Alnoor Dewshi
September 11th, 2008, 06:36 AM
There are several apps for the iPhone that work as Depth of Field calculators. You set the parameters (aperture, focal length, distance, circle of confusion) and get a read-out of depth of field info (hyperfocal distance, near and far points etc). I'd love to be able to use one, or indeed any other DoF calculator, with the V1.
The first part of my question is: What Circle of Confusion (CoC) value should be used for the V1?
I've seen several different formulae for CoC, (e.g CoC = d / 1500 , where d is the diagonal measure of the original image) but my understanding of CoC is that it takes into account both the format dimensions and the "normal" viewing circumstances of the image for an "acceptable" degree of focus. e.g The criticalness of sharpness for a 10x8" photographic print viewed at arm's length is different to a billboard viewed across the street. The above formula is specific to photography with an assumption of the desired print resolution and enlargement factor built in. I'm guessing that SD or HD resolution is a limiting factor in any formulae for video image CoC, so should be taken into account.
For my purposes I'd be interested in two distinct viewing circumstances:
1. watching on a tv monitor.
2. viewing projected onto a screen in a cinema.
I'm guessing I need to work with a different CoC value if I know the piece is aimed for projection rather than tv screen.
Any light on a CoC formulae for video production would be very much appreciated.
Wrt format size: in this thread http://www.dvinfo.net/conf/sony-hvr-v1-hdr-fx7/77393-1-4-inch-sensors-even-harder-shallow-dof.html Tim Le uses a CoC value of 0.003mm for a 1/4" sensor. I'm not sure how he's arrived at this figure. I must admit I'm confused as to whether 1/4" measures the width of the sensor or its diagonal. To make matters even more confusing, it says in Sony's V1 Manual that the 1/4" type (sic) CMOS sensor is 4.5mm. That's significantly less than a quarter of an inch. Can anyone clarify actual dimensions?
The second part of my question relates to focal length:
The focal length of the V1 lens ranges from 3.9 - 78 mm. You can't actually get these figures in the viewfinder readout, but the numerical scale goes from 0 - 99, and I'm hoping to figure out an index to retrieve the actual focal length. (i.e 0=3.9mm, 10=5mm (normal) etc)
Should I assume that the numerical zoom scale works linearly? Or is it exponential?
I guess as a last measure i can do a through-the-lens comparison with a 35mm stills camera and figure it out from there.
Of course I'm not expecting to get absolute precision here; If I was, I wouldn't be using this camera! But a rough guide to the DoF would be very useful to the kind of stuff I'm doing. Thanks in advance for any help, and if you're interested, the iPhone apps are DoF, DoF Calculator, and iSee4K (free and geared to Red) available via the iTunes store.
The first part of my question is: What Circle of Confusion (CoC) value should be used for the V1?
I've seen several different formulae for CoC, (e.g CoC = d / 1500 , where d is the diagonal measure of the original image) but my understanding of CoC is that it takes into account both the format dimensions and the "normal" viewing circumstances of the image for an "acceptable" degree of focus. e.g The criticalness of sharpness for a 10x8" photographic print viewed at arm's length is different to a billboard viewed across the street. The above formula is specific to photography with an assumption of the desired print resolution and enlargement factor built in. I'm guessing that SD or HD resolution is a limiting factor in any formulae for video image CoC, so should be taken into account.
For my purposes I'd be interested in two distinct viewing circumstances:
1. watching on a tv monitor.
2. viewing projected onto a screen in a cinema.
I'm guessing I need to work with a different CoC value if I know the piece is aimed for projection rather than tv screen.
Any light on a CoC formulae for video production would be very much appreciated.
Wrt format size: in this thread http://www.dvinfo.net/conf/sony-hvr-v1-hdr-fx7/77393-1-4-inch-sensors-even-harder-shallow-dof.html Tim Le uses a CoC value of 0.003mm for a 1/4" sensor. I'm not sure how he's arrived at this figure. I must admit I'm confused as to whether 1/4" measures the width of the sensor or its diagonal. To make matters even more confusing, it says in Sony's V1 Manual that the 1/4" type (sic) CMOS sensor is 4.5mm. That's significantly less than a quarter of an inch. Can anyone clarify actual dimensions?
The second part of my question relates to focal length:
The focal length of the V1 lens ranges from 3.9 - 78 mm. You can't actually get these figures in the viewfinder readout, but the numerical scale goes from 0 - 99, and I'm hoping to figure out an index to retrieve the actual focal length. (i.e 0=3.9mm, 10=5mm (normal) etc)
Should I assume that the numerical zoom scale works linearly? Or is it exponential?
I guess as a last measure i can do a through-the-lens comparison with a 35mm stills camera and figure it out from there.
Of course I'm not expecting to get absolute precision here; If I was, I wouldn't be using this camera! But a rough guide to the DoF would be very useful to the kind of stuff I'm doing. Thanks in advance for any help, and if you're interested, the iPhone apps are DoF, DoF Calculator, and iSee4K (free and geared to Red) available via the iTunes store.