GH4 Aperture Preference for Interviews?

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Ianscreations

Well-known member
Assuming you can control all other conditions, what is your aperture of choice for formal interviews? That is...assuming you want a shallow DOF, what aperture do you find gives you a decent focal plane so that the slightest movement doesn't fall out of focus yet still manages to separate the subject from the background. I realize a lot of that can depend on lens choice, but with all else being equal...what do you find the best to work with? I have found anything under 2.8 to be too shallow.
 
I tend to not go under 5.6 especially if the interviewee moves a lot. Nothing is worse than having the focus point on the nose and not the eyes. I used to do a ton of interviews and it always made me very nervous specially if it's VIP's.
 
Shallow depth of field in an interview should never blur any portion AT ALL of the person speaking. That's just horrid and looks amateurish.

How much of the background to blur? That is the question.
Well that depends a lot on what exactly the background is, right?
If it's just some curtains or a fabric photo backdrop - then just the slightest amount of blur will give a great soft effect.
But if it is a complex background with a lot of objects or textures that could be distracting - then it makes sense to blur it a little more.
One of the best ways to do this without risking focus problems is to get the subject as far away from the background as is reasonably possible.
Also. if you have space, use a longer lens - like a 50mm or an 85mm and place the camera further back. This will help keep the entire person in focus while blurring the background a little more evenly.

The exact f-stop on the lens is not what you should be judging this by. Especially when you consider that that same lens will give a different depth of field depending on the size of the sensor on the camera you are using. And there is lens optics - a 20mm lens at f-2.8 will give a deeper depth of field than an 85mm lens at f-2.8 tends to. (Adjusted for realistic distances of course.)
 
This question is a can of worms unless you know the distance to the subject, sensor size/crop factor, focal length and f/stop. Distance to subject is much more important that either of the other factors in DOF. The closer you are to the subject the shallower the depth of field, exponentially speaking. Take any focal length in GH4 4k UHD and move a few feet in vs. a few feet out and see how radically it effects DOF.

With GH4 4K I like much faster than f/2.8, always. The depth of field at 10 feet of a 25mm is measured in feet not inches at f/2.8. I've never been able to get anything cinematic looking at less than f/1.8 in 4k, EVER !!!

There is another piece of this equation which is whether you are doing a narrative piece or a corporate piece. The more creative you want it to look the shallower depth of field you might need. With a full frame dslr you never have to worry about getting too shallow a depth of field. With a GH4 in 4K it's always an issue in my experience.

Getting separation is not so much a factor of f/stop as it is composition. Making that happen with Gh4 4k is more difficult than it might seem IMHO.

Cheers,
Pete
 
Greg_E said:
How does a speed booster change this?
Click to expand...

several questions are answered here:

http://www.bhphotovideo.com/explora...how-emulate-super-35mm-4k-video-panasonic-gh4

First off you can't use a speed booster with native m4/3 lenses, and the main topic discussed in the link is the speed booster with lenses optimized for the DX or APS-C sized sensors with about a 1.5 crop factor, and the GH4 in 4K where the image "crop" is an additional 2.3X. And it's an even different game with the speed booster and lenses designed for full frame.

I just read this piece this morning and it was an eye opener for me, I've just acquired two pristine Nikkor "legacy" lenses: The 24mm f2.8 AI and the 50mm f1.4 AI, and was planning on ordering a speedbooster thinking I would get wider FOV than what it turns out will happen.

In 1080p with a crop factor of 2x the 24mm with a "plain" adapter will give me a 48mm full frame equiv FOV (24mm x 2). With a current speed booster it would result in just under 35mm full frame equiv FOV (24 x speed booster's reduction factor of 0.7 x m4/3 crop factor of 2).

The image formed in the focal plane by this lens is enough to cover full frame 24 x 36 mm negative size and the portion that falls on the m4/3 sensor is much smaller. If a same focal length lens optimized for DX or APS-C is used, the image at the focal plane is MUCH closer to the m4/3 sensor size so the resulting FOV is much wider.

With 1080p in the GH series camera there could be some vignetting but the 2.3 crop factor of the GH4 4K might help "get away" from that.

