Could someone do the FULL math, please?

I’m getting a bit tired of all the frolicking about “fast” m4/3 (micro four-thirds) or other crop sensor lenses that are so much lighter and so much more compact than their full frame equivalents, and how people are wondering what Nikon or Canon will “do about that.”

Lately, Olympus’s 40-150mm/2.8 telezoom gets a lot of attention. Let’s have a look: it weighs 1.94 pounds (880 grams) and is 6.25 inches (15.8 cm) long. For a lens that offers the focal length equivalent of an 80-300mm on full frame, that sounds pretty cool at first, especially at f/2.8… but wait.

The crop factor applies to the field of view as well. So on a m4/3 camera with its 2.0 crop factor, that lens translates to the full frame equivalent of an 80-300/5.6 lens! Yes, you get the brightness and “light gathering ability” of f/2.8 – but you’re not getting the (smaller) depth of field of an f/2.8 lens. You’re getting the full-frame equivalent DOF of an f/5.6 lens!

Depending on where your priorities lie (hello, subject isolation), this may or may not be (very) important. Yes, there’s probably thousands of people who don’t care about that, because subject isolation isn’t everything. Of course, I get it. But if you want a “true” 80-300/2.8 equivalent for a 2.0 crop sensor, it would have to be a 40-150mm/1.4 lens! Now how much would that cost, and what would its size and weight be?

Dog standing on a mossy rock.
Forest guardian — near Frillensee, Inzell.
Our dog Toni, photographed with a 50mm lens at f/1.8 on a full frame sensor camera – if you wanted to make this photo with a m4/3 camera, you’d need a 25mm/f0.9 lens. Which doesn’t exist.

Or look at it this way: my cheap-ish Nikon 70-300mm/4.5-5.6VR weighs 1.64 pounds (744 grams) and is 5.67 inches (14.4 cm) long. If I do the full math and transfer that to the m4/3 specs and crop, that’s a 35-150/2.25-2.8 lens. It both weighs less and is shorter than the Olympus lens. Hu?

The Olympus 40-150/2.8 costs $1500. The Nikon 70-300/4.5-5.6 costs $600. Yes, that’s comparing apples and oranges because the Nikon is “slow” in its light-gathering abilities* and there’s no doubt that the consumer Nikon zoom is no optical match for the Olympus. But on the other hand, it doesn’t even cost half as much as the Olympus lens!

So can we please stop this black & white thinking and the useless comparisons? Mirrorless crop sensor cameras and full frame DSLR are two different camera systems. Right? They can happily exist next to each other, and they can not be compared directly. Each has its advantages and disadvantages. Get over it.

Rant over.

*) but then again, larger sensors are producing better high ISO quality. Maybe not worth full two stops, but still. 😉

10 thoughts on “Could someone do the FULL math, please?

  1. I have noticed this for some time, but kinda in reverse after having used my old film cameras. I just never could get the same DOF from my crop sensors with equivalent lenses on my film cameras and it really bothers me. With a 5.6 lens on my 4×5 film camera the DOF is amazing but with a 2.0 lens on my Fuji XE-1 it is barely noticeable. On the other hand, my Fuji with some $20 adapters allows me to use all my old Zuiko/Minolta/Pentax lenses and they work great!

      1. I have been looking at the A7 line up and am impressed. My issue is that their multiple exposure is more of an after-thought through an app and limited to two exposures…that could be deal killer. And battery life? I’ve read the reviews….battery life should not even be a thought, this isn’t 2004. Of course the real bust is lenses….bodies come and go, but lenses are like children…..
        Well, I have about another year before I make a plunge.
        But it’s looking more like the D810

      2. Currently using the 700 full frame. The 750 looks nice, but it’s limited to 3 frames for multiple exposures. My 700 is aging so I am looking at a replacement that will give me the multiple exposure options as well as video

      3. Well, that pretty much limits it to the D810 then. Which you’ll never regret getting. The D800 is a fantastic camera and it got some necessary refinements with the D810. You cannot possibly make anything wrong with it IMHO.

  2. It’s “MATHS”. With an “S”. Jesus …. 😉

    And while I agree (on paper) and own two FX Nikon Bodies, with all the expensive primes to go with ’em, it’s my Olympus E-M5 that comes out the most. Because it’s the smallest. And because portability is a factor, I use the E-M5 / 17mm F1.8 much more often than the D800E / 35mm F1.4. I don’t care how much better then latter is on paper, the former is better in my pocket. Don’t get me started on face detect, live EV preview, 5-axis IS ….

    1. First, it’s not necessary to call me Jesus. Alexander is just fine.

      Second, math vs maths… the latter is chiefly British, so you’re forgiven – and I think I can leave it like it is. 😉

      Third: I frankly don’t care what conscious decisions (a good thing!) you make to pick your favorite camera system – as long as you’re not trying to tell me that neither physics nor optics apply to your camera system and/or convince me that I’m missing out. I make the same conscious decisions about my camera system of choice, and I find the excellent photon gathering abilities of the big DSLR more important than size and portability.

      Forth (with regards to face detect AF and live EV preview) I suggest you consult the friendly manual of the D800 again. Mine does that stuff (face detect AF in “AF auto” mode reliably places the focus point on the closest eye; and pressing “OK” in live view switches between EV preview and normal live view).


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