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Matching focal lengths between camera


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#1 Brian Craig

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Posted 03 November 2007 - 09:09 PM

Hi I am new here and new at this cine stuff as well.

I am not sure if tis is the right place to post this my apologies up front.

Well As every camera uses different numbers for the same focal length - that is one camera might have a focal length of 22mm and another might be 32mm, both saying thy are the 35mm equivalent of a 50mm lens- how would one go about matching focal lengths between different cameras? In this case between my still camera, and my DV camera.

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#2 David Mullen ASC

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Posted 03 November 2007 - 09:42 PM

Well As every camera uses different numbers for the same focal length -


I think you're just confusing yourself thinking in those terms. The focal length is the focal length, a 50mm, let's say. It just has a different field of view for different sized formats.

So what you're really asking is how to match field of view when changing formats. The rough rule is that a format that is half the horizontal width would use a focal length that is half that of a lens on a format that is twice the horizontal width, assuming you are matching horizontal field of view. So you'd use a 25mm lens on a 16mm camera to match the field of view of a 50mm lens on a 35mm movie camera or a 100mm lens on a 65mm movie camera. More or less.

To be more precise, you can either look on tables to match field of view for the same distance, or you can use a calculator, like at:

http://www.panavision.com/tools.php
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#3 Chris Keth

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Posted 03 November 2007 - 10:55 PM

If you're familiar with how various focal length look on a certain format, you can use the diagonal of that format, the diagonal of the format in question, and a lens (on either format, your choice) and do a simple proportion calculation to figure out the unknown.

For example, lets say you like the look of a 18mm lens on the regular 16 format (1.33). You want to find the focal length to give you that look on full super 35 format (1.33).

The diagonal of 16 is 12.70mm and the diagonal of super 35 is 31.11mm (I figured these diagonals from number in wikipedia. I did not check their accuracy so consider this for demonstration purposes only.)

18mm/12.70=x/31.11

Solving that gives you a 44mm lens on super 35.


For quick calculations, which are usually more useful than knowing the exact number, you can just figure an enlargment or reduction ratio from a format you are familiar with. The example above would be a 2.45x (2.5x for brievity) conversion if you know 16mm lenses and want to know S35. That's how I think of it, anyway.
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#4 Chris Keth

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Posted 03 November 2007 - 11:00 PM

In this case between my still camera, and my DV camera.


I missed this the first time. I would have used those formats in my example. The diagonals of those formats is easy to find, just be careful since the aspect ratios will likely be different. It may be most useful to you to use the horizontal leasure of the format rather than the diagonal if you're comparing very different-shaped formats.
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#5 Brian Craig

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Posted 04 November 2007 - 01:02 AM

Ok maybe I should start over and say I am sorry for confusing myself and others.
Ok here is what I am working with in the way of hardware I have a Canon PowerShot G3 still camera and I have a JVC GR-DVL720U which is my video camera.
I have add these names so you might assisted me when I ask direct question towards lens etc...

Ok here is what I am doing .Well I use the G3 still camera to take the widest shot I could with this camera of a pretty empty street at 1:38 pm to be used as part of a matte shot this is where the JVC video camera comes in. So at a different location I will lock off the camera about 1:30 pm and shoot as wide as the JVC GR-DVL720U can while my friend drive white car into

So be new and all what is the question I should be asking myself here?
And what information do you guys need from about either camera meaning specs that can help?
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#6 Chris Keth

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Posted 04 November 2007 - 01:55 AM

Ok maybe I should start over and say I am sorry for confusing myself and others.
Ok here is what I am working with in the way of hardware I have a Canon PowerShot G3 still camera and I have a JVC GR-DVL720U which is my video camera.
I have add these names so you might assisted me when I ask direct question towards lens etc...

Ok here is what I am doing .Well I use the G3 still camera to take the widest shot I could with this camera of a pretty empty street at 1:38 pm to be used as part of a matte shot this is where the JVC video camera comes in. So at a different location I will lock off the camera about 1:30 pm and shoot as wide as the JVC GR-DVL720U can while my friend drive white car into

So be new and all what is the question I should be asking myself here?
And what information do you guys need from about either camera meaning specs that can help?


Before we get things like camera specs you should tell us what this plan is supposed to do in the final product. I don't get it.
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#7 David Mullen ASC

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Posted 04 November 2007 - 02:18 AM

I don't really understand the question, but if you're trying to find the equivalent focal lengths on your Canon Power Shot and the JVC, you'd need to know the dimensions of the sensor in both cameras first.
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#8 Bob Hayes

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Posted 04 November 2007 - 12:08 PM

It sounds like you want to take a digital still with your still camera. And then go to another location with your DV camera and shoot a shot that will be composite with it. You face several problems.

My Cannon Power Shot A630, which I think is similar to yours, gives no indication of lens change when you zoom. Not even little symbolic dots. So I have no idea what the lens is. I don?t know how the Cannon DV designates lens size. Is it on the barrel of a video type lens or just symbolic dots or percentages? Some DV cameras will give you a number like 22 but it means 22% of its capability so that can be a relative guide. So here is my advice.

Take the two cameras to the first location set them up side by side and match the dv camera to the still shot. Record the zoom size on the DV even if it ends up as a % number and use it as guide at the next location.

If you do not have access to the DV camera or this method doesn?t work for you, take a tape measure and a broom stick to the first location. After setting the still camera up record the lens height, angle of declination, and distance to your subject. Then hold the broom stick horizontally and walk away from the still camera until the pole just fits the frame and measure the distance from the camera. Now when you get a hold of the DV measure out the same distance and hold the broom stick horizontally change your zoom until it fits. Place the camera where you want it with out changing the lens size. Match the parameters of the still shot. Also realize the frame dimensions won?t match up because of the different ratios of their respective frames. My still camera shoots 8 mega pixels which is higher resolution then the DV camera so you may want to shoot the still photo slightly wider then you want and on a slightly wider lens to give you some wiggle room when it comes to matching with the DV.
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#9 Brian Craig

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Posted 06 November 2007 - 03:26 AM

Hi Everyone I haven't forgot your help here.I will be back soon :)
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#10 Brian Craig

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Posted 13 November 2007 - 09:59 PM

Well I guess this project will have to wait for now I hurt my leg so hopping is all I can do.So I will ask question and help for at home for now.But again I really thank you for that great ideas.
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