Bright background and decrease in contrast

[arashdejkam]

Hello Everybody,

 

When I shoot something against a very bright background like a head

shot with the sky as background

I do spot metering on the subject and the subject becomes well

exposed and the sky is

rendered plain

white as expected but the contrast of the subject decreases very much

(like when you photograph something from

behind a dirty glass), why does this happen? does it have something

to do with physical behaviour of light or

it is just a problem with digital cameras?

 

Thanks in advance.

[bobatkins]

It's flare. It's due to light bouncing around and getting where it shouldn't due to internal reflections inside the lens and camera. It's not directly related to things being digital.

[arashdejkam]

Thanks Bob, this is very interesting, when I read lens reviews I thought when they talk about "flare" it only means those circullar shapes on the photo which you can simulate using photoshop>render>lens flare. you opened my eye ;) so low-flare lenses don't have the problem I mentioned above?

[bobatkins]

"Flare" covers a multitude of sins. There's "ghosting" which is multiple images of a bright light, "aperture ghosting" which reveals itself as multiple colored images of the lens aperture, "veiling" which is an overall reduction in contrast due to multiple diffuse reflections within the lens body, "halos" which can be all sorts of bright streaks in the image - plus any combination of the above.

 

The better the lens, the better the anti-reflection coatings on the elements, the better the internal baffling and reflection supression, the less flare you'll see. A lens hood helps if the bright stuff is outside the frame, but does no good when the bright light source is part of the image.

 

All lenses some some flare under extreme conditions. The best bet for a cheap lens with low flare might be one with few elements such as a standard 50mm lens, assuming the coatings are good. The more elements, the greater the likelyhood of flare problems. Low cost zooms tend to show quite a bit of flare.