acceptable focus and circle of confusion for 1/3 ccd hvx

[negative]

Quick question about figuring out acceptable focus for the hvx. First off, when figuring out the hyperfocal focus for 35mm the circle of confusion is .001 inch and for 16mm it's .0005 of an inch. Now would a 1/3 ccd camera be equivalent to 8mm circle of confusion and what would that be? Another question I have is once I find out what the circle of confusion for a 1/3 cam is, should I use the focal length of the HVX lense or should I use the 35mm equivalent which is the focal of the HVX multiplied by 7.74 and then use that number with the hyperfocal distance formula and then should I also use the 35 equivalent when calculating near limit and far limit depth of field of a subject? But then I'm wondering, would this also be limited to the sharpness of an HD image, would the acceptable focus range even be narrower because of this? Should I use a soft filter to compensate or maybe just calculate it by going a step down to a lower f-stop?

[Barry_Green]

It's never as easy as it seems.

First, the circle of confusion is not some sort of fixed standard. It's all relative to the size of the screen you're displaying the footage on.

The circle of confusion came about in relation to theatrical projection. Movie screen projection involved blowing the image up to a certain size, and since 16mm is smaller than 35mm, 16mm needs to be magnified more to fill the screen. Which means that you need to execute a tighter "circle of confusion" to survive that blowup process. It all nets out about the same; with a diameter 1/2 the size of the diameter of 35mm's CoC, that means a point of light needs to be basically 1/4 as large to be considered "in focus" after being blown up to the big screen; and with 16mm having a total surface area of 1/4 the area of 35mm film, that means that when you project the image from 16mm you'll be blowing it up to 4x the magnification that 35mm would undergo, which means that the individual point of light will end up being about the same size as it was on the 35mm shot.

And following that same schedule, that would mean you'd need a CoC of yes, approximately 8mm film size, for HVX calculations. The size of the HVX's imager is somewhere around 5.3 x 3mm. So technically it'd even be smaller/tighter than Super8mm film, which is typically around 6x4mm.

But it's only relevant if you're intending to blow up to movie-screen size. The smaller you blow it up, the less tight the CoC needs to be. If you're aiming for a 60" HDTV, you can get away with a much, much looser CoC. If you're aiming for a 13" TV, you can get away with a relatively massive CoC.

As for calculating the actual DOF, forget 35mm equivalencies and use the HVX's actual focal length in your calculations.

[negative]

Thanks.

[Dan Vance]

Just to complete the numbers from Barry's post, the CoC for 1/3" would be approximately half-again the 16mm CoC, or .00025", if you were proportioning for movie- screen blow up. But as Barry says, for smaller screens you can use a bigger number. Or you can just plug in .00025" in your calculations, knowing it's a conservative number.