ampguy
Veteran
I agree. A Calculator for "diffraction limited" is about as misleading as dofmaster is for DOF.
It expects an aperture to be perfectly round, something say a 4 bladed PEN lens will never achieve ...
It expects an aperture to be perfectly round, something say a 4 bladed PEN lens will never achieve ...
sper
Well-known
I was working with a photographer once and we had a V Hasselblad, a 120mm Macro, and a 22mp Phase back. We were shooting jewelry and he was using f16 to get the depth of field we needed. He was still complaining, however, that he was just not getting the sharpness he wanted, and that he would have to sharpen after the fact.
Thinking something was amiss, I suggested we open up to f11 and see what happens. We changed our set up a bit and made another capture and sure it enough, the pieces were tack sharp.
In practical photography I use the aperture I need to use to make the picture I want to make, simple as that. But it does help to know that if you require a lens to perform at its best, use the middle apertures.
Thinking something was amiss, I suggested we open up to f11 and see what happens. We changed our set up a bit and made another capture and sure it enough, the pieces were tack sharp.
In practical photography I use the aperture I need to use to make the picture I want to make, simple as that. But it does help to know that if you require a lens to perform at its best, use the middle apertures.
ampguy
Veteran
yup. I was looking at a few of the ~10,000 photos my kids took of Yosemite and SF the past few weeks, and for a while my daughter's dslr was on F2 the whole time.
Incredible photos, on par with not only those from Ansel, but of Uncle Earl's too!!
Incredible photos, on par with not only those from Ansel, but of Uncle Earl's too!!
PKR
Veteran
You must remember, the P25 you were using, a digital back, has pixel islands (with lenses/filters) that accept light at 90 deg. Film, has silver rocks (halide) that will accept light at any angle it's delivered to the rock. This accounts for the difference in DoF between film and digital capture. The use of some of the "digital formula" lenses, like the Rodenstock digital series, will help.. but there is a difference in the media.. not just an issue with blade diffraction.
semilog
curmudgeonly optimist
PKR
Veteran
The amount of light being delivered at 90 deg. is increased by opening up by one stop. More pixels are properly excited in the "correct" manor with out the smoothing algorithm performing the function.
semilog
curmudgeonly optimist
I don't buy it.
Firstly, smoothing algorithms are not particularly relevant here. Algorithms to account for vignetting and color shift might be relevant, but not smoothing algorithms, as such.
Secondly, the amount of light being delivered near (not at) 90° is increased by opening up, but so is the amount of light at more acute angles. The average angle of incidence at each pixel should not be markedly different at different f/stops for a given lens focused at a fixed distance.
If you disagree, please either show your math, or link to someone who's done the relevant calculations.
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Luddite Frank
Well-known
I can't offer any math or big science here, just some observations.
Most of my reading in musty old books ( including several editions of the Leica Manual ), suggests that most [film] standard lenses(focal legnth = diagonal measurement across the film plane) achieve maximum definition "stopped-down 1/3 to 1/2 way".
That same reading also cautions that stopping-down more than 1/2-2/3 can result in diffraction.
My experience with digital cameras is lmited to my first and only, an "antique" Canon Powershot G-1, 3.3 megapixel, which has a 7-21mm f:2.0-2.5 zoom lens. I found to my surprise when using the manual exposure settings that this camera only stops-down to f 8.
For those citing the numerically-larger f-stops on larger format cameras, some of the really old lens & shutter combos are marked in the "Uniform System" of stops, which runs up into f-264 territory... the actual aperture is not as tiny as the number suggests; this system seems to have been abandonded about 1915-1920.
Regards,
Luddite Frank
Most of my reading in musty old books ( including several editions of the Leica Manual ), suggests that most [film] standard lenses(focal legnth = diagonal measurement across the film plane) achieve maximum definition "stopped-down 1/3 to 1/2 way".
That same reading also cautions that stopping-down more than 1/2-2/3 can result in diffraction.
My experience with digital cameras is lmited to my first and only, an "antique" Canon Powershot G-1, 3.3 megapixel, which has a 7-21mm f:2.0-2.5 zoom lens. I found to my surprise when using the manual exposure settings that this camera only stops-down to f 8.
For those citing the numerically-larger f-stops on larger format cameras, some of the really old lens & shutter combos are marked in the "Uniform System" of stops, which runs up into f-264 territory... the actual aperture is not as tiny as the number suggests; this system seems to have been abandonded about 1915-1920.
