DV Info Net

DV Info Net (https://www.dvinfo.net/forum/)
-   Techniques for Independent Production (https://www.dvinfo.net/forum/techniques-independent-production/)
-   -   What effects Depth of Field (https://www.dvinfo.net/forum/techniques-independent-production/2452-what-effects-depth-field.html)

Al Osmond June 26th, 2002 07:45 AM

Costs rather more than twice as much as a complete XL1s outfit, and once you've paid for it you can start saving up for a lens.

But when you've got it all up and running, every single one of your shots can then have an out of focus foreground, or background, or both, just like the Mini 35 demo video.

Why, one asks, does a dog lick his private parts?

I just wonder how often film camera users find themselves wishing for a little more depth of field...


Adrian Douglas June 26th, 2002 07:53 AM


to reduce the Depth of Field in video a common method is to shoot long. As Al said this increases the focal length and therefore reduces the depth of field.

This is the same reason that wide angle lenses don't require as much focusing as telephoto zooms, for example the 3x vs the 16x

Charles Papert June 26th, 2002 07:50 PM

Regarding your (maybe rhetorical) question, Al, we prize the shallow depth of field of film in almost all circumstances.

I shot a commercial this weekend on Super 16 that was originally supposed to be on 35mm. Film stocks and telecine have improved to the point where, for a television delivery, the gap between the formats has diminished greatly (especially in regards to grain structure), yet I was admittedly disappointed that we had to go to 16 for budgetary reasons, since it forced me into a different lighting design. When you don't have focus as a means to separate foreground and background, you have to work with other tools such as color and shade to achieve the desired effect. There are some tricks also, using smoke to haze the background of a set will give a shallower feel.

Instances where the minimal depth of field of 35mm is problematic: when working with long lenses, it can be tricky for the focus puller to nail it (usually when there is six inches of depth or less). We help them out by lighting to a higher level or removing ND if applicable to give them a fatter stop and thus more depth to work with.

I sometimes think about the tricks that were employed on "Citizen Kane" to achieve the deep focus shots on that film. I think the filmmakers would have been delighted to work with the massive depth of field available in the DV format!

Rob Lohman June 26th, 2002 11:45 PM

Thanks for all the responses, invaluable! I haven't had time to
test anything yet with this new data. And since I have some
party's to attend this weekend it probably won't happen for
another week. Charles, can you talk some more about the
Citizen Kane thing? What was their problem and how did they
solve it? Always interested in hearing such stories. Thanks.

Charles Papert June 27th, 2002 12:08 AM


On "Citizen Kane", Orson Welles and his cameraman Gregg Tolland sought to achieve frames that had actors and elements staged at multiple distances but with all remaining in focus. Generally they achieved this by doing the opposite of the things described here to make the image more shallow; they used a lot of light (minimizing the size of the aperture), wide lenses, and in a few instances a split diopter, which is sort of like a large glass contact lens chopped in half. This lens (mounted like a filter) will allow for multiple planes of focus within a given frame. The catch is that the edge of the diopter will be seen in the shot as an abrupt transition and it needs to be buried by being placed over an existing line within the frame so it can't be noticed. There's a banquet scene in the movie that at one point features some ice sculptures which appear to be inches from the lens; and they are as sharp as the rest of the foreground and background, due to split diopters being brought in from either side.

A more elgant approach to hiding the transition is to use slant-focus lenses, also known as swing-and-tilt or swing-and-shift, which pivot the lens relative to the film plane. These were popular in commercials a few years back in achieving that look where one side of the frame was oddly out of focus. Also seen recently in the opening scene of "Swordfish" with Travolta in the coffee shop.

OK, my all-time favorite split diopter story...a few years back I worked on the movie "Office Space" which was directed by Mike Judge of Beavis & Butthead/King of the Hill fame. This was Mike's first live action movie, and he was always curious about the technology, so he would occasionally ask us things like "now, what do you guys mean when you say 'split diopter'? or "what are sticks, exactly?" We'd tell him, he'd listen and nod, and that was that. And then days later, an Entertainment Tonight camera crew would show up, and he'd ask them "OK? Are you guys rolling?". Then he'd lean over to our camera department , clear his throat and announce authoritatively "Alright guys, now I want you to go ahead and put the split diopter on the sticks for this setup..."

Funny guy.

Margus Kivilaan June 27th, 2002 01:26 AM

<Margus, that product is widely known (check www.mini35.com).
We even have one user here on this forum using this rig!>

yeah now i noticed this stuff is been mentioned in this forum earlier also. It was new for me

Josh Bass June 27th, 2002 03:08 AM

Here's my two cents, for what it's worth (keep in mind I'm a moron). I bought the manual 16x lens recently, and while playing around with it, I found you get excellent shallow depth of field (that's what you want, right?) If you use the macro function on there. It's not very orthodox, but you don't have to get real far away and zoom in that way. Other than that, the other guys said everything. Not a cheap solution either.

Rob Lohman June 27th, 2002 08:09 AM

Hehe... thanks Charles! Fun to read. Margus, no problem. I was
just pointing it out to you, no need to appologise.

Bill Ravens June 27th, 2002 09:00 AM

Since DOF is intimately affected by the maximum aperture of the lens, that is to say the design diameter of the primary optic, I would suggest you consider the following. 35mm lenses are designed for an aperture consistent with 35mm film format. As such, the depth of field is LESS than for a 1/3 inch format(as in XL1s CCD)at the same iris setting(f/stop).

Therefore, if you're looking for a film look, one important maneuver is to use 35mm lenses with your XL1s. Use an EOS or FD lens adapter and a Canon 35mm lens. Unfortunately, you'll have to back away from your subject by a factor of 7, but, oh well.

Al Osmond June 27th, 2002 09:06 AM

I'll hire you a pair of handy-talkie radios, Rob, if you're backing off that far!

The builders say they can come along and knock a hole in the studio wall but they won't be here until next Wednesday morning...


Charles Papert June 27th, 2002 11:02 AM

Hmmm...Bill...at an equivalent field of view, won't the depth of field characteristic remain the same? i.e. once you've taken the 7x magnifcation into account, and thus zoomed in your 1/3" lens to match the framing, you should end up with the same depth of field--hmmm?

Bill Ravens June 27th, 2002 11:06 AM

nope....it's a function of the overall light gathering ability of the lens...i.e. max diameter, even if you're only using a small central portion of the image plane.

Justin Chin June 27th, 2002 12:43 PM

My head's going to explode.

Charles, I think you're right.

If you put a 35mm lens on your XL1 with an EF adaptor you're basically only seeing the center part of the image, which effectively "increases" the circle of confusion. In order to match framing by backing up your camera, you're effectively defeating the purpose of the 35mm lens.

In general the limiting factor is the size of the film plane (ccd).

This is how I understand it. Generally by moving the camera and zooming in you flatten the image. This is not always desirable since it separates the viewer from the action.

Justin Chin June 27th, 2002 12:51 PM

If anyone on this thread hasn't seen this already. Here are some test images I shot with my Mini35 rig.

I used a 35mm cine (35mm focal length) lens at T1.4. The subjects at their nearest are just less than 3 feet.

As you can see I have less then 2 inches of focus.


Bill Ravens June 27th, 2002 12:58 PM

...and that is why 35mm lenses are so great. Even at that, 35mmx7=245mm. Great for portraits.....kind of compresses everything, tho'. Not to mention the film/sound stage needs to be REAL big....LOL.

All times are GMT -6. The time now is 06:30 AM.

DV Info Net -- Real Names, Real People, Real Info!
1998-2021 The Digital Video Information Network