aCuria wrote:
The Nyquist theorem (or Nyquist-Shannon sampling theorem) states that to accurately record or digitize a continuous analog signal without losing information, you must sample it at a rate greater than twice the highest frequency component present in that signal.
This means we want the Airy disk to cover at least 2 pixels on the sensor. If you use 1.5 you are losing information.
Uhm, that way you do loose information. You generally loose information as your airy disk gets bigger and also if you sample with less pixels. So your requirement of using no more than two pixels per airy disk is the wrong way around if you do not want to loose information. Meanwhile it is a valid approach to reduce Moire.
If the lens is not perfect you can think of this as the airy disc being larger than the calculated value.
Approximately if the lens is soft. CA means that the airy discs for different colors do not coincide. Coma means that they are not round.
EB-1 wrote:
I most always use focus stacking now, usually at f/8. My landscape lenses are typically between 50-500mm, mostly 100-400 range. About 8-12 images are often adequate for stacking prior to stitching. I'd probably focus bracket the a7RVI at f/6.3 or similar for the single frame/composition if necessary. I have not tested how well the increment of one covers depth however.
I suspect that Dan shoots subjects more like me, in UT/AZ/NM/CO and places like that normally on a tripod. MS mode at ISO 100 looks great with the DGO. It certainly has more DR than the 5DsR, which was mostly adequate despite theroetically being lower than some sensors.
For my landscape photography, that’s exactly right.
(I usually don’t use the tripod for bird photography and I essentially never use it for street/travel, and for those types I don’t shy away from higher ISOs when needed.)
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Another reply to the same EB-1 post was…
aCuria wrote:
What do you think about pixel shift? I was thinking it might be more valuable than focus stacking for landscape photography, while focus stacking seems more useful for macro photography.
Its a pity the A9iii doesn't have pixel shift
Generally, I don’t think pixel shift has a whole lot of value with high resolution full frame cameras. There is obviously the potential plus of wildly higher pixel resolution (and some other stuff), but these high res cameras already have enough resolution to make very good, very large prints without introducing some of the issues that pixel shift can create. (Note: some of those can also be issues with focus bracketing, especially subject motion.)
I think that pixel shift may have more potential value for those using much lower pixel resolution cameras who occasionally want to get much higher pixel resolution. (Your A9 example makes sense.)
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Jack Flesher wrote:
If we have to sample at 2x, doesn’t that imply the airy disc needs to be the inverse, or 0.5 pixel instead of 2?
We’re getting very deep into a thick growth of very tine weeds here, but I think that technically you are right. (Unless the goal is to most accurately record the blur?)
Larger blur will affect the degree of (never perfect) accuracy of what is recorded at a larger number of pixels.
Having said that, I urge people to maybe take a step back from the theory and take a look at actual photographs using these various combinations of apertures and photo site densities… and note that what things actually look like as finished products is the ultimate benchmark.
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Or as woofwoof70 wrote:
I'm always a little surprised when people dive deeply into diffraction and discs but if someone is committed to doing this there's the theory and there's taking pictures and looking at the effects. With digital on screen viewing is cheap (but do we really need to look at pictures at 100% on screen?) but prints maybe not so much so.
I do on occasions stop down past f8 to f11 and even beyond and find that the main hit for me is reduced contrast and there's always the sliders if they can help with that. My own opinion is that if you/we want to stop down for reasons of DoF or shutter speed then we should assuming we can still end up with acceptable image quality for our needs. In general I think there's a bit too much fear around this IMO....Show more →
Amen.
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Someone blustered: …hand wringing always seems to come from those that would prefer to think about taking about photos than actually going and doing it.
It turns out that “ think about taking about photos” and “ actually going and doing it” are not unrelated practices in photography.
Okay, so f7.1 is it. That actually aligns pretty well with what I am seeing with my best lenses; f5.6 is about as sharp as it gets, and by f8 I am seeing visible micro detail degradation at 100% view. Granted that it’s tiny and probably irrelevant to most of my images, but nonetheless visible. I can probably accept f9 some of the time but f11 is definitely into iffy territory except when I want sun stars with my extreme wide angle lenses.
I'm trying to learn more about the technical side of discussions like this as a relatively new photographer. Can someone explain what an airy disk is, or point me to an article they found particularly good at describing it? Yes I could google it, but part of the enjoyment of this site is direct interaction with some of the more knowledgable people here.
Keep in mind that while you might be able to calculate (or not?) the "best" sharpness of a lens with a particular sensor, there are multiple apertures that will still produce "excellent" sharpness. Yes, "excellent" is a fuzzier concept than "best" (or so we hope), but excellent really matters more.
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Tarekith wrote:
I'm trying to learn more about the technical side of discussions like this as a relatively new photographer. Can someone explain what an airy disk is, or point me to an article they found particularly good at describing it? Yes I could google it, but part of the enjoyment of this site is direct interaction with some of the more knowledgable people here.
Much appreciated.
