Printable View
Hi,
To get really long depth-of-field (and/or force a longer exposure), do you use apertures narrower than f/8-f/11? In my attempts I found that IQ drops noticeably if I go that narrow. I use XTi/40D and I've experimented with a few of my lenses...
Tony
Bryan (the author here) has started to publish data regarding the Diffraction-Limiting Aperture of various Canon bodies. For the XTi/40D (i.e. 10MP at 1.6x crop; it's all about the pixel spacing so the body model doesn't matter) the DLA is reported as f/9.3. I haven't seen much impact with DLA, but I'm not a pixel-peeper either (usually).
Of course I stop down! What else would I do? Not take the photo? I don't know the meaning of them horrible words. :)
If the shot calls out for deeper DOF, I stop down. It doesn't matter if it's f/11, f/16, f/22, or f/32. I'm going to do what it takes to get the shot. (Of course, it would be far better if I could use focus stacking or some other technique to get the shot without diffraction, but many times that's impossible.) You can get back some of the resolution lost to diffraction through sharpening if the image has very little noise.
Diffraction is a fact of life. A picture that has visible diffraction is better than no picture at all.
It's the same way with noise. If a shot calls out for underexposure (high ISO), I underexpose. It doesn't matter if it's ISO 1600 or 56,000; I'm going to do what it takes to get the shot. Of course, it would be better if I could use image stacking, flash, or some other technique to get the shot without underexposure, but many times that's impossible. You can get back some of the image lost to noise through noise reduction software (desaturation, etc.).
Noise is a fact of life. A picture that has visible noise is better than no picture at all.
Personally, I use a wider aperture as you mention. Some advice I picked up somewhere was that the close objects can be a little out of focus, because they are big and you don't notice it as much. The objects further away need to be sharp to make out the intricate detail. Of course this is talking landscapes with say, a log, as the foreground object of interest, but the background is what you are really looking for.
Tom
Rarely. When I shot film, I used f/16 frequently, but that was before the days of dust on sensors and DLA. (It was also before the days of change-on-the-fly ISO--we're talking film here--and sometimes the camera would be loaded with higher ASA* film than the situation called for...again, in the days before shutter speeds went above 1/1000th*).
Today, with other ways to control light, it's a rare situation when I have to use narrow apertures--only when I want to make an image that calls for thatmuch DOF. Usually selecting f/8 - f/11 and using a wide-angle lens give me all I need.
* Man, am I dating myself here or what? (Saying "man" probably does that too...guess i should be saying "dude" or "bro"?)
<span style="font-size: 6pt; color: black; font-family: 'Verdana','sans-serif';"]
<span style="color: black; font-family: 'Arial','sans-serif';"]<span style="font-size: small;"]To get the max Depth of Field (DOF) you need to use a wider angle lensat the proper shooting distance. There are DOF calculators that can help. Using apertures larger than f11 usually start to soften the image.<o:p></o:p>
<span style="color: black; font-family: 'Arial','sans-serif';"]<span style="font-size: small;"]Try this URL to use the DOF calculator.<o:p></o:p>
<span style="color: black; font-family: 'Arial','sans-serif';"]http://www.cambridgeincolour.com/tutorials/DOF-calculator.htm<o:p></o:p>
<span style="color: black; font-family: 'Arial','sans-serif';"]<span style="font-size: small;"]Bob<o:p></o:p>
There are apertures narrower than f/8? Who would have known. Honestly, I spend all my time at f/2.8-f4.0 because I like really shallow depth of field, which also explains why I toss so many pictures because only one of the brides eyes are in focus.
I don't think I've ever been above f/8.0, at least that I can remember.
:) I uses 2,8 to 8 depending on light situation but F8 is sharpest
Quote:
Originally Posted by Tony Printezis
Tony,
I have used my XTi with F16 for a good number of times and I barely found any image degression. I will use F11 or narrower to get great DOF or I need to push for long time exposure. If you're shooting night scenes with long time exposure, first make sure that your camera is supported steadily and you use a remote controller or cable release. I found myself not getting sharp enough shots because of slight camera shaking (some time it'sdue tothe wind). The diffraction (regarding XTi at least) should not be a concern at F16 in my opinion.
Ben
I rarely go above f/13. It depends on the camera, of course, and the sensor pixel size.
I did take a number of f/22 shots a while back, and I was disappointed in their IQ. Since then, I've stuck with f/8 or wider, and an occasional f/11-13.
Film? That's a different story. F/16-22 will give sharp images with a deep DOF, but not a digital camera. Not yet, at least.
Because of digital, go ahead and take the shot anyway.
I wish I had taken those f/22s at f/8, too, but I didn't. So, I got what I got.