With both types of lenses you still gain one stop of exposure because the speed booster "condenses" the light forming the image enough to do that.
 
c3hammer said:
This question is a can of worms unless you know the distance to the subject, sensor size/crop factor, focal length and f/stop. Distance to subject is much more important that either of the other factors in DOF. The closer you are to the subject the shallower the depth of field, exponentially speaking. Take any focal length in GH4 4k UHD and move a few feet in vs. a few feet out and see how radically it effects DOF.

Pete
Click to expand...

I appreciate the responses. I'm not sure I am asking this the correct way :)
I do understand how many variables can affect DOF. What I'm trying to ask is assuming all else being equal (the GH4 sensor, amount of background blur, shot framing, iso, etc)...what f-stop have you found to be a "safe zone" for maintaining the subject in full focus while stlll creating a shot that is not fully in focus. Obviously f/22 would work on a long lens, but what is the lowest you are willing/able to go for most interviews?

Perhaps a better way to ask is: How do you determine your f-stop for focus? After you have set up your shot with the lens of choice, framing, background, etc....how do you determine what f-stop will keep you subject in full focus while keeping the DOF as shallow as possible?
 
A handy smart phone app for figuring out these things is pCAM.

It will let you discover depth of field, splits, field of view, focal length match, relative size, triangulation, exposure, running time to length, shooting to screen time, HMI flicker free, color correction, diopter calculation, macro, time lapse, underwater distance, scene illumination, light coverage, mired shifts, and much more. It is well worth the money!

All the Best!

Dave
 
I've done interviews at f/2.8, and the focus has turned out great. Usually I go for f/3.5 to f/4. My usual interview setup is Cam A with the Panasonic 35-100 @ around 90-100mm. Then Cam B with the Sigma 8-16 at 8-9mm.

Something to add, a lot of it has to do with how far away you seat your subject from the background. Many people miss this, and it's what sets local TV apart from national broadcasts. Companies like CNN have the luxury of large spacious sets where the hosts/anchors can be seated a measurable distance from the background and the cameras also at a far distance. This of corse depends on size of TV markets, etc.
 
Most cameras used for news broadcast like CNN are 2/3"

Another little trick used on news sets is to print your backgrounds like duratrans slightly out of focus.
 
Daniel Brown said:
I've done interviews at f/2.8, and the focus has turned out great. Usually I go for f/3.5 to f/4. My usual interview setup is Cam A with the Panasonic 35-100 @ around 90-100mm. Then Cam B with the Sigma 8-16 at 8-9mm.

Something to add, a lot of it has to do with how far away you seat your subject from the background. Many people miss this, and it's what sets local TV apart from national broadcasts. Companies like CNN have the luxury of large spacious sets where the hosts/anchors can be seated a measurable distance from the background and the cameras also at a far distance. This of corse depends on size of TV markets, etc.
Click to expand...


Thanks! This is the sort of answer I was looking for. I have also found f/2.8 with the 35-100 to be a nice range. I have the 42.5 f/1.2 and have found that subjects easily drift in and out of focus with the smallest movement when it is wide open.
 
On my AF100, I tend to shoot f/3.5-5 (it's situational), at usually between 50mm and 80mm (again, situational). The key is what focal length are you shooting at. I shoot over 50mm... and usually in the 70mm-80mm range... simply because most interview subjects have never been interviewed before, so having the camera right up in their face doesn't help put them at ease. Below f/3.5 at that range, and you start to run into issues of folks going in and out of focus.
 
I found a FANTASTIC free app that provides you with the ability to input your camera, lens, aperture, distance from the subject, etc. and it calculates your DOF and even provides a visual representation of your focal plane. It is EXCELLENT and free! It's called "LensTutorial."
I used it to calculate the aperture I needed for the interview for this video. I used my 42.5 at 1.2 but used the right distance from the subject to give me about 3 inches of "wiggle" room. I still had some places where the subject moved out of focus, but I needed a very shallow DOF b/c of the setting.

https://vimeo.com/131219902

Password is "Carol"
 
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