Gel Filters

I'm keen to try a magenta filter on my lens - water around here is a bit too green. Plan was to add a green filter to the strobe.

Questions:

1/Gel filters. My 17-40L has a rear slot in it around 2cm * 2cm, for gel filters. But I've never actually seen one. I tried googling this and just came up with some crap I'd written myself on the Digideep forum a year ago!

This is the closest I could find on B&H

http://www.bhphotovideo.com/bnh/controller...ku=26842&is=REG

However, it's not clear to me if this is designed for a rear filter holder - would the thickness be correct?? Do I cut it down to size myself?

The fisheyes (Canon and sigma) I think both have a rear gel filter holder - is it the same size?

2/Strobe filter

Resin filter for Cokin P holder was the plan here, I was going to try a CC30G eg Hi-Tec brand. I was going to try and stick the cokin holder onto the flash diffuser, this would be on a DS-125. I think this is the traditional way to do this?

What do you think of my filter selection? As mentioned, the water here seems pretty green to me, all my pics get white balance adjustment and color correction during raw conversion at this stage and I'd like the color out of the camera to be a bit closer.

Let me know your thoughts!

lenses with rear gel holders are shipped with a template that you use to cut a gel to fit. get a razor blade and be very careful! It's tedious. I haven't added a filter to the DS-125 but that would be the way to do it if you can. Gels can't be exposed to salt water.

You could probably fit a resin type filter (read plastic) to the front of a DS125 if you used the Ikelite diffuser as a template and cut it to the same size. I have done this with pieces of milk-jug to make diffusers in a pinch...:-)

Cheers

James

Hi Rob,

My suggestion would be to change the white balance setting in your camera if you are shooting JPGs or adjust the white balance in your raw converter if you are shooting raw files.

A filter will reduce the amount of light available for image exposure, and possibly reduce resolution and increase flare. The color cast that a filter imparts to the image can be accomplished with much less image cost digitally.

Arthur

Hi Art,

You are taking a position that has been discussed back and forth here at Wetpixel many times. I think if you read the articles, and actually try it you will see that a filter can be very beneficial COMBINED with the absolutely necessary white balance RAW adjustments.

The filter may block light - but it's the overwhelming green light that we don't want hitting the sensor. So the filter is DESIGNED to block light...:-)

For a good read and some sample photos check out the articles by Craig Jones and Alex Mustard in the Features section.

Cheers

James

Yes, removing undesrable light is something you want to do! Light alone is not a good thing. Well color-balanced light is.

In any event, complementary filters accomplish more than white balance. If fact they don't effect white balance at all. Instead, complimentary filters alter the color balance between the subject and the background, something that no adjustment in the raw converter can possibly do. Filters aren't just for "imparting a color cast".

Art, if you're unconvinced check out Craig's Sipadan wide angle shots. Very nice indeed.

Speaking of white balance, what is everyone doing here? I'm shooting everything in RAW, setting white balance to daylight or auto in the raw converter (C1), adjusting the magenta/green tint setting on the white balance adjustment and then performing further color correction as required pre conversion. I then normally do some selective color adjustment in photoshop, usually to the cyan chanel to add more black and magenta (using an adjustment layer).

Some of the photos seem to look better if the white balance is set to a very high color temp (say 8500), and then adjust the magenta/green tint to suit.

I'm still experimenting with the above, so I'm interested if anyone has any clever workflow ideas.

And back to the gel filter - I figured on having to cut to size. But I'm guessing the thickness is important if it's going to fit. Craig/James - is the gel filter I linked to the correct item for the task at hand?

Cheers,

RW

Hey Rob,

That Kodak CC30M looks fine. I use Lee because that's what my local pro shop have. I cut with sharp scissors while still sandwiched between the sheets of tissue the gel's come in. Works great with Sigma 15mm FE.

It's generally best to pop the filter in the back, because any defects/dust are generally softer than when the filter is in front of the front elelment, especially when focusing close, behind a dome port.

As for white balance, I shoot raw on AWB. I then tweak in Photoshop CS camera raw. Best advice is to get your monitor calibrated, then just adjust to taste.

Regards,

Martyn

I would go for at least a 40 or 50CC filter rather than a 30 - although it depends on what depth you will be shooting (approx a 30CC is good in 3m, 40CC in 3.75m and 50CC in 4.5m.

I find the best way to cut filters is using a pair of curved nail scissors.

For deeper than 5m I have found that fluorescent filters (such as the URPro) are better. This image was taken in 9m of water with available light and URPro.

Alex

With regards White balancing. If I am diving on a flat seabed in shallow water then I prefer to set the white balance manually using a grey card. However on a open water dive I now shoot in AUTO and then fine tune in ACR. I have found that with my Nikon D100 the cameras AUTO white balance works very well with the URPro, but tends not to do such a good job with Gels. Maybe this is because the Fluorescent filter is a mix of both Colour Compenstation and Colour Temperature (conversion) filtration?

Yes, the Kodak gels are the right ones.

I agree with Alex that a 50 or 50CC is a better choice. I've only used 30 but will try 50 the next time. Remember that it has no effect on the color of your subjects.

I also agree that flourescents work better for ambient shooting and that cameras can auto white balance better when they are used. The light entering the lens is simply much closer to white and that's what you want after all.

I just love available light shots with so much color. That one can't be taken with a strobe.

Hi Folks,

I don't mean to belabor this subject to death, but nothing is gained when using a filter to correct color balance when shooting raw files. A filter cannot add color, it can only subtract color. As long as the scene is exposed correctly, white balance correction in Photoshop CS RAW can remove any unwanted color without the drawbacks of removing color with a filter. The sensor array is quite cabable of recording the unfiltered light from a scene as recording filtered light from the scene.

