Depth of field on A1u?

[Michael Stowe]

Does anyone have an recommendations on this? I am looking for ideas on how to accurately get accurate DOF of a large croud from certain distances. There is no known F value setting so any help is appreciated.

[Stu Holmes]

DOF is a zone in front of and behind the exact focus point, that is *perceived* to be in focus to the human eye. In fact ONLY the focus point is in sharp focus, but due to the way optics work, objects closer to and further away from the camera can still look sharp and in-focus.
Most people think that the DOF is evenly distributed around the focus point (for example 10meters in-front of focus-point and 10metres behind the focus-point) but this isn't actually true - there will actually be 'more' DOF behind the focus-point than in front of it. So if you're focused on an object at, say, 30metres from the camera, the area considered to be in focus BEYOND that may be an additional 10metres, but the area considered to be in focus IN FRONT of that point may be just 5metres-ish.

I'm not aware of any easy way to measure/calculate the DOF at certain apertures. DOF is affected by the distance that the focus-point is away from the camera, and the focal-length of the lens used (i.e. wideangle - to - telephoto) and also the physical size of the sensor.
Also remember that the A1 has 2 or 3 ND filters that physically move into the optical path for light levels over a certain value (the PHYSICAL aperture leaves will stay at i think f4). ND filters will NOT affect the DOF, but physical aperture changes DO affect DOF. So even if you camera reported f5.6, chances are that the physical aperture is STILL at f4 but there's now part of an ND filter in the optical path and that's how the camera acheives a 'bogus' f5.6

To cut a long story short, the best way to judge DOF for an object that you want to appear to be fully in-focus is to look carefully through the viewfinder (higher resolution than the LCD screen on the A1) and use the expanded focus setting to check what you want is accpetably in focus.

IMO.

[Frank Howard]

A couple of general notes though: set the exposure as high as possible (without clipping or getting seriously over-exposed) and zoom in as much as possible (before starting to shoot) to maximze DOF...
Play with it a bit until you get some settings that work dependably for you.

[Stu Holmes]

Originally Posted by Frank Howard

and zoom in as much as possible (before starting to shoot) to maximze DOF...

uhh, i think i've just entered the Twilight Zone...
Don't you mean zoom *out* as much as possible to maximise DOF?

Generally to maximise DOF for a certain camera:
- Select small aperture / iris on the lens (must be physical aperture! - see above)
- increase distance to subject
- use as wide-angle zoom setting as poss. (obviously within the constraints of getting the shot you want)

DOF is inherently pretty big on a camcorder with a 1/3in sensor. That's why it's hard to get that really nice very-shallow DOF that you can get on a film SLR or a digital SLR that uses a BIG sensor or even a full-sized 35mm sensor (very very expensive cams these are).

[Michael Stowe]

Originally Posted by Stu Holmes

uhh, i think i've just entered the Twilight Zone...
Don't you mean zoom *out* as much as possible to maximise DOF?

Generally to maximise DOF for a certain camera:
- Select small aperture / iris on the lens (must be physical aperture! - see above)
- increase distance to subject
- use as wide-angle zoom setting as poss. (obviously within the constraints of getting the shot you want)

DOF is inherently pretty big on a camcorder with a 1/3in sensor. That's why it's hard to get that really nice very-shallow DOF that you can get on a film SLR or a digital SLR that uses a BIG sensor or even a full-sized 35mm sensor (very very expensive cams these are).

Technically there is no aperature setting on the A1 or atleast it does not show it. This was what my question was regarding. I understand, to a point, DOF from my DSLR days. I am trying to figure out the best settings on the A1 for this. Basically I will be shooting from around 20 feet and would like a large DOF to caputre a fairly big group. I imagine the more light I had the smaller the Aperature I could get, there by increasing my DOF. I will not have an extreme amount of light to work with which may be an issue.

Thanks

[Frank Howard]

Stu:
As you increase the focal length (zoom) any background object in the out of focus area is magnified so you get more blur. Back the camera up away from the subject and zoom in with the iris wide open to get more DOF action.

Try it for yourself and then tell me if I'm wrong. :)

Michael:
There are aperture settings, they just aren't in the form of f-stops... Just bring up the Exposure to as high as you can get away in order to get the most DOF

[Evan Dowling]

I think there may be some confusion on here as far as terminology. What does "more" or "less" DOF mean to you? If you open the apeture wide and zoom in close, you will get the narrow depth of field seen in movies where the subject is in focus, but everything behind it is not. It helps to have the background as far away from the subject as possible. The smaller the apeture and the more wide angle you shoot, the DOF will become wider, making a wider range of distance appear to be in focus.

[Frank Howard]

Exactly Evan. If a person wants to have that softness for items outside of focus (that you see in film), then they would need to zoom in. This is what most people are trying for I believe.

If, on the other hand, you want everything to be in focus then wide is definitely better...But usually the auto settings on the HC1/A1 will do pretty well give you a pretty wide DOF without help.

[Stu Holmes]

Originally Posted by Evan Dowling

I think there may be some confusion on here as far as terminology. What does "more" or "less" DOF mean to you?

I think you got it Evan - definitely a terminology issue here, not a disagreement with the fundamentals.

My interpretation of what Frank said : "and zoom in as much as possible (before starting to shoot) to maximze DOF"
is that he meant you get MORE depth-of-field by zooming in and this isn't correct.
So it's a terminology thing : I think what Frank means by "DOF" is his wording for *shallow* depth-of-field, i.e. not much in focus in front of or behind the focus-point.

