View Single Post

Old 02-05-2010, 08:52 PM
DamianDinning DamianDinning is offline
Registered User
Join Date: Sep 2009
Location: UK
Posts: 132
DamianDinning is on a distinguished road
N8 focus in video

Originally Posted by Unregistered View Post
If i understand well, there's no continuous autofocus on the video mode? This is the must have feature i wait on any mobile ! The vivaz from sony ericsson do a very well job in this now i have to keep my Omnia HD for its great well colored videos, Vivaz for it continuous autofocus feature, and N8 for what then?
We use a system called Active Hyper Focal Distance. The resolution when shooting video is lower than when shooting stills. This means there is a larger tolerance to focus (circle of confusion) than with stills. Given the wideangle optics (28mm equivalent) we have a huge amount of depth of field. By pre-setting the lens to the hyper focal distance we are able to create the widest distance range where objects will appear to be sharp. This range equates to roughly 60cm to infinity. To reduce the size of the camera module we use a lens drive system which to some degree relies on friction. As a result of this the lens can íslipí causing a focus error. To avoid this with the N8 we are for the first time using a system where we continuously check the lens is still in this position, if not it is readjusted.

The benefit of this system is that works in the vast majority of conditions and regardless of subject movement, illumination and contrast. All of these can cause problems with autofocus systems in video resulting in focus hunting and/or out of focus objects. However, we do recognise the benefit of such systems for close-ups. We have been developing a CAF system for video but at this time we don't want to compromise the majority of usage for something youíll do much less often. But we are continuing to investigate whether we can create a system for in the future which combines the benefits of both. If you look at the sample video on Nokia Conversations there are many examples in the sequence where CAF would have not focused correctly for example.