Lens characteristics for shallow DOF? at DVinfo.net

Paul Gale · April 3rd, 2007, 06:00 AM

I've been using a number of techniques for achieving shallow DOF in IV shots - some successful, others definately not as shallow as I'd like.

When I shoot, I try to get as far from the subject as possible and zoom right in, use -3dB gain and ND filter if possible, keeping lights slightly further away to get the right exposure while opeinign the iris right up. Most of the time though, this isn't possible due to very cramped locations.

I'm also still planning on going with a F350 and new lens and was wondering what specifications affect the DOF? Should I be looking for a particular type of lens that will give this shallow DOF field look easily?

Oh, I also do conference work occasionally which needs long zooms (or extender) - probably at odds with the IV work?

Any ideas or recommendations?

Thanks,

Paul.

Greg Sherris · April 9th, 2007, 10:35 PM

You might already have some firm ideas about acheiving this look. I was poking around and noticed no replies so I thought I'd offer up a couple. Forgive me if I touch on the things you've already tried.

1. crank in enough ND to force your iris wide open for short depth.
2. don't back up so much - focus is more critical with camera closer to the subject. you want to use some focal length, but at the long end of the lens it gets harder to get the deep focus look.
3. zoom in while closer to subject - you might even have to use macro or choose to use macro. depth of field is extremely limited to negligible with macro engaged. (don't zoom of course -macro eliminates variable focal length)
4. have you got a 2x extender on the lens - you can throw that to help with the above suggestions
5. you can use filter plug-ins as well in post to help acheive a shallow depth look.

hope this helps and that I haven't given you info you already have or know

Daniel Browning · April 10th, 2007, 12:16 AM

Quote:

Originally Posted by Paul Gale

I'm also still planning on going with a F350 and new lens and was wondering what specifications affect the DOF? Should I be looking for a particular type of lens that will give this shallow DOF field look easily?

You are confused between depth of field and background blur. To narrow the depth of field, use a larger aperture or largest sensor (or film size).

To improve background blur, use a longer lens to magnify a smaller portion of the out-of-focus (OOF) area, and increase the distance between your subject and the background. The bokeh will have a large effect on the OOF appearance too.

Paul Gale · April 10th, 2007, 04:13 AM

Thanks Guys, that's useful.

Not confused between DOF and background blur - I understand that the DOF and focus does not change when you zoom in, it just appears to due to magnification etc.

So to my original question - what characteristics of a lens gives a more pronounced shallow DOF i.e. should I be looking for a certain type of lens if I do a lot of IV work and want shallow DOF a lot?

Thanks,

Paul.

Daniel Browning · April 11th, 2007, 05:44 PM

Quote:

Originally Posted by Paul Gale

So to my original question - what characteristics of a lens gives a more pronounced shallow DOF i.e. should I be looking for a certain type of lens if I do a lot of IV work and want shallow DOF a lot?

I'm sorry I didn't answer your question the first time. There's only one lens characteristic that affects DOF: focal ratio. However, changes to the background blur can make a given field depth appear more "pronounced".

Paul Gale · April 12th, 2007, 01:34 AM

Thanks Daniel,

Is the focal ratio expressed in the specs of a lens normally? I couldn't see it with the supplier I normally use. What's is the definition of focal ratio anyway?

Cheers,

Paul.

Alister Chapman · April 12th, 2007, 02:59 AM

The focal ratio is the ratio between the focal length of the lens and the size of image produced. Depth of field and thus background blur is a function of focal length and aperture, so any lens operating at the same focal length with the same aperture will give the same depth of field. All lenses will give the same DOF. Opening up the aperture will reduce the DOF, but more than f4 and you may find that the lens starts to look a bit soft (depending on the quality of the lens).

Daniel Browning · April 12th, 2007, 08:31 AM

Quote:

Originally Posted by Alister Chapman

Depth of field and thus background blur is a function of focal length and aperture.

You forgot subject distance. It's very important because otherwise a novice may think that framing a shot with a telephoto lens will yeild a thinner DOF than the same shot with a normal or wide lens. It wont: all that will change is the background blur.

That's why I prefer to say that DOF is a function of focal ratio and framing, since framing encapsulates focal length and subject distance, tying them together. Background blur is a function of DOF, focal length, subject to background distance, and bokeh.

