Understanding 590nm (Goldie) Issues

Understanding And Working With  590nm Infrared…

 

B+W 090 590nm IR Filter (Super Color or Goldie)

I LIKE shooting with a 590nm B+W 090 (Goldie) filter!  It really is sort of an obsession with me. On my recent trip to Greece, when I shot in Infrared it was ALWAYS with a 590nm filter.  I find that I get really good results when working towards Faux Color images, but yet still get GREAT B&W images.  Sometime I would get lucky enough to get really stunning RAW conversions without even bothering for a Faux or B&W image!  BUT, there are some issues… These issues are not dependent upon camera make and model but rather the infrared band.  All attempts at 590nm and 665nm (to a lesser extent) are subject to the challenges noted below!

I keep almost every type of Infrared filter on hand but for reasons of experience I always seem to go towards the 590nm.  As you can see from the image to the left, the 590nm Goldie filter is a bright red color.  You can understand from the picture that there is a LOT of visible light leakage from this filter which is one of the issues we are going to discuss here today!

 

Various IR Filter Curves, Look At the 090 For 590nm

There are some minor issues when using a 590nm filter that you must understand in order to overcome.

• 590nm is firmly in the realm of the visible spectrum creating visible overexposure from 590nm to 700mm.
• White Balance is ALL important to getting good color and proper exposure.
• The Camera Histogram is ALWAYS wrong in the Red channel when mixing visible and infrared light.

The first listed issue really is the most important one to understand.  Our camera’s electronics and algorithms are designed with color images in mind.  When we remove the hot mirror (UV/IR Cut Filter)  and attach a dedicated 590nm or 665nm filter OR a clear glass filter (Full Spectrum) and use a 590nm external filter, we are allowing a small amount of visible light from 590nm to 700nm strike the sensor along with the infrared spectrum from 700nm to 1000nm.  Since 590nm is in the deep red area of the visible spectrum the RED channel is overwhelmed with bright red light and the blue & green channels see more of the 700nm and up light.   This tends to confuse the camera computer and while it will display a normal looking histogram (monochrome), if you look at the separate RGB histograms the red is off the edge and way overexposed!  Usually you can overcome this during the RAW conversion process by changing the exposure down 1 or 2 stops in conversion.  Sometimes the overexposure is so bad that you are out of the range of repair during the conversion process.  So I following the following steps to overcome this in camera:

1. Proper White Balance to equalize the color Channels
2. Set the camera histogram to separate RGB channels so that I can directly monitor the RED channel
3. Check the exposure on EVERY shot and dial in the appropriate exposure compensation.  Normally this is around -1 or -2 but some subject matter like lots of leaves will require you to switch to manual exposure  to go – 3 or more!  A cloudy sky will actually force you to add + exposure compensation.  Just take a test shot and check the red channel histogram then make the proper adjustment.
4. ALWAYS use your lens hood to prevent lens flare as well as to keep contrast up by stopping light from hitting the objective lens at extreme angles.

Here is an example of the red channel being 2 stops more exposed than the blue and green. Remember that for this exposure I had dialed in -.7ev exposure compensation.:

 

RAW Histogram

Looking at the Histogram you will notice that the red section is a full 2 stops over (shifted right) the other colors!  If I had not set -.7ev in camera this image would be a full stop off the right hand side!  Yes, you can adjust it down during the conversion process but you must agree that better images are properly exposed the first time and not repaired after the face!

Here is the converted RAW image.  It looks great all by itself (rare) and I processed it as such! I also processed as Faux Color and B&W which follows.  As you can see here with the RAW image, it has a much different color scheme and is quite interesting all by itself.  All that was done was to properly White Balance the camera, take the picture, download it to the computer and do the RAW to TIFF conversion either in ACR in Photoshop or like I did using Capture One Ver 6.  Then run come contrast and levels adjustments and save the image as a PSD!  Once in a while you can get some stunning images this way.

 

Converted RAW but NOT Channel Swapped

Following is a Faux Color Post Processed image using the following steps:

DETAILED FAUX COLOR WORK FLOW

• Taking the picture I adjusted the exposure compensation to -.7ev to keep the red channel under control and not blow out the sky.  I also set the White balance using a BRNO neutral WB lens cap.
• After moving the image to the computer via Downloader PRO (see recent post) and RAW processing with  Capture One V5 where I added a little contrast and clarity, I opened the image in CS5.
• I cropped for my master library size (8.5×12.5) and ran the Khromagery Faux Color Action (down load on the right).  In the Master Color Channel I simply increased the Saturation which brought out the blue sky & water and the yellow plants.  I then choose the Cyan and Red channel adjustments and made sure to adjust the HUE to where I liked it.
• The ABOVE Cyan adjustment is important, I hate sky’s and water looking blue-green, so I always adjust the Cyan HUE to go to normal blue!
• I then flattened the Adjustment Layers.
• Next I ran NIK Software’s Viveza (a Photoshop plug in) and simply made point selections of the color I wished to modify, ran up the structure to bring out detail and adjusted the brightness.  I did this to all of the color areas I needed to like the water surface, the yellow plants and the blue sky. I also selected the warm colored wood of the Trunk and the rocks in the foreground and removed color saturation forcing them to be B&W!
• Again flatten the image.
• Save as a PSD file

Faux Color Post Processed (Swap Red & Blue Channels)

Here then is the screen shot showing the equalized histogram for the Faux Color image. See how they are all pretty much in line in terms of exposure?  This is what we are striving to accomplish!

 

Faux Color Histogram

And lastly the same image processed in B&W by taking the Faux Color image (above) and running it through NIK Software’s Silver EFX Pro using the High Structure Filter:

 

B&W Post Processing

As you can see, this is one of those rare images that produce great photographs in all 3 formats!  All of this from the 590nm (Goldie) filter.  You can see why I like this spectrum so much!  If you have any questions please drop me a line.