At a basic level, digital photography is just like analog photography...manipulating the amount and quality of light that the recording medium (film or sensor) senses.
This means that things such as exposure, aperture, ISO (ASA), grain (noise), color temperature and composition remain close to being the same.
Once you get past the basic level, digital photography allows exponentially more photo manipulation than film ever did or could. However most DSLR's are still machines, with mechanical shutters that would work equally well with film instead of a sensor surface. Lenses still focus, still have an iris allowing us to choose the f-stop, and cameras still allow us to choose the shutter speed (if you're using something other than a point & shoot or cellphone camera!)
On the other hand, many of the aberrations that were inherent with lenses are now eliminated by the camera body's software, and even the amount of sharpness (or lack thereof) can be chosen. On many modern DSLR's, fine-tuning an individual lens's critical focus is easily possible in just a few seconds, and the camera body remembers the setting. Some cameras allow you to set individual photographic parameters for two divergent scenarios, such as one set of parameters for portraits, and one for sports.
Although I appreciate old techniques and equipment such as pinhole cameras, long exposures combined with small f-stops to increase DoF, the image suffers greatly from diffraction using a pinhole lens or "normal" lenses stopped way down. Also, the closer you get, the more limited your DoF becomes, which these old techniques do nothing to overcome, and were just something we had to live with.
That is, until FOCUS STACKING!!! ...possible only through the inclusion and use of certain software into the photo-creation stream. Since when shooting multiple photos to stack, you don't have to worry about the lens's DoF, you can shoot at your lens's "sweet spot" for the best possible photos to stack (usually between f-5.6 and f-8.0) instead of sacrificing image quality through diffraction for more DoF. And, DoF now becomes only limited by your lens's ability to close focus, not by what is distant.
Truthfully, although it certainly takes less time and effort to shoot a composition using a long exposure and a small f-stop with your camera mounted on a tripod, you have much more control over DoF using focus stacking. With a lens that will focus 1:1, you are really not limited any longer by DoF in miniature, static subject photography.
Until you use it, play with it and get to know it, you really don't know what quality focus stacking software can do for your model railroad photography if you desire realistic photos.
As for wiggling artifacts to look like smoke and steam during long exposures....I've done that many times back in the last century, but it always looked like wiggled artifacts to me. Sure, just like anything else, if you don't do it correctly and with thought, cloning a photo of real smoke into a model railroad scene can look hideous. BUT, done correctly, it can look sublime....ommmmmmmmm...
Seeing the OP's wiggled smoke/steam brought back a lot of happy memories of the 80's and 90's...but, the digital age is here, and since I sold my pro Nikon bodies, I haven't looked back....
Cheerio!
Bob Gilmore