I'd rather have a better image quality, then a lousy one with a great depth of field.
Diffraction is an optical effect, it is not affected by capture mediums. The size of the capture medium (e.g. APS-C vs FF35) only comes into play in that larger mediums have lower reproduction magnification, so narrower f/stops may be used. People think it is different for film/digital because of at least two reasons:Quote:
Originally Posted by Alan
* Digital sensors are usually much smaller than film (e.g. APS-C), so magnified more for display.
* People routinely examine digital at much higher display magnifications than film.
For example, people routinely examine digital photographs with 100% crops, whereas they never printed their film negatives to the same size (a 5-foot-wide print).
I'd rather have an image where the entire shot is slightly blurred by diffraction than one where only some important parts of the image are in focus, but other parts are heavily blurred by being out of focus because it's not within the depth of field.Quote:
Originally Posted by Alan
To me, the subject and composition are far more important than resolution and contrast. If I am struck with the idea for a composition of a certain subject that requires f/22, I will not hesitate to use it. I lose resolution and contrast to diffraction, but I gain a composition/subject that would not be possible to photograph at any other f/stop.
Quote:
Originally Posted by Alan
I think you mean, not any more. As pixel density increases, DLA decreases. I bet the original 1D had a very high DLA, since it was a 4MP camera in APS-H size.
Rarely, usually only for macro and long exposures.
Quote:
Diffraction is an optical effect, it is not affected by capture mediums. The size of the capture medium (e.g. APS-C vs FF35) only comes into play in that larger mediums have lower reproduction magnification, so narrower f/stops may be used. People think it is different for film/digital because of at least two reasons:
* Digital sensors are usually much smaller than film (e.g. APS-C), so magnified more for display.
* People routinely examine digital at much higher display magnifications than film.
Daniel, you're totally right. The question I always ask: What does the print look like?
But here is another difference in how people perceive "problems" in digital compared to film (and perhaps it's more a phenomenon of the generation than the medium):
There are numerous factors that cause unsharpness in an image. Subject motion, camera motion, lens aberrations, defocusing, lack of acuity in the sensor, stray light striking the sensor (flare), et cetera.
Now, as you remove or reduce any of the factors, the image becomes sharper than it had been. Put the camera on a tripod to remove camera motion, and the image is sharper. But removing one factor makes the other factors more easily identified, which for some perverse reason a great many people see as a worse situation. They seem to have liked it better to have a less sharp image as long as they don't know the reason it's less sharp.
That's where the silliness about high-resolution sensors being a disadvantage. With the higher resolution sensor reducing unsharpness caused by the sensor, it's easier to identify unsharpness caused by lens aberrations. Now at 100% magnification we can clearly see chromatic aberration for what it is, when before with an inferior sensor we just saw a larger, less specific blur.
But if you actually print the picture, the picture is sharper.
This is an older thread, but I've got some questions.
While it is true that the medium for capture doesn't make any difference on diffraction, the type of digital sensor does. There are many full frame versions out there, yet diffraction occurs less with some, than others.
With the increasing resolution of digital sensors, which I presume is a matter of squeezing those pixels tighter together, isn't this a disadvantage for diffraction?
For example, the 5D has about a 13 Mp sensor, vs the Mk 2's 21. Diffraction kicks in above f/13 on the 5D, but around 10 on the Mk 2.
So, in this case, with full frame sensors on both, one is clearly different (worse) than the other.
Diffraction IS a undesirable thing, otherwise there wouldn't be so many examples of authors recommending keeping it to a minimum.
Seems to me that landscape photographers will see this as a negative.
A solution seems to be, then, to make a larger sensor, but how practical is that?
Just talking out loud....
Quote:
Originally Posted by Alan
Two full frame sensors shot with the same lens, subject at same distance, same f/stop give the same diffraction. Anyone who tells you different is selling something.
Quote:
Originally Posted by Alan
Diffraction is the same for both sensors. However, because the 5DII has a higher resolution, you can *see* diffraction more readily. It is the same for other optical defects: for example, particular lens may be good enough that you see no aberrations when used with a 12mp sensor, but you may start to see them with a higher pixel density. That doesn't mean the lens got worse when moved to the higher resolution camera, it just means you can see more. Same with diffraction.
Quote:
Originally Posted by Alan
Yup. And macro photographers. Life is tough. [:)]
There are ways around it: one can deconvolve diffraction or get multiple exposures. But there are tradeoffs, and anyway none of this has anything to do with the design of the sensor.
