Saturday, November 17, 2012

Aperture and Light Sources Experiment

Some weeks ago I read an article about how aperture influences the appearance of light sources in a photo. (Sorry I can't find this article anymore.) On my recent vacation I wanted to try this out for myself. One morning at a lake I got a nice scene with low sun, colorful Fall trees and the lake in the back. Although the mentioned article was about lights in night shots I thought the sun might be a nice light source for playing with different aperture values.

This first photo was taken with an aperture value of f/10. It is quite a nice scene with nearly no disturbances. The appearance of the sun is beautiful. It shows some nice rays and looks bright and sparkling. There are only few and weak spots  and you can see nearly no lens flare effect. I like this one very much.

I took the second photo with a much higher aperture value of f/22. The most visible difference is the appearance of the sun. It is now smaller but with much more intensive rays. This is because the light is more diffracting at the edges of the aperture blades. In this photo you can clearly see that the aperture of the lens I used has 6 blades. When I saw the preview of this photo at the camera screen I thought: Wow, looks great. But at home on my large monitor the photo showed a lot of disadvantages. First of all it looks blurred. This is a usual behaviour with high aperture values and is an effect of diffraction. Another big disturbance is that ugly and huge lens flare spot at the bottom of that yellow tree. But there are further things that disappointed me. Just above the yellow tree there are two darker spots. A further dark spot is above the right sun ray and there are more around the whole image. These are dust particles on the sensor. They are invisible or weak with lower aperture values but with higher ones they suddenly get clearly visible. Same with dust at the front of the lens. It is usually invisible but with high aperture value in combination with front light it appears as bright spots. You can see it around the sun and the center tree. I must admit that in the end I do not like the photo very much even if the sun has awesome rays.

My conclusion out of this experiment is that with higher aperture values light sources may look more like stars with beautiful rays, but I also learned a lot about the disadvantages of those settings. It will always be a balance between good image quality and nice looking light sources. As the dark season is just beginning the chance is good that I will take some new night shots within the next months. And then I will play again with aperture values to see how it influences street lights. Maybe in the dark the dust on sensor and lens will not that much visible.

At last just the other camera settings for both photos. I used my EOS 600D with my EF-S 18-55mm kit zoom lens at a focal length of 18mm. Even it was bright light I chose an ISO value of 200 to get reasonable shutter speeds at high aperture values. The camera was in Av mode with fixed aperture value and calculated shutter speed automatically.

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