DoF question at DVinfo.net

Glen Chua · June 19th, 2005, 02:09 AM

Hey guys,
i've seen in some films how they lower the depth of field to make the image focused on the main character, but then everything else behind is blurred making hte focused thing stand out more. I was wondering how I would be able to acheive this with a GL2. Is it a special type of lens or something? Thanks.

Glen Chua
www.moonlitefilms.com

Mathieu Ghekiere · June 19th, 2005, 05:19 AM

Well the biggest difference is not the lens, but the chips.
In movies, they work with a 35mm frame.
Your camera works with a chip that is 1/4 of an inch, so that way smaller, and that is the main reason. A 1/3 camera gives you less DOF, an 1/2 cam even less and so on...

How can you get a small DOF?
Well, you can zoom in all the way on your character, which will make DOF less, you can open up your iris to 1.6 (or just the smalles number, gives you less DOF too)...

For 1/3 chip cameras there are very expensive adaptors that allow you to put 35mm lenses on them. Then your camera films a 35mm ground glass where the image of the prime (or still) 35mm lens is on projected, and then your image is a tad softer, but you have the same DOF as a 35mm camera.
But such an adaptor costs sometimes more than 8000 dollars, I don't know the exact price. You also now have the Micro 35, somebody who made his own adaptor, I think his name is JAmes Hurd or something, and it costs around 500 dollars to order one, or 70 dollars to order a guide which tells you how to make your own with which materials.

I advise you to look at the 'Towards a Film look' boards here, and at the Mini35 boards, and the Alternative Image Methods boards, and this article:

http://www.dvinfo.net/articles/optics/dofskinny.php

Good luck!
There is already many many many things about discussed on these boards, so if you do a search you will get tons of information.

DJ Kinney · June 19th, 2005, 09:27 AM

The simple answer is to open her up all the way 1.6, move the camera back as far as possible, and then zoom in (never going into the digi range, though--only optical. In fact, turn the digi zoom off). The camera will automatically readjust the 1.6 to 1.8 or even 2.0 depending on the zoom. If those settings are too bright, DO NOT compensate with shutter speed. Keep that at 1/60. Use the in-cam ND filter instead, and if it's still too bright, which it will be on a sunny day, buy an additional ND screw-on filter.

Audio will suck at the distance necessary to achieve a really filmic depth of field, so additional recorders or wireless mics will come into play.

And that's the simple answer.

DJ

Jeff Phang · June 19th, 2005, 09:41 AM

www.micro35.com

www.guerilla35.com

If you have $100 to spend, I would suggest getting the DIY guide from www.micro35.com and then building an adapter yourself. The guide costs $45 and then there are around $50-$70 in parts to buy.

Tom Hardwick · June 22nd, 2005, 05:47 AM

The bare essentials:

Close focus, wide aperture, long focal lengths and having the background as far away as possible will give you the narrowest DOF.

Jeremy Davidson · June 23rd, 2005, 02:13 PM

DJ, why can't the shutter speed be adjusted? I would think that would be a good way to leave the aperture as wide open as possible. Granted it will give motion more of a strobe effect, but does shutter speed actually affect DoF? I'm not saying it couldn't -- I'm just curious why.

Thanks!

Graham Bernard · June 23rd, 2005, 03:41 PM

My understanding is that if you reduce the shutter speed you are, in essence, reducing exposure. Reducing the exposure this way allows you to have the IRIS as wide as you can. This gives the shorter depth of field.

Soooo... wide iris you get more light. This leads to over exposure. The two ways I know to reduce exposure is:

a) Put a filter - NDs here - in front of the lens. I've got 0.3 , 0.6 and my onboard 0.9 ND gives me nearly a total of nearly 2.0 ND! And THAT is before I need to reduce the shutter speed.

. .. or .. .

b) Reduce the time the shutter is actually open.

Grazie

Pete Wilie · June 23rd, 2005, 05:11 PM

Here are some good resources on DoF:

DoF Tutorial by DVCreators.net
http://www.dvcreators.net/media/depthoffield.html

DoF tutorial by DVXUser.com/Barry Green:
http://www.dvxuser.com/V3/showthread.php?t=894

The Ultimate Depth-of-Field Skinny at DVInfo.net
http://www.dvinfo.net/articles/optics/dofskinny.php

And here is an interesting discussion on the subject:
Depth of Field
http://www.dvinfo.net/conf/showthrea...ht=depth+field

Nate Ford · June 24th, 2005, 11:54 AM

there are 2 things that affect depth of field-
focal length aperture.

