Depth of field and f-stop

Michaelrosenblum

Michaelrosenblum

Well-known member
How much total control can you exercise over depth of field in video?
When I shoot stills, I know exactly where the focal plane is going to fall because of the hyperfocal distance scale on my 35mm lenses. I can set it exactly. But I can also manipulate shutter speed and ISO.
But when I shoot video, because you can't really change film speed all that much without things falling apart, and shutter speed is also pretty much a fixed event, there does not seem to be much room for movement.
Of course, I am using very inexpensive cameras, and the first place you pay for this is in the quality of the lenses.
I see in movies that rack focusing can be done with great precision, but (never having shot one), I assume this a function of 1) very expensive lenses on film cameras and 2) greater sensitivity of film over video.
How much depth of field control do you guys have and when you do rack focusing in video, is it hit or miss, or can you control where the focal plane begins and ends with as great precision as one can with film?
Thanks.
 
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Lens control is one of the major differences between less expensive cameras and those considered by many as "professional".

The cameras you are using for your VJ classes generally are unable to give you the depth of field sensitivity you speak of. That being said, I've got a very small Sony Mini DV tape camera. Perfect for the pocket and pretty much point and shoot. And in reality I've been able to get a subject in focus with the background soft and out of focus...but it takes forever to set up and, because the camera is so small, it is impossible to do any kind of rack focus without severe shaking of the image the moment my hand touches the camera.

it is actually quite easy to achieve on the larger cameras. More sensitivity under low light situations and the lens controls are easy to access without causing image shake.

The advice I give others who use the small cameras and ask your very same questions? Forget it. You are wasting your time and making a very basic mistake. You are trying to make a small camera into a big camera. It's the same mistake other make by trying to use a big camera to do a small camera job. It's all about using the proper tool for the job required. That's not a knock against the cameras. It's no different than using the wrong sized screw driver on a too big or small screw.

The key to getting a good depth of field with video is two fold. Distance from the subject of the image and using as low a level of light as possible to increase your depth of field. Sometimes using a higher shutter speed on a camera will achieve a greater depth of field...but again it's a trade off since that can affect the look of movement within the image frame. No problem with static objects. It's a bigger problem if the subjects you are racking back and forth between have movement. Because you have to be so far away with a little camera to even begin to get "good" depth of field, you find it impossible to keep the image stable, let alone the moving subjects in the frame to achieve a smooth look.

Rack focusing with larger "professional" cameras is not hit or miss most times. It's knowing your camera and being able to adjust the focus ring accordingly. Tiny cams have no focus ring. Just buttons. The speed of the rack focus is also impossible to control on a small camera. It's all electronic while larger cams with larger lens' allow the operator to rack focus as fast or as slow as they like easily.

So from my point of view...forget the rack focus and depth of field desires with the little cams. You'll just drive yourself nuts trying to do it and waste a lot of time in the process.

Long winded post here on my part but...just trying to be thorough. ;)
 
thanks
all makes sense, and it has been driving me nuts.
much appreciated.
But while we are on the subject, have you shot much with the DSLRs?
Here you have great lenses, but the audio is a problem. I assume they'll get that fixed.
Is this the future for small, but higher quality?
 
I've produced training DVDs for several Canon and Nikon DSLRs that shoot video. Most recently the 7D and D300s. In my opinion, they were awful to work with compared to a real video camera. I could give you a list of two dozen CONS to shooting with a DSLR and only three PROS: Small size, low cost and shallow DOF. That's it, and in my opinion those benefits are not enough reason to give up XLR audio inputs, a viewfinder, zebra, peaking, a better codec, etc.

I'm sure that SLR video shooting will continue to gain in popularity in the short run, but I still contend it is just a fad for specialized situations. When I think about my favorite, big-budget, Hollywood films, extreme shallow DOF is rarely used. It's a fad that will look as dated in a few years as fog filters from 30 years ago.

I've seen some great looking stuff from DSLRs, so in the right hands they are entirely capable of nice work. But anything someone can do with a DSLR, they could do better with something like an EX1 -- except for extreme shallow DOF.

To answer your original question, I have no problem getting shallow DOF with a video camera as long as it has a 1/2" or 2/3" sensor. It's all a matter of f-stop, ND filters, focal length, gain (same as ISO) and shooting angle. No different than SLR photography, except you can't change the shutter speed for video.
 
I love civilized topics.

