you to shoot full colour available light images in bright, tropical waters from the surface down to 15m+. The filter is not a perfect correction for seawater - as such filters work over too narrow a depth range to be practical for normal UW shooting. As photographers we want to be able to swim at depths where the subject matter is - and the Magic Filter was designed to allow us to do this.

To make the point that the Magic Filter is designed the way it is on purpose, I would like to add that I have also developed a Point and Shoot magic filter (using a different combination of the same three donor filters). This filter is designed to work WITHOUT manual WB. It is designed specifically for AUTO-everything compact cameras. In otherwords this filter produces great results without flash - in AUTO exposure and AUTO WB. The design brief was to make it totally point and shoot.

The draw back of this new filter is that it operates over a slightly narrower depth range than the original Magic filter - producing pleasing results from 5-6m down to 15-17m (depending on the type of compact used). We are yet to decide whether to manufacturer this filter.

Alex

Anyway these results below are all taken with a totally point and shoot camera, and OLY C40 (set on AUTO-everything) - shooting in JPG with no adjustments in Photoshop. Depths 12-14m. This filter makes underwater photography very easy indeed.

Alex - If we did not white balance at all and left in Raw mode auto WB can we get the same result by editing in the computer. Does the manual WB just save computer time later or is it a matter of correct color to start rather than guess later?

Magic filter question: I would like to know what your descision process is on using this and no strobe, or when not to use it and go with the strobe. Sorry if you have answered this before. Thanks

Steve

The Magic Filter is designed for shooting without strobe.

It will work with strobe, but you just end up setting a white balance on the camera that counteracts the effect of the filter. In the end this is less desireable than using no filter because this white balance is quite extreme and does cause some degradation of image quality. So you are better off without a filter if you are shooting flash.

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The reason to set WB underwater is it is 1) very easy, takes no longer than jut taking an extra frame once you get used to it, 2) gives you the satisfaction of getting the shot at the time of shooting, 3) by seeing the final colours of the image it should influence how you compose a shot. For example in the pictures above - seeing how nice the warm coloured sponges look in the photos above, influenced my composition to set these against blue water for maximum impact.

But yes you are right that you can jut shoot RAW and do it all in a GOOD raw converter to end up with the same result.

Alex