Blue Filters - Still Useful?

BeaKeR

I was reading an old book about black & white film photography over the weekend. The author talked about using blue filters to reduce the dynamic range between sunlit and shadowed areas. Because the shadows have a blue cast from sunlight the blue filter doesn't knock them down as much as the sunlit areas.

It seems like this technique might be useful still, particularly if the scene has so much dynamic range that you could otherwise be forced to clip highlights or shadows. It seems like it might work for color photography as well, if you removed the blue cast in PP. Has anyone tried using a blue filter this way on a dSLR? Is there some reason it wouldn't work?

I'd like to find out if I'm missing something before I charge out and buy another piece of gear.

ziggy53

BeaKeR wrote:

I was reading an old book about black & white film photography over the weekend. The author talked about using blue filters to reduce the dynamic range between sunlit and shadowed areas. Because the shadows have a blue cast from sunlight the blue filter doesn't knock them down as much as the sunlit areas.

It seems like this technique might be useful still, particularly if the scene has so much dynamic range that you could otherwise be forced to clip highlights or shadows. It seems like it might work for color photography as well, if you removed the blue cast in PP. Has anyone tried using a blue filter this way on a dSLR? Is there some reason it wouldn't work?

I'd like to find out if I'm missing something before I charge out and buy another piece of gear.

In terms of digital photography, I don't know of any simple color filtration that cannot be applied in software digital image processing. Possible exceptions might be graduated filters, including color graduated filters and such.

I would simply try to use a more advanced image processing software, like PhotoShop, before purchasing an expensive and size limited color filter.

In particular a blue filter would simply pass more blue and restrict the other wavelengths of light. This should be simple using any number of PS color processing methods, depending on how much blue you want to pass. Conventional BW conversion would follow.

Post a color image and I'd be happy to post some basic procedures with "after" results.

BeaKeR

Ziggy,
Much of the time Photoshop will let you "fix" a photo if need be. But what if the dynamic range is such that the camera can't capture it? eg, the lighting range is 11 stops but your camera sensor maxes out at 9. In that case you'd have to clip something, and once you do that Photoshop can't help you much. You could do a bracket and blend the images, but that's not always feasible. I run into this a lot in the mountains - the thin air leads to lots of high contrast scenes with very bright sunlit areas and very dark shadows.

In a case like that having some trick to reduce the contrast at capture time could be very handy. I'm wondering if a simple blue filter might do it by passing the blues from the shadows and cutting down the yellows from the sunlit areas.

pyry

You could just use the blue channel from the RGB-image to make a BW out of.
However, whatever you can do to make the scene fit into the camera's dynamic range is always good.

jfriend

BeaKeR wrote:

Ziggy,
Much of the time Photoshop will let you "fix" a photo if need be. But what if the dynamic range is such that the camera can't capture it? eg, the lighting range is 11 stops but your camera sensor maxes out at 9. In that case you'd have to clip something, and once you do that Photoshop can't help you much. You could do a bracket and blend the images, but that's not always feasible. I run into this a lot in the mountains - the thin air leads to lots of high contrast scenes with very bright sunlit areas and very dark shadows.

In a case like that having some trick to reduce the contrast at capture time could be very handy. I'm wondering if a simple blue filter might do it by passing the blues from the shadows and cutting down the yellows from the sunlit areas.

Here's a very interesting and somewhat technical thread discussing the possible use of filters to increase dynamic range. My conclusion from reading the thread is that there are some lighting circumstances and some matching filters that can increase dynamic range, but there is no generic solution that works in all lighting situations because it depends upon the dominant type of light in the situationn (G, B or R) and what is important in the image and you probably have to be shooting RAW to get the main benefit (otherwise the camera will mess it up).

And a couple similar dpr threads here and here.

ziggy53

jfriend wrote:

Here's a very interesting and somewhat technical thread discussing the possible use of filters to increase dynamic range. My conclusion from reading the thread is that there are some lighting circumstances and some matching filters that can increase dynamic range, but there is no generic solution that works in all lighting situations because it depends upon the dominant type of light in the situationn (G, B or R) and what is important in the image and you probably have to be shooting RAW to get the main benefit (otherwise the camera will mess it up).

And a couple similar dpr threads here and here.

I think John has said it pretty well. By the time you help one component of the image, another area is often hindered. In the case of a blue filter it rarely has a benefit for skies, rendering them with little interest or, in the case of clear skies, overexposure.

If you were to use 2 exposures, one with the blue filter and one without, and then carefully mask and blend, I think you could achieve much of what you desire.

Completely off topic, I love Colorado. I have a couple of cousin families that live in the Pueblo and Colorado Springs area and I used to travel to Colorado quite a bit. (... Before marriage and high gas prices that is. :cry)

I found some great opportunities around the East and West Spanish Peaks one year.

davidweaver

Interesting reads here. We still use UV1 and UV0 filters to cut some haze so I would think that color filters still have their place. Ohhh...now I want to go shoot some dramatic sky shots with a red filter and a polarizer.

I want a new filter that will expand the range of the narrow bandwidth red LED stage lighting that so many clubs in Austin favor.

ziggy53

davidweaver wrote:

Interesting reads here. We still use UV1 and UV0 filters to cut some haze so I would think that color filters still have their place. Ohhh...now I want to go shoot some dramatic sky shots with a red filter and a polarizer. ...

Oh yeah.

davidweaver wrote:

... I want a new filter that will expand the range of the narrow bandwidth red LED stage lighting that so many clubs in Austin favor.

Yikes! LEDs!

BeaKeR

Thanks!

jfriend wrote:

My conclusion from reading the thread is that there are some lighting circumstances and some matching filters that can increase dynamic range, but there is no generic solution that works in all lighting situations because it depends upon the dominant type of light in the situationn (G, B or R)

Thanks for the links, that's exactly what I was looking for, and pretty much matches what I was expecting.

jfriend

davidweaver wrote:

Interesting reads here. We still use UV1 and UV0 filters to cut some haze so I would think that color filters still have their place. Ohhh...now I want to go shoot some dramatic sky shots with a red filter and a polarizer.

I want a new filter that will expand the range of the narrow bandwidth red LED stage lighting that so many clubs in Austin favor.

There are some really nice Photoshop techniques for using the red channel in an image to increase the drama in a sky. The idea is that the red channel contains the most difference between white clouds and blue sky so using it as some sort of contrast enhancer can work really well. That operation is not about increasing dynamic range in the source image, but can work really well.

There's an example of this use of the red channel here to create this:



from this:

jogle

davidweaver wrote:

I want a new filter that will expand the range of the narrow bandwidth red LED stage lighting that so many clubs in Austin favor.

eeek, LED's throw such a tiny range of light that you're going to be stuck. Even the white ones when looked on the colorimeter are just 3 spikes of red green and blue, not a smooth range of colours, that's why they split apart so easily when refracted through glass.

Filters only change the balance of light passing through them, not actually shifting the frequency. A blue filter may look like it's turning everything more blue, but it's really just cutting down the red end of the spectrum that gets through.