In still photography depth of field control was vital to good photography. Cameras used to have a depth of field scale on each lens and there was a manual control to stop down the lens to the exposure set F stop in order to visually see the depth of field, as viewing from SLR camera was always done at the maximum aperture for brightness purpose but that wasn’t accurate as after pressing the shutter for the exposure the lens would stop down to the selected aperture.

"Exposure value" was also an important term that I haven't heard lately. This is the combination of shutter and F stop that will properly expose the image. You can go in either direction within the value if you needed depth or speed. On Hasselblad lenses you set first the exposure value then you could move both together for either depth or speed without changing the exposure. On modern automatic cameras the same can be accomplished with automation by selecting either the aperture or shutter priority. On digital camera we can also select the ISO speed, but going upward with the speed will effect the quality of the image.

Coming from still photography depth of field has always been one of my main priorities, even behind the video cameras. Video doesn’t have all the options that we have with still cameras, but nevertheless there are methods of controlling depth of field.

The size of the chip has a lot to do, this is why prosumer and now also some low end professional cameras with 1/3 chip are in my opinion good only to create visual records but not good to manipulate the picture for creativity. These shortcoming is what separate professional from amateurs equipment. Those who insists that they are both alike do not really understand how short these small cameras are on technical creativity.

Having said all this I’ve been doing a lot of experimenting trying to get the most, better yet the least depth of field out of small cameras, but first you must understand the control we have with full size cameras.

First, the longer the telephoto you use the shallower the depth will be, this goes with all cameras. This is why personally I only use my wide angle lenses when I need a wide angle shot, long lenses is what I always prefer to use. We can not use shutter speed on video cameras as this will effect the actual video, but we can control how much light will enter the camera with the selection of ND (neutral density) filters as most professional cameras has a ND control with four settings; and I use these setting constantly. If I shoot sports action, especially when using the 2X converter I will want the most depth, in this case I use the lowest setting on my ND filters trying to keep my lens at an F11 stop, sometime I even put a plus 3db. in order to stop down the lens . When I do interviews I reverse that, I want my aperture not to be smaller than 2.8, and with cameras like the HDX900 that’s very good in low light I have to put a 2 ND filter and also use a -3db. Of course the distance of camera to subject and subject to background is vital for a good and controllable depth, but that’s another topic.

On small camera, and I have a few of those, I was able to achieve something close (not too close) by cheating the camera in how much light was there by placing ND filters in front of the lens. The results were clearly visible.

For optimum low depth right now there’s nothing better than the new generation of DSLR, The only time I use my Canon 5D is when I need very very low depth. Caution because those also have different chip or sensor size. The 5D Mark II has the equivalent of a full size 35mm film, while the newer 7D, although it has many more video functions it also has a 20% smaller (cheaper) sensor, and that makes a BIG difference.

As far as rack focus goes it is a very nice effect when done properly and with good equipment. It is, at least when I do it, a pre set effect, meaning I try it several times without recording and placing objects and camera at optimum distance. The most effective one, and we’ve been seeing this done a lot on Planet Earth, is close up rack focusing between objects and/or subjects. For these I use my lens maximum aperture.
 
Very interesting and informative indeed.
I shot for years on a Hasselblad 500c/m and hand metered with an old Westin that gave out EV readings. You remember the red metal brackets on the Hasselblad lenses - this gave you such precision for depth of field. It is this kind of precision I am looking for in small cameras, but apparently it may not be possible yet. I understand the amount of control you get from the big cameras - and the far better lenses, but I am very intrigued by your use of ND filters with the small cameras. I am going to try this one.
Many thanks for the info. Very helpful.
 
with reference to rack focus - keep in mind that cheaper lenses with have very noticeable breathing when changing focus. this is one thing that you pay for with the more expensive lenses: lack of breathing. not sure how it plays out in the DSLR world, however - but if you're watching a rack focus, you can generally tell how "good" of a lens is in use by how much it breathes.
 
The Canon 5D with its full 35mm frame sensor gives incredible DOF along with great L series glass. For production a DSLR works just fine aside from CMOS rolling shutter issues but its physical form factor makes it very awkward for ENG work.

There's a few adaptors for XLR inputs and there's been unauthorized Canon 5D mkII firmware hacks that have added zebras and audio metering. The XLR adaptors with manual levels basically "trick" the audio AGC in the camera with a 30khz tone that keeps the AGC at bay.

Not sure when Canon will come out with better audio control, maybe after Nikon does it? Nikon can do it anytime as they won't be treading on any other market their company is in but Canon if they improve too much would hit their prosumer video division...
 
