Mere mention of filters with black & white brings back some very distant memories. Including vague recollection of a Camera Bag piece I wrote in Railfan & Railroad on choosing the right filter for the proper rendering of paint schemes in grayscale. While I'm on lunch break at work, I'll try to revisit the basics here as best I can.

As mentioned previously, a yellow filter was the most common way to go among B&W train shooters, but not the only way. Darn near any colored filter will boost contrast to some degree by suppressing its like color and enhancing opposite colors. When shooting general landscapes or whatever, it's just a matter of how much contrast you want, but pay attention to what you're doing to blue sky, green trees, etc.

However, when it comes to things like locomotive paint schemes, or any other combination of critical colors, your choice of filter can make or break a B&W photo. Back in the day, a K2 yellow filter was the gold standard among those shooting B&W on Cajon or anywhere else that SP, UP, or even ATSF ran. Unfiltered, an SP unit's red nose and tail usually blended right in with the medium gray body in B&W. But with a yellow filter, those red ends lightened up just enough to be clearly visible against the gray. The yellow filter also made a clear distinction between the gray roof, yellow sides, and red pinstriping on UP units. With Santa Fe blue and yellow, a yellow filter could be a bit extreme, often making the yellow unnaturally light and the blue unnaturally dark. Still within range of acceptibility though (and in some ways it made Santa Fe units look cleaner than they might have actually been). All of which made a yellow filter a good overall choice for much of the West. Oh yeah, it worked fine on BN units too.

Now, try shooting those SP units with a red filter, like some folks did, and the red nose and tail were rendered much too light in B&W (looking pretty much white), in my opinion.

Then came the late 80s and early 90s, where some new (and renewed) paint schemes prompted me to re-examine filter choices. First came those LMX GE leasers with the small red LMX logo on the side of a light gray body. Yellow and red filters virtually erased the red lettering. Couldn't see it in a B&W photo. Dark red on dark gray (SP) worked well with a yellow filter. But dark red on light gray (LMX) did not.

I soon found than an XO green filter darkened the red lettering, making it stand out in proper value against the light gray LMX body. Santa Fe's red and silver warbonnet, resurrected for the Super Fleet, posed a similar challenge. Yellow and red filters lightened the big red face to the point where it had about the same tonal value as the silver body. Too washed-out. But a green filter rendered the red in a darker tone than the silver, looking completely natural in B&W.

Food for thought.