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#141 f10ab1b

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Posted 05 March 2005 - 08:11 PM

Hi Alex and Craig,

I've really enjoyed your posts over the past couple years! I regularly check this thread for any new info. After originally reading the thread, I tried a B+W FL-D in 2003 in Hawaii and got this photo.

Posted Image

The interesting thing is the noise in the red channel, that gets worse towards the bottom. As I understand it, the idea of the filter is to cut down on the red channel plugging up? Do you think the B+W FL-D is too weak for the depth at the bottom of the photo (I was only 15 -20 feet down), but too strong for the light areas at the top (in the original RAW file, the light areas near the top are too pinkish)?

Looking at the channels on this jpeg is not a good representation, as i did some levels & channel mixing to make it look better on screen. But in the original RAW file, the red channel noise is so thick in the bottom half, that it's hard to get a decent print. The photo was shot with a 1Ds at ISO 400.

After all your experiences over the past year, what are your suggestions for the appropriate FL (or UR Pro equivalent) filter this type of natural light shot (wide angle, large subject(s), relatively shallow depth)? I love the colors you have achieved, and want to play with it some more, but the splotchiness of the red channel turned me off on the shots I've taken so far!

Also, I've read over on the Rob Galbraith site, that it's better to use a white card for custom WB with Canon SLRs. Are you guys using gray or white cards these days? Any suggestions on appropriate waterproof cards at this point?

Many thanks for all the valuable knowledge you (and many others) provide on this site!

Corey

#142 craig

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Posted 06 March 2005 - 06:39 AM

I don't think any filter change can help with the noise or splotchiness. What determines the right filter is the settings that are required to achieve good white balance. I've never used a white card with still photography though I have with video. Alex has done that and I believe it's a standard technique with him. With RAW you can adjust WB after the shot so a white card only helps with accuracy since sometimes there isn't anything white in the scene to help get the WB accuractely set. I'd think a wide angle shot like you've posted would be hardest to use a white card with.

Basically, what you are achieving with the filter is balancing white light back close to white as it enters the lens. In order to get a clean image from that there needs to be enough available light so that the camera can perform well even after the filter has removed a great deal of it. Stronger filters have little effect on the red portion of the spectrum so they won't cause the red channel to be noisier---the noise you see is always present but just stronger relative to the other color channels since the filter makes it so.

I order to avoid the image problems you see you may need to be careful with the perspective of your camera (shooting up/down, toward/away from the sun, etc), you may need better ambient light quality or clearer water, or you may benefit from higher ISO performance in your camera. A weaker filter will improve the situation but only at a proportional cost to color since you aren't getting an improvement in the red channel (you're just overpowering it in blue and green).

Careful application of NeatImage or Noise Ninja may be useful og you haven't tried those things.
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#143 f10ab1b

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Posted 06 March 2005 - 12:14 PM

Craig, thanks for your input. I'm thinking that maybe I didn't phrase my questions very well. :blink: In a post from September 2003, CeeDave said:

"When there is excess blue-green light, the blue ( B ) and green (G ) pixels in the CCD array will tend to limit the exposure time (to avoid blooming), whereas the "not blue-green" ( R ) pixels will have low input and thus will be subject to noise. Inserting a red filter will block portions of the blue and green light. Thus, a longer exposure (or lower f-stop) can be used. This allows the red pixels to "fill up" better and avoids noise in the R without blowing pixels in BG." Now, here's the important part, to me: "This is fundamentally different from postprocessing the image, because if BG is blown/clipped or R is noisy, these are hard to repair without introducing artifacts. 'Precorrecting' the light balance with the filter better uses the dynamic range of all pixels, which can theoretically lead to a superior image."

That made sense to me, and seemed a good explanation for why a filter, during image capture, is a better solution than just adjusting WB later in the RAW converter. In fact, looking at the histogram of the image from my last post in ACR (showing each channel seperately), the bulk of the red channel pixels are farther to the left (underexposed... more noise) than the blue (farthest to the right) and green (most central) ones.

I always shoot RAW files, but I'm trying to figure out which filter, when used in conditions similar to the shot in my last post, would yeild the least red channel noise and would require the least drastic RAW conversion settings, without making the highlights too red.

I realize there is no perfect "one size fits all" solution, but I was just curious if you or Alex (or enyone else with experience in this technique) had any comments about which filters, in your experience (nearly 2 years after the start of this thread), have worked best for this type of situation (wide angle, blue water, relatively shallow).

Regarding the white card, I usually try to take a couple shots with one at the depth and lighting conditions I will be shooting in, so I can use it later in ACR to click adjust the white balance of the white card shot, save the settings, and load them as a starting point on other images from the shoot if AWB isn't yeilding a good starting point. I was using the white card in a set of Warm Cards, but I recently lost it and was curious what anyone else was using before I get anything new.

