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Archive 2016 · Same focal length and aperture... different DoF?

  
 
mikeski30
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p.1 #1 · p.1 #1 · Same focal length and aperture... different DoF?


Hi everyone!

Apologies in advance for the long story!

I'm a big fan of extreme macro insect photography, and have had some luck getting some halfway decent shots using a 105mm with extension tubes on an APS-C sensor camera (Nikon d7100 mostly).

For the longest time, I was using an older Sigma 105mm EX DG lens. I found that f11 provided just enough DoF to allow say, all the front eyes of a jumping spider to be in focus if I got it just right before diffraction started in. I never had any real luck with focus stacking of shots taken out in the field... probably a combination of my twitchy, flailing technique and skittish subjects. So basically I had to get it right in one shot, which leaves very, very little room for error.

After a while I got pretty good at tweaking all my settings (all fully manual) depending on the bug's environment (darker leaves, lighter bricks etc.), but for the most part with my flash and diffuser setup, I could reliably set my ISO to 100, aperture to f11, and flash to 1/2 power and be good to go; only changing the flash power settings depending on the environment.

I traded the Sigma in and got the Nikon 105mm IF-ED because I wanted the VR, and was excited to see how the Nikon would blow the Sigma out of the water in every respect. I set the camera up with all the usual settings, but found that f11 gave me nowhere near the same DoF that the Sigma had provided. I found that I had to stop down to f16 to even come close, but that's as far as I wanted to go because the in focus parts were starting to lose sharpness and detail due to diffraction.

I've read everywhere that f11 is f11 is f11, no matter what lens you use if they're the same focal length, but I swear these two lenses performed in wildly different ways. Has anyone ever experienced anything like this? Could it have something to do with the fact that the Nikon had internal focusing and the Sigma would extend? Or could it be that even the slightest variations in a lens's build would just be more evident when focusing much more closely with extension tubes?

Anyway, it's just been bugging me (no pun intended) for the longest time, and I'm just curious if anyone else has any idea what the issue might be (I could just be going nuts!)

Thanks all!

Mike

Nikon 105mm at f13
Nikon 105mm at f13

Sigma 105mm at f11
Sigma 105mm at f11



Apr 28, 2016 at 05:42 PM
Julian Nell
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p.1 #2 · p.1 #2 · Same focal length and aperture... different DoF?


I can't answer your question, but I can compliment you on your excellent jumper shots!


Apr 28, 2016 at 07:16 PM
tntcorp
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p.1 #3 · p.1 #3 · Same focal length and aperture... different DoF?


but did you maintain the same distance to the subject?


Apr 28, 2016 at 08:07 PM
Dalantech
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p.1 #4 · p.1 #4 · Same focal length and aperture... different DoF?


What you're seeing is the difference between shooting flat on against the subject and taking a shot at a "magic angle" -an angle that makes the most out of what little depth exists in the scene. In the first shot the angle of the front legs and palpes are different, and the front legs are out of focus. In the second shot both are at the same angle and in focus. Now the trick is to not only look for those magic angles, but start creating them yourself. Find something in the foreground to focus on, and then twist the camera slightly in your hand so you can lay as much of the depth around the curve of the subject. The higher the magnification the more you bennefit from it.




Apr 28, 2016 at 10:45 PM
LordV
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p.1 #5 · p.1 #5 · Same focal length and aperture... different DoF?


One other possibility is that the Nikon cameras report effective aperture rather than set aperture with lenses they recognise. this means that an aperture set at F11on the camera focused at infinity will become F22 when the lens is focused at minimum focus (assuming it's a 1:1 macro lens). Just wondering if the sigma lens was not fully recognised so shooting at a set F11 would actually be equivalent to shooting at F22 with the Nikon lens.
It's always been a source of confusion for macro shooters.

Brian v.

Edited on Apr 29, 2016 at 02:23 AM · View previous versions



Apr 29, 2016 at 12:58 AM
Dalantech
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p.1 #6 · p.1 #6 · Same focal length and aperture... different DoF?


LordV wrote:
One other possibility is that the Nikon cameras report effective aperture rather than set aperture with lenses they recognise. this means that an aperture set on the camera focused at infinity will become F22 when the lens is focused at minimum focus (assuming it's a 1:1 macro lens). Just wondering if the sigma lens was not fully recognised so shooting at a set F11 would actually be equivalent to shooting at F22 with the Nikon lens.
It's always been a source of confusion for macro shooters.

Brian v.


Definitely could be part of the problem, and I get emails form Nikon users who want to know how I can get so much depth at F11.

I came back to this thread to give you some examples of creating magic angles. Here's a shot that I took at 2x and F11, focusing on the bee's mandible and then twisting the upper right hand corner of the frame a little deeper toward the back of the eye:

Newborn Blue Mason Bee V by John Kimbler, on Flickr

For this shot I focused on the back leg on the left hand side of the frame and pushed the upper right corner toward the bee's eye.

Bees in a Wallflower Series 1-3 by John Kimbler, on Flickr

Very slight movements that make a big difference in where the area of acceptable focus is going to be.



Apr 29, 2016 at 01:43 AM





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