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Sigma 105mm f/2.8 Macro DG OS HSM:optimum aperture

Which F is the best for the Sigma 105 (on nikon D 800)?

Lens: Sigma 105mm f/2.8 Macro DG OS HSM

Many thanks.

Martino Papesso


I have the Nikon Micro 105/2.8 and I try to avoid apertures closer than f/8. "Then there's not enough DoF!". Yes, right, it never is enough DoF and from f/11 the DoF is paid with lower resolution. But there's a cure against that: Have a look at Helicon Focus stack.


See also in case you haven't heard about that possibility. Downsides: Not possible for moving (also breathing) creatures or in windy situations outside.
Does exist test for to know with is the best aperture for Sigma 105 at minimun distance of focus (about 32 cm ) and at another distance?


Many thanks.

I'm not aware of such a test, but the internet is a big thing. You might research on dedicated macro-websites. As a rule of thumb, 2-3 f-stops from wide open is the optimum aperture of every lens. The higher the cameras MP, the sooner sharpness and/or resolutuon will decrease after a certain aperture.


Maybe a good read:


quick summary from that article: "The general rule that lenses get much sharper stopped down two stops from wide open is generally true."

Quote:Does exist test for to know with is the best aperture for Sigma 105 at minimun distance of focus (about 32 cm ) and at another distance?


Many thanks.
There is no such thing is "best aperture, really, as JoJu points out.


For shallow DOF, wide open usually is best. For best contrast, closing down usually is a good idea. For most DOF, you need to stop down a lot, and for best sharpness, f5.6 usually is the best idea (for medium close up to infinity).


When you go close, the effective f-stop diminishes. 

See for instance this thread:

Your Nikon D800 will actually show a close approximation of the effective aperture (try it yourself.. set for instance f4 at medium distance, then focus on something very close up and you will see that the camera shows a different f-value than you originally set).


What is the best aperture to use totally depends on what you are trying to achieve for a certain shot. 

There's maybe no such thing in the weird cosmos of BC. If you're able to read German (no offense meant, I just didn't find it in another Wikipedia language) you can check for "Förderliche Blende", "Beugungsunschärfe" or also Kritische Blende which simply means the aperture number Martino is looking for, and leads to maximum resolution. I know, you're addicted to DoF, but this is not necessarily leading to best resolution or good pictures  Tongue


And the effective f-stop diminuishes because the diameter of the front lens remains, but the focal length changes - it gets longer, meaning the f-number gets higher. The focal length is calculated at infinity, as you for sure know two days longer than God. [Image: oldno23x25.gif]

FoCal Pro seems to be able to do this. I never played with it that much beyond AFMA so haven't tried this feature myself. I believe it can use arbitrary targets so you could go different distances.
<a class="bbc_url" href="">dA</a> Canon 7D2, 7D, 5D2, 600D, 450D, 300D IR modified, 1D, EF-S 10-18, 15-85, EF 35/2, 85/1.8, 135/2, 70-300L, 100-400L, MP-E65, Zeiss 2/50, Sigma 150 macro, 120-300/2.8, Samyang 8mm fisheye, Olympus E-P1, Panasonic 20/1.7, Sony HX9V, Fuji X100.
AFMA??? Oh sorry, just read the full sentence now. Yes, FoCal Pro can try to find out the best aperture and print a nice graph. But this is "the best aperture at any costs, preferrably in the center of the image, no matter how much the corners blurr". It looks nice, but honestly I didn't see much of a difference. You meant this here?

[Image: i-HVzvJtQ-M.png]



I just didn't see that much of a difference between wide open, the best and the worst aperture...


[Image: i-ZVhQKdj-L.png]


[Image: i-DQQxSwS-L.png]



[Image: i-k5dpnXL-L.png]
 The problem with the sharpest apertures is how the effective aperture changes with the distance:


 I used to have the Sigma 105mm macro non OS version shooting on the Pentax K3. (sold,can't give figures)


But looking at the Nikor AF 55mm F2.8 macro,  aperture changes with distance are:


Infinity...F2.8       0.35 mts...F3.5      0.27 mts....F4    0.24 mts... F4.5     0.23 mts ...F5    at 1:1...F5.5.  nearly minus 2 stops.


And for the Sigma 150mm EX F2.8 non OS version.


Infinity...F2.8      3.0 mts.   F3.5         0.8 mts...F3.8    0.58 mts...F4      0.5 mts...F4.5   at 1:1 .. F5.6....minus 2 stops.


 So finding which aperture is the sharpest will vary according to the distance. resolution tests would have to be done at a range of distances at all apertures, not something I will pursue!


 In practice when not "focus stacking"  we compromise to have a visually pleasing depth of field, often F11, which is way beyond the lens's  optimum sharpness which is commonly F4.5-5.6.

Dave's clichés
This fly is taken with the Nikor 55mm F2.8 micro at F11  D7100, very small depth of field, I tried F16 for more DOF but sharpness suffered.
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Dave's clichés

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