petedawgg1989 wrote in post #17804803
Hi guys been into Photography for a while now and getting into Flash, getting a lend of a profoto 1200 7b pack and head. What I'm wondering is if I'm looking to under expose the ambient light by two stops can i do the following working with a 5d mark ii and a vari nd filter.
Get my ambient exposure by setting my camera to 125th of a sec and finding my aperture from there for a even exposure on the background lets just say its F16 and then getting my Flash to flash at F16 on the model. Then use a Vari Nd filter to bring down my aperture to say F2.8 and I'm thinking my flash will stay the same power as I'm opening the aperture anyway to let in more light that the nd filter takes away.
after this is done then knowing that i want to under expose by 2 stops just take my shutter up to 200th of a sec which is two stops under exposed.
i might be all wrong here or over complicating things but just thought id ask.
Heya,
There's different ways to do it. You can meter with flash. You can chimp. You can be creative.
You establish ambient light with the camera settings. This is a separate exposure from your flash exposure. Meter your hand if you have to. And you can meter it down about -2 stops from normal exposure pretty easily, just with your hand in the ambient light (if there is enough). Once you get that exposure, you know what you need to do. Say you're at F2.8, ISO 100 and your meter says 1/800s in the ambient light to drop ambient exposure by -2 stops according to your meter. Just random numbers to help it make sense. But you want to shoot at sync speed of 1/200s. That's +2 stops of light, and you wanted -2 stops of light for what you metered. So you'll need to make up those 4 stops of ambient light with an ND filter to get back to your intended exposure of -2 stops of ambient for that new shutter you needed based off what you metered. Now you add flash, as a separate exposure. Meter if you have one. Chimp if you have to.
I generally don't use variable ND filters. I prefer a good quality non-variable. I find I generally get by with 3 stops or 6 stops just fine for dropping ambient. 6 stops in bright light. 3 stops in morning/evening light. If I have to raise exposure up and don't want to open shutter more, I just use ISO to raise exposure. I don't mind if my filters underexpose by a bit, since I can make up for it with ISO. This allows me to not have to worry with a variable ND filter.
Here's an example of that described process from above:
Camera settings to exposure. When I metered (with the camera, I don't use a light meter, I chimp), at F2 and ISO 100, I got 1/1600s. Fairly overcast, still a wee bright, but that's due to wide aperture of F2. To be able to stay at F2, and get back down to sync speed with my my speedlites, 1/200s, I needed to block 3 stops of light. But I also wanted to drop ambient exposure a little more than normal to let the flash isolate the subject. I had a CPL with me, and those are about 1 stop of ND actually, so I put that on there. That dropped the light by 4 stops total after stacking the 3 stop ND and the CPL. Flash was still at 1/1 power (full power) and was used to expose subject at very close distance behind an umbrella suspended over subject's head. Ultimately I opened up to 1/100s to get another stop of light back, after reviewing, because I didn't feel like taking the CPL off. But you get the idea.
by
Martin Wise, on Flickr
Very best,
)