everything else only affects it indirectly. for example, mathieu is talking about chip size (better known as format, if we want to consider film here too.) chip size, in itself does NOT affect depth of field. a 50mm lens at f1.8 will produce the same depth of field on the thing behind it whether that thing is a 1/4" ccd or a 2 1/4" negative. the difference is, what will the angle of view look like. to a 1/4" chip, 50mm is big time telephoto. to a 35mm camera, it's "natural" (not tele, not wide.) to a 2 1/4" neg, it's wide angle. but the depth of field is the same. so where chip/format size comes into the equation is that the smaller formats/chips require shorter focal lengths to achieve the same look/"angle of view" as the bigger formats.

therefore, as has been said, you have to really zoom in with prosumer video cameras to get to a short-DOF focal length. that, and open your aperture. compensate for the wide aperture however you want (shutter speed or nd filters,) but understand the effects of this compensation. (ie- fast shutter speed will change the rendering of motion. on the other hand, good optical nd filters will cost you a lot of money.)

DJ Kinney · June 26th, 2005, 11:55 AM

To clarify the shutter speed, I said to keep it at 1/60 because increasing it to compensate for a lot of light will cause strobing, and also, if you wanted to do any "film look" processes later, 1/60 looks best and converts the best.

Of course, the strobe look is pretty cool for action shots.

Mathieu Ghekiere · June 26th, 2005, 12:26 PM

Nate,

I thought that how bigger you went in format, the lesser DOF you got.
I always heard guys on these boards claiming that if you use a 2/3 camera for example, you got much less DOF.

Thanks for clearing that up!

I wouldn't adjust the shutter speed.
You want normal motion in your picture, and nothing that lookse like strange slow motion or a kind of movement that looks stroboscopic.
I would just leave it at 1/60. But that's my opnion.

June 19th, 2005, 02:09 AM	#1
Glen Chua Regular Crew Join Date: Aug 2004 Location: British Columbia Posts: 98	DoF question Hey guys, i've seen in some films how they lower the depth of field to make the image focused on the main character, but then everything else behind is blurred making hte focused thing stand out more. I was wondering how I would be able to acheive this with a GL2. Is it a special type of lens or something? Thanks. Glen Chua www.moonlitefilms.com

June 23rd, 2005, 02:13 PM	#6
Jeremy Davidson Regular Crew Join Date: Aug 2004 Location: Eau Claire, WI Posts: 167	DJ, why can't the shutter speed be adjusted? I would think that would be a good way to leave the aperture as wide open as possible. Granted it will give motion more of a strobe effect, but does shutter speed actually affect DoF? I'm not saying it couldn't -- I'm just curious why. Thanks! __________________ There's no way for you to know if what I'm saying is true unless you know what the truth is, and there's no way for you to know what the truth is unless there is a truth that you can know. -- Frank Peretti

June 19th, 2005, 05:19 AM	#2
Mathieu Ghekiere Inner Circle Join Date: Jun 2004 Location: Belgium Posts: 2,195	Well the biggest difference is not the lens, but the chips. In movies, they work with a 35mm frame. Your camera works with a chip that is 1/4 of an inch, so that way smaller, and that is the main reason. A 1/3 camera gives you less DOF, an 1/2 cam even less and so on... How can you get a small DOF? Well, you can zoom in all the way on your character, which will make DOF less, you can open up your iris to 1.6 (or just the smalles number, gives you less DOF too)... For 1/3 chip cameras there are very expensive adaptors that allow you to put 35mm lenses on them. Then your camera films a 35mm ground glass where the image of the prime (or still) 35mm lens is on projected, and then your image is a tad softer, but you have the same DOF as a 35mm camera. But such an adaptor costs sometimes more than 8000 dollars, I don't know the exact price. You also now have the Micro 35, somebody who made his own adaptor, I think his name is JAmes Hurd or something, and it costs around 500 dollars to order one, or 70 dollars to order a guide which tells you how to make your own with which materials. I advise you to look at the 'Towards a Film look' boards here, and at the Mini35 boards, and the Alternative Image Methods boards, and this article: http://www.dvinfo.net/articles/optics/dofskinny.php Good luck! There is already many many many things about discussed on these boards, so if you do a search you will get tons of information.

