In my never ending quest to learn more in the field of macro and keep myself amused as my TVs still bust after 8 months a test tonight to determine the results of doubling the DOF by increasing aperture well above what I would normally use which is f16/f22.
I have always been made aware by reading of the increased diffraction at small apertures, have seen review controlled tests showing crops of the effect but never really looked at this in the real world.
So, the criteria for my test was to simulate a typical critter pic as per the shield bug I posted a few nights ago and to do this I used a match 15mm long (standard bug length) to simulate approx 3/4 length coverage in the frame and some green tomatoes with hairy stems, the hairs simulating fine hairs on a bug.
The object was to try and get an idea of image quality loss if I was only producing images for web viewing at 1100/1200 pixel width.
Equipment was D300 with 105VR and two SBR-200s attached to the lens front both in TTL mode. Tripod, remote and mirror up. Manual settings and focus.
Camera (film plane) to subject distance was almost the closest possible at 300mm.
From DOF calculator - 300mm @ f16 DOF = 3.2mm. 300mm @f40 DOF = 8.1mm
These Jpegs are SOOC at 'standard settings', opened in Elements 7, reduced to 1100 pixel width and then using unsharp mask at 100% 0.3 pixels on each. No other adjustments were made although I suspect there is a slight drop in exposure in the f40 one due to having the diffusers in place.
The focus point was the bright hair at the centre which I appear to have missed
f16, ISO400, 1/60th
f40, ISO400, 1/60th
I ran tests through to min aperature of f57
Any comments especially with respect to where any degradation in IQ between the two can be seen will be appreciated as always.