I can't tell you how many times lately I've seen an interview where the background is in focus and the interview subject is out of focus. Auto focus...its for amateurs.

A Producer told me about a shooter she was forced to work with and she asked him to throw the background out of focus. His reply "Why would you want that"? She said she was ready to hit him. I think he just didn't know how to create depth.

Warren
 
Baltimore Shooter said:
I can't tell you how many times lately I've seen an interview where the background is in focus and the interview subject is out of focus.
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I see that all the time too, but it may not be as common as you think. Sometimes what you're actually seeing is compression problems. The non-moving background compresses nice and cleanly (especially if there is a lot of detail or motion), but the moving human face in the foreground becomes soft and mushy from the compression. The compressor is too stupid to know what part of the shot is important. I've seen this phenomenon on video that I know for a fact was shot in-focus.

However, that does not excuse the shooter from having so much DOF that the background was in-focus in the first place. If shallow DOF had been achieved in the shot, then the compressor software would have used it's muscle on the face and left the background alone. Just something I have noticed in the last few years -- compression problems that look like focus problems.
 
One of the main reasons rack focuses in movies (film or digital doesn't matter) look so smooth and are spot on is due to the focus being pulled by the 1st AC.. and often off camera via remote, especially if shake is a concern. On many systems like the variZoom you can set your start and end points, your rack speed, and simply need to push a button to activate it. Other times there will be marks on the floor and on the focus dial for the AC to track the subject as it moves through space.

Shallow DoF is attainable in small cameras, but you'll have to use a longer focal length to compensate for the small sensors (and aperture.)
 
Michaelrosenblum said:
Very interesting and informative indeed.
I shot for years on a Hasselblad 500c/m and hand metered with an old Westin that gave out EV readings. You remember the red metal brackets on the Hasselblad lenses - this gave you such precision for depth of field. It is this kind of precision I am looking for in small cameras, but apparently it may not be possible yet. I understand the amount of control you get from the big cameras - and the far better lenses, but I am very intrigued by your use of ND filters with the small cameras. I am going to try this one.
Many thanks for the info. Very helpful.
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Talking about the Hasselblad brings back excitement and great memories. It was my main camera even thou I used formats from 35mm Nikons to 8x10 Sinars.

Try convicing someone today that we had accuracy without batteries, everything was mechanical and everything including that patented DOF indicators were always there and always worked right.

I started in 1970 with the original C and I paid $ 500 for a display model. Few years later I had six Hasselblads, 2CM, 2ELM, and 2 superwide, and every lens they made, back then it was a major investment. I sold everything in 1985 and doubled my money from what I paid more than 10 years earlier, that's how much those camera prices went up.

I just priced the digital Hasselblads and they go from $25,000 to $36,000. Unless I get some major still contract I guess my Canons will have to do it.
 
I can't stand most digital still cameras. I loved the Hasselblad and shot with it for years. Once you get used to the 6x6 it's almost impossible to go anywhere else. I also loved the incredible control it gave you. I completely agree with the world before electronics sense. My old Westin meter ran off the light and nothing else. I used to be so careful with metering, using a gray card and trying to replicate Adam's zone system as best I could including bracketing all the shots. It was a labor of love.

When I moved to Leicas, it took some time to get used to the 35mm format. It never seemed the same in the darkroom, but it was so much easier to carry around. I got one of the very first digital Leicas about 3 years ago, the M8, serial number 000000745. Then I shot with it in the rain in England and the viewfinder fogged and the electronics stopped. I sent it back to Solm in Germany and they quoted me 5500 Euros to repair it! Repair! That's when I had the moment when I could have gone back to Hasselblad, so I looked at the digital Hasselblads. $25,000! And that was before you started with the lenses or the meter prism. Crazy! Who could buy such a thing?

Instead I bought the M9, which is as far from digital as you can get for a digital camera. Even though it's 16mpl, it's still paralax focus through a viewfinder. None of this autofocus. You have to set the f-stops and shutter speed manually. In fact, its all mechanical, except the record mechanism. Lovely camera, lovely images, but I still miss the 6x6.
 
I know we've seen enough 5D movies here to choke an elephant but this may not be a bad spot to see a few more. Canon hosted a contest for video's shot on their DSLR's

http://vimeo.com/groups/beyondthestill/videos

I consistently shot with my shutter up to 1/100 or 1/125 (I'm still on SX) to get my iris open a bit more for DOF and because I like the sharper definition.
 