June 19th, 2005, 09:27 AM	#3
DJ Kinney Major Player Join Date: May 2005 Location: Portland, OR Posts: 277	The simple answer is to open her up all the way 1.6, move the camera back as far as possible, and then zoom in (never going into the digi range, though--only optical. In fact, turn the digi zoom off). The camera will automatically readjust the 1.6 to 1.8 or even 2.0 depending on the zoom. If those settings are too bright, DO NOT compensate with shutter speed. Keep that at 1/60. Use the in-cam ND filter instead, and if it's still too bright, which it will be on a sunny day, buy an additional ND screw-on filter. Audio will suck at the distance necessary to achieve a really filmic depth of field, so additional recorders or wireless mics will come into play. And that's the simple answer. DJ

June 19th, 2005, 09:41 AM	#4
Jeff Phang Regular Crew Join Date: May 2005 Location: Arlington, VA Posts: 34	www.micro35.com www.guerilla35.com If you have $100 to spend, I would suggest getting the DIY guide from www.micro35.com and then building an adapter yourself. The guide costs $45 and then there are around $50-$70 in parts to buy.

June 22nd, 2005, 05:47 AM	#5
Tom Hardwick Inner Circle Join Date: Mar 2003 Location: Billericay, England UK Posts: 4,711	The bare essentials: Close focus, wide aperture, long focal lengths and having the background as far away as possible will give you the narrowest DOF.

June 23rd, 2005, 03:41 PM	#7
Graham Bernard Old Boot Join Date: Aug 2002 Location: London UK Posts: 3,633	My understanding is that if you reduce the shutter speed you are, in essence, reducing exposure. Reducing the exposure this way allows you to have the IRIS as wide as you can. This gives the shorter depth of field. Soooo... wide iris you get more light. This leads to over exposure. The two ways I know to reduce exposure is: a) Put a filter - NDs here - in front of the lens. I've got 0.3 , 0.6 and my onboard 0.9 ND gives me nearly a total of nearly 2.0 ND! And THAT is before I need to reduce the shutter speed. . .. or .. . b) Reduce the time the shutter is actually open. Grazie

June 23rd, 2005, 05:11 PM	#8
Pete Wilie Major Player Join Date: Nov 2004 Location: Houston, TX Posts: 331	Here are some good resources on DoF: DoF Tutorial by DVCreators.net http://www.dvcreators.net/media/depthoffield.html DoF tutorial by DVXUser.com/Barry Green: http://www.dvxuser.com/V3/showthread.php?t=894 The Ultimate Depth-of-Field Skinny at DVInfo.net http://www.dvinfo.net/articles/optics/dofskinny.php And here is an interesting discussion on the subject: Depth of Field http://www.dvinfo.net/conf/showthrea...ht=depth+field

June 24th, 2005, 11:54 AM	#9
Nate Ford Regular Crew Join Date: Jun 2005 Location: new york, ny Posts: 121	there are 2 things that affect depth of field- focal length aperture. everything else only affects it indirectly. for example, mathieu is talking about chip size (better known as format, if we want to consider film here too.) chip size, in itself does NOT affect depth of field. a 50mm lens at f1.8 will produce the same depth of field on the thing behind it whether that thing is a 1/4" ccd or a 2 1/4" negative. the difference is, what will the angle of view look like. to a 1/4" chip, 50mm is big time telephoto. to a 35mm camera, it's "natural" (not tele, not wide.) to a 2 1/4" neg, it's wide angle. but the depth of field is the same. so where chip/format size comes into the equation is that the smaller formats/chips require shorter focal lengths to achieve the same look/"angle of view" as the bigger formats. therefore, as has been said, you have to really zoom in with prosumer video cameras to get to a short-DOF focal length. that, and open your aperture. compensate for the wide aperture however you want (shutter speed or nd filters,) but understand the effects of this compensation. (ie- fast shutter speed will change the rendering of motion. on the other hand, good optical nd filters will cost you a lot of money.)

June 26th, 2005, 11:55 AM	#10
DJ Kinney Major Player Join Date: May 2005 Location: Portland, OR Posts: 277	To clarify the shutter speed, I said to keep it at 1/60 because increasing it to compensate for a lot of light will cause strobing, and also, if you wanted to do any "film look" processes later, 1/60 looks best and converts the best. Of course, the strobe look is pretty cool for action shots.

June 26th, 2005, 12:26 PM	#11
Mathieu Ghekiere Inner Circle Join Date: Jun 2004 Location: Belgium Posts: 2,195	Nate, I thought that how bigger you went in format, the lesser DOF you got. I always heard guys on these boards claiming that if you use a 2/3 camera for example, you got much less DOF. Thanks for clearing that up! I wouldn't adjust the shutter speed. You want normal motion in your picture, and nothing that lookse like strange slow motion or a kind of movement that looks stroboscopic. I would just leave it at 1/60. But that's my opnion.