Do optical WB filters improve RAW color latititude?

Started Aug 26, 2012 | Discussions thread
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Re: Do optical WB filters improve RAW color latititude?
In reply to Vitruvius, Aug 29, 2012

Hi there Vitruvius

Your question is actually quite significant but the answer is more complicated than I feel most of the respondents appreciate.

The short answer is absolutely and you can gain a whole lot more than just extended colour balance options.

Up front I have to say I am only going to provide some limited information on this but it should help. Please bear in mind I have actually tested all of this over a 3 year period with at least 5000 frames, it is in fact part of a whole imaging system I teach in Australia (the workshop manual is almost 400 pages) and I regularly shoot using pre-filtering as a standard process. I have just returned from a 6 week US/Canada holiday where I captured at least 2000 frames using pre-filtering under all sorts of lighting conditions and I use it on paying jobs regularly.

Many posters have raised valid points but I think it is fair to say most are talking in terms of theoretical and accepted wisdom rather than actually having done it.

The negatives:

Yes the exposure will be longer, effectively it is like shooting at about 32 ISO instead of 100, but for high quality work using tripods it is irrelevant. There is little point doing fully sensor balanced capture if you are going to compromise somewhere else in the chain. Under daylight conditions any increased noise from longer exposures is insignificant, you're still typically in the 1/60-1/500th range.

Yes you can get flare from the filters but it is rarely an issue and Gel CC filters detract zero clarity or if they do the gains that can be made far outweigh them. In my implementations the filters are behind the lens where ever possible, this radically reduces flare, and in fact of the 2000 images shot on my last holiday not one has any significant flare issue.

Raw conversations are some what harder due to the radically different colour temp corrections needed but most can handle it OK.

You do not achieve the same result using software after the fact but it can be close if the shooting circumstances were not too challenging, in other words normal contrast, average white balance issues.

Regardless of how good the sensor is you will reap gains, they not be quite so significant with the best new sensors......BTW I have used this with what is probably one of the best sensors out there, the 16 Meg NEX 5N and yes the files are better.

What you really need to know!

To obtain the full benefit of pre-filtered or "sensor balanced" shooting you need to rethink your whole process of capture, raw conversion and editing. It offers entry to a pathway of improved image quality that will result from a myriad of small but significant changes. In truth few photographers are prepared to apply the rigour needed or take the time to optimise processes, it is not simply a matter of throwing a filter on the front of the lens.

What Is Possible?

Balanced clipping points will largely eliminate weird and difficult to fix colour shifts in upper highlights and lower shadows.

Noise is luminance in nature, chrominance noise can be greatly reduced or eliminated.

Image are subtly sharper and will withstand higher levels of sharpening

Colour quality is subtly better, more natural in effect

Mono conversations can be radically better as the three channels all have near identical noise signatures meaning conversions are more film like.

Extended dynamic range overall, in fact fully sensor balanced files look flat compared to regular ones before conversion.

And on it goes..........

NOW the issue of tungsten is a bit messy in particular because the native sensitivity across the three channels is actually not correct for daylight balance so the filters needed are nothing like what is needed for shooting daylight film with tungsten. In fact the increased red output of tungsten light sources actually helps get the red channel back in kilter quite a bit, believe it not tungsten colour temperature is not that far removed from the native sensitivity of most sensors across the three channels. There is not pre-potted solution for the correct filter pack, you have to test.

One of the biggest reasons people get poor tungsten images in general is that the cameras histogram and metering lie to you big time in this instance and most times that actual files are very underexposed, which is easy to see when you open them in raw and analyse what it actually captured across the three channels.

So before you get too carried away with filters just try shooting with tungsten but over-expose the RAW files a bit and see how the converted files look, you may be surprised. JPEGs shoot under tungsten are as far as I am concerned pretty much useless so lets not even go there.

By all means email me if you want more information.

Trying to make the complex simple

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