What is wrong with f22

When I first got into photography I learned that the smaller the aperture the more depth of field you would get in a

picture. Therefore If I wanted allot of DOF I wasn't hesitant to close down to an aperureof f16 and even f22. These

days you hear allot of talk about staying away from those apertures, because they will degrade the picture and invite

pin-cushion distortion and allot of other nonsense.

 

Tell you the truth, if I had a lens that had a maximum aperture of f200 I would be happy. Most LF lenses have

apertures of f32 or greater, that's why they are used in studio work that require that sort of precision. But now the

story line is, to stay away from those high aperture values. Then why have them there in the first place ? Why not

just build lenses with f5.6, f8 and maybe f16 as the only apertures and skip the rest ?

 

I was just skimming through some pictures in the December edition of Shutterbug magazine. I see some excellent

pictures taken with an f22 aperture value. The pictures are clean and as far as I can tell,(I don't have my microscope

with me) they do not show any pin-cushion distortion, vignetting or any other nonsense.

<p>Actually, it is not nonsense but an <em>optical fact</em>. Depending on the lens, when stopping down past f/16 you will start losing image quality, especially in the corners, due to <em>diffraction</em> around the aperture blades. The lens may correct quite well for CA, Coma, etc., but may not be correctable for diffraction. How noticeable the image degredation is will depend on the degree of enlargement. What may seem insignificant in a 5 x 7 print may become quite objectionable in an 11 x 14 or 16 x 20.</p><p>Also keep in mind, you cannot necessarily use a magazine image as a guide for judging the sharpness of an image, regardless of aperture. Unless you have perfectly horizontal or vertical lines it may not be obvious if there is barrel or pincushion distortion. It doesn't have to look like a fisheye to have distortion. With so many DX format zooms starting in the teens for focal length, you are more likely to see it anyway. Most images in magazines are reductions of very large files.</p><p>Although it is not a hard and fast rule, three stops down from maximum aperture is considered optimum aperture for most lenses. Am I saying never use anything past f/16? Of course not. Just keep in mind that physics will always dictate things regardless of the quality of the lens.</p>

<p>"Pin cushion" distortion is a product of long focal length lenses, not small f-stops. And "barrel distortion" is it's wide angle cousin. "Diffraction" softening images on the other hand comes into play at small apertures. And I can assure you it isn't "nonsense".</p>

<p>The reason for this is that the edges of the diaphragm blades in the lens tend to disperse the light. At larger apertures this diffracted light is only a small percentage of the total amount of light hitting the sensor or film, but as the aperture is stopped down the amount of diffracted light becomes a larger percentage of the total amount of light being recorded.</p>

<p>The rule of thumb is to stay at least 2 stops away from a lens' minimum F stop to avoid diffraction. Most 35mm or MF glass will start to get soft from diffraction if you stop down too far. Almost all LF lenses are designed to be shot at F22, and quite often these lenses stop down to F45 or F64.</p>

<p> </p>

<p>I did some experimenting a couple of years ago using a nice sharp Nikkor lens that goes down to F32, and good sharp slide film. I did find that above F11 or 16 on that particular lens diffraction could be detected, but it was pretty hard to spot. To suggest that it will inevitably result in lousy pictures is obviously nonsense, but the diffraction is real, and can show up, especially, in my experience, at contrasty edges. Obviously, there can be times when the added diffraction is not as important as the need for added DOF. On the other hand, since there's really no advantage to a very small aperture other than added DOF, I'd avoid the smallest unless needed. </p>

Scott do you have any proof images. I'm just an an amatuer and by no means an expert but yelling wolf, is preventing some of us from using our cameras and lense to their full capabilities.

<p>You could allot yourself a pinhole camera. With their very high apertures, you'd have to allot quite a long exposure time though.</p>

<p>Harry I think it would be better if you saw it for yourself rather than rely on another's images. It's quite simple. Find a scene with good horizontal and vertical lines and lots of detail both in the center and edges. With the camera mounted on a sturdy tripod, use a combination of EV shutter speeds and apertures, go from as wide an aperture as you can, given the light conditions, to the lens' minimum aperture. Then look at the images in PS or something else where you can enlarge them on your monitor to a great extent. Depending on the lens, printing them to an 8 x 10 may not be enough to make the diffraction noticeable. Though you can take little pieces of the images and print them 8 x 10 so you can see the differences.</p>

<p>HTH</p>

"<I>Most LF lenses have apertures of f32 or greater, that's why they are used in studio work that require that sort of precision.</I>"<P>

 

Not really. If you check a depth of field calculator you will find that f/64 on an 8x10 camera lens DOF is about the same as f/16 on a 35mm camera lens. f/32 on a 4x5 camera lens DOF is also about the same as f/16 on a 35mm camera lens.

<p>I understand that diffraction is a factor of the <em>absolute</em> diameter of the aperture. The f/stop is a <em>relative</em> ratio of the length of the lens to the diameter of the aperture. In a very small and/or short lens, like those on 35mm or APS-C cameras, f/22 is a very small absolute measurement and diffraction at f/22 or f/32 should be high.</p>

<p>On the other hand, I am thinking that f/22 on a very large format lens would have an absolute diameter that is much larger than the same f/stop on a smaller lens (e.g., my 6x6 Biometer 120mm at f/22 is about 5mm in diameter, while a Domiplan 50mm 35mm lens at f/22 is less than 3mm in diameter). Should this not make diffraction less of a factor on a large lens until you are down to a much smaller f/stop, like say f/128?</p>

<p>Tell me if I'm wrong here, if I am (it's been a long time since I have had physics-of-light instruction)<br>

If I am right, then view camera shooters like Ansel can safely stop down to f/22 and more without worrying about diffraction, while little puny 35mm camera shooters had better stick to f/16 and larger.</p>

"Find a scene with good horizontal and vertical lines and lots of detail both in the center and edges. With the camera mounted on a sturdy tripod, use a combination of EV shutter speeds and apertures, go from as wide an aperture as you can, given the light conditions, to the lens' minimum aperture."

