Monday, September 14, 2009

APS-C vs FF vs P&S Macro

I am sure you know what Point & Shoot aka Compact camera is. But what's APS-C? What's FF? Let's take a look at this image:

Shot at life size ie 1:1, or 1X, with a Canon 40D. What lens? It doesn't matter, if it's 1:1, it's 1:1, regardless of what macro lens you used to shoot it.

Shot with a Canon 40D, Canon MP-E65 1X-5X Macro Lens and Canon MT-24EX Twin Flash.
IMG_5377 copy

40D is an APS-C with a 1.6X crop factor. Its sensor dimension is 22.2 x 14.8 mm and the image was shot at 1:1 i.e. life size, so naturally, you can more or less guess the actual size of the wasp. If you say 22mm including the antennae, yep, you're right!

What if i used the same lens but an FF (full frame) DSLR such as the 5D or 5DM2 (or D700, D3) and shot the same wasp at the same distance? Would it take up almost the whole width of the frame as the shot taken with the 40D? Yes? No?

Well, no, of course. A FF's sensor size is normally 36mm x 24mm. The same wasp would still appear as 22mm on the 36mm frame...that's about only 61% of the width.

Therefore if you want the wasp to fill up the frame as it did with the 40D shot, you'll have to either:

1) increase the magnification to 1.6X, and the 22mm wasp will appear as 22 x 1.6 = 35mm in the FF sensor. However, do be aware that at higher magnification, you get thinner DOF.

DOF = 2 N c x [ (m+1)/m^2]

N - f number,
c - circle of confusion, = 0.018mm for aps-c, 0.029mm for FF,
m - magnification

How much DOF did you lose? Let's calculate. Assume we shoot at F11:

So with a FF at 1.6X, the DOF = 2 * 11 * 0.029 [ 2.6/1.6^2] = 0.648 mm

For APS-C, 1X, F11 as well, the DOF = 2 * 11 * 0.018 [2/1] = 0.792 mm

So there you have it, you lose as much as 0.792 - 0.648 = 0.144mm of DOF

2) still shoot at 1:1 but crop away about (100 - 61 = 38.9%) of the frame. You'll notice that you actually gain a bit of DOF by shooting with a FF then crop to the 1.6X crop factor.

So with a FF at 1X, the DOF = 2 * 11 * 0.029 [ 2/1] = 1.276 mm

For APS-C, 1X, F11 as well, the DOF = 2 * 11 * 0.018 [2/1] = 0.792 mm

So there you have it, you gain as much as 1.276 - 0.792 = 0.484mm of DOF by shooting at 1X with the FF and crop to 1.6X crop factor.

So what about the P&S cameras? Say the Lumix LX3. The sensor size is 1/1.63". Hmm..i am not too sure what that means either but i know Uncle Google or Wiki are always there for me :). This is what i found. Scroll down to check out the table:

A 1/1.6" sensor has a dimension of 8.08 x 6.01 mm. That's like 36/8.08 = 4.46X crop factor! My 40D's crop factor is only 1.6X (36/22.2).

If you have already grasped the concept of crop factor vs DOF, then you will surely know that you get even higher print magnification by shooting with the P&S. The other way to look at it is this - You don't have to get as close to fill up the small frame of the sensor (8.08mm). If you still don't get it..go back and read (1) eg the DOF advantage of shooting with a 1.6X. The only difference here being we're talking about even higher crop factor i.e. even bigger DOF advantage.

But of course, smaller sensor size also means poorer Signal to Noise win some, you lose some!


  1. This is a wonderful guide! Just the thing I was looking for since I'm looking to upgrade from my current APS-C camera. Thank you! :D

  2. Thanks Kurt i gain many knowledge from your wedsite, thanks for sharing .



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