I have a need a to film some welding. More specifically... the client would like to actually see the bead of weld close up as it's being welded. The client manufactures welding products and would like this kind of detail. Can this be done? I've shot a lot of people welding. But I've always shot it with a nice star burst on the welding head. Has anyone done something like this in the past? What about filtering with welding glass? Am I crazy?
Well first just a little bit of symantics -- you say you want to film welding. Do you indeed want to film welding, or do you want to videotape welding?
I normally wouldn't ask, but even though this is the cinematography forum, 99% of the questions in here are videography and people throw the word film around all the time even though they mean tape. I honestly can't remember the last cinematography question.
But yes, I would think you can most certainly film welding and probably get pretty good results. In fact I am pretty sure you will get better results than if you tried to videotape it. I have videotaped welding before but have always been afraid I would burn a sensor even though people apparently do it all the time.
If you want to go the film route use slow film of course (something like 5201), pile on ND filters (maybe a couple of .9's) and meter it. I wouldn't hazzard a guess as to exposure, but welding is damn bright of course, expect to iris down plenty. A variable shutter camera would help, I can forsee having to narrow the shutter some even with your highest f-stop. You might even have to overcrank some, too (maybe 48fps?). Hard part will be metering. I'd suggest a really good spot meter, but then again how do you look through it without burning your eyes? Maybe an incident meter would work. You might bracket several exposures to be sure to get a good take. And a camera with a VA would be super helpful so you don't have to look through the finder during the actual take and risk a burn.
My other suggestion would be to throw LOTS of light at it (daylight balanced). As you stop down to hold exposure on the welding the rest of the scene will go very dark (especially if you are using a slow film stock, a couple of n.9s, a narrow shutter and 48fps or any combination there of). If you can rent at least a 2500 or 1200 hmi you can keep the scene from looking like welding at night. A 4k or 6k par would be even better.
As far as operating the camera, if it's film, can you use a video assist monitor? If it's video, you can use the viewfinder just turn the brightness down. I have tried to operate a camera in this situation using a welding mask, just a little too dark.
Let me offer this. There is a special filter which is made in the form of glasses for people who work in the glass making biz. I can not remember the name of the thing, sorry, but what it does is extreamly odd. This purple colored filter actual eliminates the flame so all you see is the subject (glass) being formed.
I dont know if this filter would work for welding but its worth a try. The only company I found that made if for a camera lens was Hoya.