optics on different cameras, how can I get consistency?

December 13, 2006 7:48 AM

2 different cameras, 2 lenses, how can I get the closest possible recreation?

Using this firewire camera as a reference, with a lens that has a focal length of 2.8mm-8mm, what sort of lens would i need on a 35mm camera, or digital SLR, to recreate the angle on an object from 7 feet away?

Please if it's the same super, and please forgive my ignorance. If it is indeed something different, what's the equation to figure it out?

posted by tip120 to technology (5 comments total)

The last calculator on this page will figure it out for you. For example at 2.8mm and F/8 you'd need a 13.5mm lense on 35mm at F/38.

FYI: a 1/4" CCD is 6.35mm per side and F/8 is probably a fair guess of the aperture.
posted by Mitheral at 8:22 AM on December 13, 2006

Angle of view depends on lens focal length and sensor size.

That camera has a 1/4" CCD. When used with a 2.8-8mm lens, the angle of view at 2.8mm is 91 degrees. At 8mm, the field of view is 43 degrees.

The equivalent lens for a 35mm film camera is about 21mm. For a digital SLR, you need to know the conversion factor (usually around 1.5 or 1.6) or the sensor size. For a DSLR with a 1.5 conversion factor, you'd need a 14mm lens (14 * 1.5 = 21).

This doesn't take into account any distortion the lens may introduce (the wider the angle, the more the distortion, usually).

Here'a good article about angle of view.
posted by jdfan at 8:30 AM on December 13, 2006

To cover the same angle, you need the same ratio between the sensor size (its diagonal, its height, or its width) and the lens focal length. For instance, the height of a "35mm" film negative is 24mm, and the sensor on a typical DSLR camera is about 16mm.

Now, knowing that the sensor in the firewire camera is "1/4 inch" doesn't say much -- the relationship between this number (which actually refers to the size of a vacuum tube in the early days of TV!) and the sensor's size is loose at best. See http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm

The datasheet for the camera's sensor gives its diagonal as 4.5mm and its ratio as 4:3, which makes its its height about 2.1mm. 2.1mm:8mm is a ratio of about 1:4, so the 35mm equivalent would be 4*24mm = 96mm, and the DSLR equivalent would be 4*16mm = 64mm. Lenses of this length are common and inexpensive. 2.1mm:2.8mm is a ratio of .75, giving 18mm and 12mm respectively. Lenses as "wide" as this are uncommon and tend to be expensive. You're in "fisheye" territory here.

I chose to use the height of the sensor for comparison, because the ratio of film is 3:2, not 4:3. (a bit "wider"). You would crop a bit from the left and the right of the 35mm or dslr photo until it had the same aspect ratio as the video camera.
posted by jepler at 8:36 AM on December 13, 2006

The datasheet for the camera's sensor gives its diagonal as 4.5mm and its ratio as 4:3, which makes its its height about 2.1mm.

(4.5/5)*3 = 2.7mm. Or alternatively 480 pixels * 5.6 microns = 2.688 mm.

(which makes the other ratios 3 and 1, or 72mm and 24mm)
posted by cillit bang at 9:23 AM on December 13, 2006

thanks cillit bang. clearly I need a math class.
posted by jepler at 11:22 AM on December 13, 2006