When I think about my favorite, big-budget, Hollywood films, extreme shallow DOF is rarely used. It's a fad that will look as dated in a few years as fog filters from 30 years ago.
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I'm glad you said that, Doug. I feel exactly the same way, but my comments have often fallen on deaf ears.

Any time something becomes overused it will end up dating the technique as people become bored of it.

The size of the chip has a lot to do
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The size of chip has everything to do with it. Size of chip along with the iris setting.

It is a misconception that zooming in changes the depth of field.. Zooming in only emphasises the difference in focus that was already there, but perhaps wasn't visible previously due to using a shorter focal length, and not being a high enough resolution to show it. So from a creative stand point it could be argued that zooming in changes the depth of field. But from a technical standpoint it doesn't.

Just something I have noticed in the last few years -- compression problems that look like focus problems.
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This issue does seem to rear its head on the EX cameras. I know that the face is in focus because the eyes are clearly defined. But the rest of the face can sometimes look soft.

especially when using the 2X converter I will want the most depth, in this case I use the lowest setting on my ND filters trying to keep my lens at an F11 stop
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As much as I can I try to keep from going above f8, even on 2/3" chip cameras as the picture does often become noticeably softer due to diffraction above this IME.
 
I wish I could find a way to slide a sensor and some electronics into my M-2!


Michaelrosenblum said:
I can't stand most digital still cameras. I loved the Hasselblad and shot with it for years. Once you get used to the 6x6 it's almost impossible to go anywhere else. I also loved the incredible control it gave you. I completely agree with the world before electronics sense. My old Westin meter ran off the light and nothing else. I used to be so careful with metering, using a gray card and trying to replicate Adam's zone system as best I could including bracketing all the shots. It was a labor of love.

When I moved to Leicas, it took some time to get used to the 35mm format. It never seemed the same in the darkroom, but it was so much easier to carry around. I got one of the very first digital Leicas about 3 years ago, the M8, serial number 000000745. Then I shot with it in the rain in England and the viewfinder fogged and the electronics stopped. I sent it back to Solm in Germany and they quoted me 5500 Euros to repair it! Repair! That's when I had the moment when I could have gone back to Hasselblad, so I looked at the digital Hasselblads. $25,000! And that was before you started with the lenses or the meter prism. Crazy! Who could buy such a thing?

Instead I bought the M9, which is as far from digital as you can get for a digital camera. Even though it's 16mpl, it's still paralax focus through a viewfinder. None of this autofocus. You have to set the f-stops and shutter speed manually. In fact, its all mechanical, except the record mechanism. Lovely camera, lovely images, but I still miss the 6x6.
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SimonW said:
This issue does seem to rear its head on the EX cameras. I know that the face is in focus because the eyes are clearly defined. But the rest of the face can sometimes look soft..
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Just to be clear, I was talking about compression that comes during post, and not when the raw footage is shot. That is where I've seen this problem crop up.
 
SimonW said:
It is a misconception that zooming in changes the depth of field.. Zooming in only emphasises the difference in focus that was already there, but perhaps wasn't visible previously due to using a shorter focal length, and not being a high enough resolution to show it. So from a creative stand point it could be argued that zooming in changes the depth of field. But from a technical standpoint it doesn't.
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You're right - the circle of confusion is the same, just emphasized through magnification. If the end result is a larger perceived CoC then you did change the DoF, since that is all perceptive anyway. All you do by using a larger focal length is change the relative size of the sensor. In this way we're both right.

This issue does seem to rear its head on the EX cameras. I know that the face is in focus because the eyes are clearly defined. But the rest of the face can sometimes look soft.
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Skin detail setting issues? I don't shoot w/an EX-1 but those should be adjustable in the menu.
 
Skin detail setting issues? I don't shoot w/an EX-1 but those should be adjustable in the menu.
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No, I don't use the skin detail settings. I always have it turned off. I prefer physical filters or post softening to in camera digital manipulation. I've heard a few other people say they have had similar issues. It doesn't happen all the time, and I haven't been able to pin down what is consistent in terms of setup when it happens.
 
Yeah, one can get carried away with this DOF business. For example, slap a f 1.2 50 mm Nikon lens on your favorite DOF adapter and your DOF might be inches. Nose in focus, ears not. I suspect this obession with DOF will go the way of the "quad-split" (anyone else old enough to remember than one? :-)
 
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