Effect of aperture on resolution for macrophotography

see also:

Using the Olympus ZD 50mm f/2.0 macro lens with 2x TC:

These photos were taken with an Olympus E510 with ZD 50mm f/2.0 macro lens coupled to a Olympus ZD EC-20 2x teleconverter and a Olympus Ring Flash, mounted on a tripod and at a focus distance of about 0.3m (ie. not the closest focus and not 1:1) and prior to each shot, AF was used on the centre spot. This centre spot region is shown here as 100% crops with no in-camera or post-processing sharpening, just straight jpegs from the camera, cropped in PS and compressed for web display.

Aperture readings are those displayed in the camera and thus are the lens aperture multiplied by 2x to account for the EC-20 2x teleconverter.

A full image of the maple leaf - image width equates to about 40mm.

 

f/4 

slightly more exposed than the remainder - TTL auto-exposure used for all

image quality is still very good for a f/2.0 wide open aperture with a 2x teleconverter!
f/5.6

f/5.6 to f/11 are the clear winners as would be expected with this combination.
f/8
f/11
f/16 - wow -  am very happy with the detail here, I was worried diffraction would be having an impact, but as you can see, you don't lose much from f/5.6 whilst you will gain consider DOF.
f/22 - usable but diffraction stating to impact resolution
f/32 - we are really starting to lose detail due to diffraction limitations here!
f/45 - only use this if detail is not as important as depth of field.

Using the Olympus ZD 50mm f/2.0 macro lens by itself:

These photos were taken with an Olympus E510 with ZD 50mm f/2.0 macro lens at its closest focus (ie. 1:2) and a Olympus Ring Flash, mounted on a tripod and at a focus distance of about 0.3m (ie. not the closest focus and not 1:1) and prior to each shot, AF was used on the centre spot. This centre spot region is shown here as 100% crops with no in-camera or post-processing sharpening, just straight jpegs from the camera, cropped in PS and compressed for web display.

Note this is the reverse side of the leaf to the above shots.

f/2.8

slightly soft probably due to shallow DOF as the leaf is not flat.
f/4.0
f/5.6
f/8
f/11
f/16 - starting to get soft due to diffraction but still worth a try if you need the DOF.
f/22 - clearly soft

With or without EC-20 2x teleconverter at the same magnification:

As a general rule, you don't want to use a teleconverter if you can get away without it.

So at 1:2 macro magnification, the only advantage of using the 2x teleconverter is that it increases your working distance which may come in handy!

But how much do we lose in image quality?

Let's see at 100% crops of the centre:

above, the ZD 50mm macro alone at f/8

and the ZD 50mm macro with EC-20 2x teleconverter at f/11 (f/5.6x2) at double working distance to give the same magnification of 1:2

Strangely, the camera's auto TTL had to be adjusted to +0.7 to get equal histogram exposures for the EC-20 image and this image had two distinct peaks in the histogram compared with a much more subtle double peak in the image without the EC20, so the EC20 image is actually a bit more contrasty. I am not sure why the in-camera processing would do this or whether it is indeed a function of the EC-20.

Nevertheless, I think you would agree, there is not much degradation in image quality in using the EC-20 in terms of resolution and image detail, even when pixel peeping at 100% as we are. The differences in a print would be minimal.

This is one excellent teleconverter!! No wonder Olympus say its one of the sharpest every made!

 

ZD 50mm f/2.0 macro lens - brick wall at ~7m:

These tests were repeated to provide more consistency, with the same exposure (via checking histogram), custom white balance, ISO 100, AF prior to each shot, tripod mounted (oops forgot IS still on!), self-timer, mirror lockup 5 sec ("antishock"), each in-camera jpeg processed the same way in PS CS/2 - unsharp mask 100%, radius 2, threshold 1; resized to 7296 pixels wide to enable a 200% image to be viewed on the web, centre portion cropped and no jpeg compression applied.

I think you can see that the image degrades considerably at f/16 and f/22 as expected from diffraction limitations.

Remember, these are in effect 200% crops!

f/2.0
f/2.8
f/4.0
f/5.6
f/8.0
f/11
f/16
f/22