Thread: problems with D90

Originally Posted by dm_td5

Basically any lens designed for digital cameras is going to be OK, some will be better lenses than others. A lot has to do with the ability to focus the light straight to the sensor which was something that wasn't as important on film. This is to do with the photosites on the sensor and the microlens technology employed to direct the light on to them.

These are called telecentric lenses. Because the surface of a digital camera sensor is shiny, they reflect a lot of light, particularly light that strikes the surface of the sensor from off axis (not perpendicular to the surface). This is also the reason why lenses designed for digital cameras have anti-reflection coatings on the rear element; this tries to stop light reflecting off the sensor, then hitting the rear element, then reflecting back onto the sensor etc etc, generating a kind of ghosting effect. This is not so much of an issue with film as film does not reflect as much light and can absorb it evenly from off axis directions.

Thanks Taz. So it looks like the lens is doing what it should do and that "F" settings are not the same on different cameras. I was under the impression that f22 should make everything sharp from front to back. Seems like a lot to do with sensor size.
So If I get a new lens I might have the benefit of the anti reflection coat on the glass. I agree that it looks nice if the background looks blure but I was testing a few things and thought f22 will give me heaps of depth. And it seems to be very extreme that sometimes the nose is sharp and the ears are not. Will be a good thing if you can control it although you do not always get f16 or f22 depending on light.

Looks like I need another few thousand test shots

Matt