Regards,
Luddite Frank
This thread is bringing back memories of High School Physics class.
To answer the OP, diffraction is real and the aperture mechanism of the lens is the object that is responsible for its introduction into an image. Diffracted light does not form a well focused image. The amount of light that is diffracted is proportional to the circumference of the aperture, the amount of well-focused light is proportional to its area.
Everyone's definition of a good image may vary, and it is in the eye of the beholder of where this threshold occurs. The differences are there, but they are small.
http://www.optics.rochester.edu/workgroups/berger/EDay/EDay2008_Diffraction.pdf
Put a pinhole on your camera and shine a LASER through it. Wish I had the EP2 in college.
To answer the OP, diffraction is real and the aperture mechanism of the lens is the object that is responsible for its introduction into an image. Diffracted light does not form a well focused image. The amount of light that is diffracted is proportional to the circumference of the aperture, the amount of well-focused light is proportional to its area.
Everyone's definition of a good image may vary, and it is in the eye of the beholder of where this threshold occurs. The differences are there, but they are small.
http://www.optics.rochester.edu/workgroups/berger/EDay/EDay2008_Diffraction.pdf
Put a pinhole on your camera and shine a LASER through it. Wish I had the EP2 in college.
tlitody
Well-known
But whilst on LF cameras you have longer focal length and therefore a bigger diameter aperture for the same F no as on a 35 lens, you also have greater magnification on the film. i.e. the diffraction is magnified on film more. So that is not the reason why LF cameras use smaller F numbers. The reasons is because the bigger diameter lenses introduce more lens aberations(which are also magnified more) and therefore require more stopping down to compensate. The result is that on LF you get much lower on film resolution than you can achieve with a lens on 35mm camera. BUT you don't have to magnify it as much to enalrge it to print. The result is that 4x5 neg printed to 20x16 blows away a 35mm neg printed to same size. That asumes your technique is good enough because LF is real bugger to get right and often results in less quality than you can achieve with MF system which is far easier to use and get right.
PKR
Veteran
I have no idea what you know about sensors. I'm a photographer who uses these devices daily. I also have an engineering background. But most important, I have two friends who design camera sensors. I'll do a little of this, but don't have time for a lengthy "typing match". Any light reaching the sensor at other than 90 deg. doesn't matter,as the sensor won't see it. The design of the Rodenstock digital lenses is to deliver more at 90. The smoothing i was speaking of was the adjacent pixels that don''t receive a photon ask their neighbor "what to do". I'm sure you are aware of this common algorithm .
http://www.foveon.com/article.php?a=74
http://www.prograf.ru/rodenstock/digital_en.html
Maybe you can add to my knowledge.. please
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semilog
curmudgeonly optimist
Let's look at it this way. People in other threads on this forum are getting hot and bothered about a meaningless-in-practical-terms 20% difference in linear resolution between APS-C and micro 4/3 sensors.
Now let's look at what diffraction does: it turns a great lens into a lousy one.
Let's look at a typical example of a good lens, the current Canon 100/2.8 L macro. The hyperlink takes you to the DP Review test results for this lens on APS-C and FF sensors.
On an APS-C sensor, at its optimum aperture of f/4, this lens resolves about 1600 lp/ph [picture height] on the Canon 50D. At f/8 it's still pretty good, about 1400 lp/ph. At f/16 it's down to about 900 lp/ph. At f/22 it's 750 lp/ph — less than half the peak resolution. At f/32 it's about 500 lp/ph — less than one third of the starting resolution!
Remember — this is linear resolution. A 3-fold decrease in linear resolution is equivalent to a nine-fold reduction in pixel count: when you stop that macro down to f/32, the 15 megapixel Canon 50D becomes, effectively, a 1.7 megapixel camera. At that point, you might consider switching to your cell phone's camera.
The results on a FF camera, the 5DII, aren't quite as bad (because of its larger pixels), but they are still pretty bad. By f/16 the 5DII is doing no better then the 50D, and by f/32 you might as well be using a small-sensor camera. In fact, if you need a lot of DOF, the small-sensor camera lets you shoot at a wider aperture with a shorter FL lens (for equivalent FOV), and in many cases will deliver overall resolution as good as or better than than the FF system. Hence the spectacular macro results that many have obtained with cameras like the G11.
Do you think that P&S digicams use ND filters instead of apertures smaller than f/8 for no good reason?
