hartz
TPF Noob!
- Joined
- Aug 23, 2010
- Messages
- 117
- Reaction score
- 3
- Location
- Cape Town
- Can others edit my Photos
- Photos OK to edit
Why do they actually work?
I expect the filter itself, being so close to the front lens element, to be so far out of focus that it would be completely invisible in the final picture.
Light coming from any one spot of the scene spreads out and hits the whole of the lens. In fact, light from every spot (in the scene) hits every spot on the lens. All the light from one spot is then focused back to a single spot in the image, eg on the sensor / focal plane. Well, at least for areas that are in focus.
Exactly half the light focused on each spot passed through the top half of the lens and thus through the top half of the filter, while the other half of the light passed through the bottom half, and thus through the bottom half of the grad filter. So every spot of the resulting image should be affected the same amount by the grad filter.
But clearly this isn't true - the filters obviously do work. So please explain to me this magic. Where is the error in my logic?
I expect the filter itself, being so close to the front lens element, to be so far out of focus that it would be completely invisible in the final picture.
Light coming from any one spot of the scene spreads out and hits the whole of the lens. In fact, light from every spot (in the scene) hits every spot on the lens. All the light from one spot is then focused back to a single spot in the image, eg on the sensor / focal plane. Well, at least for areas that are in focus.
Exactly half the light focused on each spot passed through the top half of the lens and thus through the top half of the filter, while the other half of the light passed through the bottom half, and thus through the bottom half of the grad filter. So every spot of the resulting image should be affected the same amount by the grad filter.
But clearly this isn't true - the filters obviously do work. So please explain to me this magic. Where is the error in my logic?