Paolo Ciccone · April 24th, 2007, 12:19 AM

Hi Paul.
I tested a few 2/3" Fujinon lenses with the adapter and the 10x10 E-Series zoom has delivered the best result for us. I had a pretty good result also with the Cinezoom C-series. I don't remember exactly the type but I believe it was a 7.xmm at the widest.

April 3rd, 2007, 06:00 AM	#1
Paul Gale Major Player Join Date: Feb 2004 Location: Oxfordshire, UK Posts: 425	Lens characteristics for shallow DOF? I've been using a number of techniques for achieving shallow DOF in IV shots - some successful, others definately not as shallow as I'd like. When I shoot, I try to get as far from the subject as possible and zoom right in, use -3dB gain and ND filter if possible, keeping lights slightly further away to get the right exposure while opeinign the iris right up. Most of the time though, this isn't possible due to very cramped locations. I'm also still planning on going with a F350 and new lens and was wondering what specifications affect the DOF? Should I be looking for a particular type of lens that will give this shallow DOF field look easily? Oh, I also do conference work occasionally which needs long zooms (or extender) - probably at odds with the IV work? Any ideas or recommendations? Thanks, Paul.

April 12th, 2007, 02:59 AM	#7
Alister Chapman Inner Circle Join Date: Dec 2005 Location: Bracknell, Berkshire, UK Posts: 4,957	The focal ratio is the ratio between the focal length of the lens and the size of image produced. Depth of field and thus background blur is a function of focal length and aperture, so any lens operating at the same focal length with the same aperture will give the same depth of field. All lenses will give the same DOF. Opening up the aperture will reduce the DOF, but more than f4 and you may find that the lens starts to look a bit soft (depending on the quality of the lens). __________________ Alister Chapman, Film-Maker/Stormchaser http://www.xdcam-user.com/alisters-blog/ My XDCAM site and blog. http://www.hurricane-rig.com

April 24th, 2007, 12:19 AM	#9
Paolo Ciccone Trustee Join Date: Apr 2005 Location: Santa Cruz, CA Posts: 1,116	Hi Paul. I tested a few 2/3" Fujinon lenses with the adapter and the 10x10 E-Series zoom has delivered the best result for us. I had a pretty good result also with the Cinezoom C-series. I don't remember exactly the type but I believe it was a 7.xmm at the widest. __________________ Paolo http://www.paolociccone.com Demo Reel

April 9th, 2007, 10:35 PM	#2
Greg Sherris New Boot Join Date: Apr 2007 Location: Brandon, Manitoba, Canada Posts: 9	You might already have some firm ideas about acheiving this look. I was poking around and noticed no replies so I thought I'd offer up a couple. Forgive me if I touch on the things you've already tried. 1. crank in enough ND to force your iris wide open for short depth. 2. don't back up so much - focus is more critical with camera closer to the subject. you want to use some focal length, but at the long end of the lens it gets harder to get the deep focus look. 3. zoom in while closer to subject - you might even have to use macro or choose to use macro. depth of field is extremely limited to negligible with macro engaged. (don't zoom of course -macro eliminates variable focal length) 4. have you got a 2x extender on the lens - you can throw that to help with the above suggestions 5. you can use filter plug-ins as well in post to help acheive a shallow depth look. hope this helps and that I haven't given you info you already have or know

April 10th, 2007, 04:13 AM	#4
Paul Gale Major Player Join Date: Feb 2004 Location: Oxfordshire, UK Posts: 425	Thanks Guys, that's useful. Not confused between DOF and background blur - I understand that the DOF and focus does not change when you zoom in, it just appears to due to magnification etc. So to my original question - what characteristics of a lens gives a more pronounced shallow DOF i.e. should I be looking for a certain type of lens if I do a lot of IV work and want shallow DOF a lot? Thanks, Paul.

April 12th, 2007, 01:34 AM	#6
Paul Gale Major Player Join Date: Feb 2004 Location: Oxfordshire, UK Posts: 425	Thanks Daniel, Is the focal ratio expressed in the specs of a lens normally? I couldn't see it with the supplier I normally use. What's is the definition of focal ratio anyway? Cheers, Paul.