===============

 

Good idea Scott as you know, I tend to learn things the hard way.

<p>I suspect a troll. Google diffraction and or diffraction limitation. This is photography 101. I would think that almost any member of photonet since 2005 would know about diffraction.</p>

<p> The limiting f/stop for diffraction can be calculated. It is basically 1/2 the diagonal of your sensor/film size. The 35mm film has a diagonal of 43mm which equates to f22. The APS-C sensor is f11 <br>

a^+b^=c^ gives you the diagonal. </p>

<p> </p>

Ah I suspect a troll ? beeb beeb beep ...

<p>A long time ago I read that, generally, the focal length divided by four should be your smallest f-stop. It's been my practice since, and seems to work okay. For medium and large format, f22 is not extreme as it is in 35mm. In 8X10 format f22 is only getting started, and with my 4X5 lenses f16 and 22 is the sweet spot. </p>

<p>Using F22 is like having a blade that is not totally sharp as can be. It doesnt matter with a giant process camera or bush hog blade; but seems to matter more with a dinky sensor or dinky piece of film; or a razor blade. Unless one knows what the blade or F22 ism used for; there is no way to say it if matters.</p>

<p>you really need to test the stops within a given lens to see the results. take the same picture at different aperture and see how they come out. argument over!</p>

<p>Say, you know, that guy sounds a bit like Frank Gra . . . nah, couldn't be. No way. A simple search of photo.net would turn up tens of pages on diffraction. But you can stir up lively discussion by pronouncing the laws of physics to be 'nonsense'!</p>

Do you think our clients really give a hoot about diffraction ?

<p>f22 on say a 35mm camera lens is very different than f22 on a LF camera. When I first started shooting LF, I thought something was wrong w/ my lens because even at f32 the hole in the aperture blades was very large. It's because it's a larger lens, optically speaking. f22 on a 35mm format lens is tiny indeed and will cause more problems w/ diffraction. Small format lenses are designed to be at optimun aperture usually around f8, whereas LF lenses are designed differently. But unless you're making really big enlargements I doubt you'll see any real difference between a small format lens that's shot at f8 vs f22. This is a genaral rule, and there are always certain lenses that may not work like this, but I haven't used them.</p>

<blockquote>

<p>I'm just an an <strong>amatuer </strong> and by no means an expert but yelling wolf, is preventing some of us from using our cameras and lense to their full capabilities.</p>

</blockquote>

 

<blockquote>

<p>Do you think <strong>our clients</strong> really give a hoot about diffraction ?</p>

</blockquote>

<p>Are you an amatuer (sic) or professional? And no they don't care about the word, mine care about the results. If you have picky clients you will do everything to make them happy, if the clients don't care, you still should care about having a professional attitude.</p>

<p>Harry, check out Michael Seewald' photos. Many were taken at f32. ie: shttp://www.photo.net/photo/2507616 Would any be sharper at f11 or f8? Perhaps, but there are other considerations like DOF, which, at the artists discression, may trump critical sharpness at times. No hard & fast rules; the correct answer being "...it depends...". Best, LM.</p>

<p>Can someone discuss how diffraction changes, if at all, when the same lens is used on a film SLR and then on a non-full frame DSLR?</p>

<blockquote>

<p>The reason for this is that the edges of the diaphragm blades in the lens tend to disperse the light.</p>

</blockquote>

<p>Actually, the edges of the aperture have nothing to do with diffraction, aside from defining the size of the aperture. Diffraction is a wave effect, each photon, despite being smaller than the aperture, potentially passes through all points in the entire aperture (probability physics can be scary, especially after a large meal). Using an apodizing disc (an aperture that has gradient neutral density edges) will increase the diffraction of an unobstructed optical system.</p>

<p>Harry,</p>

 

<p>If I may cut to the chase?</p>

 

<p>At apertures small enough for diffraction to have an affect, you will decrease the sharpness of

the items in the subject plane (due to diffraction) while increasing the sharpness of items outside

the focal plane (due to the increased depth of field).</p>

 

<p>For example, if you’re shooting both the flowers at your feet and the distant mountains,

you can either shoot at the “optimal” aperture and have one or the other (or perhaps

something inbetween) in focus and everything else blurry, or you can have everything in focus, but

not <em>quite</em> as sharp as if you had used the optimal aperture and focussed on just that

one item.</p>

 

<p>And, as usual, how large you’re printing is also a factor. If your printer sits on your

desktop, it really doesn’t matter how much you stop down, as the effects won’t be

visible at those sizes. But if you buy your ink by the pint and your paper by the roll, then, yes, take

it into consideration when you shoot.</p>

 

<p>Oh — if your camera has live view, use it in these situations while holding down the DoF preview button and focussing manually. By pixel peeping on the scene before you release the shutter, you can decide <em>exactly</em> how much to stop down and where to set the focus; no more guesstimating from charts of hyperfocal distances or DoF calculators or the like. You’ll be shooting at the optimal aperture and focus setting <em>for that scene / camera / lens combination,</em> which is as good as it can possibly get.

 

<p>Cheers,</p>

 

<p>b&</p>

<p><em>I understand that diffraction is a factor of the absolute diameter of the aperture. </em></p>

<p>Actually, diffraction (the diameter of the Airy disk) is proportional to the relative aperture and the wavelength. The photographic effects of diffraction are less in large format because less enlargement is needed.</p>