Thanks again for taking the time to answer, and for all your valuable input in these forums. Lurkers like myself have learned alot here.

Corey

#144 craig

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Posted 06 March 2005 - 01:06 PM

I think CeeDave's explanation is good, but keep in mind that the noise we're talking about is inherent in the imager. What makes the red channel noisy is lack of signal combined with excessive gain to fix the white balance. Ideally a filter will give you well exposed information in all three channels so if you're seeing red histograms that are significantly underexposed compared to blue/green then you could probably use a stronger one. Not all "noise" in the image is noise though. Particulates can appear as red noise too.

I made some recommendations on filter strength relative to depth in the original article so maybe you might revisit that. I think FL-D's are good to around 20 feet or so and FL-B's are useful deeper.

I think the way you are using the white card makes a lot of sense. I haven't done that myself but can't think of any reason not to do that.
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#145 Tom_Kline

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Posted 06 March 2005 - 01:31 PM

This is a very interesting thread. I have printed color negatives of UW shots and by filtration attempted to correct for blue (after the fact as it were). It is possible to remove the excess blue but one ends up with is a near black and white photograph. I think there will be a point of diminishing returns as a function of depth at a given location.
An interesting aside is that BBC does not use artificial lights when they shoot UW. They were here in Prince William Sound doing part of the Blue Planet series for the Discovery Channel. A lot of gear but no lights. The producer told me that lights were a no-no. Need to stay rather in shallow water - especially here.

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#146 f10ab1b

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Posted 06 March 2005 - 01:41 PM

Particulates can appear as red noise too.

<{POST_SNAPBACK}>

That's interesting... I hadn't thought about that or noticed that before. Are you saying that in your experience, you notice particulates in the water showing up more in the red channel than the blue or green channels? I remember the water did have some particulates in it that day, so maybe they are contributing to the splotchiness in the red channel?

I made some recommendations on filter strength relative to depth in the original article so maybe you might revisit that.  I think FL-D's are good to around 20 feet or so and FL-B's are useful deeper.

<{POST_SNAPBACK}>

I remember reading that from the original article. But since the article was over a year and a half old, I was just curious if you had come to any additional observations in the past year. What you are saying makes sense though. I was using a FL-D on a 16-35mm lens at 16mm. I was at 15-20 feet. With the wide angle of view the lens provided, the water below me was deeper, and maybe needed a FL-B, and the water above me has less noise in the red channel, so the FL-D was probably fine.

#147 Tom_Kline

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Posted 06 March 2005 - 02:37 PM

f10ab1b,
Your subject (in your avatar), a killer whale has built-in white- and black point targets! Have you used them this way?
Cheers!
Tom

Thomas C. Kline, Jr., Ph. D.
Oceanography & Limnology
Canon EOS-1Ds MkII and MkIII and Nikon D1X, D2X, D2H cameras. Lens focal lengths ranging from 8 to 180mm for UW use. Seacam housings and remote control gear. Seacam 150D and 250D, Sea&Sea YS250, and Inon Z220 strobes.
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#148 f10ab1b

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Posted 06 March 2005 - 03:23 PM

Tom, I tried, but then the whites were getting blown out and the blacks plugged up. :blink:
Corey

#149 craig

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Posted 06 March 2005 - 04:27 PM

Yes, I think particulates can do that. It seems to be more a function of excessive gain in the red channel causing posterization of red details. Theoretically a proper filter and good exposure would eliminate that but in deeper water no filter will be strong enough. I used to see that with video frequently where I'd shoot 80 feet deep and still get good color but with somewhat noisy or grainy footage.

Tom, filtering after the shot doesn't do the same thing as filtering before the shot. You're right about the diminishing returns but color can still be had at pretty significant depths. Filtering a negative is a lot like color balancing in photoshop. :blink:
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#150 Tom_Kline

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Posted 06 March 2005 - 04:53 PM

Roger on the filtering. Nevertheless if almost no red in ambient light is present, filtering will not help much. The concept of reducing the blue with a filter to keep from having to amplify the red later and so generate noise is a great concept but there must be depth limitations.

Hard to find true black and white even on a killer whale, same thing in topside shooting.

