AutoFocus vs. Manual Focus

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eager2learn

Guest
As a 'Newbie' with a 3+ year old TRV-900, I'd like know if it is more advisable to shoot with Manual Focus rather than AutoFocus.

On moving shots, it would seem to me a bit difficult to maintain clear focus if set on Manual, however to try and blur the background a bit so the actors stand out more, it seems like this is the only way to do it.

Any tips are appreciated.

Thanks.
 
Hello again. I recommend against ever using auto focus, unless you're shooting documentary type stuff. The focus will drift off of your subject, unless they stay motionless in the frame, if someone walks in front of them, etc. etc. Get used to pulling focus when you need to. In the pros, camera assistants are paid to do mainly that. When you set up a shot. Zoom in and find your focus, then zoom out to the desired focal length. Then do the shot.
 
? Prouductions

All due respect, autofocus isn't meant for film-makers.

Hope that doesn't come across as aloft. lol

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You just need control on your focus, and setting the focus is a basic part of set-up.


Take it easy


Case/repeat
 
Manual is Mantastic!

Don't use Auto Focus at all. If doing a moving shot critical focus on your target before hand and shoot wide. It won't be the greates it could be, but it will stay in focus.

Poke
 
Re: Manual is Mantastic!

pokewowplayer1 said:
If doing a moving shot critical focus on your target before...

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well, focus-pulling is not always the answer; can create problems, and mean missed shots.

horses for courses, people. :)


case/repeat
 
One note, most cameras auto focus on the center of the image because that’s where most know-nots put their point of focus. If you know about the rule of thirds or have ever composed a decent looking shot, you should know that the center is rarely where you want your main focus to be.

“however to try and blur the background a bit so the actors stand out more, it seems like this is the only way to do it. “

Manual and auto-focus don’t really deal with this issue; it’s depth of field you’re concerned about. If you haven’t looked at it, check out the “Filmmaker’s Handbook” by Edward Pincus (http://www.amazon.com/exec/obidos/t...f=sr_1_5/103-2197005-4606215?v=glance&s=books) I would recommend it. There’s a newer version of it (http://www.amazon.com/exec/obidos/A...8731786/sr=2-1/ref=sr_2_1/103-2197005-4606215) but I haven’t read it. The original deals almost exclusively with celluloid film, but it has very very good pictures and demonstrations of how zoom, lighting, and depth of field affects picture composition and other theory that’s just as applicable for video as film. I think it’s worth it just for the pictures and when I was at on Amazon someone was selling it used for only $.88. Anyway, depth of field is the area in front of and behind the plane of critical focus that is still in acceptable focus. I’m trying to do this from memory so I apologize if I get confused because I don’t use this knowledge that often. There are 2 ways to adjust depth of field: distance to subject and iris. The best way to affect depth of field is to change the camera (focal plane) distance from the subject. If the subject is far enough from the camera you will reach the point on the focus ring that has the infinity mark. This means that from that point on everything is in focus. As you get physically closer to the subject (because zoom does not affect depth of field) you will start to have to adjust focus to find optimal focus. The closer you get to a subject, the shorter the depth of field. Most consumer lenses have a minimum distance of 2 to 3 feet (professional lenses are different in several ways). So if you are as close as you can get to the subject but still be in focus your depth of field will be as small as possible and your background will look as out of focus as possible.

Adjusting the iris will affect your depth of field. This is an inverse relationship, so the larger the aperture the, the smaller the depth of field and vice versa. There are some extremely good drawings about this in the book above also. So if you can’t get closer to the subject, reduce the lights and open the iris.

Now, that being said, most video lenses are poor quality and aren’t as accurate as professional video mean they have a larger depth of field. A Panavision 35mm prime can have a subject’s eyeball in focus but the tip of the nose and the ears will have soft focus. You just can’t do this with a cheap lens (by cheap I mean less than about $4000). Consumer quality lenses have an almost infinite depth of field except at extremely close ranges. That’s about all I have to say about that.
 
Good stuff there.

Is this correct then?

Wide angle lenses (less than 25mm) will give you a large depth of field,

Telephoto (50mm & above) will give you a shallow depth of field.
 
Depth of Field

Primarily, a wider angle lans has a lower f number; which means you can step the exposure right down, and still have adequate light hitting the film.

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This means you can increase your depth of field with this kind of lens.

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The focal length of your lens is not the only factor which governs the f rating.


Case
 
>So if you are as close as you can get to the subject but still be in focus your depth of field will be as small as possible and your background will look as out of focus as possible.

>Adjusting the iris will affect your depth of field. This is an inverse relationship, so the larger the aperture the, the smaller the depth of field and vice versa.

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So if wider angle lenses increase the depth of field, especially at close range to the subject, that creates more contrast between in-focus subject to out-of-focus background? Then you f-stop down to further bring out the subject (as in a close-up)?
 
So if wider angle lenses increase the depth of field, especially at close range to the subject, that creates more contrast between in-focus subject to out-of-focus background? Then you f-stop down to further bring out the subject (as in a close-up)?
No. A wide angle lens will _decrease_ the depth of field. This means that the area before and after the plane of critical focus is smaller (so you can get someone’s eyeballs in focus but their nose and ears will be out of focus). But essentially everything else is correct. You have to watch out for wide angle lenses because they can show warping at the edges of the frame. Wide angle is generally considered anything with a wider angle than the frame size. So 35mm is wide angle for 35mm film, but not for 16mm. Another note, wider angle in conjunction with closeness to a subject will exaggerate whatever is closest to the lens and minimize whatever is farther away. So if someone is looking straight into a camera and it is very close to them, their nose will look disproportionately large and their ears too small. You can cheat this a little by having the person sit at a bias so they are looking to the side of the camera but you may still notice some warping. Changing the iris will not warp the picture, however at extremely small apertures it can cause slight ghosting and / or increased blurriness because the light is actually being bent by the tiny hole. This is similar to a person who needs glasses looking through a piece of paper with a pin hole in it and being able to see clearly. This would only be a concern if you were throwing a lot of light onto the subject and trying to increase the depth of field, or if you were in a bright situation and were trying to stop down to cut the light rather than using a ND filter.
 
? ? ? ?

A shorter focal length lens will give you a greater depth of field

If you want a 'contrast' between main object and fore/background, you can achieve this by being close up, or using a telephoto lens.

However, you must remember, if the object is at distance, depth of field is large.

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f-stop does not have a huge impact on D of F, except in close-up, where the effects can be striking and usable.


Repeat, Case, whoever I am.
Sod it, forgot.
 
So wide angle would be used for a panoramic landscape (John Ford) or Deep Focus shot (Orson Welles).

Extreme telephoto flattens the shot, like the watery-looking riders in Spaghetti Westerns (Sergio Leone).
 
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