Photography: Prime lenses, focal length, and minimum focusing distance comparison
After having had my first DSLR (an entry-level Canon with an APS-C sensor) for about 18 months, I finally decided that I prefer prime lenses to normal or telephoto zoom lenses. The main reason is because it enables me to afford faster lenses (lenses with a larger maximum aperture) and therefore take sharper photos in lower light. The secondary reason is because the higher end telephoto zoom lenses are super heavy—for me, anyway—especially if they have image stabilization, which is pretty much a must unless you’re using a tripod.
So I needed one more prime lens, something wider than my 40mm pancake lens. Luckily, towards the end of last year Canon introduced the EF-S 24mm f/2.8 STM with a price tag under $200. To make sure it would work for me I used my 18-55mm kit lens to take photos at both 24mm and 40mm. It did indeed work for me, so I ordered one.
I love it—almost as much as my 40mm, but not quite.
Once it arrived, I decided to take out all my prime lenses (except the 50mm f/1.8 II, otherwise known as the “plastic fantastic” or “nfity fifty”, which I hate). I lined them up and proceeded to do some tests. For readers who may not know, the “effective” focal length is what it would be comparable to on a camera with a full frame sensor (for Canon cameras with APS-C sensors you multiply the focal length by 1.6, so 24 * 1.6 = 38.4 (rounded down to 38mm). The minimum focusing distance (MFD) is how close you can get to your subject and still be able to focus on it clearly, and the angle of view (AOV) is exactly what it sounds like.
Since this was just a practice exercise for me to understand the differences in the focal lengths, I wasn’t concerned with lighting and didn’t drag out the tripod until I used the macro lens, so some images are less than razor sharp. Most of the images were shot in AV (aperture priority) mode.
The following is a list of what I tested and the results.
EF-S 24mm f/2.8 STM: 38mm effective, AOV 59° 10’, MFD 6.30 in
EF 40mm f/2.8 STM: 64mm effective, AOV 57° 30’, MFD 11.81 in
EF 85mm f/1.8 USM: 136mm effective, AOV 28° 30’, MFD 2.79 ft
EF 100mm f/2.8 Macro USM: 160mm effective, AOV 24°, MFD 1 ft
The general rule of thumb is that you use extension tubes with wide/normal lenses and close-up lenses with telephoto lenses: 250D (+4 dioptres) with 30 to 135mm lenses, 500D (+2 dioptres) with 70 to 300mm. Both extension tubes and close-up lenses can be stacked. With close-up lenses you might lose a bit of sharpness, especially if you use cheap ones (which is why I opted for the Canon brand), but you don’t lose any light. With extension tubes you don’t lose any sharpness but you lose some light (how much depends on how many you stack). With some of the cheap extension tubes your auto-focus won’t work because the necessary electronics aren’t present (again, I opted for Canon—the build quality is great).
Here’s a reference image of the paw print motif on my coffee cup for the close-ups:
Here’s the same 24mm lens with a 24mm extension tube added to it. As you can see, it’s a bit blurry due to the slow shutter speed, but it’s even larger than 1:1 life size (as with the macro). I don’t know what the actual ratio is because I hate math and was too lazy to look up the formula to calculate it. BTW, that shadow you see on the left side is actually the camera lens—yes, it was that close.
Please ignore the dust on the phone!
100mm Macro Lens
Best for actual macro work as there is no loss of sharpness or light. Nice bokeh, good for portraits (but the 85mm is better, IMO). Also good as a short-medium telephoto lens, but it is heavy and has no image stabilization (IS), so plenty of light will be the best bet (so faster shutter speeds can be used to compensate for camera shake). Forget trying to do handheld video with it.
There’s not a significant difference between the results of the 85mm with the 250D close-up lens and the 24mm lens at MFD, so I think the 85mm will be best reserved for portraits, as originally intended, or for skittish creatures who don’t like you getting too close. As with the 100mm macro above, the lack of IS means it’s not suitable for video, but the wider f/1.8 aperture allows for more light & faster shutter speeds in overcast or nighttime photo situations, so that’s another plus. It has a nice bokeh.
Still my favorite. Decent bokeh, nice walking around/street lens. Also good as a portrait lens (remember, I’m on ASP-C sensor). To be honest, I’ve never attempted to do video with it—maybe that needs to be my next test. Using the 25mm extension tube makes close-ups almost life size—another plus, in a pinch.
Very nice nice walking around/street lens—AOV is similar to that of the human eye. Nice close-ups, but you need to get in really close, so it’s only useful in that regard if you’re shooting something that’s inanimate or not skittish. The 25mm extension tube makes you get way too close, so maybe the 12mm one would work nicely in a pinch. I haven’t tested this one for video yet either as that’s not really my thing. My understanding is that with wider angled lenses like this, IS isn’t as critical. I guess I need to find out if that holds true with an APS-C.