As pixels shrink, diffraction becomes a more serious limitation, and pixels are getting smaller across the board, from cell phones to FF DSLRs.
Diffraction matters. It certainly matters as much as using a good lens vs. a mediocre one, or a good film vs. a mediocre one.
If you are not critical (and most of us are not, most of the time), diffraction usually won't matter. On those occasions when you are critical, it will matter, and it will matter a whole lot more than some of the details that many here sweat over.
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peterm1
Veteran
Every time this blasted subject comes up (and it comes up too often) it seems to degenerate into a p#ssing match between people who want to out nerd each other on the technical details. For crying out loud everyone, why not just say "Yes it is real" then move on to something more interesting rather than argue with each other on details that are irrelevant for everyone except lens designers.
semilog
curmudgeonly optimist
Some of us like to understand the equipment and media that we work with. Others just want to use the stuff.
Both approaches are valid, but if you prefer the latter you should not make the mistake of assuming that everyone else shares your preference. Vast threads appear here concerning differences that are far less consequential.
PKR
Veteran
I agree, it's a waste of time for most. I was just responding to semilog..I'll drop it. Sorry for the nerdism..
jamesdfloyd
Film is cheap therapy!
Gentlemen (and any Ladies I've missed), I have to agree with Peter on this. All to often I ask a question on a forum (not only here but on Linked-In related to financial & accounting issues) and it degenerates.
Be it in my day job as a Chief Financial Officer or in my true love of photography & cameras, discussions always degenerate when more than one person has an "absolute" view of a technical issue or for that matter an issue where everyone thinks there is a right or wrong answer.
I appreciate all the responses and I am amazed how technical most have been. What this posting has done is to remind me that there are vocal defenders on every one of the typical questions here - RAW vs. JPEG, TMax vs. Tri-X and my personal favorite - UV filters on your lens vs. "ah natural".
J.D.
Be it in my day job as a Chief Financial Officer or in my true love of photography & cameras, discussions always degenerate when more than one person has an "absolute" view of a technical issue or for that matter an issue where everyone thinks there is a right or wrong answer.
I appreciate all the responses and I am amazed how technical most have been. What this posting has done is to remind me that there are vocal defenders on every one of the typical questions here - RAW vs. JPEG, TMax vs. Tri-X and my personal favorite - UV filters on your lens vs. "ah natural".
J.D.
Many photographic subjects are technical in nature, at least in part. It's useful to be better informed, to understand some of the technology that affects how our pictures look. So threads such as this one can be useful and entertaining, as usual moreso to some than others. There's often some misinformation mixed in too that we can sort out. I appreciate the sharing of information and understanding, and the efforts to explain clearly. 
I could put in a few formulas and numbers regarding diffraction and resolution from Neblette and Hecht, but it would not be of much value to the discussion. Personally, I almost never stop down below F5.6 and almost always shoot wide-open and at F4. I really want to put the new 12.5mm F1.3 Cosmicar on the EP2 because the aperture closes down all the way, and then hit it with a LASER. Remarkable Restraint.
But- if you need depth of field in an image, the way to get it is to stop down. The benefit gained by having a larger depth of field for the overall image will outweigh the resolution lost due to diffraction. If you focus at 10ft, and stop down to F11, an object at 5ft will be better resolved even with the increased effects of diffraction compared with opening the lens up to F4. The object at 5ft will not be as resolved at F4 as it would be at F11. That is the call that the photographer must make for the sake of overall quality of the image. If you are shooting test targets at a fixed distance, then DOF does not matter. But in the real world, it is DOF vs diffraction.
But- if you need depth of field in an image, the way to get it is to stop down. The benefit gained by having a larger depth of field for the overall image will outweigh the resolution lost due to diffraction. If you focus at 10ft, and stop down to F11, an object at 5ft will be better resolved even with the increased effects of diffraction compared with opening the lens up to F4. The object at 5ft will not be as resolved at F4 as it would be at F11. That is the call that the photographer must make for the sake of overall quality of the image. If you are shooting test targets at a fixed distance, then DOF does not matter. But in the real world, it is DOF vs diffraction.
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PKR
Veteran
Hi Semilog; i'll try sending you an email if you like.. we can continue this outside the form. Just post a reply. I don't feel comfortable doing this kind of thing here.
p.
semilog
curmudgeonly optimist
No one here has argued otherwise. I certainly have not. The choice of aperture depends on the lens, the sensor, and the subject. Not necessarily in that order.