I've been using SLR's since the 1980's so i'm fully conversant with DOF issues and also studied quite a lot of optics - it's just frank's term for "DOF" isn't the same as mine! (or the vast majority of other people's either for that matter)

[Stu Holmes]

Originally Posted by Frank Howard

Michael:
There are aperture settings, they just aren't in the form of f-stops... Just bring up the Exposure to as high as you can get away in order to get the most DOF

Having said that (previous post) i *am* going to disagree with this.

Exposure itself has nothing at all, inherently, to do with Depth-of-field (shallow or deep).
It's *aperture* that affects it (amongst other things), and i believe Frank's comment stems from the fact that most camcorders tend to hang onto their default shutter speed as long as they can. So by "giving it more exposure" (& assuming the shutter speed is constant and we leave gain out of the picture) then the aperture will be bigger, i.e. tending to max. aperture and this will give a shallow Depth-of-field.
If you fix shutter speed, and fix gain then, yes, in that sense an increased exposure will mean shallow DOF, but it's ONLY cause if shutter and gain are fixed then the only thing that can vary is aperture and that's what affects DOF.

Finally, you CAN see what aperture that the A1 has used for any footage.
Not *during* footage, but immediately after, replay the footage, with 'Data Code', 'camera data' enabled and it will give you shutter speed, aperture (as an f-stop), gain in dB, what white-balance was used, and also whether expsoure was automatic or manual.
So if you're unsure what aperture cam is using for a scene, shoot 5secs of that scene, quick review with data code on, and then you know.

Remember that above a certain brightness the camera will hang on to a physical aperture of f4 and throw in Neutral-Density filters to control light-levels to avoid nasty resolution-limiting diffraction effects.
Ultimately it WILL stop down the physical aperture more than f4 but this is in really extreme situation when even all the ND filters in the optical path aren't helping enough.

[Frank Howard]

I definitely agree with you Stu that it is *aperture* that is really changed, but the place to change it on the HC1/A1 is in the Exposure part of the menu. So again we're really saying the same thing in different ways for the most part. I apologize for the confusion.

What I do personally is lock down the shutter speed to 60 (taking those variables out of the picture) and set the Exposure up to open the aperture more.

BTW - It has been mentioned that the Camera Data feedback may not be entirely accurate, which ticks some people off no end.

[Michael Stowe]

Ok. So basically I am looking at a dark picture to get the widest DOF possible? This is assuming I lock down to 1/60 SS.

[Frank Howard]

So you DO want more depth. I'm so used to everybody wanting a shallower DOF so their output will look more like film. Heh.

I owe you a beer Stu!

Like most other things, it will be a tradeoff. The best picture will be come from lowering the exposure/aperture settings, but not going so low that it creates gain and noise and pulling the zoom out to the widest shot possible.

Have you thought of adding a wide angle lens? They aren't terribly expensive and it looks like you might find it useful..

[Michael Stowe]

Originally Posted by Frank Howard

So you DO want more depth. I'm so used to everybody wanting a shallower DOF so their output will look more like film. Heh.

I owe you a beer Stu!

Like most other things, it will be a tradeoff. The best picture will be come from lowering the exposure/aperture settings, but not going so low that it creates gain and noise and pulling the zoom out to the widest shot possible.

Have you thought of adding a wide angle lens? They aren't terribly expensive and it looks like you might find it useful..

Thanks guys...Frank...you are correct. For this event I need more depth and it will not be a very well lit area. I will experiment. I have the Sony wide angle sitting on my camera right now :-)

[Floris van Eck]

Originally Posted by Stu Holmes

Having said that (previous post) i *am* going to disagree with this.

Exposure itself has nothing at all, inherently, to do with Depth-of-field (shallow or deep).
It's *aperture* that affects it (amongst other things), and i believe Frank's comment stems from the fact that most camcorders tend to hang onto their default shutter speed as long as they can. So by "giving it more exposure" (& assuming the shutter speed is constant and we leave gain out of the picture) then the aperture will be bigger, i.e. tending to max. aperture and this will give a shallow Depth-of-field.
If you fix shutter speed, and fix gain then, yes, in that sense an increased exposure will mean shallow DOF, but it's ONLY cause if shutter and gain are fixed then the only thing that can vary is aperture and that's what affects DOF.

Finally, you CAN see what aperture that the A1 has used for any footage.
Not *during* footage, but immediately after, replay the footage, with 'Data Code', 'camera data' enabled and it will give you shutter speed, aperture (as an f-stop), gain in dB, what white-balance was used, and also whether expsoure was automatic or manual.
So if you're unsure what aperture cam is using for a scene, shoot 5secs of that scene, quick review with data code on, and then you know.

Remember that above a certain brightness the camera will hang on to a physical aperture of f4 and throw in Neutral-Density filters to control light-levels to avoid nasty resolution-limiting diffraction effects.
Ultimately it WILL stop down the physical aperture more than f4 but this is in really extreme situation when even all the ND filters in the optical path aren't helping enough.

I believe that you are completetly right about this one. Video cameras, opposite of DSLR cameras, try to shoot at their default shutter speed (PAL - 50fps or 1/50, NTSC 60fps or 1/60) as long as possible. The only way to achieve this is by opening or closing down aparture. To prevent it from closing down to much, a ND filter can be used. Another way to get some control over the aparture is with the spot meter. I personally think it is one of the best ways to control exposure as you can use a 18% gray card as well as use natural/environment colors to get the correct parts of the image properly exposed. Although this does not answer the question asked here, it is a way to get the best exposure for your shots and by spot metering darker or lighter objects you can open or close down. The 18% gray card is your "0" point. But again, I think Stu got it right.