Shooting portraits in large format film is extremely rewarding. There's a simplicity of the process, from the posing to the static camera position, that helps ground both the photographer and the subject in the moment. Beautiful images may be your reward for such patience, but it's not without its challenges. For me, the biggest challenge shooting portraiture is not working with the camera, but the insane amount of light you need to throw at it. For the uninitiated, here are some facts about the format and its light-eating characteristics that you may need to consider.
When I decided that I would use my 4x5 camera for my portraits for my American We project, I hadn't considered the amount of light I'd have to regularly throw at my subjects. I quickly found that my pared down kit of speedlights and umbrellas wasn't going to cut it. Here's why.
One of the first things you'll notice, especially if you're coming from a 35mm sized frame or sensor, is that the maximum lens apertures are much smaller than the format you're used to. A top quality 35mm portrait lens will usually have a maximum aperture of f/1.4 or f/1.2. You don't need to throw a lot of light at it to get a proper exposure. When you're dealing with typical large format portrait lenses, say a 210mm in 4x5, an f/5.6 might be as wide as you can get. So right off the bat, you're losing about four stops of light if you want to shoot wide open. That's fine in daylight outdoors, but when you start shooting indoors, you're going to need strobes with some power to get any action stopping going on. Either that or you're going to have to have a very, very still subject.
Don't be disheartened by that large number, though. There's roughly a four-stop difference in depth of field from 4x5 to 35mm. So, f/11 on 4x5 would be the same depth as about f/2.8 on 35mm. And that's another reason you'll need more light: you don't need to shoot wide open on 4x5 to get shallow depth. In fact, if you want optimum lens sharpness, just like with 35mm, you'll want to stop down a bit. More light gone.
There are some lenses that have wider maximum apertures, but they don't usually fit into traditional leaf shutters, so you'd need a camera with a focal plane shutter to use them, such as a Speed Graphic.
The Bellows Factor
When dealing with the large format, you're more than likely using a camera with bellows. The bellows is the light-tight accordion looking thing that connects the front and rear standards of the camera and lets you adjust the distance between the lens and film plane so that you can focus. They're very handy and let you pull off some great effects and movements. However, because of the nature of bellows-focusing, the distance between the lens and film plane can vary greatly, and that needs to be compensated for. In order to compensate for it, there's a formula that you use. I use an app on my phone. Yes, I'm lazy. If you're as lazy as me but you're an iPhone user, try this one. On my wooden field camera, if my bellows are fully extended and I'm using my 210mm, I'll easily lose an additional 1.5 stops of light. When you're doing macro work on a big studio camera, the light loss can be even more significant, as the closer you need to focus, the further the lens needs to be from the film plane.
Even at medium distances, you still will easily lose a half a stop of light to bellows compensation.
Ways to Compensate
First of all, if you want to use artificial lighting at all, get powerful strobes. Most large format lenses have sync ports on their shutters so you can sync with no problems using cords or your favorite wireless solutions. I use PocketWizards with no issues. I use Einsteins and a Godox AD600 in the field and I've never been wanting for power. But that's typically shooting at no smaller than f/16 (roughly f/4 equivalent on 35mm). If you plan on doing really close work in studio, you may want even more power. A pack and head solution, such as a Dynalite or Profoto Acute2 might be the way to go for you.
Grain is not as much of an issue at large format sizes. You can get away with a grainy emulsion because the size of the negative will compensate for it. That's why I prefer to shoot 400-speed film. You'll get greater light sensitivity, which will counteract some of your light-eating factors. There are fantastic 100 and 125 speed films out there, such as Kodak T-max 100 and Ilford FP4 125, but I find that compensating for the slow speed is more trouble than it's worth in large format. I've been using Ilford HP5 Plus 400, Kodak T-max 400, and Kodak Portra 400 for color with no issues with graininess.
Pushing Your Film
If you don't have enough light, pushing your film in development is always an option. One of the benefits to the increased tonality and larger negative of large format is that the hazards of pushing film, namely increased contrast and graininess, are minimized. Some films respond to pushing better than others, however, so if you think you might push your film to gain back some light, get a film that's known to perform well when pushed, such as HP5. The other factor when pushing film is the type of developer you're using, which brings me to my last way to compensate.
Picking Your Developer
When dealing in black and white film, the type of developer you're using matters. Some, such as Rodinol, are famous for the great amount of grain they bring to the table. That makes them less than ideal for pushing film, at least by normal developing means. You can stand-develop your film as well, and I've heard great things about that process, although I've never tried it. Ted Forbes did an informative video about stand-developing over at The Art of Photography if you're interested in it. For normal processing, developers like XTOL, Microphen, and DDX are very good for minimizing grain while pushing.
It's Worth It!
Of course, I'm biased on this last point, but I totally feel that it's worth dealing with the light issues of large format. The results are beautiful and different from anything captured with a smaller frame. I just want you to go in with the knowledge that, just like any format, there will be challenges. Bring some flashes and your A-game and get shooting!