Choosing Lenses for 3D rig at DVinfo.net

Norm Becerra · May 4th, 2008, 01:01 AM

Hi, I am currently building a 3d rig for two SI-2K Mini Cameras. I have not worked with 3D cameras before. And I was curious about the Interocular distance between cameras I have seen other rigs that can spread them out pretty far for longer distance shots. How does that work? Also, I have been googleing around for a primer on the different aspects to consider when planning a rig. Tow in/out, interocular distance etc. Can you point me in a direction where I can get the basic theory down so that I can understand he 3rd dimension in shooting? Thanks

Tim Dashwood · May 4th, 2008, 07:49 PM

The absolute best beginner's primer to stereoscopic cinematography I've seen was in last month's American Cinematographer (April 2008.) It is the issue with the film "21" on the cover. The article is a really good introduction, but then you'll want to find some of the books mentioned in the recommended reading sticky.

Interaxial distance is the distance between the centres of the two taking lenses (or CCDs/film planes if toeing in.) Ideally it should be equal to that of the human interocular distance, which averages 65mm (2.5"). It is difficult to achieve this distance with most cameras in a side-by-side configuration, but it would be possible with small handycam style bodies.

Sometimes you may want to increase the interaxial distance to "deepen" the 3D effect in landscape shots. You can't go too far or you may be victim of "hyper-stereoscopy." This happens to me sometimes in my rig (which has a wide interaxial of 104mm) and it feels like your sitting on the ground even though the camera was mounted at about 6 feet from the ground.

Interaxial would be decreased for microscopic or macro stereophotography of subjects very close to the taking lenses.

Have you given any thought to adjusting convergence (toe in) in your rig?

Norm Becerra · May 5th, 2008, 02:08 AM

Hi, I downloaded the sticky suggestion and I haven't read it yet and I have considered creating a tow in adjustment into my system. What I am trying to do is figure out how much effect I will get with the different settings. We will be doing lot of landscape type shots. I would like to start building the relationship between Interaxial distance and actual distance in the landscape. Maybe there is a chart some where that has that information. Also I am not to so sure what the effect of tow in is. I know these are really rudimentary questions but I am on my third day of researching this project and I am not quite up to speed. Thanks for your help I will find the American Cinematographer article and read what I down loaded.

Ken Plotin · May 6th, 2008, 10:14 AM

Norm,
You need to be careful with toe-in (convergence adjustment), particularly at wide angles. Too much will cause "ghosting" of BG elements...really obvious if you are using the anaglyph system for viewing (red/cyan). Also hard on the eyes. Convergece adjustment while shooting works better at slightly longer focal lengths.

An easy way to check the "right" convergence point for close ups (where the problem is greatest) is to use a pen sized laser in the accessory shoe of the minicams to align them...just don't use it directly on a face:).
Otherwise, many folks just keep the lenses parallel and use a smaller interocular distance (like 2") and adjust the convergence in post.
In either case, shoot a "line up" target (fancy way of saying a sheet of paper with magic marker grid lines on it) so that you will be able to more easily converge the separate camera images in post. Just line up the grid so that the red/cyan lines become one in your NLE, and you are converged at the viewing window for that scene. If you want the main subject to appear behind (further away) or pop out in front of the window, adjust to taste.
Hope this helps.
Ken

Norm Becerra · May 21st, 2008, 02:54 AM

I am designing a 3D rig using the SI- mini2K cameras. This camera heads will be enclosed inside a water proof case. I have zero experience with this camera and I am having trouble selecting the proper lenses for this project. In order for me to design the case I need to know the dimensions of the lenses that we will be using. I have narrowed down the focal length on a super16mm lens to be somewhere between 10mm and 18mm for this application. Now I need a lenses that are lighter in weight and not to expensive. Also it does not have to be a fast lens somewhere around 2.5 or slower.
we will be shooting in bright daylight and I heard that the slower lenses are less expensive. Also the total diameter must not be more than 65mm. I am looking for c mounts as well. I am open to suggestions as to what may work or if I am overlooking something.

Where can I find these lenses?