It is interesting and useful to understand the concept, though do be careful about going down the technical rabbit hole that sometimes is alluring but maybe less relevant to real photography than it might seem. This is a special list for "new photographers." :-)
Well used to that kind of thing from the audio world (I'm an audio engineer and musician). People argue all the time about concepts and theory that don't make a lick of difference to writing good songs
Tarekith wrote:
Well used to that kind of thing from the audio world (I'm an audio engineer and musician). People argue all the time about concepts and theory that don't make a lick of difference to writing good songs
Ah, yes. I have a sort of odd academic background — my speciality was what we used to call “electronic music” — synths and recording and all that, with a focus on composing. But my background is wider than that, and in my college teaching life my position also involved teaching classical stuff… and years ago I was a dare-carrying union musician who free-lanced.
Like you, no doubt, I’ve heard a lot of nonsense about music and audio. ;-)
I could tell stories, but I’ll keep it to one. At one point I was the stage manager for a professional symphony orchestra. I got to know the fellow who recorded the concerts and whose business was live recording of classical and jazz performances. At one point he related to me that he had been reading about an audiophile product that was, IIRC, called “Wonder Solder.” As he explained that one was supposed to achieve an “expanded sound stage” and other acoustic wonders by UNSOLDERING the components of expensive gear and resoldering them with Wonder Solder, he began to chuckle, then laugh out loud, and soon he was laughing so hard that he couldn’t control himself…
;-)
I don’t know where you are on your “new photographer” path, and you may well have already figured out what I’m about to write, but what the heck: Lots of times, for all kinds of reasons, new photographers focus a whole lot on the gear. Gear is important — you want to get stuff that meets your needs. But it is easy to get distracted by all of the people swearing up and down that you need Perfect Camera A or Astonishing Lens B and so on.
You really don’t. Decent gear, acquired slowly and used to gain more experience will make you a smarter shopper and better photographer in the long run.
And, most importantly, photography isn’t really about the gear — it is about learning to see and think visually. That’s the thing to focus on. :-)
Daran wrote:
Uhm, that way you do loose information. You generally loose information as your airy disk gets bigger and also if you sample with less pixels. So your requirement of using no more than two pixels per airy disk is the wrong way around if you do not want to loose information. Meanwhile it is a valid approach to reduce Moire.
Approximately if the lens is soft. CA means that the airy discs for different colors do not coincide. Coma means that they are not round.
I think you are right I made a mistake there.
We want to use a fast enough aperture such that the airy disk covers 2 or less pixels.
Jack Flesher wrote:
My question is what is the optimal aperture for DoF vs diffraction on the A7R6?
My empirical testing suggests that f8 is about the pinnacle of the two curves intersecting for a typical landscape shot. Beyond that, diffraction seems to start negating the DoF gains. This is viewing at 100%. Things improve viewing at print size, possibly allowing f9 for a large print. I can actually see some loss when viewing at 100% going from f5.6 to f8, minimal but visible in central frame detail. I noted similar behavior with my GFX100 and its best lenses.
If I calculate DoF with a 50mm lens and this cams pixel pitch, f8 allows 25 feet to infinity; f9 adds 1 ft or 24ft to infinity; and if I want 20 ft to infinity, I need around f12.7, or accept compromising infinity focus. The problem here is diffraction can make the image worse than the DoF gained. Hence this presents a conundrum for me as a landscape shooter.
Obviously this problem has been here all along and I’m just better able to see it now. I also realize wider lenses may mitigate the issue while longer lenses accentuate it — for yet another conundrum. I am curious how others deal or plan to deal with this?
PS: historically I have never bothered focus-stacking, but may now need to experiment with it as one solution, so additionally curious to hear from folks that do this specifically with landscape style images.
PPS: I have used TS lenses in the past, but not interested in going that route now as I appreciate the added compositional flexibility I get from zooms. ...Show more →
Airy disk diameter on a perfect lens is 2.44 * λ * N
where λ is the light frequency (400nm = blue, 550 = green, 700 = red)
and N is the f-stop.
To maximize dof, we want the airy disk diameter to be similar to the size of 2 pixels. so we solve for
Red:
3605.77nm * 2 = 2.44 * 700 * N
N = f/4.22
Green:
3605.77nm * 2 = 2.44 * 550 * N
N = f/5.37
Blue:
3605.77nm * 2 = 2.44 * 400 * N
N = f/7.39
Note that 2.44 * λ * N is the airy disk diameter for a perfect lens. If the lens is not perfect then you can stop down more than the computed f-stops before running into diffraction.
Based on this (lenses in real-life are not perfect) I would try to shoot faster than f/4.5 when possible.
snapsy wrote:
If that's the case then I guess Jack can close this thread
No, the thread is about sharpness maximization, stopping down some reduces aberrations and increases sharpness. Jack is asking exactly how much to stop down, its a reasonable question.
Tarekith wrote:
I'm trying to learn more about the technical side of discussions like this as a relatively new photographer. Can someone explain what an airy disk is
At a high level, when light from a point source passes through a lens, diffraction prevents the lens from focusing the light to an infinitesimally small point. Instead, the light forms a small diffraction pattern, whose central bright region is known as the Airy disk.
aCuria wrote:
No, the thread is about sharpness maximization, stopping down some reduces aberrations and increases sharpness. Jack is asking exactly how much to stop down, its a reasonable question.
Jack's first sentence in his OP:
"My question is what is the optimal aperture for DoF vs diffraction on the A7R6?"
