stopping down hurts?

[arthurking83]

Ok I've seen a few images around here where the exif says ... f=22 or similar.

diffraction!

There's usually no issue and the images have appeared fine, but(!!) I've been seeing a lot of lens tests/comparisons where the tester has noted things like "diffraction causes problems from f/16, as is to be expected..." or words to that effect.

It appears to afflict certain cameras worse than others, they all do it, but to what degree?

As I've read many lens tests proclaim it to be a problem, I tend to use a min f/11-13(f/16 on some occasions) for any landscapes where there's excessive light... many at f/8.

I'm wondering if any folks here are aware of this 'problem'?

I finally found a technical link that many folks can "visually understand" (meaning I finally see what they're on about ).

THE TECHNICAL LINK!

the site is interactive, so you can see what diffraction does to an image, and explains technically what's happening within you camera(the sensor).

OK here's the catch! The sharper the lens the WORSE the diffraction appears!!

It actually makes sense really, if your lens is sharp as a tack(hey Dowden, you still got that 70-200? ) then you will notice any blurry abberation more than you would if the lens was already softish

[Knawful]

Hmm, gunna have to experiment tomorrow me think's.
I usually shoot f2.8 - f11 with the 70-200 and havent really noticed to be honest.

[arthurking83]

I'd like to see some samples of a brick wall at f8 and f16(and smaller) just to see.

f/5.6 is supposed to be the sharpest setting on that beast..

I don't think I have a lens sharp enough to really make a definitive example...but all those MTF tests and info like that link can't be wrong

brick wall(maybe a paling fence?) is good because of the texture, and focal plane!

ps I'll stop posting tonight, and post my 1000th post tomorrow .... headache/cold is wearing me out... and it's only 12:30!

[dejavu]

Diffraction is noticable from around f16 and up (exclusive). Now, the thing is why do you want to shoot at f22+?

The increase of DoF from f22 to f32 is absolutely minimal, even in macro. There are much more effective methods of achieving higher DoF without resorting to bumping the aperture up that high.

Be careful reading some of those image test online though. Unless the tests have been conducted with the strictest standards, the test will biase against high aperture settings since the longer exposure will be more susceptible to vibrations.

[xpantz]

Diffraction is noticable from around f16 and up (exclusive). Now, the thing is why do you want to shoot at f22+?

There are much more effective methods of achieving higher DoF without resorting to bumping the aperture up that high.

Got tips? :-)

[xpantz]

Got tips? :-)

hey I got one of my own. :-)

poking around looking for technique to increase DOF I came across a couple of pieces of softare to help you do the job.

it's like HDR for DOF

Helcion Focus
http://heliconfilter.com/pages/index...e#heliconfocus
and
CombineZ5
http://www.hadleyweb.pwp.blueyonder..../combinez5.htm

I used Helcion to create this image... perfectly in focus from back to front.



Created from these 6 images.. focus moving from back to front in steps.
All shot at f/11







I've only used the Halcion software so far but I believe the CombineZ5 does the same thing and is free. Halcion costs 30$ for the basic version and 70$ for the pro which can clone and copy bits from any of the source images to the processed image and a few other tricks... you can just live with the lite version I rekon.

Really easy to use.. just take a few shots with focus ranging from one side to the other... open them up in the Helcion softare and hit the process button.

if you can get your bug to sit still long enough you can have him from focus from eye to tail.

kinda feels like cheating but hey :-) it works!

[Knawful]

Cheer's X...Top info....

Now my puter will be even slower.
I'm like AK with his gadget's, only my vice is software.

[Knawful]

Shed wall pictures here

[TassieSnapper]

Since I am relatively new to photoshop CS, does it have a feature where you can combine different DOF images or different focus planes automatically or manually?

[arthurking83]

Diffraction is noticable from around f16 and up (exclusive). Now, the thing is why do you want to shoot at f22+?

.....

The point I was trying to establish, for anyone coming from film (me!) when shooting landscapes, I was 'taught' to stop down for DOF.

I suppose p&s(digital) folks probably never had this issue ... (dunno.. .. I've never had one)

I have seen some folks shooting at f22, I felt compelled to point this phenomenon out.


My main concern with those MTF charts and lens comparisons are more about sample variation... more so, than controlled environments...
I have no reason to suspect (nor seen evidence to the contrary) that they are not done to a standard.... ie. consistent environments.
Further to that, many lens tests seem to report similar findings anyhow ... that Lens X is generally sharper than Lens Y, yet Lens Y may have better color or CA control, or it may feel less robust.. etc.... a pattern does emerge (only from what I've read on the lenses that I have any interest in!)

