TAOP- IntroductionPosted: January 11, 2011
9.1.11 Exercise 1: Focal length and angle of view (p.16)
The aims of the exercise were to: –
- Establish the standard focal length of my camera
- Take 3 photographs of the same scene from the same spot utilising standard, wide and telephoto settings
- Hold each of A4 printed photographs and move them towards or away from me until the printed scene appears the same size as my view of the real scene to establish the distance from my eye.
a – Establishing the standard focal length of my camera.
My camera is an APS-C format Canon EOS 500D with a crop factor of 1.6x. I bought the body only and then purchased a separate EFS 15-85mm lens. My husband has a full frame Canon EOS 5D. I can use the lenses from his camera on mine but not vice versa (unfortunately for him). As an experiment, I focussed on the window looking through his camera viewfinder, with a prime EF 50mm lens. I then took my 500D with my EFS zoom lens and rotated it until I could see the same view widthwise. The lens is marked with 15; 24; 35; 50; 70 and 85 distances and, to my eye, the focal length looked around 30. I took a photograph so that I could look at the exif data and this showed 31mm, which is equivalent to 49.6-just about 50mm. (Just for comparison I took a photograph with my camera fitted with my husband’s prime 50mm EF lens and the exif data showed 50mm although my understanding is that this is actually a focal length equivalent of 75mm on my camera. Certainly, when I use the EF 100mm Macro which he donated to me I get much more magnification on my camera at the same distance than he does using it on his camera).
I decided I would set my own camera and EFS lens as near to 3mm as I could tell when I took the three photographs.
b- 3 photographs at different settings
To begin with I set the camera on AV priority, f11, ISO200 and evaluative metering. I used a tripod and switched off the image stabilisation on my camera.
“Standard’ focal length
I set my camera to what I thought was 31mm. The two views (unaided and through the viewfinder) did appear about equal. However, when I looked at the exif data of the photograph it only showed 29mm so slightly less than ‘standard’. This could have been due to the approximate markings on the lens. Also, I am slightly long-sighted so I don’t know whether that made a difference as well.
When I compared the photograph with my own view a comfortable viewing distance was holding it at a slight extension, which is the way I read a book normally. Obviously this allows for my longer sight. The birdbath appeared just about at the same spot as my own view. However, the distance from that to the stone table seemed slightly compressed, as did the distance between the table and the shed and beyond. I also had to make sure that I looked straight ahead without allowing my peripheral view to kick in so that I was looking at the same scene. Looking at this particular photo was like looking with a slightly flattened view. I also noted some flare on the photograph, which must have been caused by the sinking sun (on the left-hand side) bouncing off the conservatory windows. I don’t have a lens hood and must get one.
15mm wide-view lens
This was more like my own vision than the previous photograph in the sense that it included what was on the periphery although the birdbath seems further away. I also noted that the lens had included the lawn behind the birdbath, which I hadn’t been aware of at the time because I was looking ahead rather than down. The depth of field overall was more expanded. I think this is probably the type of view which an estate agent would use as it makes the side garden look slightly more expansive than it actually is. The front of the conservatory appears slightly distorted. I wasn’t sure whether I hadn’t got the image quite straight in the viewfinder. The other images did seem straight and I had checked the spirit level on the tripod. The lens flare was less noticeable.
85mm telephoto zoom
I had to hold the photograph well away to see similarity. I was immediately aware of the much more compressed depth of field between objects. Also, the stone table is more squashed, although it has more emphasis. To me there is a focus on the table, which leads into a reasonable composition, although I had the viewfinder just focussed straight ahead. As a photograph it appeals to me more than the two others, although I would have liked it to be clearer.
The whole process took much longer than I had anticipated. In fact it seemed to take all day! I gained more confidence in using the tripod, which is really good because previously I had avoided using one. My two mini macro projects (see above) had started me off but I can now set it up more quickly. However, I took two sets of photographs because there were too many shadows on the first set. Shadows can be very effective in images but on this occasion they subtracted from the effect I wanted. So I went back later in the day and re-took.
I only did minimal editing in Photoshop from camera raw, with no straightening etc as this might have cropped the images and changed the view. I have been given a good printer – an Epson Stylus Photo 1400 which I thought I understood how to use. However, the first photo came out looking posterized and, with help, I spent a long time going through all the settings again to make sure that I really did understand them. It’s set to be managed by Photoshop but it then reverts back to its defaults so I’ve learned that I have to systematically go through the settings every time to check they are correct. I also realised later that, in my haste to get everything printed, I had put the first photo paper in the printer the wrong way round which is why it came out looking posterized. Still, it did help me to understand my printer better.
In comparing the three images I learned that the longer the focal length the more the depth of field is compressed at the same f-stop so that objects seem closer than they are. A wider-angle lens captures more of an overall scene, whilst extending the depth of field, so that objects which are closer can seem further away. None of the different focal lens is exactly like my own view. As a photograph I preferred the 85mm image.