Video varying Depth of Field

sirch

Lu-Tze
Admin
Messages
104,416
Name
The other Chris
Edit My Images
Yes
Just wondering, is there a "technical" term for varying the depth of field during a video scene. I should add that I know nothing about video but suppose, say, you were videoing someone walking down a path and you started with a shallow DoF and as they walked way you increased DoF to keep them in focus, rather than changing focus. Is that actually a thing?
 
You can use a depth of field pull. You can do it by using a variable ND filter or ISO to compensate for the change in aperture. You need to be able to vary the ND or the ISO smoothly or you are going to get steps in the exposure variation.
 
Yea, it's called "pull focus"


Pete is the above wrong,? it's a typo or sommit surely????????? Chris is asking about an apeture DOF pull. erm I think ??

Mate not being pedantic trying to work out how to make a vid tis all I know nothing but it's bestI'm able to understand the terms

Pull focus is the same as focus pull ie moving point of focus from one point to another.?? that is right isn't it


sorry mate I'm spinning from video input but had to ask as it might not be a typo, you might be right I need to understand:)




You can use a depth of field pull. You can do it by using a variable ND filter or ISO to compensate for the change in aperture. You need to be able to vary the ND or the ISO smoothly or you are going to get steps in the exposure variation.

AH , more specifically can you elabourate at all on how auto ISO can be used to compensate for an DOF change .

I normally shoot stills my camera body is a 1dx mark ii I shoot wildlife . Due in part to C19 sheilding etc I find myself making video , which I have never done before. I normally work with natural light all these vids are made at night. Simply I have a mum fox that scavenges our bird feeders has done for ages, I just didn't know she brought her cubs here. I can film then from feet away and am trying to absorb every thing I can as fast as I .can

So basically from just siimply shooting, i'm aware I'd like to have a method of varying DOF and also aware just changing the F looks horrible . Is this as simple as using auto ISO. . Is auto ISO a crude start point that will need more work in post? Does one severely limit auto ISO options to pre determined f changes? Andrew you shoot something very very different to I. The ND grad is a non starter for me ,I had wondered about ISO being an option. My subjects at this distance allow me to barely move a lens ,they is simply no way an NG grad can work but ISO in auto seems logical. If I can understand a working method I might be able to adapt it to my needs. Sorry for the Q's I could ask a million at the moment, I need to grasp the basics of so much,so fast
many thanks if you reply.


Chris @sirch sorry if this is a derail, I feel like i've commandeered your thread bro, my humble apologies . It just seemed so silly to ask elsewhere start another when the topic is what I wanted to ask about and am also slightly confused by Pete's post

thanks lads

take care

stu
 
AH , more specifically can you elabourate at all on how auto ISO can be used to compensate for an DOF change .

stu

If you set your camera to shutter priority and auto ISO as you vary the aperture the camera will change the ISO to keep the same exposure value. As you vary the aperture the DoF will obviously change. If you are shooting at night I wouldn't have thought you would have the ability to vary your aperture or ISO and keep a sensible exposure.

Also I think you may be a bit confused by some of the terminology. A variable ND filter is one where the density is the same across the filter but by rotating the front element you can increase or decrease the overall density but the density is always constant which ever part of the filter you look through.
 
Pete is the above wrong,? it's a typo or sommit surely????????? Chris is asking about an apeture DOF pull. erm I think ??


Pull focus is the same as focus pull ie moving point of focus from one point to another.?? that is right isn't it


Same thing in this case i think, just that in this instance the subject is moving, you're still pulling/pushing focus to keep the subject IN focus.
 
Thanks Andrew yes I am confused about the terminology, many things actually,I shot my first vid maybe 2 weeks back . Every thing is new to me really, making a video is such a different disciplin to photography, similar tools maybe but so very different. , So although I can see some improvements as I keep doing this I know absolutley nothing yet, the chance is so special though Andrew I have to try and make something out of it


i'm working very close to the fox/cubs Andrew between 3 and 8 meters mostly around the 3 yo 4 M mark I guess but getting a constant exposure is incredibly difficult,due to light fall of , I was curios if the DOF pull might be of use to me when a fox comes very close to a light potentially a way to combat blown hilights and add a bit more DOF at the same time. thanks for the advice i'll have a go and see what happens. I'm not talking huge shifts in DOF just trying to get my head around not only what and what is/isn't possible but also how things pan out in my particular situation .
 
Trying to video wildlife is not something I know anything about but in your situation I would be trying to expose for the brighter parts of the image and then work on the shadows in post production. Try and keep your ISO as low as possible to give the best dynamic range. You could also try lowering your shutter speed to give you a better exposure. If there's not a lot of movement in the frame you can sometimes get away with as low as 1/25s.
 
i've been largely shooting at 1/50 SS wise Andrew, doubling up on the 1/25 FPS largely f4 iso is landing around around 1250 . I normally ETTR for stills which I guess is the same methodology for video. although at this stage I feel i'm underexposing a tad because of the situation, A wild animal does what it wants couple in variations in distance to the light sources ,it isn't straight forwards . It's not just dealing with the light fall off it's also learning how to place the lights to best advantage. . i'm certainly not finding many folks I can talk to who have done what i'm trying to do either stills under constant light or video at night of wildlife, IR accepting . But I was told it would be a big ask of lights and wouldn't be easy , so I've gone in with my eyes open. The chance is just so good I have to try even if I end up failing dismally.

many thanks.
 
Back
Top