Quote:
Originally Posted by Alan
A larger sensor doesn't help, because with a larger sensor you need to stop down more to get the same DOF. When you do that, diffraction gets worse. For example, a 400mm f/5.6 lens on a ff camera acts the same as a 200mm f/2.8 lens on a camera with a fovcf of 2x. The ff sensor has twice the linear size, but the diffraction patterns are twice as large. So you're in the same boat.
Jon already answered this one excellently, but since I already wrote up a response I may as well post it.
I kindly disagree. The type does not make a difference: diffraction is the same for all of them. This can be seen in the actual prints, but I'll try again to explain why.Quote:
Originally Posted by Alan
You are correct that increasing megapixels for a given sensor size involves making the pixels smaller. However, smaller pixels are not a disadvantage for diffraction.Quote:
Originally Posted by Alan
- More pixels always result the same or more resolution.
- Sometimes it's a lot more.
- Sometimes it's slightly more.
- Sometimes it's so infinitesimally more that it might as well be the same.
- Never, under any circumstances, is it less resolution.
The increase in linear resolution is directly proportional to the decrease in pixel pitch. Even after diffraction causes the MTF to drop below the Raleigh criterion for luma, additional gains are possible in order to oversample chroma infomration and make it possible to remove the OLPF.
For example, going from the 5D1 to the 5D2 the linear resolution increased 28% (sqrt(21.1/12.8)). Translated to line pairs per millimeter (the standard measurement of resolution), at 2 pixels per line pair (Nyquist limit), the 5D1 has is 60 lp/mm whereas the 5D2 is 78 lp/mm.
With both cameras at f/8, the 5D2 gives the full expected 28% increase. As the aperture closes down, the resolution increase gets less and less, but it's never goes negative: just diminishing returns.
It doesn't "kick in" because it was always there. It's just that the large pixels of the 5D1 were too coarse and blurry to make out the fine detail that was squashed by diffraction. If the blurriness of large pixels is improved by switching to the 5D2, it becomes possible to see the diffraction blur that was always there. You can always resize 21 MP back down to the same spatial resolution as the 5D1 if you want to hide the diffraction.Quote:
Originally Posted by Alan
Yes, the 5D classic is worse.Quote:
Originally Posted by Alan
Agreed. Gravity can also be a bother sometimes. [;)] They're constant, like death and taxes.Quote:
Originally Posted by Alan
A larger sensor does not help at all because depth of field scales with diffraction. If you increase sensor size and keep f/number and field of view the same, then diffraction improves... but depth of field gets thinner. So you stop down more. Which worsens diffraction back to the exact same spot you were when you started. A smaller sensor doesn't help either. You can use a wider f-number, but the smaller pixel size cancels out the advantage. Another way to see it is that diffraction scales with the aperture diameter (AKA focal length divided by f-number).Quote:
Originally Posted by Alan
The reason why so many people get the wrong impression about diffraction and pixel size was explained aptly by RDKirk. Some users perform very flawed comparisons. Chief among these flaws is comparing two completely different magnifications through the use of 100% crop. The spatial frequency must be scaled before any analysis is completed. This can be done, for example, by looking at actual prints, or simply resizing images before creating crops.
Kind regards,
--Daniel
Jon, Daniel, thanks. Lots of info to digest.
I got lost in all the verbage about seeing the difference in the print. If I'm using the same lens, at the same f/stop, carefully ensuring proper steadiness of the camera (tripod, mirror lockup, etc.), then exactly what will the prints show, in terms of difference?
If there is a difference, and the diffraction is the same for both cameras, then what does that difference translate into? Resolution?
Thanks for the helpful insight.
Quote:
Originally Posted by Alan
28% more resolution, in the case of the 5D1 -> 5D2 at f/8, no aberrations, and sufficiently large print sizes (or magnification).
0% more resolution at f/64.
Somewhere in between at other f-numbers, by an amount that varies with post processing (since demosaic, diffraction deconvolution, and USM sharpening can recover some resolution).
Quote:
Originally Posted by Daniel Browning
Until I have a 5D mkII, can we just say that the 5D classic isn't just quite as awesome? Daniel, you've sold me. I want more pixels. I really do. I just don't want to pay for them right now [:(]
Quote:
Agreed. Gravity can also be a bother sometimes. [img]/emoticons/emotion-5.gif[/img] They're constant, like death and taxes.
No Kidding. My new torpedo-sized target arrows, between 20 and 30 yards, drop more than a foot. Makes diffraction limitations seem like a relatively minor thing [:)]
Quote:
Originally Posted by Daniel Browning
It isn't clear to me that deconvolution can't recover more resolution on a higher resolution sensor, even at very high f numbers such as f/64. In fact, I'd be very surprised if it couldn't. (I've never actually *tried* it, though [:S])