[xpantz]

Since I am relatively new to photoshop CS, does it have a feature where you can combine different DOF images or different focus planes automatically or manually?

not to my knowledge.... no... there may be a plugin somewhere but I havnt seen it.

photoshop does image stacking for HDR and there are plenty of methods for creating fake DOF blur (bokeh) in photoshop.

AFAIK if you want image stacking for DOF (to create sharp images... usually from macro shots) you need to use one of the programs I posted earlier.

both are easy to use and extremely effective.

[dejavu]

I guess without arguing over triviality (as some people on some forums do), DoF is DoF regardless of whether it is film or digital. The crop factor of the digital sensor changes that a little, but not much. When you shoot landscape, the proper way of getting the DoF you want is setting your lens to its hyperfocal distance, and composing the shot such that foreground interest is placed at the start of the hyperfocal distance.

Shooting at the hyperfocal distance gives foreground to inifinity sharpness. Well it appears to our eyes that everything is in focus. View cameras takes this concept further by allow shift & tilt to greatly increase foreground DoF. You can do similar thing with the Canon TS lenses.

In macro, to increase the DoF, try shooting with your camera's sensor parallel to the subject. While this is not strictly "increasing DoF", it ensures that the interesting parts fall within the focus plane.

Take this shot for example:


I could have shot the spider from an angle, but I wanted both eyes to be in the plane of focus. If you look carefully, you can see exactly where the plane of focus is. This is not always possible, since sometimes "paralleling" the sensor to the subject would result in crappy composition, but it's something to keep in mind, especially if that particular shot is of a documentary nature.

Anyhow, rules are there to be broken, but you need to know the rules to know how to break them properly. At the end of the day, if the shot looks good to you, then that's all that matters.... unless you are shooting for a client

[TOM]

diffraction is dependant on two variables

1. the distance fromt he lens, of the object affected by diffraction
2. the size of the lens being used

one cannot simply say, diffraction kicks in at fxx.

[Tannin]

~~ Huh?

Neither of those have anything at all to do with diffraction. Zip. Nothing. Nada.

[Kym]

Diffraction can work for you! The 'star' effect is due to diffraction.

f/16, 30 seconds, ISO 100, 43 mm

[TOM]

Neither of those have anything at all to do with diffraction. Zip. Nothing. Nada.

the amount of diffraction is determined by lens size, and the amount of affect that diffraction has on part of your image, depends on how far that part of your image is from the lens. so for an image with a film camera (not that sure with a Digital Camera), i work on s=D/1600d where s is the diffraction limited size of object, D is the distance from the lens in feet, and d is the lens size (focal length/f stop). so if i am photographing the on the Sturt Reserve in Murray Bridge with a 35mm lens at f11, and the twin bridges are 1km in the background, i know that anything that is just over a half a foot in size or larger will be rendered sharply in my image. So as you can see, by using a larger aperture, we get better resolution and less diffraction, however our dof is limited. But just over half a foot (16) allows me to render the basic structure of the bridge, but rivets and the shape of the beams are not detectable.

so beams of light travel ina straight line, but when they are squeezed through a diagraphm opening, they divert. they still travel forward, but now at an angle, so obviously the further away an object is from the lens, the more that diffraction will affect said object. now with a Digital Camera, you can just chimp, but if you ever graduate to a larger format camera, you may not have that luxury. the above calculation doesn't have to be worked out every time, you will become familiar with these figures. i know that for max dof for most of my scenic shots, that f9.5 on my 35mm will give me great results.

as for lens size, Ansel Adams named his school "f64". this was an f stop that he often used. the lens that he was quite partial to was a 300mm lens, and he used this for alot of his work. Lens size = 4.6mm

[Steve Axford]

the amount of diffraction is determined by lens size, and the amount of affect that diffraction has on part of your image, depends on how far that part of your image is from the lens. so for an image with a film camera (not that sure with a Digital Camera), i work on s=D/1600d where s is the diffraction limited size of object, D is the distance from the lens in feet, and d is the lens size (focal length/f stop). so if i am photographing the on the Sturt Reserve in Murray Bridge with a 35mm lens at f11, and the twin bridges are 1km in the background, i know that anything that is just over a half a foot in size or larger will be rendered sharply in my image. So as you can see, by using a larger aperture, we get better resolution and less diffraction, however our dof is limited. But just over half a foot (16) allows me to render the basic structure of the bridge, but rivets and the shape of the beams are not detectable.

so beams of light travel ina straight line, but when they are squeezed through a diagraphm opening, they divert. they still travel forward, but now at an angle, so obviously the further away an object is from the lens, the more that diffraction will affect said object. now with a Digital Camera, you can just chimp, but if you ever graduate to a larger format camera, you may not have that luxury. the above calculation doesn't have to be worked out every time, you will become familiar with these figures. i know that for max dof for most of my scenic shots, that f9.5 on my 35mm will give me great results.

as for lens size, Ansel Adams named his school "f64". this was an f stop that he often used. the lens that he was quite partial to was a 300mm lens, and he used this for alot of his work. Lens size = 4.6mm

This doesn't seem right to me. The diffraction works from the iris to the sensor (film or digital), not from the subject to the iris. Am I missing something?

