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Shooting at less that 24fps


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#1 Mihail Ursu

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Posted 13 May 2009 - 08:42 AM

First of all, greetings to everybody on this forum and that you for your time and knowledge.

Now... I need to make a short 3-5 minute film for my cinematography exam and I will be shooting a mix of Kodak Plus-X and Kodak Double-X (iso 100-250) on an ancient Mitchell special effects camera.

I want to shoot at 4-8-12 frames per second while moving the camera slowly on a dolly or a trav to compensate for the faster movement.

My questions are:

1- will there be any reciprocity failure at these frame rates?

2- how about stroboscopy? will I have problems with cars, people and statis objects? if I will, how will the focal distance of the lens influence it? (i remember that there is a relation between focal distance and the panning speed, but I not sure how).

3- any other problems that I am not aware of?

Thank you very much for reading this and for any replies.
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#2 Saul Rodgar

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Posted 13 May 2009 - 10:14 PM

I want to shoot at 4-8-12 frames per second while moving the camera slowly on a dolly or a trav to compensate for the faster movement.

1- will there be any reciprocity failure at these frame rates?

2- how about stroboscopy? will I have problems with cars, people and statis objects? if I will, how will the focal distance of the lens influence it? (i remember that there is a relation between focal distance and the panning speed, but I not sure how).


Do you plan to compensate the exposure time for the different shutter speeds you are shooting at? As long as you do that, there will be no reciprocity failure as light intensity (falling on the photosensitive surface) and duration of exposure are correlated:

http://en.wikipedia....y_(photography)


As for stroboscopy, I am unsure as to what problems you could encounter, other than additional motion blur. I have heard of people having flicker when shooting at 24 fps on a dolly and using Kinos. I have shot cars driving by at 6 and 8 fps while panning the camera and have not had any problems.

Edited by Saul Rodgar, 13 May 2009 - 10:16 PM.

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#3 Dominic Case

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Posted 14 May 2009 - 06:29 PM

There will be no reciprocity failure at the speeds you are using. Reciprocity holds up well for exposures of a second or so. That is, a stop of aperture equals a stop of exposure time.

Strobing appears when you pan past an object too fast, and the smooth pan movement is obviously seen as jerky. It is all about the distance on the screen between an objects position in one frame and the next.

So, if you are shooting at 12fps instead of 24fps, you will need to pan at half the speed. And if you use a lens of twice the focal length (eg 50mm instead of 25mm) you will need to pan at roughly half the speed, as the image is twice as big on the screen.

If the movement you are worried about will be the tracking movement of the dolly, rather than a pan, then slowing down the tracking to compensate for the slower frame rate will exactly solve the strobing problem.

The American Cinematographer Manual has tables of recommended panning speeds for static scenes, at various frame rates and focal lengths, in terms of degrees per second, time for a 90 degree pan, and so on. At least my now very elderly 6th edition does. And the laws of physics and geometry haven't altered much since it was published.
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#4 Mihail Ursu

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Posted 20 May 2009 - 09:39 AM

Thank you very much for you answers. I will take into account all the information you shared.
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#5 David Rakoczy

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Posted 20 May 2009 - 09:45 AM

I do 15 second exposures on 7212.. no reciprocity issues...
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#6 Mihail Ursu

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Posted 20 June 2009 - 08:55 AM

I wanted to give you an update as to how things worked out.

It was a very interesting and pleasing experience working with film for the first time and none of my fears regarding strobo. and exposure came true.

Because luckily the laboratory in our school did a good job developing the material and I exposed properly the night shots came out exactly as I wanted them to, in fact I found out that I could have pushed the material some more.

A very pleasant suprise was how the film handled the very contrast scenes at sunrise, I expeted to see some bleading of white to black in the scenes where I had the sky about 3-4 stops over the exposure value.

One regret that I have is that i didn't push the film to the limits so that I would know where they are and how they look.


Thank you all again,

Mihail Ursu,
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