Try this simple experiment. First, set up a standard scene and lighting, then shoot with a filter to simulate a scene illuminated with "unbalanced" light, ie., shooting under water. Second, shoot the same scene without the filter. Third, correct the white balance of the filtered scene in your raw converter. You fill find that the image of the corrected filter scene matches the image of the unfiltered scene.

In the attached example, I used a 50cc green filter to simulate how the water often looks in my area. The shot with the green filter also required an additional stop of exposure. The histograms of the unfiltered shot and the corrected filtered shot were a very close match.

Arthur

Hi Art,

Take those same slates down to 30 feet and repeat the shots at various exposures. Have a look at the red, green, and blue histograms.

As the exposure goes up, you'll notice that the blue and green cnannels start to "blow out" ie clip on the right of the histogram, while the red is barely there at all. That means you can't push the exposure up as far as you want, because of the filtering effect of the water - it creates an imbalance. No amount of white balancing can fix that. At some point, you may not even be able to white balance at all!

Now put on a CC30 or 50 filter and repeat the experiment. Watch your histograms, etc. You'll see that you can now get the exposure you want. - good exposure with no blown G or B channels.

Now throw a strobe into the equation. Using the filter, the foreground will look too pink. That's why you use a complimentary filter on the strobes. Put on both sets of filters (strobe and lens) and go into a dark room. Take a photo and you should have a good color balance (ie, the shot should look like a normal shot) if your filters are matched right.

In this way, you can get a balance between ambient and strobe light, without having too much green and blue saturating the sensor. You may not believe me until you actually try this in sunlight in deeper ocean water. But it's cheap, so give it a shot next time you shoot wideangle. In Maine's green water this should help a LOT.

Cheers

James

This is wrong on many levels. First, the fact that filters subtract light rather than add it is exactly the reason why Photoshop correction can never be the same. As James said, try making your small differences into 10 stop color imbalances then get back to us on how well photoshop can color balance them. Second, even if you could color balance you wouldn't want to. The best SNR, and therefore performance, will be achieved when the white balance of the light matches the natural white balance of the sensor. Every camera has one including digital. Now, if you don't mind crappy noise performance then by all means use heavy color correction instead of filters. Finally, the point of complementary filters is not to effect white balance at all. The purpose there is to effect the color balance between the subject and the background. Filters effect white balance of subjects only when using ambient light. When using strobes you should not use lens filters only.

A 50CC green filter (1) requires more than 1 stop of exposure compensation, (2) is not enouigh alone to matter in your test (where cameras have 8+ stops of dynamic range, and (3) does not simulate how water works at all unless your talking about 5 feet of turbid water. Rather than do such simplistic and nonrepresentative tests, drop down to 40-50 feet and shoot an ambient light shot with and without filters. You'll see why they're good then.

This is a good discussion.

I agree with James and Craig. In practical terms. In practical terms I find if I shoot too deep without filter and then try and white balance my RAW file the whole picture goes too red before I can get decent colours on the subject. I end up with reddy-purple water.

The filter means I have more red/magenta in my histogram to start with compared with the blue/cyan/green (although I take your point Art that there is no more red red light in situ than an unfiltered shot - there is just the filter means that there is a higher proportion of warm colours in the filtered shot). And this makes final white balancing adjustments much more effective.

I agree that White Balancing is necessary, but below 15ft/3m, it works much better and introduces less noise (and maintains more colour depth) when used in conjunction with filters.

Alex

I think the above sums it up pretty well.

However, i don't find the idea of white balancing underwater very attractive or useful. White balance settings can be easily adjusted post shot (ie in the RAW converter), there's no particular advantage in getting it exactly right at the time. As opposed to altering the color balance of the light hitting the sensor at the time of the shot, which can only be corrected in post processing with some potential loss of image quality. And complementary filters on lens and strobe, which as far as I'm aware can't be simulated in post processing at all.

What other lenses have the rear filter holder? I have the 10.5mm nikkor and the 15mm Sigma both with a rear holder. Are there any others? A rectilinear WA would be nice in particular.

Is there any way to add a rear holder to a lens without one? Say the 12-24mm or the 18-70mm? My local photo store has a bunch of gel filters they are getting rid of at $1 ea and you get enough to cut for lots of stacking. Screw on filters are very expensive and stacking is prohibitively expensive.

It seems strange that this wouldn't be standard on all lenses?

I think the lens makers do the rear holder for lenses (like fisheyes) where a front mount filter just won't work.

Cheers

James

Hey guy's here is a link to a inexpensive source of Cyan filter gel for your flashes, they are less than 8.00$ for a sheet of 20"X24" (non optical quality, but who care it goes on the flash)I did a bit of research and tracked down this company that supply the movie business. Check the link it has very useful info, it come in 15cc or 30cc Cyan.

Other solution are all fairly costly, these gel are taped in front of window on movie set to balance the daylight (AKA Strobe light) with fluorescent fixture. Just make shure you put good money on the magenta filter, cause that one goes on the lens and must be the best you can afford.

http://www.rosco.com/index.asp

Regard's to all

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What other lenses have the rear filter holder? quote]

 

The AF 14mm from Nikon and Sigma uses rear gel filter, so does the fisheye 8mm and 15mm from Sigma. these lenses include a metal template for cutting the filter to the proper size, which by the way is not the same size between Nikon & Sigma, for Canon I dont know. you would think the manufacturers would make an effort to standarized...

What other lenses have the rear filter holder? I have the 10.5mm nikkor and the 15mm Sigma both with a rear holder. Are there any others?

The Canon 15 mm FE also has a filter holder.

-Brad