I find that f18 is the limit for my 180mm macro (at close distances). For my MP-E it is f16, which is the maximum. It is worth remembering that the effective aperture is also dependent on how close is the subject (angle of incidence to the lens). This really is irrelevant for most lenses, but for the MP-E it can change the f16 to f64 at 5x magnification. For some of the other lenses it may be a little less, maybe f13. This is for the 1Ds Mk3, but it would be less for a camera with higher pixel density. You really need to experiment a little to find what is best for your lens/camera combinations.

[DAdeGroot]

The point I was trying to establish, for anyone coming from film (me!) when shooting landscapes, I was 'taught' to stop down for DOF.

Diffraction existed in the film world too - on a 135 format (full frame in the digital world) body, you'll start to get diffraction from f/16. The issue with film is most people weren't shooting high quality, low grain film in order to notice it.

On an APS-C body, diffraction creeps in from f/11 onwards. You can usually get away with f/16 and not notice too much, but beyond that, and with a sharp lens you'll see softness compared to a wider aperture.

So while stopping down will get you more depth of field, you will lose sharpness past the diffraction point of your camera system. It should be noted that the point at which diffraction becomes noticeable is related to the size of your film/sensor and the lens construction. Thus, large format shooters using 8x10" film can happily shoot away at f/32, while small format (135 format) users cannot without getting a fairly soft image.

[arthurking83]

...

On an APS-C body, diffraction creeps in from f/11 onwards. You can usually get away with f/16 and not notice too much, but beyond that, and with a sharp lens you'll see softness compared to a wider aperture.

.....

in many cases this may be 'correct' but from what I've noticed, diffraction is more about lens design(design brief??) and less about the size of the sensor.

Tammy 70-200/2.8 is sharp at f/2.8 and starts to diffract at about f/8. Not very noticeable, but on a resolution chart(the cheapo downloadable version with warnings not to print it up on your home printer version ) I've noticed a slight loss of very fine detail with this lens at f/8, compared to f/5.6 at least, and it looks closer in sharpness/detail at f/8 as it is at f/2.8.
Not an overly concerning issue tho, as the loss is very slight and not noticeable in a real image anyhow.

But I think Steve is on the right track, as someone(can't remember who now) pointed out to me a while back. When I use my old manual Tamron 300/2.8 it gets sharper from f/4 to f/8 and maintains that sharpness level at f/8 up to f/16(there goes the f/11 rule ) but when I add the Tamron specific teleconverters, there's very good sharpness right up to f/32 where I simply ran out of light!(at 30sec exposure, and I was too lazy to delve any deeper into the curiosity). So as the TC's are added and stacked, it was mentioned that the iris is being moved further away from the film/sensor plane, and the 'diffracted image is now being relayed to the sensor via more lenses(hopefully not diffracting or altering the image any more).. but the images produced were definitely sharper at f/22 than at f/11, using various combinations of TC's on this lens. Subject to lens only decreased by a few inches at most, maybe 75mm, over a focus distance of 5-6 meters, so the subject to lens difference in distance could be regarded as irrelevant (or 0.015% difference). But the iris to sensor plane difference was huge with the addition of the TC's.

Then there's the design of the lens to be taken into account too.
Diffraction doesn't necessarily have to exist at smaller apertures, but I think must be a design compromise that the engineers have to deal with as best as they can
If the lens is of a smaller aperture design(such as those found in the MF/LF format, where a 135mm f/8 or 300mm f/8 prime lens is not uncommon, then the engineers don't have as much of a compromise to deal with as they would if the lens was an f/2.8, or f/1.4 type. There's obviously a very good reason why that 50mm f/1.4 lens only stops down to f/16, and not f/22 or f/29 as most f/2.8 lenses do.
I doubt very much that a fast lens couldn't be designed to delay the onset of diffraction till much later than the normal f/11 or whatever, but at what cost? Who's willing to pay $10k for a fast prime that's still as sharp at f/22 or f/29? I suspect no one really, as the lens's primary purpose would be for it's speed.

[Tannin]

Hoolie doolie that's a hard way of thinking about an easy subject Tom! To summarise, you are saying that you can .... no, that's too hard for me. My brain hurtz when I try to summarise what you just wrote. Let's do it the other way:

Diffraction depends on your f stop.

Wasn't that easier? And it also has the advantage of being 100% correct. Diffraction increases as aperture gets smaller; the higher the f/ number, the more the diffraction. For any given camera, no other factor is relevant. Diffraction depends on your f stop. End of story.