Macro Work - DPChallenge Forums

12/31/2005 06:55:39 PM · #1

I've been doing a lot of macro work with my Sigma 105mm 2.8. Because I use 3 flashes, my choice of aperture is simply a DOF vs Sharpness issue. I've noticed that above f/22, severe softness is inevitable, but the DOF is still too shallow for some of my subjects near 1:1 magnification.

I've been looking at the Nikon 60mm 2.8 macro. My question is whether this lens may resolve some of my issues. Basically, the DOF will be better for a given aperture with the 60mm, but the actual aperture size
at f/22 (for example) is much smaller for the 60mm, therefore causing more diffraction.

105mm/22 = 4.8mm
60mm/22 = 2.7mm
60mm/12.6= 4.8mm

Now, if the softness of the 105mm is ONLY due to diffraction, we could except that I would need my aperture at 12.6 on the 60mm to have the same diffraction limited imaging, therefore losing the DOF advantage of the 60mm lens.

So how can I go about increasing my DOF in 1:1 macro photography but maintaining sharpness?

Anyone have a solution to my problem?

12/31/2005 06:59:42 PM · #2

Actually, there is no advantage of DOF switching to the 60mm from the 105mm. If both lenses are at 1:1 at the same AV the DOF will be the same.

12/31/2005 07:12:18 PM · #3

Originally posted by kyebosh:

Actually, there is no advantage of DOF switching to the 60mm from the 105mm. If both lenses are at 1:1 at the same AV the DOF will be the same.

But say your taking a portrait of someone. If you want a blurrier background, you cant double your distance and focal length to get a shallower depth of field even with the same magnification (since you'll crop the face in the same way)

So DOF is not a direct function of magnification, but of focal length and aperture.

right?

12/31/2005 07:16:05 PM · #4

in the case of macro photography, 1:1 on any lens is the same FOV. When you have the same FOV on the same sensor at the same AV you have the same DOF.

//www.dofmaster.com/dofjs.html

try it with say... 50mm at 10 feet, 100mm at 20 feet, same AV, same camera.

12/31/2005 07:30:20 PM · #5

Ok, maybe this is a misunderstanding... what's an AV?

12/31/2005 07:31:49 PM · #6

Originally posted by labuda:

Ok, maybe this is a misunderstanding... what's an AV?

Aperture Value.

12/31/2005 08:36:58 PM · #7

That's what I thought. So basically, the DOF calculator is starting to freak me out. I mean, DOF is obviously very different when you crop someone's face with a 200mm at 2.8 vs 18mm at 2.8.

You could maybe argue that the DOF is the same if you keep the aperture SIZE (in mm) the same. in which case, 20mm f/2.8 would be equivalent to 200mm f/28.0 (But even then, that's probably wrong)

Message edited by author 2005-12-31 20:41:44.