Any suggestions and insights would be appreciated.

oh, I made my calculations from the Panavision online calculator. http://www.panavision.co.nz/main/kba...bleLensEqv.asp

May 4th, 2008, 01:01 AM	#1
Norm Becerra New Boot Join Date: Sep 2006 Location: La Habra Ca Posts: 18	Building 3d Rig Hi, I am currently building a 3d rig for two SI-2K Mini Cameras. I have not worked with 3D cameras before. And I was curious about the Interocular distance between cameras I have seen other rigs that can spread them out pretty far for longer distance shots. How does that work? Also, I have been googleing around for a primer on the different aspects to consider when planning a rig. Tow in/out, interocular distance etc. Can you point me in a direction where I can get the basic theory down so that I can understand he 3rd dimension in shooting? Thanks

May 4th, 2008, 07:49 PM	#2
Tim Dashwood Wrangler Join Date: Aug 2005 Location: Toronto, ON, Canada Posts: 3,637	The absolute best beginner's primer to stereoscopic cinematography I've seen was in last month's American Cinematographer (April 2008.) It is the issue with the film "21" on the cover. The article is a really good introduction, but then you'll want to find some of the books mentioned in the recommended reading sticky. Interaxial distance is the distance between the centres of the two taking lenses (or CCDs/film planes if toeing in.) Ideally it should be equal to that of the human interocular distance, which averages 65mm (2.5"). It is difficult to achieve this distance with most cameras in a side-by-side configuration, but it would be possible with small handycam style bodies. Sometimes you may want to increase the interaxial distance to "deepen" the 3D effect in landscape shots. You can't go too far or you may be victim of "hyper-stereoscopy." This happens to me sometimes in my rig (which has a wide interaxial of 104mm) and it feels like your sitting on the ground even though the camera was mounted at about 6 feet from the ground. Interaxial would be decreased for microscopic or macro stereophotography of subjects very close to the taking lenses. Have you given any thought to adjusting convergence (toe in) in your rig? __________________ Tim Dashwood

May 5th, 2008, 02:08 AM	#3
Norm Becerra New Boot Join Date: Sep 2006 Location: La Habra Ca Posts: 18	Tow in Hi, I downloaded the sticky suggestion and I haven't read it yet and I have considered creating a tow in adjustment into my system. What I am trying to do is figure out how much effect I will get with the different settings. We will be doing lot of landscape type shots. I would like to start building the relationship between Interaxial distance and actual distance in the landscape. Maybe there is a chart some where that has that information. Also I am not to so sure what the effect of tow in is. I know these are really rudimentary questions but I am on my third day of researching this project and I am not quite up to speed. Thanks for your help I will find the American Cinematographer article and read what I down loaded.

May 21st, 2008, 02:54 AM	#5
Norm Becerra New Boot Join Date: Sep 2006 Location: La Habra Ca Posts: 18	Choosing Lenses for 3D rig I am designing a 3D rig using the SI- mini2K cameras. This camera heads will be enclosed inside a water proof case. I have zero experience with this camera and I am having trouble selecting the proper lenses for this project. In order for me to design the case I need to know the dimensions of the lenses that we will be using. I have narrowed down the focal length on a super16mm lens to be somewhere between 10mm and 18mm for this application. Now I need a lenses that are lighter in weight and not to expensive. Also it does not have to be a fast lens somewhere around 2.5 or slower. we will be shooting in bright daylight and I heard that the slower lenses are less expensive. Also the total diameter must not be more than 65mm. I am looking for c mounts as well. I am open to suggestions as to what may work or if I am overlooking something. Where can I find these lenses? Any suggestions and insights would be appreciated. oh, I made my calculations from the Panavision online calculator. http://www.panavision.co.nz/main/kba...bleLensEqv.asp

May 6th, 2008, 10:14 AM	#4
Ken Plotin Major Player Join Date: Jan 2004 Location: Los Angeles, CA Posts: 254	Norm, You need to be careful with toe-in (convergence adjustment), particularly at wide angles. Too much will cause "ghosting" of BG elements...really obvious if you are using the anaglyph system for viewing (red/cyan). Also hard on the eyes. Convergece adjustment while shooting works better at slightly longer focal lengths. An easy way to check the "right" convergence point for close ups (where the problem is greatest) is to use a pen sized laser in the accessory shoe of the minicams to align them...just don't use it directly on a face:). Otherwise, many folks just keep the lenses parallel and use a smaller interocular distance (like 2") and adjust the convergence in post. In either case, shoot a "line up" target (fancy way of saying a sheet of paper with magic marker grid lines on it) so that you will be able to more easily converge the separate camera images in post. Just line up the grid so that the red/cyan lines become one in your NLE, and you are converged at the viewing window for that scene. If you want the main subject to appear behind (further away) or pop out in front of the window, adjust to taste. Hope this helps. Ken