Field of View

So I was thinking about how does the focal length of a lens actually manifest itself to how much is my camera able to ‘see’. For example, if I have a 50mm lens, and I replace it with a 85mm, how much more/less is the camera able to capture. One measure of this is the ‘Field of view’ (FOV) or ‘Angle of View‘. Now given that the camera sensor is not square, the FOV in horizontal and vertical direction will be different. Without any reason to choose one, I focus on the horizontal FOV.

Shown below is the horizontal FOV (in degrees) as it changes with the focal length of the lens. The blue curve shows the FOV for a full frame camera (36mm wide sensor) and the red for a 1.6 crop factor camera (22.5mm sensor width). I have a Canon 30D which has 22.5mm sensor. So, a 50mm lens gives me a 25° horizontal FOV. Buying a 85mm lens would decrease that to about 15°. Although still not very intuitive, these numbers do give me something to visualize.

More modifications on my photoblog

Finally after months of wait, I can say that my photoblog is ready for launch. I know that I have been publicizing it from few months, but this is the first time that it feels complete. If you have seen the site in past week, go now and you will notice some changes.

1. The first major change is the recent comments tab, where all the top recent comments (top == 50) are documented. It should solve two problems – one, allow me to see who has posted on the pictures, and two, allow you to see if I/anyone else has replied to your comments. This will help in better communication, and help me to further improve with your useful comments.

2. The second one is the about page, where I have made a weak attempt to explain the relation of photography to me. I plan to update it as time passes, as I am more clear myself about what it means to me, nonetheless, its good enough to remove the under construction tag.

Is this front focus

I earlier had the problem of front focus on my camera, after getting it repaired, I tried a few focus test. I get mixed results on this, so anyone with more experience claim about the focus issues here?

Test 1

100% crop 1

This is the test chart from http://www.focustestchart.com/chart.htm. Here I feel that none of the lines are properly in focus. The pink box shows where I tried to focus. Is this because of low light condition.

ExposureTime – 1/200 seconds
FNumber – 1.80
ExposureProgram – Aperture priority
ISOSpeedRatings – 400

Test 2

100% crop 2

In this second test I just cranked up a Corel vector graphic and tried to focus on the monitor screen. This looks good to me and in focus.

ExposureTime – 1/25 seconds
FNumber – 1.80
ExposureProgram – Aperture priority
ISOSpeedRatings – 100

Test 3 (Worst)
100% crop 3

This last test blows me away, I try to focus on the corner and this shows a heavy front focus. Is this because of low light? Is this because the actual area where the camera focus from is slightly shifted? I just used the center AF point for all the three tests.

ExposureTime – 1/15 seconds
FNumber – 1.80
ExposureProgram – Aperture priority
ISOSpeedRatings – 100