17 December 2013 (updated 9 May 2015)

Stu Maschwitz has interesting advice on how to take good family photos for under US$1000. The long and short of it is buy a cheap DSLR and use it with a f/1.8 50 mm prime lens set to wide-open. This combination will give fast exposures (to freeze motion), excellent bright-light and low-light performance, and a deliciously shallow depth of field. In photographic terms, I can’t fault it.

So, you spend your $1000 (or a little less), and then it’s down to you. Maschwitz writes

Now that you’ve bought all this stuff, the only thing that remains is the habit of actually doing this stuff. Your iPhone camera is damnably good. Good enough that often you’ll be tempted not to schlep your big, heavy DSLR. If you succumb to this temptation, we’re right back to terrible photos.

How big is “big”? How heavy is “heavy”? Maschwitz’s suggested Canon DSLR and lens weights 710 g (about 1.6 lb). Before you zip over to amazon.com and start pressing buttons, visit your local camera store, and try out one of his suggested combinations. Think about carrying it with you everywhere you go with your family - good photographic opportunities can crop up when you least expect them. If you’ve left your DSLR at home or in your car, then it’s not going to take very good photographs. Having mulled this over, if you are prepared to carry a DSLR everywhere, then follow his advice.

If you’re not up for carrying a DSLR, what can you do? Are you condemned to “terrible photos” from smartphones? Well, no. Just follow the spirit of Maschwitz’s advice: buy the fastest camera you can afford that you are prepared to carry with you at all times.

Now, by “fastest”, I mean “fastest equivalent f-number at 75 mm equivalent focal length”; I explain these terms in my post on compact camera electro-optics. I’ve chosen an equivalent focal length of 75 mm since a 50 mm lens on a entry-level DSLR has an equivalent focal length of about 75 mm. That’s an excellent focal lengths for outdoor or individual portraits, and compresses the depth of focus quite nicely; Maschwitz didn’t choose it by accident.

To determine the equivalent f-number N’, you need to multiply the sensor crop factor C and the lens real f-number at 75 mm equivalent focal length N. So, for example, the Canon T6i/750D DSLR (crop factor C of 1.6) with a Canon 50 mm f/1.8 lens (real f-number of 1.8) has an effective f-number N’ of about 3. It takes a little bit of effort to dig up the necessary characteristics, but the reviews on dpreview.com are often helpful. As a short cut, they often show plots of equivalent f-number against equivalent focal length. For example, this figure from their review of the Canon G15.

So, let’s look at some the equivalent f-number for some cameras. For the iPhone, I’ve assumed a digital crop to increase the equivalent focal length from about 30 to about 75 mm.

CameraWeight (g)Equivalent f-number N’
Canon T6i DSLR with 50 mm f/1.8 lens6853
Sony a6000 with 50 mm f/1.8 lens5463
Sony a6000 with kit 18-55 mm f/3.5-f/5.6 lens5589
Panasonic LX1003936
Canon G7X3048
Sony RX-100 III2908
iPhone 511045

You can see that in terms of image quality, the only thing that gets close to Maschwitz’s recommendation is a Sony a6000 with a f/1.8 prime lens. That’s not a surprise, since a a6000 is basically a DSLR without the mirror. Losing the mirror saves weight and bulk; it’s worth considering. Other major manufacturers have mirror-less cameras similar to the a6000.

Maschwitz disparages kit lenses. Comparing the Sony a6000 with the kit 16-50 mm lens to the same body with a prime 50 mm f/1.8 lens, you can see why. The kit lens is a lot slower, and the photographic performance is more like a compact camera without the advantage of lightness and compactness.

The Panasonic LX100, Canon G7X, and Sony RX-100 III are photographically significantly worse than the best options, with effective f-numbers of about 6 to 8 compared to 3, but have about less weight and less bulk. They will easily fit in a hand-bag, man-bag, satchel, or jacket pocket, and the Canon and Sony will even fit in a trouser pocket. These cameras is photographically worse than a DSLR, but they are so much better than even a good smartphone; an iPhone when cropped to an effective focal length of 75 mm has an effective f-number of 45. There are many other cameras with similar price and bulk, but most have slower lenses or smaller detectors and will not perform as well.

So, here’s my modification to Maschwitz’s advice:



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