Author Topic: Optimal Aperture  (Read 318 times)

Offline TimH

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Optimal Aperture
« on: June 12, 2017, 12:24:21 AM »
Could I ask folks what their rule of thumb is for setting aperture?   With most of my lenses (and I use most of the H lenses), with a landscape, cityscape, or architectural scene, on a tripod with reasonable light, I tend to set my aperture at f/9.5 or f/11.  Somewhere over the years I came to believe that was the sweet spot between maximizing depth of field and minimizing lens refraction.  When people are moving around in the scene, I may use wider aperture, but more often I'll increase the ISO.  Without any sort of scientific testing, I've begun to suspect that something closer to f/8 or f/7.1 might be a better everyday target to work around.   Again, as a general rule, do others have a different "default"? 

Tim Hyde
Washington, DC

Offline jerome_m

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Re: Optimal Aperture
« Reply #1 on: June 12, 2017, 08:31:15 AM »
On my H4D-50, I can barely see the first effects of diffraction at f/11 on specially crafted test settings, but it is not a big deal. At f/8, depth of field may still be lacking, so these are the constraints.

Offline Hassilistic

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Re: Optimal Aperture
« Reply #2 on: June 15, 2017, 08:24:18 AM »
Hi Tim,

Proof in the testing, and variables (Focus - Distance - Light - Exposure) impact results dramatically.  As a rule of thumb as you mentioned, which I refer to as a quick goto setting would be f8. 

However, many lenses do better wide open as well stopped down, such as HC 300mm/4.5 which is just as impressive at f4.5 as it is at f8.0.  So is, HC 35mm/3.5, which is astonishingly good at f3.5, most users miss that part about the 35mm, and f8 does even better by improving sharpness at the edges.  And for me the king of wide open is the HCD 28mm/4, which has extreme sharpness towards the middle and a slight loss (yet still sharp) at the edge, which I take into account when shooting I go wider than my actual scene, and then crop at processing and retain the Sweet Spot of the lens.

With the HC 50mm/3.5, I stay at f8 and go all the way to f16 easily without any bother.  HC 80/2.8 & HC 100/2.2, optimum starts at f5.6, and the HC 120mm /4 Macro + HC 150N/3.2 + HC 210/4 are all safe at f8, that said, they can easily preform way beyond f16.

With that in mind, I still leave it to each situation to dictate and determine the outcome of each setting, if I am shooting glamour with the 150mm, and I needed to blur back ground then I will definitely open up, a little loss in sharpness might even work best for the model.  As appose to image degradation due to diffraction which personally I have seen clearly at f29, but even though, I changed focus away from infinity to near by subject, and the results amazed me once more, with a sharp focus on subject and blurred background but not as a result of bokeh ;)

Hope that helped
« Last Edit: June 15, 2017, 08:27:01 AM by Hassilistic »

Offline ChrisL

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Re: Optimal Aperture
« Reply #3 on: June 15, 2017, 07:48:48 PM »
This is a seemingly simple question but actually quite complicated. No one AFAIK ever won a competition, award or job by submitting the sharpest ever test chart so we must look at real life and the requirements. The OP has correctly stipulated requirements of the scenes he takes that is important as lenses are designed to work optimally at specific subject distances. The CF 100m f3.5 is optimal at infinity where it beats the 100mm HC f2.2 even when that lens has DAC applied, closer work and the HC lens is superior, that is independent of f stop. Some designs have more field curvature, giving less sharp edges when a central plane is in focus that stopping down can address and all this softness can on digital be ameliorated by techniques such as deconvolution sharpening. As a general principle the HC lenses were designed for optimal work at closer distances so the OP for architectural and landscape work may find the older CF lenses which were optimised for infinity,(Macro) excepted,"better": at a given f stop, complicated by the superior correction in colour of the HC lenses, they tend more to apo correction. Previously with the depth of colour film emulsions a lenses which corrected colours to the same plane of focus was wasted as optimal sharpness in the green layer meant the red layer was softer with pixels that is removed and the plane is very shallow and uniform (in a 6x7 film was rarely flat and don't mention 8x10).
The creative uses of aperture can trump sharpness for perfectly good reasons as Hassilistic says and in the OPs case using shift to manipulate the plane of focus may be more useful in obtaining the desired sharpness than simply stopping down more and hitting diffraction.
Traditionally and for good reasons f8 has always been a "sweet spot" but some lenses notably well corrected teles which tend to be slower anyway are optimal wide open and no improvement is seen stopping down. Again the OP mentions increasing ISO to allow a chosen f stop that of course compromises dynamic range of the sensor which may or may not be important depending on the scene, so to the question posed: I don't think you can have a rule of thumb that implies good for all situations it may be good for some but not all so why compromise and treat each case individually and aim for the best result with the variables presented.
This is an interesting paper by Hasselblad which expands and explains many of these points on design and compromises and f stop changes from which some of my points are extracted:

 http://static.hasselblad.com/2015/02/the_evolution_of_lenses.pdf


Offline TimH

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Re: Optimal Aperture
« Reply #4 on: June 15, 2017, 11:01:47 PM »
These are very helpful, thank you.  One observation:   I've owned a half dozen Hasselblad H systems, beginning with the H2D.  The H6D-100c, which I've only had a few weeks, feels like a pretty big jump forward on several fronts, not the least being dynamic range.  I find myself shooting at ISO1600 quite often, and have been surprised at how well IQ and dynamic range hold up at these settings.  Sounds like, from the above, I'll be okay at f/11 but if depth-of-field is less important for a particular subject matter I might open it up a stop.  I understand it's better to analyze the scene and carefully consider both my lens and setting options, and perhaps bracket, but often that's not possible, thus the default or rule of thumb.

tim


Offline Hassilistic

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Re: Optimal Aperture
« Reply #5 on: June 16, 2017, 09:56:14 AM »
On a photo expedition 5 years back, with a group of 7 people, all standing at the same scene, all listening to the same instructor, all capturing the same time of day, quality of light, camera settings..... etc

The result was... Not 2 photos were identical!

It is what makes it so fascinating and unique.


Offline Michael H. Cothran

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Re: Optimal Aperture
« Reply #6 on: June 17, 2017, 01:56:05 PM »
My two cents worth - I have owned a slew of Zeiss lenses in film days, several H lenses for my H4D, and now the three X lenses currently available for the X1D. I have never been disappointed with image quality, at any aperture.
My recommendation would be to quit worrying about a particular sweet spot, and focus (no pun intended) on either how much DOF you want, or how fast you would like your shutter speed to be.
« Last Edit: June 17, 2017, 01:57:46 PM by Michael H. Cothran »