| David Heath |
June 15th, 2008 01:55 PM |
Quote:
Originally Posted by Ali Husain
(Post 889435)
there's an OLPF in front of almost every digital sensor in every camera. it's just a blur filter. sampling won't quite work right without it.
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I'll agree with the third statement, but not the other two. A true OLPF is NOT in every camera, only in the more expensive ones - and that's why (as you say) the sampling for cameras in the low/mid price range doesn't work quite right! (At least compared to the more expensive cameras.)
It's not "just a blur filter", but rather a birefringent filter. (See http://en.wikipedia.org/wiki/Birefringence .) A simple blurring filter would not be able to reject alias frequencies sufficiently without severely affecting wanted resolution - the response of the birefringent filter rolls off far more sharply, and can be controlled (to match the sensor) by getting the thickness right. Hence they are expensive, hence only used on higher end cameras.
All this is far from academic when you compare two cameras with 960x540 pixels - the HPX500 has an OLPF, the HVX200 doesn't. Hence the HPX500 may actually seem slightly softer than the latter - but has far less aliasing than the HVX200, and is better overall. You get what you pay for. As Chris reminds us many times, there's more to cameras than simple pixel counts, and here we're dealing with two cameras with identical pixel counts!
The advantage of 1920x1080 chips is that as well as naturally improving the resolution, they ease the aliasing problem by doubling the spatial sampling frequency. The downside (compared to 960x540 chips) is each photosite being smaller, all else equal. Which is why the EX1/EX3 moving to 1/2" chips, in a form factor more normally reserved for 1/3" cameras, is very clever indeed. |
