Thursday, January 31, 2013

Knitwear Photography Pt. 2: Lenses

Last week I talked about what equipment I currently have. This week I wanted to go over why I chose certain lenses over others. I'll start by focusing on my current favorite: the 50mm f1.4.

Among 50mm Canon lenses, you currently have a choice between the f1.8, f.14, and f1.2. I will be passing over the f1.2. It costs over $1000 more than the f1.4. What you are paying for is the extra stop, but the quality is very similar. In my opinion, there is a bigger difference between the f1.8 and f1.4. Cost wise, there is currently a $200 difference. But what you gain with the extra $200 is a hardier lens, an extra stop, and the number of blade in the aperture. It was the blade number that pushed me into getting the f1.4. The f1.8 has five blades, which make the aperture pentagonal. The f1.4 has eight blades, making the aperture octagonal. Why does this matter?

The shape of the aperture affects the bokeh. Bokeh is the out of focus light. With a pentagonal aperture, the bokeh is much less circular. In the picture below, you can see that the bokeh has an octagonal look to it at f4.0. When the camera is set to f1.4, it is hardly noticeable. If I was using a lens with 5 blades, the bokeh would be much more angular. But because an octagon is much closer to a circle than a pentagon, it looks more natural. Certain f stops will make the shape of your aperture more obvious than others.

The other lenses in my arsenal are a wide angle and a telephoto. There is a distinct difference in the kinds of photos you can and where you'll have to stand in order to take said photos. A wide angle does indeed capture a wider angle. It also elongates the background from the foreground. A telephoto lens does the opposite. It compresses the background with the foreground. I've put in an arrow pointing out the same leaf in the first two pictures. Notice how the leaf looks much further away in the image taken with the wide angle lens. In the photo taken with the telephoto lens, the leaf looks like it practically on top of the yarn. 
I've also added an image take with the 50mm to see how it compares to the other two lenses. All images were taken 1/100, f5.6. I used the extreme ends of my wide angle and telephoto so you could see their full capabilities.

Here is an image showing where I was standing for the above three images. The arrow is pointing at the yarn. The first "X" shows where I was standing when taking pictures with the wide angle zoomed completely out at 16mm. When taking pictures with the wide angle lens, I practically was touching the yarn with the lens. The second "X" indicates where I was standing when using the 50mm lens. The third "X" is where I was standing when I was using the telephoto lens zoomed completely in at 135mm.

When zooming in and out with a camera, keep in mind that you are not simply magnifying the image. You are changing the focal length of the lens. The focal length refers to how far light is having to travel to hit the camera sensor.  With a shorter focal length such as 18mm, you have a wide angle of view, but a lower magnification of the image. And as we saw in the images above, the lower magnification of the wide angle lens made the background look further away from the foreground. The longer focal length of the telephoto lens shows a narrower view, but it also increases the magnification of the image. This is why the leaf looked closer to the yarn in the above image. To take full advantage of your lenses, sometimes you'll need to walk closer or further away from what you are photographing rather than zooming in or out. 
Certain lenses such as the 50mm have fixed focal lengths. This means that it will always be 50mm, so you have to move yourself around to get the image you want rather than standing still while zooming in or out. Of all the focal lengths, the 50mm is the closest to what our eye sees. So images taken at this focal length will look the most natural. Other focal lengths seem distorted to the eye. 

I feel that a 50mm is a good all around lens to use for knitwear photography. But if you are buying a lens to use for other things like landscapes or wildlife photography, you may need to look into something different. To finish off this post, here are a few things I look into when buying a new lens.

1. Maximum aperture: I like to work in low light, so I look for lenses that allow me to do so. Right now I'm not looking at lenses that don't go down to at least f2.8
2. Number of blades that create the aperture: I want my bokeh to look as circular as possible. 6-8 blades are a must.
3. Hardiness: I want a lens that can take a beating. A cheaply made lens won't cut it for me.
4. Purpose: What kind of pictures am I going to be able to get. What will my restrictions be. ie. A wide angle lens is great for capturing images in a tight area such as a room. But it is less useful if you want to take pictures of wildlife.
5. Weight: If the camera is too heavy, I'm less likely to carry it around.
6. Zoom Mechanism: Does the lens visibly move when you zoom in or out. The outside case of some lenses covers the movement, so the lens always appears to be the same length. Others, like the lens in the above image, visibly moves in or out. The advantage to having a lens who's housing covers the zoom mechanism is that dirt can't stick in it.

Next time I plan on talking about lighting and working with a reflector. Also, if there are any particular lighting points you guys are interested in, do leave a comment. I want to make this series as useful as possible.


Pumpkin said...

This was a very useful post, I've never seen these points explained this well before. The example photos are fantastic. You've definitely sold me on the f1.4, I'll be saving up for one (I'm hoping for a decent tax refund this year). Thank you so much for taking the time to carefully craft these posts!

Anonymous said...

Very interesting! Well thought out and beautifully explained. Thank you! I didn't know about the bokeh.

Anonymous said...

This is so interesting. I just bought a new body (Canon 60D) and got a zoom lens to go with it. I've been playing with my new lens a lot, but this has reminded me not to give up my 50mm, which has just been sitting on my desk.

Lighting-wise, I'd love to know how you would handle indoor crappy lighting. My apartment gets almost no good light, and when it's too cold/gross to be outside and the photos can't wait, I'd love to know how to maximize what I have.

Unknown said...

I've never seen these things explained before, thank you! Do you know of any online sources or books that you would recommend for learning more about what the f stops and the focal lengths and all that? (Also, as an aside, nice yarn choice! I just purchased some and am looking forward to making my first colorwork socks with it.)

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