Re: Flange focal distance / DOF question
 

Brian explained things very well, but I'd like to add my two cents anyway.

Bokeh is not the same thing as thin depth of field (or defocus blur). Bokeh is the quality of the blur, not the quantity. So even a 1/3" chip, with only a slight amount of defocus blur, can have good bokeh. While a large 35mm camera, with a huge amount of defocus blur, can have bad bokeh.

No. First, 3-chip cameras have to have a relatively large flange distance in order to provide room for the prism.

No. 35mm rangefinder lenses can be (and sometimes are) just a few millimeters away from the sensor.

The flange distance is identical between those two, but the *backfocus* distance is ever-so-slightly different.

No.


Wide iris diameters (i.e. long focal length and slow f-numbers or short focal lengths and fast f-numbers)

Hope that helps.

Re: Flange focal distance / DOF question
 

Thanks for the replies,

by "bokeh" I meant it was very hard to get an XL1S to blur the background (thus very little bokeh ).

Razor sharp DOF, we all know large aperture creates blur, what I was asking is why the F3 etc has it, most prior pro sumer camcorders could not achieve this thin DOF.

Re: Flange focal distance / DOF question
 

Some will say that the reason is because of the larger sensor, but I think a better answer is the lenses that are available. By this, I mean that for any given angle of view and focus distance, the F3 has lenses available that are capable of wider iris diameters. That's why it can achieve thinner DOF than other camcorders.

For example, when I zoom my XHA1 to a 40-degree angle of view (the so-called "normal" focal length), the focal length is 7mm, and the widest f-number is f/1.6. The iris diameter is 7 divided 1.6, which is 4.4mm.

With the F3, a 40-degree angle of view requires a 32mm lens. You can find lenses in this range with an f-number as wide as f/1.2, but even if you only use f/2.8, the iris diameter still results in 11.4mm. That is still much wider than the 4.4mm maximum diameter possible with the XH-A1 set to f/1.6. That is why it's possible to have a depth of field so much thinner.

In general, larger sensors tend to have lenses available with wider iris diameters. However, that's not always true. For example, many digital Medium Format cameras have lenses with such slow f-numbers (e.g. f/2.8) that they cannot achieve the same iris diameter as lenses on the 36x24mm FF35 format (which open to f/1.0, f/1.2, etc.).