Thomas C. Kline, Jr., Ph. D.
Oceanography & Limnology
Canon EOS-1Ds MkII and MkIII and Nikon D1X, D2X, D2H cameras. Lens focal lengths ranging from 8 to 180mm for UW use. Seacam housings and remote control gear. Seacam 150D and 250D, Sea&Sea YS250, and Inon Z220 strobes.
www.flickr.com/photos/tomkline/

 

 


#151 craig

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Posted 06 March 2005 - 06:07 PM

That's true and red is essentially gone by 30 feet. Orange and yellow light stimulate the red sensor though and they're good to 80 feet or so. What the maximum depth is really depends on the sensitivity of your sensor.
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#152 Drew

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Posted 08 March 2005 - 01:28 AM

An interesting aside is that BBC does not use artificial lights when they shoot UW. They were here in Prince William Sound doing part of the Blue Planet series for the Discovery Channel. A lot of gear but no lights. The producer told me that lights were a no-no. Need to stay rather in shallow water - especially here.

<{POST_SNAPBACK}>

Well the salmon sharks they were shooting were shallow. The lights would've probably distracted the salmon and their predator. Plus mixed light shots hardly ever come out nice. Most pro shooters want the realism of being underwater, where everything is blue/green to the human eye.

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#153 CeeDave

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Posted 08 March 2005 - 09:13 AM

<edited to add link to earlier thread>
Hey Guys,

As I posted earlier in the Galley, I am tinkering a bit with conceptual (certainly not yet practical) transmitted light calculations. The very simple results so far might be of interest, given the earlier posts here.

First, I assumed a simple black-body illumination profile for the sun (about 5700 K). Then I neglected surface reflection (promise to do better later), and used Pope and Fry's frequency-dependent attenuation profiles. That gave me the profiles linked in below, with the expected "collapse" of the red (wavelength >~ 600 nm, different profiles are for different depths in meters).

Posted Image

If you then go to 4m, and slap on a a wratten CC20M and an 85 (data from Kodak), you get:


Posted Image

It does get you a little closer (at moderate depth, moderate filters).

More to follow when I've made some progress.

All the best,

Chris/CeeDave
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#154 motionsync

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Posted 15 April 2005 - 04:34 AM

Great

I will soon go to Egypt Dahab and i will try my new Hoya FL-D filter

I own a olympus 5050 with a pt015 housing and a Inon UWL100 lens.
I will pursale a Inon Dome port for the UWL100

Now it is the first time that i visit egypt. I am a frediver and 90% off the photos are between 0-10 meters

Moast off the time my Cameras settings are A-priority , Macro mode & I shoot RAW

My Question is. Sould I have custom White balance or Auto?
If i use custom sould I do grey or White balance?

Any tips are welcome

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#155 CeeDave

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Posted 15 April 2005 - 07:38 AM

Shooting RAW, I'd just use auto white balance -- although Alex Mustard, who along with Craig Jones knows a lot about this, has advocated preset WB in the past. Hopefully he'll share his current thoughts here.
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#156 tie

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Posted 15 April 2005 - 10:11 AM

I will soon go to Egypt Dahab and i will try my new Hoya FL-D filter

I own a olympus 5050 with a pt015 housing and a Inon UWL100 lens.
I will pursale a Inon Dome port for the UWL100


How do you mount the filter with the UWL100 lens? Is there a vignetting issue?

#157 motionsync

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Posted 15 April 2005 - 12:38 PM

The filter is 67 mm. The same Pt015 housing and UWL100 lens

I skrew the filter on the lens and then the both om the housing. I havent experience vignetting problems.....

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#158 ilnave

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Posted 21 March 2006 - 11:16 AM

Hi guys, this is my first post!
I will be leaving soon for a dive vacation in Indonesia, and I will be using my Canon A80 with canon WP-DC900 housing.
After shooting for 10 diving days, I realized that I definitely need a filter, since I cannot use the built-in flash due to backscatter problems.
I was looking for the UR pro filters, but they are quite impossible to find here in Italy.
I have already at home a COKIN 002 ORANGE filter, which I thought I could cut and adapt to my housing.
Do you think this is an appropriate filter for tropical diving, up to 30-40 M?
Or at least, can it be used to improve my blueish pictures or there are some drawbacks which shouls suggest to avoid using this specific filter?
Thank you very much for any feedback.
Regards

Navè

#159 CeeDave

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Posted 21 March 2006 - 11:45 AM

Nave,

Honestly, I don't think many filters can do you much good at 30 m. The orange filter will really impose a large hit on your exposure at that depth, too. Myself, I would just accept the blue or go with a strobe for depths beyond (at most) 20 m or so -- even in clear tropical waters.

Chris
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#160 ilnave

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Posted 14 April 2009 - 12:05 AM

Nave,

Honestly, I don't think many filters can do you much good at 30 m. The orange filter will really impose a large hit on your exposure at that depth, too. Myself, I would just accept the blue or go with a strobe for depths beyond (at most) 20 m or so -- even in clear tropical waters.

Chris


Hi Chris,
thanks for your prompt reply! Unfortunately I received only today (3 years later) the notification email from wetpixel...
Bye
Nave