How shallow can you get? — Messing around with lenses

Just before midnight, I took a look at my bed and tried to figure out whether I should blame entropy or Murphy's Law for the current state it was in. It then struck me that this mess was suitable for demonstrating several properties of camera lenses.

So I upped the geekiness in the room by a notch and brought a few figurines out of their boxes to experiment with varying focal lengths, levels of magnification, and degrees boke.

Canon EF-S 18-135mm f/3.5-5.6 IS

18mm, f/3.5

Canon EF-S 18-135mm f/3.5-5.6 IS

48mm, f/4.5

Canon EF-S 18-135mm f/3.5-5.6 IS

135mm, f/5.6

Canon EF 50mm f/1.8

50mm, f/1.8

(1) 
Although prime lenses are nowhere near as convenient as zoom lenses when it comes to framing subjects, they're still irreplaceable when it comes to capturing boke. Having a larger maximum aperture means that a shallower depth of field is possible, allowing better isolation of subjects in the photograph by blurring out unnecessary/distracting details in the background or immediate foreground. Here, the lowly EF 50mm f/1.8 easily outperforms the EF-S 18-135mm f/3.5-5.6 which was set to 48mm.

For those who insist on using zoom lenses with relatively smaller maximum apertures, the only option available for forcing boke of noticeable quality would be to back away from the subject and using the longer telephoto end of the lens. As demonstrated by the first 3 photos, the background gets blurrier as the focal length of the lens is increased from 18mm to 135mm.

Lensbaby Sweet 35 optic on the Composer Pro

35mm, f/2.5

Lensbaby Sweet 35 optic on the Composer Pro

35mm, f/8

Lensbaby Sweet 35 optic on the Composer Pro

35mm, f/22

(1.1)
Conversely, switching to a smaller aperture (ex. from f/2.5 to f/22) will result in having more objects in focus.

Here, even the Lensbaby, which is specialized for producing blur, can have sharp details in the background and immediate foreground if the smallest aperture is used.

Lensbaby Fisheye optic on the Muse

12mm, f/4

Lensbaby Fisheye optic on the Muse

12mm, f/8

Lensbaby Fisheye optic on the Muse

12mm, f/22

(1.2)

Switching to a wide angle lens such as the fisheye makes capturing boke difficult, if not impossible. This can be a blessing for casual camera users who have no intention of dealing with the complications of focusing.

Lensbaby Fisheye optic on the Muse

12mm, f/4, minimum focusing distance

Canon EF 50mm f/1.8 on reversing ring

50mm, f/1.8

(1.1) explains the inherent limitations of using a reversing ring. Although it is, hands down, the cheapest option for macro photography, most of the cheap setups do not allow manual or automatic adjustment of the aperture. As such, cheapskates such as myself are stuck at maximum aperture of the lens (f/5.6 in this case), and the resulting depth of field is razor thin. Simply put, moving the subject by a few millimeters is enough to throw it out of focus.

Besides the closer minimum focusing distance, another feature that sets dedicated macro lenses from other lenses is the minimum aperture size. Whereas most lenses could be stepped down to f/22, macro lenses could go all the way up to f/64. This means that more of the subject could be kept in focus even at the closest focusing distance.