Keeping the Background Sharp

Just recalled one of my colleague, who bought a GF1 for a holiday trip, came back and complained to me why the images are blur. After some clarification, it is the background of group photos are blur, not the subject itself (the people in the group photo). The effect of this “blur” is even worse when taking a group picture with a large landmark at the back. Unlike myself, my colleague is a compact camera user upgraded to GF1. Therefore, has very little understanding of technicalities such as shutter speed, DOF, aperture etc.

Recalling on my own trip, I also had similar problem when wanting take a photo of my wife with a landmark at the back. I have some understanding of DOF, which thought my to lower down my aperture setting for a sharper background. However, it wasn’t sharp enough even at f5.6, with the subject approximately 2 metres away. So how much lower should I set? So I decided to do a quick test.

Short of a test subject, I have the Starbucks bear here (about the size of a human head) sitting on top of my tripod, frame it with enough view of the tripod to portray a subject from head to upper body. My neighbour’s roofing and window will act as the background landmark. The GF1 is mounted with the 20mm f1.7 lens, and on a table with a Joby Gorillapod.

P1150301_GF1_Full

Below are sequence of shots taken with different aperture settings, shown in 100% crop. Focus was fixed on the bear, and fixed ISO of 800 (it’s kind of late evening). Shutter speed was adjusted accordingly so that the background is well exposed. Do note that my own window has a layer of mosquito net, which will affect sharpness slightly.

P1150301_GF1 P1150302_GF1 P1150303_GF1

20mm f1.7 @ f16

20mm f1.7 @ f14

20mm f1.7 @ f11
     
P1150304_GF1 P1150305_GF1 P1150306_GF1

20mm f1.7 @ f8

20mm f1.7 @ f5.6

20mm f1.7 @ f4

At the highest aperture setting of this lens (f16) the image wasn’t as sharp. Seems like diffraction has set in. Below aperture f11 we can see the background starts to get blur. The background seems to be sharpest from f11 to f14. Even the mosquito net is visible at these apertures. So, this is a mental note to self that, next time if I’m in a situation of shooting a small group photo and want the background tact sharp, f11 onward it is.

By the way, there's a good article about Diffraction at the Micro 43rds Photography blog. Just in case you want to know why images at f16 wasn't sharp.

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I remember my first experience of using a SLR was about 10+ years ago. My father own a Nikon F3 with a Nikkor 24mm f2.8 prime, and a push-pull zoom-Nikkor 35-105mm. With his permission, I took the small dry box containing the gears from him and started playing with it photography. Still a student then, I learned about photography through the F3 manual, and seek advice from some of my friends who were also into photography. Taking photo is the best way to learn, but I do not have the luxury of experimenting too much since film isn't cheap, and developing a 36-shot row would cost around RM30 (I think) for 3R prints, not to mention not all shots are good. Eventually, I stopped due to cost, and my studies. I was reintroduced back into photography about 3 years ago through a colleague. He also came from the film era, and were still shooting with his fully manual Nikon FM2 before getting his first DSLR, Nikon D70. While working on a project in Singapore, I bought my first DSLR, Nikon D70...
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