For this project, I've been using two lenses--a wider angle Derogy Petzval lens and a 20" Wollensack lens. So far, the Derogy is the lens I've used the most. It doesn't fully cover my plate, but I am liking the vignette that it's giving me and I love the softer contrast that I'm getting with it.
Some antique lenses have slots on the top of them, which my Derogy does. These slots accommodate small inserts called "Waterhouse stops." Waterhouse stops serve to allow the lens to "stop down" giving the user more depth of field. This means that the focus will carry more in the photograph. My Derogy is so old that it does not have a shutter in the lens and to make an exposure, I remove the lens cover for the amount of exposure. For this project, the exposures have been 3 seconds. Most antique lenses have long since lost their original Waterhouse stops and if a set is desired, they have to be hand made to fit the lens exactly. We ordered ours about a year ago for two antique lenses that we use regularly.
I decided that my #selmaportraitproject photographs needed just a tad more depth of field to them and decided to use the set of Waterhouse Stops my friend Tracey Storer handmade for Doug and me. He doesn't have them listed on his website, but has let me know that he will accommodate special orders for these if you own an antique lens. He does need the lens to be able to measure the lens and make the stops so that they correctly fit your lens. For my images, I'm only stopping down 1/2 stop which does give me a little more "carry" with my focus and allows me to have a 3 second exposure. If I chose not to use the stop, I'd need to have a shorter exposure and once I get into the 1-2 second range, it's hard to remain consistent when removing and replacing the lens cover.
If you're interested in a set of Waterhouse stops (which I highly recommend if you're using an antique lens that accommodates them), you can contact Tracey Storer of The Mammoth Camera Company at: http://www.mammothcamera.com/mammothcameracompany.html. Everything that I have commissioned from Tracey has been handcrafted with great care and precision.